WO1998053103A1 - Nucleic acid arrays - Google Patents

Abstract

Arrays of polynucleotide spots and kits comprising the same, as well as methods for their preparation and use are provided. The subject arrays include a plurality of polynucleotide spots stably associated with the surface of a solid support. At least a portion of the polynucleotide spots comprises a polynucleotide probe composition that is made up of unique polynucleotides, where all of the unique polynucleotides of the array correspond to a common type of gene. Also provided are sets of a representational number of gene specific primers suitable for use in generating target nucleic acid for use with the subject arrays. The subject arrays find use in hybridization assays, particularly in assays for the identification of differential gene expression patterns among two or more different types of cells.

Description

NUCLEIC ACID ARRAYS

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of application serial no. 08/859,998 filed on May 21, 1997 and application serial no. 09/053,375 filed on March 31, 1998, the disclosures of which are herein incorporated by reference.

INTRODUCTION Technical Field The field of this invention is biopolymeric arrays.

Background of the Invention

"Biochips" or arrays of binding agents, such as oligonucleotides and peptides, have become an increasingly important tool in the biotechnology industry and related fields. These binding agent arrays, in which a plurality of binding agents are deposited onto a solid support surface in the form of an array or pattern, find use in a variety of applications, including drug screening, nucleic acid sequencing, mutation analysis, and the like. One important use of biochips is in the analysis of differential gene expression, where the expression of genes in different cells, normally a cell of interest and a control, is compared and any discrepancies in expression are identified. In such assays, the presence of discrepancies indicates a difference in the classes of genes expressed in the cells being compared.

In methods of differential gene expression, arrays find use by serving as a substrate to which is bound polynucleotide "probe" fragments. One then obtains "targets" from analogous cells, tissues or organs of a healthy and diseased organism. The targets are then hybridized to the immobilized set of polynucleotide "probe" fragments. Differences between the resultant hybridization patterns are then detected and related to differences in gene expression in the two sources. A variety of different array technologies have been developed in order to meet the growing need of the biotechnology industry, as evidenced by the extensive number of patents and references listed in the relevant literature section below.

Despite the wide variety of array technologies currently in preparation or available on the market, there is a continued need to identify new array devices to meet the needs of specific applications. Of particular interest would be the development of an array capable of providing high throughput analysis of differential gene expression.

Relevant Literature

Patents and patent applications describing arrays of biopolymeric compounds and methods for their fabrication include: 5,242,974; 5,384,261; 5,405,783; 5,412,087;

5,424,186; 5,429,807; 5,436,327; 5,445,934; 5,472,672; 5,527,681; 5,529,756; 5,545,531 ; 5,554,501 ; 5,556,752; 5,561,071 ; 5,599,895; 5,624,711; 5,639,603; 5,658,734; WO 93/17126; WO 95/1 1995; WO 95/35505; EP 742 287; and EP 799 897.

Patents and patent application describing methods of using arrays in various applications include: 5,143,854; 5,288,644; 5,324,633; 5,432,049; 5,470,710; 5,492,806; 5,503,980; 5,510,270; 5,525,464; 5,547,839; 5,580,732; 5,661,028; WO 95/21265; WO 96/31622; WO 97/10365; WO 97/27317; EP 373 203; and EP 785 280.

Other references of interest include: Atlas Human cDNA Expression Array I (April 1997) CLONTECHniques XII: 4-7; Lockhart et al., Nature Biotechnology (1996) 14: 1675- 1680; Shena et al., Science (1995) 270: 467-470; Schena et al., Proc. Nat'l Acad. Sci. USA (1996)93: 10614-10619; Shalon et al., Genome Res. (1996) 6: 639-645; Milosavljevic et al., Genome Res. (1996) 6: 132-141 ; Nguyen et al., Genomics (1995)29: 207-216; Pietu et al., Genome Res. (1996) 6: 492-503; Zhao et al., Gene (1995) 166:207-213; Chalifour et al., Anal. Biochem. (1994) 216:299-304; Heller et al., Proc. Nat'l Acad. Sci. USA (1997) 94: 2150-2155; and Schena, M., BioAssays ( 1996) 18: 427-431.

.?- SUMMARY OF THE INVENTION Arrays of polynucleotide spots stably associated with the surface of a solid support and kits comprising the same, as well as methods for their preparation and use in hybridization assays, are provided. The subject arrays comprise a plurality of polynucleotide spots, wherein each different polynucleotide spot is made up of a polynucleotide probe composition and at least a portion of the polynucleotide probe compositions are made up of unique polynucleotides. The arrays are further characterized in that all of the unique polynucleotides on the array correspond to the same type of gene. The subject arrays find particular use in differential gene expression analysis. Also provided are sets of a representational number of gene specific primers useful in generating target nucleic acids for use with the subject arrays in hybridization assays.

BRIEF DESCRIPTION OF THE FIGURES Fig. 1 provides a representation of an array according to the subject invention.

DEFINITIONS The term "nucleic acid" as used herein means a polymer composed of nucleotides, e.g. deoxyribonucleotides or ribonucleotides.

The terms "ribonucleic acid" and "RNA" as used herein mean a polymer composed of ribonucleotides.

The terms "deoxyribonucleic acid" and "DNA" as used herein mean a polymer composed of deoxyribonucleotides.

The term "oligonucleotide" as used herein denotes single stranded nucleotide multimers of from about 10 to 100 nucleotides in length. The term "polynucleotide" as used herein refers to single or double stranded polymer composed of nucleotide monomers of greater than about 120 nucleotides in length up to about 1000 nucleotides in length.

The term "array type" refers to the type of gene represented on the array by the unique polynucleotides, where the type of gene that is represented on the array is dependent on the intended purpose of the array, e.g. to monitor expression of key human genes, to monitor expression of known oncogenes, etc, i.e. the use for which the array is designed. As such, all of the unique polynucleotides on a given array correspond to the same type or category or group of genes. Genes are considered to be of the same type if they share some common linking characteristics, such as: species of origin, e.g. human, mouse, rat, etc.; tissue or cell type of origin, e.g. muscle, neural, dermal, organ, etc.; disease state, e.g. cancer; functions, e.g. protein kinases, tumor supressors and the like, participation in the same normal biological process, e.g. apoptosis, signal transduction, cell cycle regulation, proliferation, differentiation etc.; and the like. For example, one array type that is provided below is a "cancer array" in which each of the "unique" polynucleotide probes correspond to a gene associated with a cancer disease state. Likewise, a "human array" may be an array of polynucleotides corresponding to unique tightly regulated human genes. Similarly, an "apoptosis array" may be an array type in which the polynucleotides correspond to unique genes associated with apoptosis.

The "unique" polynucleotide sequences associated with each type of array of the present invention are sequences which are distinctive or different with respect to every other polynucleotide sequence on the array and correspond to the same type of gene, as defined above. For example, in a cancer array, each unique polynucleotide has a sequence that is not homologous to any other known cancer associated sequence. Moreover, each polynucleotide sequence on the array is statistically chosen to ensure that the probability of homology to any sequence of that type is very low. Morever, in the cancer array embodiment, all sequences are statistically chosen to insure that the probability of homology to any other sequence associated with cancer or of human origin is very low. An important feature of the individual polynucleotide probe compositions of the subject arrays is that they are only a fragment of the entire cDNA of the gene to which they correspond. In other words, for each gene represented on the array, the entire cDNA sequence the gene is not represented on the array. Instead, the sequence of only a portion or fragment of the entire cDNA is represented on the array by this unique polynucleotide.

The term "polynucleotide probe composition" refers to the nucleic acid composition that makes up each of the spots on the array. Thus, the term " polynucleotide probe composition" includes nucleic acid compositions of unique polynucleotides and control or calibrating polynucleotides (e.g. polynucleotides corresponding to housekeeping genes). The polynucleotide compositions are made up of single stranded polynucleotides (i.e. polynucleotides that are not hybridized to each other), where all of the polynucleotides in the probe composition may be identical to each other or there may be two different polynucleotides (polynucleotides of different nucleotide sequence) in each probe composition, where the two different polynucleotides are complementary to each other. The term "gene specific primer" means a polynucleotide of sufficient length to specifically hybridize to a distinct nucleic acid member of the sample, e.g. RNA or cDNA, where the length of the gene specific primers will usually be at least 8 nt, more usually at least 20 nt and may be as long as 25 nt or longer, but will usually not exceed 50 nt. The gene specific primers of the subject invention are sufficiently specific to hybridize to complementary template sequence during the generation of labeled nucleic acids under conditions sufficient for first strand cDNA synthesis, which conditions are known by those of skill in the art. The number of mismatches between the gene specific primer sequences and their complementary template sequences to which they hybridize during the generation of labeled nucleic acids in the subject methods will generally not exceed 20 %, usually will not exceed 10 % and more usually will not exceed 5 %, as determined using the FASTA program using default settings.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS Arrays of polynucleotide spots and methods for their preparation are provided. In the subject arrays, a plurality of polynucleotide spots is stably associated with the surface of a solid support, where at least a portion of the polynucleotide spots on the array are made up of unique polynucleotides and all of the unique polynucleotides of the array correspond to one particular type of gene, e.g. tightly regulated human genes, genes associated with a particular disease state, genes associated with cell cycle regulation, etc. The subject arrays find particular use in gene expression assays. Also provided are sets of a representational number of gene specific primers useful in generating target nucleic acids for use with the subject arrays. In further describing the subject invention, the arrays first will be described in general terms. Next, methods for their preparation are described. Following this, a description of representative specific array types falling within the scope of the invention will be provided. Finally, a review of representative applications in which the subject arrays may be employed will be provided, where this review includes a description of the sets of a representational number of gene specific primers according to the subject invention. Before the subject invention is further described, it is to be understood that the invention is not limited to the particular embodiments of the invention described below, as variations of the particular embodiments may be made and still fall within the scope of the appended claims. It is also to be understood that the terminology employed is for the purpose of describing particular embodiments, and is not intended to be limiting. Instead, the scope of the present invention will be established by the appended claims.

In this specification and the appended claims, the singular forms "a," "an," and "the" include plural reference unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs.

ARRAYS OF THE SUBJECT INVENTION-GENERAL DESCRIPTION

Array Structure

The arrays of the subject invention have a plurality of polynucleotide spots stably associated with a surface of a solid support. Each spot on the array comprises a polynucleotide sample, i.e. polynucleotide probe composition, of known identity, usually of known sequence, as described in greater detail below. The polynucleotide spots on the array may be any convenient shape, but will typically be circular, elliptoid, oval or some other analogously curved shape. The density of the spots on the solid surface is at least about 5/cm² and usually at least about 10/cm² but does not exceed about 1000/cm², and usually does not exceed about 500/cm², and more usually does not exceed about 300/cm². The spots may be arranged in any convenient pattern across or over the surface of the array, such as in rows and columns so as to form a grid, in a circular pattern, and the like, where generally the pattern of spots will be present in the form of a grid across the surface of the solid support. See Fig. 1.

In the subject arrays, the spots of the pattern are stably associated with the surface of a solid support, where the support may be a flexible or rigid solid support. By stably associated is meant that the polynucleotides of the spots maintain their position relative to the solid support under hybridization and washing conditions. As such, the polynucleotide members which make up the spots can be non-covalently or covalently stably associated with the support surface. Examples of non-covalent association include non-specific adsoφtion, binding based on electrostatic (e.g. ion, ion pair interactions), hydrophobic interactions, hydrogen bonding interactions, specific binding through a specific binding pair member covalently attached to the support surface, and the like. Examples of covalent binding include covalent bonds formed between the spot polynucleotides and a functional group present on the surface of the rigid support, e.g. -OH, where the functional group may be naturally occurring or present as a member of an introduced linking group, as described in greater detail below.

As mentioned above, the array is present on either a flexible or rigid substrate. By flexible is meant that the support is capable of being bent, folded or similarly manipulated without breakage. Examples of solid materials which are flexible solid supports with respect to the present invention include membranes, e.g. nylon, flexible plastic films, and the like. By rigid is meant that the support is solid and does not readily bend, i.e. the support is not flexible. As such, the rigid substrates of the subject arrays are sufficient to provide physical support and structure to the polymeric targets present thereon under the assay conditions in which the array is employed, particularly under high throughput handling conditions. Furthermore, when the rigid supports of the subject invention are bent, they are prone to breakage.

The solid supports upon which the subject patterns of spots are presented in the subject arrays may take a variety of configurations ranging from simple to complex, depending on the intended use of the array. Thus, the substrate could have an overall slide or plate configuration, such as a rectangular or disc configuration. In many embodiments, the substrate will have a rectangular cross-sectional shape, having a length of from about 10 mm to 200 mm, usually from about 40 to 150 mm and more usually from about 75 to 125 mm and a width of from about 10 mm to 200 mm, usually from about 20 mm to 120 mm and more usually from about 25 to 80 mm, and a thickness of from about 0.01 mm to 5.0 mm, usually from about 0.1 mm to 2 mm and more usually from about 0.2 to 1 mm.

The substrates of the subject arrays may be fabricated from a variety of materials. The materials from which the substrate is fabricated should ideally exhibit a low level of non-specific binding during hybridization events. In many situations, it will also be preferable to employ a material that is transparent to visible and/or UV light. For flexible substrates, materials of interest include: nylon, both modified and unmodified, nitrocellulose, polypropylene, and the like, where a nylon membrane, as well as derivatives thereof, is of particular interest in this embodiment. For rigid substrates, specific materials of interest include: glass; plastics, e.g. polytetrafluoroethylene, polypropylene, polystyrene, polycarbonate, and blends thereof, and the like; metals, e.g. gold, platinum, and the like; etc. The substrates of the subject arrays comprise at least one surface on which the pattern of spots is present, where the surface may be smooth or substantially planar, or have irregularities, such as depressions or elevations. The surface on which the pattern of spots is present may be modified with one or more different layers of compounds that serve to modify the properties of the surface in a desirable manner. Such modification layers, when present, will generally range in thickness from a monomolecular thickness to about 1 mm, usually from a monomolecular thickness to about 0.1 mm and more usually from a monomolecular thickness to about 0.001 mm. Modification layers of interest include: inorganic and organic layers such as metals, metal oxides, polymers, small organic molecules and the like. Polymeric layers of interest include layers of: peptides, proteins, polynucleic acids or mimetics thereof, e.g. peptide nucleic acids and the like; polysaccharides, phospholipids, polyurethanes, polyesters, polycarbonates, polyureas, polyamides, polyethyleneamines, polyarylene sulfides, polysiloxanes, polyimides, polyacetates, and the like, where the polymers may be hetero- or homopolymeric, and may or may not have separate functional moieties attached thereto, e.g. conjugated. The total number of spots on the substrate will vary depending on the number of different polynucleotide probes one wishes to display on the surface, as well as the number of control spots, calibrating spots and the like, as may be desired depending on the particular application in which the subject arrays are to be employed. Generally, the pattern present on the surface of the array will comprise at least about 10 distinct spots, usually at least about 20 distinct spots, and more usually at least about 50 distinct spots, where the number of spots may be as high as 10,000 or higher, but will usually not exceed about 5,000 distinct spots, and more usually will not exceed about 3,000 distinct spots. In many embodiments, it is preferable to have each distinct probe composition presented in duplicate, i.e. so that there are two spots for each distinct polynucleotide probe composition of the array. In certain embodiments, the number of spots will range from about 200 to 600.

The amount of polynucleotide present in each spot will be sufficient to provide for adequate hybridization and detection of target nucleic acid during the assay in which the array is employed. Generally, the amount of polynucleotide in each spot will be at least about 0.1 ng, usually at least about 0.5 ng and more usually at least about 1 ng, where the amount may be as high as 1000 ng or higher, but will usually not exceed about 20 ng and more usually will not exceed about 10 ng. The copy number of each polynucleotide in a spot will be sufficient to provide enough hybridization sites for target molecule to yield a detectable signal, and will generally range from about 0.01 fmol to 50 fmol, usually from about 0.05 fmol to 20 fmol and more usually from about 0.1 fmol to 5 fmol. Where the spot has an overall circular dimension, the diameter of the spot will generally range from about 10 to 5,000 μm, usually from about 20 to 2,000 μm and more usually from about 50 to 1000 μm.

A critical feature of the subject arrays is that at least a portion, usually the majority, of the polynucleotide spots on the array are made up of polynucleotide probes that all correspond to the same kind or kind of gene, i.e. genes that all share some common characteristic or can be grouped together based on some common feature, such as species of origin, tissue or cell of origin, functional role, disease association, etc. Other spots which may be present in the pattern include spots comprising genomic DNA, housekeeping genes, negative and positive control genes, and the like. These latter types of spots comprise polynucleotides that are not "unique" as that term is defined and used herein, i.e. they are "common." In other words, they are calibrating or control genes whose function is not to tell whether a particular "key" gene of interest is expressed, but rather to provide other useful information, such as background or basal level of expression, and the like. The percentage of spots which are made of unique polynucleotides that correspond to the same type of gene is generally at least about 30 number %, and usually at least about 60 number % and more usually at least about 80 number %. Therefore, the arrays of the subject invention will be of a specific array type, where representative array types include: human arrays, mouse arrays, cancer arrays, apoptosis arrays, human stress arrays, oncogene and tumor suppressor arrays, cell-cell interaction arrays, cytokine and cytokine receptor arrays, rat arrays, blood arrays, mouse stress arrays, neuroarrays, and the like, where some of these representative arrays are described in greater detail below. With respect to the polynucleotide probes that correspond to a particular type or kind of gene, type or kind can refer to a plurality of different characterizing features, where such features include: species specific genes, where specific species of interest include eukaryotic species, such as mice, rats, rabbits, pigs, primates, humans, etc.; function specific genes, where such genes include oncogenes, apoptosis genes, cytokines, receptors, protein kinases, etc.; genes specific for or involved in a particular biological process, such as apoptosis, differentiation, cell cycle regulation, cancer, aging, proliferation, etc.; location specific genes, where locations include organ, such as heart, liver, prostate, lung etc., tissue, such as nerve, muscle, connective, etc., cellular, such as axonal, lymphocytic, etc. or subcellular locations, e.g. nucleus, endoplasmic reticulum, Golgi complex, endosome, lyosome, peroxisome, mitochondria, cytoplasm, cytoskeleton, plasma membrane, extracellular space; specific genes that change expression level over time, e.g. genes that are expressed at different levels during the progression of a disease condition, such as prostate genes which are induced or repressed during the progression of prostate cancer.

The average length of the polynucleotides on the array is chosen to be of sufficient length to provide a strong and reproducible signal, as well as tight and robust hybridization. As such, the average length of the polynucleotides of the array will typically range from about 120 to 1000 nt and usually from about 120 to 800 nt, where in many embodiments, the average length ranges from about 200 to 700 nt, and usually 200 to 600 nt. The length of each polynucleotide on the array is less than the length of the mRNA to which it corresponds. As such, the polynucleotide represents only a fraction of the full length cDNA to which it corresponds. As mentioned above, the subject arrays typically comprise one or more additional spots of polynucleotides which do not correspond to the array type, i.e. the type or kind of gene represented on the array. In other words, the array may comprise one or more spots that are made of non "unique" polynucleotides, i.e common polynucleotides. For example, spots comprising genomic DNA may be provided in the array, where such spots may serve as orientation marks. Spots comprising plasmid and bacteriophage genes, genes from the same or another species which are not expressed and do not cross hybridize with the cDNA target, and the like, may be present and serve as negative controls. In addition, spots comprising housekeeping genes and other control genes from the same or another species may be present, which spots serve in the normalization of mRNA abundance and standardization of hybridization signal intensity in the sample assayed with the array. Polynucleotide Probes of the Arrays

Each spot of the pattern present on the surface of the substrate is made up of a unique polynucleotide probe composition. By "polynucleotide probe composition" is meant a collection or population of single stranded polynucleotides capable of participating in a hybridization event under appropriate hybridization conditions, where each of the individual polynucleotides may be the same — have the same nucleotide sequence— or different sequences, for example the probe composition may consist of 2 different single stranded polynucleotides that are complementary to each other (i.e. the two different polynucleotides in the spot are complementary but physically separated so as to be single stranded, i.e. not hybridized to each other). In many embodiments, the probe compositions will comprise two complementary, single stranded polynucleotides.

In those polynucleotide probe compositions having unique polynucleotides, the sequence of the polynucleotides are chosen in view of the type and the intended use of the array on which they are present. The unique polynucleotides are chosen so that each distinct unique polynucleotide does not cross-hybridize with any other distinct unique polynucleotide on the array, i.e. the polynucleotide of any other polynucleotide probe composition that corresponds to a different gene falling within the broad category or type of genes represented on the array. As such, the nucleotide sequence of each unique polynucleotide of a probe composition will have less than 90% homology, usually less than 85 % homology, and more usually less than 80% homology with any other different polynucleotide of a probe composition of the array, where homology is determined by sequence analysis comparison using the FASTA program using default settings. The sequence of unique polynucleotides in the probe compositions are not conserved sequences found in a number of different genes (at least two), where a conserved sequence is defined as a stretch of from about 40 to 200 nucleotides which have at least about 90% sequence identity, where sequence identity is measured as above. The polynucleotide will generally be a deoxyribonucleic acid having a length of from about 120 to 1000, usually from 120 to 700 nt, and more usually 200 to 600 nt. The polynucleotide will not cross-hybridize with any other polynucleotide on the array under standard hybridization conditions. Again, the length of the polynucleotide will be shorter than the mRNA to which it corresponds. Array Preparation

The subject arrays can be prepared using any convenient means. One means of preparing the subject arrays is to first synthesize the polynucleotides for each spot and then deposit the polynucleotides as a spot on the support surface. The polynucleotides may be prepared using any convenient methodology, such as automated solid phase synthesis protocols, preparative PCR and like, where preparative PCR or enzymatic synthesis is preferred in view of the length and the large number of polynucleotides that must be generated for each array.

For preparative PCR, primers flanking either side of the portion of the gene of interest will be employed to produce amplified copy numbers of the portion of interest.

Methods of performing preparative PCR are well known in the art, as summarized in PCR, Essential Techniques (Ed. J.F. Burke, John Wiley & Sons)(1996). Alternatively, if a gene fragment of interest is cloned into a vector, vector primers can be used to amplify the gene fragment of interest to produce the polynucleotide. In determining the portion of the gene to be amplified and subsequently placed on the array, regions of the gene having a sequence unique to that gene should preferably be amplified. Different methods may be employed to choose the specific region of the gene to be amplified. Thus, one can use a random approach based on availability of a gene of interest. However, instead of using a random approach which is based on availability of a gene of interest, a rational design approach may also be employed to choose the optimal sequence for the hybridization array. Preferably, the region of the gene that is selected and amplified is chosen based on the following criteria. First, the sequence that is chosen should yield a polynucleotide that does not cross-hybridize with any other polynucleotide that is present on the array. Second, the sequence should be chosen such that the polynucleotide has a low probability of cross-hybridizing with a polynucleotide having a nucleotide sequence found in any other gene, whether or not the gene is to be represented on the array from the same species of origin, e.g. for a human array, the sequence will not be homologous to any other human genes. As such, sequences that are avoided include those found in: highly expressed gene products, structural RNAs, repeated sequences found in the sample to be tested with the array and sequences found in vectors. A further consideration is to select sequences which provide for minimal or no secondary structure, structure which allows for optimal hybridization but low non-specific binding, equal or similar thermal stabilities, and optimal hybridization characteristics.

The prepared polynucleotides may be spotted on the support using any convenient methodology, including manual techniques, e.g. by micro pipette, ink jet, pins, etc., and automated protocols. Of particular interest is the use of an automated spotting device, such as the Beckman Biomek 2000 (Beckman Instruments). As mentioned above, the polynucleotide probe compositions that are spotted onto the array surface are made up of single stranded polynucleotides, where all the polynucleotides may be identical to each other or a population of complementary polynucleotides may be present in each spot.

SPECIFIC ARRAY TYPES OF THE SUBJECT INVENTION

A variety of specific array types are also provided by the subject invention. As discussed above, array type refers to the nature of the polynucleotide probes present on the array and the types of genes to which the probes correspond. These array types include: human array; mouse array; cancer array, apoptosis array, human stress array, oncogene and tumor suppressor arrray, cell-cell interaction array, and cytokine and cytokine receptor array, as well as other types of arrays, e.g. rat array, rat stress array, blood array, mouse stress array, and nueroarray. Each of these arrays is described separately below.

Human Array

One specific array type provided by the subject invention is the human array. In the human array of the subject invention, the majority of the spots on the array have a polynucleotide sequence corresponding to a human gene of interest. As such, all of the unique polynucleotide probes on the array correspond to human genes. The human genes represented on the human array are typically those genes that have been identified by those of skill in the art as key genes. By "key" is meant that the genes are relevant and related to the purpose of the array, e.g. the identification of difference in the expression profiles of different cell or tissue types, where the key genes are generally functionally important to the cell. In many embodiments, the genes represented on the human array are tightly regulated human genes. The term "tightly regulated gene" is used herein in accordance with its art accepted definition and use. As such, by tightly regulated human gene is meant a gene which is not "leaky," as opposed to housekeeping genes which are generally expressed at similar levels in different cells and different tissues, i.e. a gene which is inducible such that in response to a specific inducing signal the gene turns "on" and when this signal is removed, the gene turns "off." In certain embodiments of the human array, human genes that may be represented on the subject arrays include: (a) oncogenes & tumor suppressors; (b) cell cycle regulators; (c) stress response proteins; (d) ion channel & transport proteins; (e) intracellular signal transduction modulators and effectors; (f) apoptosis-related proteins; (g) DNA synthesis, repair and recombination proteins; (h) transcription factors & general DNA binding proteins; (i) growth factor & chemokine receptors; (j) interleukin & interferon receptors; (k) hormone receptors; (1) neurotransmitter receptors; (m) cell surface antigens & cell adhesion proteins; (n) growth factors, cytokines and chemokines; (o) interleukins & interferons; (p) hormones; (q) extracellular matrix proteins; (r) cytoskeleton & motility proteins; (s) RNA processing & turnover proteins; (t) post-translational modification, trafficking & targeting proteins; (u) protein turnover; and (v) metabolic pathway proteins.

In view of the length of the polynucleotides of the probe compositions of the spots, each polynucleotide of a probe composition typically has a nucleotide sequence of only a portion of the human gene. Specific sequences to which the polynucleotide sequence may correspond include those identified in Table 1 below, where by "correspond" is meant that the polynucleotide could have the same sequence as specified or a sequence complementary to the specified sequence. Whether the polynucleotide sequence is the same as a portion of the sense strand of the gene to which is corresponds or complementary thereto is based primarily on the nature of the target which the array is to be used, e.g. if the target is first strand cDNA, the polynucleotide will have a sequence found in the anti-sense DNA strand of the gene to which it corresponds.

Of particular interest is a human array of the subject invention as shown in Fig. 1. In the array, each spot on the array comprises a known polynucleotide, as specified in Table 1 , where the array comprises spots which: (a) correspond to 588 different tightly regulated human genes; (b) comprise plasmid and bacteriophage polynucleotides; (c) comprise polynucleotides corresponding to housekeeping genes; and (d) genomic DNA. Each of the different types of polynucleotide spots are positioned at a known location on the membrane surface. >

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Mouse Array

In the mouse array according to the subject invention, all of the unique polynucleotide probe compositions will correspond to a mouse gene of interest. Mouse genes that are represented on the array are key genes, by which is meant that they have been reported to play primary roles in a variety of different biological processes. Typically the mouse genes represented on the array are genes that are under tight transcriptional control. Genes of interest that may be represented on the array include: oncogenes, cell cycle genes, apoptosis genes, growth factor genes, cytokine genes, interleukin genes, receptor genes, and genes associated with different stages of embryonic development. In certain embodiments, of particular interest is an array having the following types of genes represented on its surface: oncogenes & tumor suppressors; cell cycle regulators; stress response proteins; ion channel & transport proteins; intracellular signal transduction modulators & effectors; apoptosis-related proteins; DNA synthesis, repair & recombination proteins; transcription factors & general DNA binding proteins; growth factor & chemokine receptors; interleukin & interferon receptors, hormone receptors; neurotransmitter receptors; cell-surface antigens & cell adhesion proteins; interleukins & interferons; cytoskeleton & motility proteins; and protein turnover. In a specific mouse array of interest, the spots are as listed in Table 2.

The mouse array of the subject invention finds use in a variety of different applications, where such applications include: profiling differential gene expression in transgenic knockout mice or other experimental mouse models; investigating processes such as embryo genesis and tumorigenesis; discovering potential therapeutic and diagnostic drug targets; and the like.

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Cancer Array

In the cancer arrays of the subject invention, the polynucleotide probe compositions on the array correspond to those genes which are associated, e.g. play a role in, cellular proliferative diseases, particularly cancer, where human genes are of particular interest in many embodiments. Types of genes that are typically represented on a cancer array of the subject invention include: oncogenes, tumor suppressors, cell cycle regulators, genome plasticity genes, apoptosis genes, cell differentiation genes, regulators of tumor host interaction and metastasis, such as extracellular matrix proteins, cell adhesion receptors, molecules that control cell invasion and motility, and genes associated with angiogenesis. In certain embodiments, of particular interest is an array having the following types of genes represented on its surface: cell cycle/growth regulators; apoptosis; growth factors/cytokines; oncogenes/tumor suppressors; cell adhesion, motility and invasion; invasion regulators; GTP ases and their regulators; cadherins; intermediate filament markers; receptors; cell fate/development regulators; DNA damage/response/repair/ recombination; and angiogenesis regulators. In a specific cancer array of interest, the spots are as listed in Table 3.

The cancer array finds use in a variety of applications, including: monitoring cellular responses to therapeutic compounds; comparing expression profiles of tumors at different developmental stages; developing diagnostic tools for distinguishing closely related tumors; and the like.

In the following Table 3, as well as preceding Tables 1 and 2, the "position" coordinate refers to the actual nucleotide residues of the listed gene that are represented on the array.

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Apoptosis Array

In the apoptosis array according to the subject invention, all of the unique polynucleotide probe compositions correspond to genes that are associated with apoptosis, e.g. cell cycle genes. In a specific apoptosis array of interest, the spots are as provided in Table 4.

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Human Stress Array

In the human stress array according to the subject invention, all of the unique polynucleotide probe compositions correspond to genes that are associated with stress responses of human cells, e.g. stress response regulators and effectors. In a specific human stress array of interest, the spots are as provided in Table 5.

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Oncogene and Tumor Suppressor Gene Array

In the oncogene and tumor suppressor gene array according to the subject invention, all of the unique polynucleotide probe compositions correspond to genes that are associated with cellular proliferative diseases, specifically neoplastic diseases. Genes of interest that may be represented on the array include: oncogenes and tumor suppressor genes. In a specific oncogene and tumor suppressor gene array of interest, the spots are as provided in Table 6.

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Cell-Cell Interaction Array

In the cell-cell interaction array according to the subject invention, all of the unique polynucleotide probe compositions correspond to genes that are associated with cell-cell interaction, e.g. cell-cell signaling. In a specific cell-cell interaction array of interest, the spots are as provided in Table 7.

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Cytokine and Cytokine Receptor Array

In the cytokine and cytokine receptor array according to the subject invention, all of the unique polynucleotide probe compositions correspond to genes that express cytokines or cytokine receptors. In a specific cytokine and cytokine receptor array of interest, the spots are as provided in Table 8.

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Cell Cycle Array

In the cell cycle array according to the subject invention, all of the unique polynucleotide probe compositions correspond to genes that are associated with the life cycle of a cell. In a specific cell cycle array of interest, the spots are as provided in Table 9.

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Other Representative Arrays

In a neuroarray according to the subject invention, all of the unique polynucleotide probe compositions will correspond to genes that are expressed in brain related tissues.

Genes that are represented on the array are key genes, by which is meant that they have been reported to play primary roles in a variety of different biological processes in brain tissues.

Genes of interest that may be represented on the array include: ion channel/transport proteins; receptors; cell cycle regulators; stress response proteins; apoptosis proteins; signal transduction proteins; transcriptional factors; growth factors/interleukins/hormones; oncogenes and tumor suppressors; cell surface/adhesion proteins; DNA synthesis/repair/recombination genes; and metabolic pathway enzymes.

In certain embodiments, of particular interest is an array having the following types of genes represented on its surface: nuclear proteins; endoplasmic reticulum proteins; golgi complex proteins; endosomal proteins; lysosomal proteins; peroxisomal proteins; mitochondrial proteins; cytoplasmic proteins; cytoskeletal proteins; plasma membrane proteins; post synaptic and dendritic proteins; axonal and nerve terminal proteins; secreted proteins, neuropeptides, hormones and growth factors; extracellular matrix proteins; astrocyte and oligodendroglial proteins; immune system proteins; developmentally regulated proteins; regionally regulated proteins; and disease related proteins.

Other representative arrays include: (1) rat arrays, in which each of the unique polynucleotide corresponds to a key rat gene; (2) blood arrays, in which each unique polynucleotide corresponds to a gene associated cells and tissues associated with the cardiovascular system; (3) rat stress arrays; and (4) mouse stress arrays, in which each unique polynucleotide corresponds to a gene associated with the stress response of murine cells.

METHODS OF USING THE SUBJECT ARRAYS

The subject arrays find use in a variety of different applications in which one is interested in detecting the occurrence of one or more binding events between target nucleic acids and probes on the array and then relating the occurrence of the binding event(s) to the presence of a target(s) in a sample. In general, the device will be contacted with the sample suspected of containing the target under conditions sufficient for binding of any target present in the sample to a complementary polynucleotide present on the array. Generally, the sample will be a fluid sample and contact will be achieved by introduction of an appropriate volume of the fluid sample onto the array surface, where introduction can be pipette, deposition, and the like.

Generation of Labeled Target

Targets may be generated by methods known in the art. mRNA can be labeled and used directly as a target, or converted to a labeled cDNA target. Generally, such methods include the use of oligonucleotide primers. Primers that may be employed include oligo dT, random primers, e.g. random hexamers and gene specific primers.

Of particular interest in the generation of labeled target is the use of a set of a representational number of gene specific primers, as described in U.S. Patent Application No. 08/ 859,998, the disclosure of which is herein incorporated by reference. As the subject sets comprise a representational number of primers, the total number of different primers in any given set will be only a fraction of the total number of different or distinct RNAs in the sample, where the total number of primers in the set will generally not exceed 80 %, usually will not exceed 50 % and more usually will not 20% of the total number of distinct RNAs, usually the total number of distinct messenger RNAs (mRNAs), in the sample. Any two given RNAs in a sample will be considered distinct or different if they comprise a stretch of at least 100 nucleotides in length in which the sequence similarity is less than 98%, as measured using the FASTA algorithm at default settings. As the sets of gene specific primers comprise only a representational number of primers, with physiological sources comprising from 5,000 to 50,000 distinct RNAs, the number of different gene specific primers in the set of gene specific primers will typically range from about 20 to 10,000, usually from 50 to 2,000 and more usually from 75 to 1500.

Each of the gene specific primers of the sets described above will be of sufficient length to specifically hybridize to a distinct nucleic acid member of the sample, e.g. RNA or c DNA, where the length of the gene specific primers will usually be at least 8 nt, more usually at least 20 nt and may be as long as 25 nt or longer, but will usually not exceed 50 nt. The gene specific primers will be sufficiently specific to hybridize to complementary template sequence during the generation of labeled nucleic acids under conditions sufficient for first strand cDNA synthesis, which conditions are known by those of skill in the art. The number of mismatches between the gene specific primer sequences and their complementary template sequences to which they hybridize during the generation of labeled nucleic acids in the subject methods will generally not exceed 20 number %, usually will not exceed 10 number % and more usually will not exceed 5 number %. Generally, the sets of gene specific primers will comprise primers that correspond to at least 20, usually at least 50 and more usually at least 75 distinct genes as represented by distinct mRNAs in the sample, where the term "distinct" when used to describe genes is as defined above, where any two genes are considered distinct if they comprise a stretch of at least 100 nt in their RNA coding regions in which the sequence similarity does not exceed 98%, as determined using the FASTA algorithm at default settings.

The gene specific oligonucleotide primers may be synthesized by conventional oligonucleotide chemistry methods, where the nucleotide units may be: (a) solely nucleotides comprising the heterocyclic nitrogenous bases found in naturally occurring DNA and RNA, e.g. adenine, cytosine, guanine, thymine and uracil; (b) solely nucleotide analogs which are capable of base pairing under hybridization conditions in the course of DNA synthesis such that they function as the above nucleotides found in naturally occurring DNA and RNA, where illustrative nucleotide analogs include inosine, xanthine, hypoxanthine, 1 ,2- diaminopurine and the like; or (c) from combinations of the nucleotides of (a) and nucleotide analogs of (b), where with primers comprising a combination of nucleotides and analogues thereof, the number of nucleotide analogues in the primers will typically be less than 25 and more typically less than 5. The gene specific primers may comprise reporter or hapten groups, usually 1 to 2, which serve to improve hybridization properties and simplify detection procedure.

Depending on the particular point at which the gene specific primers are employed in the generation of the labeled nucleic acids, e.g. during first strand cDNA synthesis or following one or more distinct amplification steps, each gene specific primer may correspond to a particular RNA by being complementary or similar, where similar usually means identical, to the particular RNA. For example, where the gene specific primers are employed in the synthesis of first strand cDNA, the gene specific primers will be complementary to regions of the RNAs to which they correspond.

Each gene specific primer can be complementary to a sequence of nucleotides which is unique in the population of nucleic acids, e.g. mRNAs, with which the primers are contacted, or one or more of the gene specific primers in the set may be complementary to several nucleic acids in a given population, e.g. multiple mRNAs, such that the gene specific primer generates labeled nucleic acid when one or more of set of related nucleic acid species, e.g. species having a conserved region to which the primer corresponds, are present in the sample. Examples of such related nucleic acid species include those comprising: repetitive sequences, such as Alu repeats, Al repeats and the like; homologous sequences in related members of a gene-family; polyadenylation signals; splicing signals; or arbitrary but conversed sequences.

Depending on the particular nature of the labeled nucleic acid generation step of the subject methods, the gene specific primers may be modified in a variety of ways. One way the gene specific primers may be modified is to include an anchor sequence of nucleotides, where the anchor is usually located 5' of the gene specific portion of the primer and ranges in length from 10 to 50 nt in length, usually 15 to 40 nt in length. The anchor sequence may comprise a sequence of bases which serves a variety of functions, such as a sequence of bases which correspond to the sequence found in promoters for bacteriophage RNA polymerase, e.g. T7 polymerase, T3 polymerase, SP6 polymerase, and the like; arbitrary sequences which can serve as subsequent primer binding sites; and the like.

Turning now to the methods employing the above sets of gene specific primers, the first step in the subject methods is to obtain a sample of nucleic acids, usually RNAs, from a physiological source, usually a plurality of physiological sources, where the term plurality is used to refer to 2 or more distinct physiological sources. The physiological source of RNAs will typically be eukaryotic, with physiological sources of interest including sources derived single celled organisms such as yeast and multicellular organisms, including plants and animals, particularly mammals, where the physiological sources from multicellular organisms may be derived from particular organs or tissues of the multicellular organism, or from isolated cells derived therefrom. Thus, the physiological sources may be different cells from different organisms of the same species, e.g. cells derived from different humans, or cells derived from the same human (or identical twins) such that the cells share a common genome, where such cells will usually be from different tissue types, including normal and diseased tissue types, e.g. neoplastic, cell types. In obtaining the sample of RNAs to be analyzed from the physiological source from which it is derived, the physiological source may be subjected to a number of different processing steps, where such processing steps might include tissue homogenation, nucleic acid extraction and the like, where such processing steps are known to the those of skill in the art. Methods of isolating RNA from cells, tissues, organs or whole organisms are known to those of skill in the art and are described in Maniatis et al., Molecular Cloning: A Laboratory Manual (Cold Spring Harbor Press)(1989).

The next step in the subject methods is the generation of labeled nucleic acids representative of the nucleic acid, usually RNA, profile of the physiological source. As mentioned above, a set of gene specific primers is used to generate the labeled nucleic acids from the sample of RNAs, where the labeled nucleic acids generated in this step may serve as "target" in subsequent assays in which the differences in the RNA profiles of at least two sources are analyzed. As used herein, the term "target" refers to single stranded RNA, single stranded DNA and double stranded DNA, where the target is generally greater than 50 nt in length.

The set of primers may be used either in first strand cDNA synthesis or following one or more amplification steps. Furthermore, the actual synthesis of the labeled nucleic acids may be at the same step during which the sets of gene specific primers are employed, or the synthesis of the labeled nucleic acids may be one more steps subsequent to the step in which the sets of gene specific primers are employed.

In a first embodiment of the invention, the set of gene specific primers is used to generate labeled first strand cDNA, where the labeled first strand cDNA is representative of the RNA profile of the physiological source being assayed. The labeled first strand cDNA is prepared by contacting the RNA sample with the primer set and requisite reagents under conditions sufficient for reverse transcription of the RNA template in the sample. Requisite reagents contacted with the primers and RNAs are known to those of skill in the art and will generally include at least an enzyme having reverse transcriptase activity and dNTPs in an appropriate buffer medium.

A variety of enzymes, usually DNA polymerases, possessing reverse transcriptase activity can be used for the first strand cDNA synthesis step. Examples of suitable DNA polymerases include the DNA polymerases derived from organisms selected from the group consisting of a thermophilic bacteria and archaebacteria, retroviruses, yeasts, Neurosporas, Drosophilas, primates and rodents. Preferably, the DNA polymerase will be selected from the group consisting of Moloney murine leukemia virus (M-MLV) as described in United States Patent No. 4,943,531 and M-MLV reverse transciptase lacking RNaseH activity as described in United States Patent No. 5,405,776 (the disclosures of which patents are herein incorporated by reference), human T-cell leukemia virus type I ( HTLV-I ), bovine leukemia virus ( BLV ), Rous sarcoma virus (RSV ), human immunodeficiency virus ( HIV ) and Thermus aquaticus ( Taq ) or Thermus thermophilus (Tth) as described in United States Patent No. 5,322,770, the disclosure of which is herein incorporated by reference. Suitable DNA polymerases possessing reverse transcriptase activity may be isolated from an organism, obtained commercially or obtained from cells which express high levels of cloned genes encoding the polymerases by methods known to those of skill in the art, where the particular manner of obtaining the polymerase will be chosen based primarily on factors such as convenience, cost, availability and the like.

The various dNTPs and buffer medium necessary for first strand cDNA synthesis through reverse transcription of the primed RNAs may be purchased commercially from various sources, where such sources include Clontech, Sigma, Life Technologies, Amersham, Boehringer-Mannheim. Buffer mediums suitable for first strand synthesis will usually comprise buffering agents, usually in a concentration ranging from 10 to 100 μM which typically support a pH in the range 6 to 9, such as Tris-HCl, HEPES-KOH, etc.; salts containing monovalent ions, such as K.C1, NaCl, etc., at concentrations ranging from 0-200 mM; salts containing divalent cations like MgC , Mg(OAc) etc, at concentrations usually ranging from 1 to 10 mM; and additional reagents such as reducing agents, e.g. DDT, detergents, albumin and the like. The conditions of the reagent mixture will be selected to promote efficient first strand synthesis. Typically the set of primers will first be combined with the RNA sample at an elevated temperature, usually ranging from 50 to 95 °C, followed by a reduction in temperature to a range between about 0 to 60°C, to ensure specific annealing of the primers to their corresponding RNAs in the sample. Following this annealing step, the primed RNAs are then combined with dNTPs and reverse transcriptase under conditions sufficient to promote reverse transcription and first strand cDNA synthesis of the primed RNAs. By using appropriate types of reagents, all of the reagents can be combined at once if the activity of the polymerase can be postponed or timed to start after annealing of the primer to the RNA.

In this embodiment, one of either the gene specific primers or dNTPs, preferably the dNTPs, will be labeled such that the synthesized cDNAs are labeled. By labeled is meant that the entities comprise a member of a signal producing system and are thus detectable, either directly or through combined action with one or more additional members of a signal producing system. Examples of directly detectable labels include isotopic and fluorescent moieties incorporated into, usually covalently bonded to, a nucleotide monomeric unit, e.g. dNTP or monomeric unit of the primer. Isotopic moieties or labels of interest include ²P, ³³P, ³⁵S, ^l25I, and the like. Fluorescent moieties or labels of interest include coumarin and its derivatives, e.g. 7-amino-4-methylcoumarin, aminocoumarin, bodipy dyes, such as Bodipy FL, cascade blue, fluorescein and its derivatives, e.g. fluorescein isothiocyanate, Oregon green, rhodamine dyes, e.g. texas red, tetramethylrhodamine, eosins and erythrosins, cyanine dyes, e.g. Cy3 and Cy5, macrocyclic chelates of lanthanide ions, e.g. quantum dye™, fluorescent energy transfer dyes, such as thiazole orange-ethidium heterodimer, TOTAB, etc. Labels may also be members of a signal producing system that act in concert with one or more additional members of the same system to provide a detectable signal. Illustrative of such labels are members of a specific binding pair, such as ligands, e.g. biotin, fluorescein, digoxigenin, antigen, polyvalent cations, chelator groups and the like, where the members specifically bind to additional members of the signal producing system, where the additional members provide a detectable signal either directly or indirectly, e.g. antibody conjugated to a fluorescent moiety or an enzymatic moiety capable of converting a substrate to a chromogenic product, e.g. alkaline phosphatase conjugate antibody; and the like. In one preferred embodiment, the member of the signal producing system bound to the nucleotide is functional group capable of covalently binding to additional members of the signal producing system to generate a detectable label. Examples of such functional groups or moieties include amino, sulfhydryl, azido, isothiocyanate, sulfoxyl, and the like. The labeled target generated using such nucleotides will thus include one or more, usually a plurality of, functional moieties. For detection, the functional moieties of the modified nucleotides can be labeled by conjugation of a label to the functional moiety. A variety of suitable labels and methods for their conjugation to functional moieties are known to those of skill in the art. Examples include labeling of amino-modified cDNA by a succinimidyl ester of an appropriate dye, e.g. Alexa, Bodipy, or Cy dyes. Alternatively, label can be entrapped or bonded into structures of microscopic-sized particles. These particles can then be conjugated with the functional moieties of the target. For each sample of RNA, one can generate labeled oligos with the same labels. Alternatively, one can use different labels for each physiological source, which provides for additional assay configuration possibilities, as described in greater detail below.

In a variation of the above embodiment, where desired one can generate labeled RNA instead of labeled first strand cDNA. In this embodiment, first strand cDNA synthesis is carried out in the presence of unlabeled dNTPs and unlabeled gene specific primers. However, the primers are optionally modified to comprise a promotor for an RNA polymerase, such as T7 RNA polymerase, T3 RNA polymerase, SP6 RNA polymerase, and the like. In this embodiment, following first strand cDNA synthesis, the resultant single stranded cDNA is then converted to double stranded cDNA, where the resultant double stranded cDNA comprises the anchor sequence comprising the promoter region. Conversion of the mRNAxDNA hybrid following first strand synthesis can be carried out as described in Okayama & Berg, Mol. Cell. Biol. (1982) 2:161-170, and Gubler & Hoffman, Gene (1983) 25: 253-269, where briefly the RNA is digested with a ribonuclease, such as E.coli RNase H, followed by repair synthesis using a DNA polymerase like DNA polymerase I, etc., and E.coli DNA ligase. One may also employ the modification of this basic method described in Wu, R, ed., Methods in Enzymology (1987), vol. 153 (Academic Press). Next, the double stranded cDNA is contacted with RNA polymerase and dNTPs, including labeled dNTPs as described above, to produce linearly amplified labeled ribonucleic acids. For cDNA lacking the anchor sequence comprising a promoter region, a polymerase that does not need a promoter region but instead can initiate RNA strand synthesis randomly from cDNA, such as core fragment of E.Coli RNA polymerase, may be employed.

In another embodiment of the subject invention, the labeled nucleic acid generation step comprises one or more enzymatic amplification steps in which multiple DNA copies of the initial RNAs present in the sample are produced, from which multiple copies of the initial RNA or multiple copies of antisense RNA (aRNA) may be produced, using the polymerase chain reaction, as described in U.S. Pat. No. 4,683,195, the disclosure of which is herein incorporated by reference, in which repeated cycles of double stranded DNA denaturation, oligonucleotide primer annealing and DNA polymerase primer extension are performed, where the PCR conditions may be modified as described in U.S. Pat No. 5,436,149, the disclosure of which is herein incorporated by reference. In one embodiment involving enzymatic amplification, the set of gene-specific primers are employed in the generation of the first strand cDNA, followed by amplification of the first strand cDNA to produce amplified numbers of labeled cDNA. In this embodiment, as a set of gene-specific primers is employed in the first strand synthesis step, only a representative proportion of the total RNA in the sample is amplified during the subsequent amplification steps.

Amplification of the first strand cDNA can be conveniently achieved by using a CAPswitch™ oligonucleotide as described in U.S. Patent Application Serial No. 08/582,562, the disclosure of which is herein incorporated by reference. Briefly, the CAPswitch™ technology uses a unique CAPswitch™ oligonucleotide in the first strand cDNA synthesis followed by PCR amplification in the second step to generate a high yield of ds cDNA. When included in the first-strand cDNA synthesis reaction mixture, the CAPswitch™ oligonucleotide serves as a short extended template. When reverse transcriptase stops at the 5' end of the mRNA template in the course of first strand cDNA synthesis it switches templates and continues DNA synthesis to the end of the CAPswitch™ oligonucleotide. The resulting ss cDNA incorporates at the 3' end, sequence which is complimentary to complete 5' end of the mRNA and the CAPswitch™ oligonucleotide sequence.

Of particular interest as the CAPswitch™ oligonucleotide are oligonucleotides having the following formula:

5'-dNl-dN2-...dNm-rNl-rN2...rNn-3'

wherein: dN represents a deoxyribonucleotide selected from among dAMP, dCMP, dGMP and dTMP; m represents an integer 0 and above, preferably from 10 to 50; rN represents a ribonucleotide selected from the group consisting of AMP, CMP, GMP and UMP, preferably GMP; and n represents an integer 0 and above, preferably from 3 to 7.

The structure of the CAPswitch™ oligonucleotide may be modified in a number of ways, such as by replacement of 1 to 10 nucleotides with nucleotide analogs, incorporation of terminator nucleotides, such as 3'-amino NMP, 3'-phosphate NMP and the like, or non-natural nucleotides which can improve efficiency of the template switching reaction but still retain the main function of the CAPswitch™ oligonucleotide i.e. CAP-depended extension of full-length cDNA by reverse transcriptase using CAPswitch™ oligonucleotide as a template.

In using the CAPswitch™ oligonucleotide, first strand cDNA synthesis is carried out in the presence of a set of gene specific primers and a CAPswitch™ oligonucleotide, where the gene specific primers have been modified to comprise an arbitrary anchor sequence at their 5' ends. The first strand cDNA is then combined with primer sequences complementary to: (a) all or a portion of the CAPswitch™ oligonucleotide and (b) the arbitrary anchor sequence of the gene specific primers and additional PCR reagents, such as dNTPs, DNA polymerase, and the like, under conditions sufficient to amplify the first strand cDNA. Conveniently, PCR is carried out in the presence of labeled dNTPs such that the resultant, amplified cDNA is labeled and serves as the labeled or target nucleic acid. Labeled nucleic acid can also be produced by carrying out PCR in the presence of labeled primers, where either or both the CAPswitch™ oligonucleotide complementary primer and anchor sequence complementary primer may be labeled. In yet an alternative embodiment, instead of producing labeled amplified cDNA, one may generate labeled RNA from the amplified ds cDNA, e.g. by using an RNA polymerase such as E.coli RNA polymerase, or other RNA polymerases requiring promoter sequences, where such sequences may be incorporated into the arbitrary anchor sequence.

Instead of using the set of gene specific primers in the first strand cDNA synthesis step followed by subsequent amplification of only a representative fraction of the total number of distinct RNA species in the sample, one may also amplify all of the RNAs in the sample and use the set of gene specific primers to generate labeled nucleic acid following amplification. This embodiment may find use in situations where the RNA of interest to be amplified is known or postulated to be in small amounts in the sample.

In this embodiment, first strand synthesis is carried out using: (a) an oligo dT primer that usually comprises an arbitrary anchor sequence at its 5' end and (b) a CAPswitch™ oligonucleotide. During first strand synthesis the oligo(dT) anneals to the polyA tail of the mRNA in the sample and synthesis extends beyond the 3' end of the RNA to include the CAPswitch™ oligonucleotide, yielding a first strand cDNA comprising an arbitrary sequence at its 5' end and a region complementary to the CAPswitch™ oligonucleotide at its 3' end. The length of the dT primer will typically range from 15 to 30 nts, while the arbitrary anchor sequence or portion of the primer will typically range from 15 to 25 nt in length.

Following first strand synthesis, the cDNA is amplified by combining the first strand cDNA with primers that correspond at least partially to the anchor sequence and the

CAPswitch™ oligonucleotide under conditions sufficient to produce an amplified amount of the cDNA. Labeled nucleic acid is then produced by contacting the resultant amplified cDNA with a set of gene specific primers, a polymerase and dNTPs, where at least one of the gene specific primers and dNTPs are labeled. When employed to generate target, as described above, the gene specific primers of the sets of primers according to the subject invention are typically chosen according to a number of different criteria. In some embodiments of the invention, primers of interest for inclusion in the set include primers corresponding to genes which are typically differentially expressed in different cell types, in disease states, in response to the influence of external agents, factors or infectious agents, and the like. In other embodiments, primers of interest are primers corresponding to genes which are expected to be, or already identified as being, differentially expressed in different cell, tissue or organism types. Preferably, at least 2 different gene functional classes will be represented in the sets of gene specific primers, where the number of different functional classes of genes represented in the primer sets will generally be at least 3, and will usually be at least 5. Gene functional classes of interest include oncogenes; genes encoding tumor suppressors; genes encoding cell cycle regulators; stress response genes; genes encoding ion channel proteins; genes encoding transport proteins; genes encoding intracellular signal transduction modulator and effector factors; apoptosis related genes; DNA synthesis/recombination/repair genes; genes encoding transcription factors; genes encoding DNA-binding proteins; genes encoding receptors, including receptors for growth factors, chemokines, interleukins, interferons, hormones, neurotransmitters, cell surface antigens, cell adhesion molecules etc. ; genes encoding cell- cell communication proteins, such as growth factors, cytokines, chemokines, interleukins, interferons, hormones etc.; and the like. Less preferred are gene specific primers that are subject to formation of strong secondary structures with less than -lOkcal/mol; comprise stretches of homopolymeric regions, usually more than 5 identical nucleotides; comprise more than 3 repetitive sequences; have high, e.g. more than 80%, or low, e.g. less than 30%, GC content etc.

The particular genes represented in the set of gene specific primers will necessarily depend on the nature of physiological source from which the RNAs to be analyzed are derived. For analysis of RNA profiles of eukaryotic physiological sources, the genes to which the gene specific primers correspond will usually be Class II genes which are transcribed into RNAs having 5' caps, e.g. 7-methyl guanosine or 2,2,7-trimethylguanosine, where Class II genes of particular interest are those transcribed into cytoplasmic mRNA comprising a 7-methyl guanosine 5' cap and a polyA tail. For analysis of RNA profiles of mammalian physiological sources, of particular interest are gene specific primers corresponding to the functional gene classes listed above. For analysis of RNA profiles of human physiological sources, the gene specific primers of particular interest are the gene specific primers identified in Table 1 as SEQ ID NO:01 to SEQ ID NO: 1372, of U.S. Application Serial No. 08/859,998, the disclosure of which is herein incoφorated by reference, where sets of these primers will usually include at least 20 and more usually at least 50 of these specific sequences.

Particular sets of primers of interest in the subject invention are those sets of primers that include primers capable of amplifying at least a portion of the unique polynucleotides present on the arrays with which the target is to be employed. By at least a portion is meant at least about 10, usually at least about 20 and more usually at least about 25 number % (where number is the number of different unique polynucleotides on the array). For examples, sets of primers that include primers capable of amplifying at least a portion of the unique polynucleotides listed in Table 1, supra, are of interest. Similarly sets of primers capable of amplifying at least a portion of the unique polynucleotides listed in Tables 2 to 8, supra, are also of interest.

In a particularly preferred embodiment, the gene specific primers are preferably those primers that correspond to the different polynucleotide spots on the array that is used in the hybridization assay. Thus, one will preferably employ gene specific primers for each different polynucleotide that is present on the array, so that if the gene is expressed in the particular cell or tissue being analyzed, labeled target will be generated from the sample for that gene. In many embodiments in which the subject arrays are employed, the gene specific primers used to generate the target from the human cell or tissue being analyzed will have the same sequence as the gene specific primers used to generate the polynucleotide probes present on the array. In this manner, if a particular gene present on the array is expressed in a particular sample, the appropriate target will be generated and subsequently identified. Representative sets of primers falling within this particularly preferred embodiment include: SET DESCRIPTION

1 I pair of primers capable of amplifying each polynucleotide listed in Table 1 , supra, as well one set of primers capable of amplifying each of the complementary sequences of each of the polynucleotides listed in Table 1.

2 1 pair of primers capable of amplifying each polynucleotide listed in Table 2, supra, as well one set of primers capable of amplifying each of the complementary sequences of each of the polynucleotides listed in Table 2.

3 1 pair of primers capable of amplifying each polynucleotide listed in Table 3, supra, as well one set of primers capable of amplifying each of the complementary sequences of each of the polynucleotides listed in Table 3.

Hybridization and Detection

As mentioned above, following preparation of the target nucleic acid from the tissue or cell of interest, the target nucleic acid is then contacted with the array under hybridization conditions, where such conditions can be adjusted, as desired, to provide for an optimum level of specificity in view of the particular assay being performed. Suitable hybridization conditions are well known to those of skill in the art and reviewed in Maniatis et al, supra and WO 95/21944. In analyzing the differences in the population of labeled target nucleic acids generated from two or more physiological sources using the arrays described above, each population of labeled target nucleic acids are separately contacted to identical probe arrays or together to the same array under conditions of hybridization, preferably under stringent hybridization conditions (for example, at 50°C or higher and O.IXSSC (15 mM sodium chloride/01.5 mM sodium citrate)) , such that labeled target nucleic acids hybridize to complementary probes on the substrate surface.

Where all of the target sequences comprise the same label, different arrays will be employed for each physiological source (where different could include using the same array at different times). Alternatively, where the labels of the targets are different and distinguishable for each of the different physiological sources being assayed, the opportunity arises to use the same array at the same time for each of the different target populations. Examples of distinguishable labels are well known in the art and include: two or more different emission wavelength fluorescent dyes, like Cy3 and Cy5, two or more isotopes with different energy of emission, like ³²P and ³³P, labels which generate signals under different treatment conditions, like temperature, pH, treatment by additional chemical agents, etc., or generate signals at different time points after treatment. Using one or more enzymes for signal generation allows for the use of an even greater variety of distinguishable labels, based on different substrate specificity of enzymes (alkaline phosphatase/peroxidase). Following hybridization, non-hybridized labeled nucleic acid is removed from the support surface, conveniently by washing, generating a pattern of hybridized nucleic acid on the substrate surface. A variety of wash solutions are known to those of skill in the art and may be used.

The resultant hybridization patterns of labeled nucleic acids may be visualized or detected in a variety of ways, with the particular manner of detection being chosen based on the particular label of the target nucleic acid, where representative detection means include scintillation counting, autoradiography, fluorescence measurement, colorimetric measurement, light emission measurement and the like.

Following detection or visualization, the hybridization patterns may be compared to identify differences between the patterns. Where arrays in which each of the different probes corresponds to a known gene are employed, any discrepancies can be related to a differential expression of a particular gene in the physiological sources being compared.

Utility The subject methods find use in, among other applications, differential gene expression assays. Thus, one may use the subject methods in the differential expression analysis of: (a) diseased and normal tissue, e.g. neoplastic and normal tissue, (b) different tissue or tissue types; (c) developmental stage; (d) response to external or internal stimulus; (e) response to treatment; and the like. The subject arrays therefore find use in broad scale expression screening for drug discovery and research, such as the effect of a particular active agent on the expression pattern of genes in a particular cell, where such information can be used to reveal drug toxicity, carcinogenicity, etc., environmental monitoring, disease research and the like.

KITS Also provided are kits for performing analyte binding assays using the subject devices, where kits for carrying out differential gene expression analysis assays are preferred. Such kits according to the subject invention will at least comprise the subject arrays. The kits may further comprise one or more additional reagents employed in the various methods, such as primers for generating target nucleic acids, including a set of gene specific primers according to the subject invention, e.g. primer sets 1 to 9 described above, dNTPs and/or rNTPs, which may be either premixed or separate, one or more uniquely labeled dNTPs and/or rNTPs, such as biotinylated or Cy3 or Cy5 tagged dNTPs, or other post synthesis labeling reagent, such as chemically active derivatives of fluorescent dyes, enzymes, such as reverse transcriptases, DNA polymerases, and the like, various buffer mediums, e.g. hybridization and washing buffers, prefabricated probe arrays, labeled probe purification reagents and components, like spin columns, etc., signal generation and detection reagents, e.g. streptavidin-alkaline phosphatase conjugate, chemifluorescent or chemiluminescent substrate, and the like.

The following examples are offered by way of illustration and not by way of limitation.

EXPERIMENTAL

Example 1 - Generation of human cDNA array

686 cDNA fragments corresponding 686 different human genes were amplified from quick-clone cDNA (CLONTECH) in 686 separate test tubes using a combination of sense and antisense gene-specific primers: (Set No. 9, described supra). Amplification was conducted in a 100-μl volume containing 2 μl of mixture of 10 Quick-clone cDNA from placenta, brain, liver, lung, leukocytes, spleen, skeletal muscle, testis, kidney and ovary (CLONTECH), 40 mM Tricine-KOH (pH 9.2 at 22°C), 3.5 mM Mg(OAc)₂, 10 mM KOAc, 75 μg/ml BSA, 200 μM of each dATP, dGTP, dCTP and dTTP, 0.2 μM of each sense and antisense gene-specific primers and 2 μl of KlenTaq Polymerase mix. Temperature parameters of the PCR reactions were as follows: 1 min at 95 °C followed by 20-35 cycles of 95°C for 15 sec and 68°C for 2 min; followed by a 10-min final extension at 68°C. PCR products were examined on 1.2% agarose/EtBr gels in 1 x TBE buffer. As a DNA size marker a 1 Kb DNA Ladder was used, ds cDNA was then precipitated by addition of a half volume of 4M ammonium acetate (about 35 μl) and 3.7 volumes of 95% ethanol (about 260 μl). After vortexing, the tube was immediately centrifuged at 14,000 r.p.m. in a microcentrifuge for 20 min. The pellet was washed with 80% ethanol without vortexing, centrifuged as above for 10 min, air dried, and dissolved in 10 μl of deionized water. Yield of ds cDNA after the amplification step was about 5 μg. The ds cDNA fragments for all 686 genes were cloned into TA-cloning vector using the manufacturer's recommendations (Invitrogen) and identity of the clones was confirmed by sequence analysis. The ds cDNA inserts with the sequence corresponding 686 genes were amplified by PCR using a combination of antisense and sense gene-specific primers, as described above. The ds cDNA was denatured by adding 1 μl of 10X denaturing solution (1 M NaOH, 10 mM EDTA) and incubating at 65 °C for 20 min. All cDNA probes were transferred in 384- well plate and loaded on positively charged nylon membrane (Schleher & Schull) using 384 pin tool and Biomek 2000 (Beckman) robot. The resultant array is described in Table 1.

Example 2 - Generation of ³²P-labeled oligonucleotides during first strand cDNA synthesis

Step A. cDNA synthesis/Labeling Procedure 1 μg of polyA+RNA or total RNA was converted into ³²P-labeled first-strand cDNA as follows. A sufficient volume of master mix for all labeling reactions and 1 extra reaction was prepared as follows to ensure sufficient volume. For each 10-μl labeling reaction, the following reagents were mixed:

2 μl 5X First-strand buffer (250 μM Tris-HCl pH8.3; 375 mM KC1; 15 mM MgCl ₂) 1 μl l OXdNTP mix (500 μM dGTP, 500 μM dCTP, 500 μM dTTP, 5 μM dATP)

4 μl [α- "P]dATP (Amersham, 3000 Ci/mmol, 10 mCi/ml) 1 μl MMLV reverse transcriptase (Amersham, 200 units/μl) 8 μl Final volume Next, the following reagents were combined in a 0.5-ml PCR test tube: l μg ( l -2 μl) polyA+R A sample I μl lOx gene-specific primers mix ( 0.2 μM of each oligonucleotide ID No.

2,4,6,8, 10, 12,.... 1372 from Table 1 of U.S. Patent Application Serial No. 08/859,998, the discosure of which is herein incoφorated by reference.)

As a control, in separate test tube were mixed 1 μg of polyA+RNA sample with 1 μl of oligo dT primer (CDS1, 5'-d(TCTAGAATTCAGCGGCCGC(T)₃₀VN) - 3'

(where V=G or A or C; N=G or A or T or C)

For each tube, ddH₂0 was added to a final volume of 3 μl and the contents were mixed and spun briefly in a microcentrifuge. The tubes were then incubated in a preheated PCR thermocycler at 70 °C for 2 min. The temperature in thermocycle was reduced down to 50°C and the tube contents were incubated for 2 min. 8 μl of master mix as prepared above were added to each reaction test tube. The contents of the test tubes were then mixed by gentle pipetting. The tubes were then incubated in a PCR thermocycler for 20 min at 50 °C. The reaction was then stopped by adding 1 μl of 10X termination mix (0.1 M EDTA, 1 mg/ml glycogen).

Step B. Column Chromatography

The ³²P-labeled cDNAs were separated from unincoφorated ³ P-labeled nucleotides and small (<0.1- kb) cDNA fragments using the following procedure for each test tube. A CHROMA SPIN-200 column (CLONTECH, Palo Alto, CA) was placed into a 1.5-ml microcentrifuge tube, the water was allowed to drain through the column by gravity flow until the surface of the gel beads emerged in the column matrix. The sample was then applied to the center of the gel bed's flat surface and allowed to be fully absorbed into the resin bed. 25 μl of ddH₂O were then applied and allowed to completely drain out of the column. 200 μl of ddH₂O were then applied and allowed to completely drain out of the column until there was no liquid left above the resin bed. The column was then transferred to a clean 1.5-ml microcentrifuge tube. To collect the first fraction, 100 μl of ddH₂O were added to the column and allowed to completely drain out of the column. The second, third and fourth fractions were collected in analogous fashion. The tubes with fractions 1-4 were then placed in scintillation counter empty vials, and Cherenkov counts for each fraction were obtained in the tritium channel. The fractions which showed the highest Cerenkov counts were pooled.

Example 3 - Generation of Cv3-labeled hybridization polynucleotide target from polyA+RNA using postsynthesis labelling procedure

In this procedure for generating labeled cDNA target, polyA+RNA is first converted into cDNA that has primary amino groups which are subsequently coupled with Cy3 succinimide ester. This technology allows for a significant increase (about 10 fold) in activity of labeled polynucleotide target and therefore increases the overall sensitivity of detection of gene expression. The same procedure can be used for labeling two (or more) samples of RNA. In this case the cDNA synthesis step was the same for both samples but at the labeling step, each cDNA sample was labeled by different and distinguishable labels, e.g. Cy3 and Cy5, Alexa 532 and Bodipy TR, Fluorescein and tetramethyl rhodamine, etc. Each labeled probe was purified separately by column chromatography and, after normalization, were combined together in equal ratio and hybridized with a cDNA array. After hybridization, the detection procedure revealed both dye-labeled hybridized target simultaneously, based on the different spectral characteristics (emission wavelength) of the fluorescent labels.

A. cDNA synthesis The 10-μl reaction described below converted 1 μg of polyA+RNA into amino- modified first-strand cDNA. For each cDNA synthesis reaction:

1. Enough master mix for all labeling reactions and 1 extra reaction was prepared to ensure sufficient volume. For each 10-μl labeling reaction, the following reagents were mixed:

2 μl 5X First-strand buffer (250 μM Tris-HC l pH8.3; 375 mM KC 1 ; ! 5 mM MgC I2) I μl l OXdNTP mix (500 μM dGTP, 500 μM dCTP, 500 μM dATP, 100 μM dTTP, and 100 μM allylamino dUTP ) I μl [ -'² P]dATP (Amersham, 3000 Ci/mmol, 10 mCi/ml) 3 μl H,0 1 μl MMLV reverse transcriptase (Amersham, 200 units/ul)

8 μl Final volume

2. The following was combined in a 0.5-ml PCR test tube: l μg (l-2 μl) polyA+RNA sample 1 μl lOx gene-specific primers mix ( 0.2 uM of each oligonucleotide ID No.

2,4,6,8,10,12, 1372) (from Table 1 of U.S. Patent Application No.

08/859,998, the disclosure of which is herein incoφorated by reference.)

As a control in separate test tube 1 μg of polyA+RNA sample was mixed with 1 μl of oligo dT primer (SEQ ID NO. 1373 from Table 1 of U.S. Application No. 08/859,998).

3. ddH₂O was added to a final volume of 3 μl.

4. The contents were mixed and the tubes were spun briefly in a microcentrifuge.

5. The tubes were incubated in preheated PCR thermocycler at 70 °C for 2 min. 6. The temperature in the thermocycle was reduced down to 50°C and incubate for 2 min.

7. 8 μl of master mix were added to each reaction test tube.

8. The contents of the test tubes were mixed by gentle pipeting.

9. The tubes were incubated in a PCR thermocycler for 30 min at 50°C. 10. The reaction was stopped by increasing temperature up to 70 °C for 5 min, then cooled to 37°C.

1 1. 1 μl of RNase H (10 units/μl) was added and the tubes were incubated at 37°C for 15 min.

12. The reaction was stopped by adding 40 μl of termination mix (0.3 M sodium acetate, pH 5.0, 1 mMEDTA).

13. An equal volume (50 μl) of phenol/chlorophorm/isoamyl alcohol mix (1 : 1 : 1/24 v/v) was added and extraction was performed. Phases were separated by centrifugation at 14,000 rpm for 10 min. 14. Upper water phase was collected and cDNA was precipitated by adding 2.5 volumes (about 120 μl) of ethanol.

15. The precipitate was collected by centrifugation at 14,000 φm for 10 min, the supernatant removed and the precipitate was washed with 80% ethanol. 16. The precipitate was air dried and dissolved in 10 μl of 0. 1 M sodium bicarbonate buffer, pH 9.0.

Step B. Post synthesis labeling procedure.

1. 1 mg of Cy3 succinimide ester was dissolved in 10 μl of dimethyl sulfoxide and 10 μl of amino-modified cDNA generated at step 16 was added to it.

2. The mixture was incubated at room temperature overnight.

Step C. Column Chromatography

To purify the Cy3-labeled cDNAs from the unconjugated label, the following was performed for each test tube:

1. CHROMA SPIN-200 column (CLONTECH) was removed from refrigerator and allowed to warm at room temperature for about 1 hour. The column was inverted several times to completely resuspend the gel matrix. (Note: Check for air bubbles in the column matrix. If bubbles are visible, resuspend the matrix in the in the column buffer (ddH₂0) by inverting the column again).

2. The bottom cap from the column was removed, and then the top cap was slowly removed.

3. The column was placed into a 1.5-ml microcentrifuge tube.

4. The water was allowed to drain through the column by gravity flow until the surfaces of the gel beads in the column matrix were visible. (The top of the column matrix should be at the 0.75-ml mark on the wall of the column. If the column contains much less matrix, adjust the volume of the matrix to 0.75ml mark using matrix from another column.)

5. The collected water was discarded. 6. The sample was applied to the center of the gel bed's flat surface and allowed to be fully absorbed into the resin bed. Care was taken not allow any sample to flow along the inner wall of the column. 7. 25 μl of ddH₂0 were applied and allowed to completely drain out of the column.

8. Apply 200 μl of ddH₂0 and allow the buffer to completely drain out of the column until there was no liquid left above the resin bed.

9. The column was transfered to a clean 1.5-ml microcentrifuge tube. 10. 100 μl of ddH₂0 were added to the column and allowed to completely drain out of the column.

1 1. The second, third and fourth fractions were collected by repeating steps 9-10.

12. Cherenkov counts were obtained for each fraction by counting the entire sample in the tritium channel. 13. The fractions (usually fractions 2-3) which showed highest Cerenkov counts were pooled. Waste column and the fractions (usually fraction 1 and 4) which showed less than 10%) counts from peak fractions.

Example 4 - Hybridization ³²P-labeled cDNA Target with cDNA Array

A solution of ExpressHyb™ (CLONTECH) and sheared salmon testes DNA (Sigma) was prepared by prewarming 15 ml of ExpressHyb™ at 50-60 °C, heating 1.5 mg of sheared salmon testes DNA at 95-100°C for 5 min followed by chilling quickly on ice, and combining the resultant heat-denatured sheared salmon testes DNA with the prewarmed ExpressHyb™.

A cDNA Array as produced in Example 1 above was then placed in a hybridization bottle and 10 ml of the solution prepared above was added to the bottle. Prehybridization was performed for 30 min with continuous agitation at 72 °C. Labeled cDNA probe (Example 1, about 200 ul, total about 2-5x10⁶ cpm) with 1/10th of the total volume ( about 22 ul) of lOx denaturing solution (1 M NaOH, 10 mM EDTA) was mixed and incubated at 65 °C for 20 min. 5 μl (1 μg/ul) of human Cot-1 DNA was then added, and an equal volume (about 225 μl) of 2x Neutralizing solution (1 M NaHPO4, pH 7.0) was added and incubation continued at 65 °C for 10 min. The mixtures were then combined and thoroughly mixed.

The prehybridization solution was replaced with the solution comprising the labeled oligonucleotide as prepared above and allowed to hybridize overnight with continuous agitation at 65 °C. Following hybridization, the hybridization solution was carefully removed and discarded, replaced with 200 ml of Wash Solution 1 (2X SSC. 1% SDS). The array was washed for 20 min with continuous agitation at 65 °C. Washing was repeated four times.

Two additional 20-min washes were then performed in 200 ml of prewarmed Wash Solution 2 (0.1X SSC, 0.5% SDS) with continuous agitation at 65 °C. Using forceps, the cDNA array was removed from the container and excess wash solution was removed by shaking.

The damp membrane was immediately wrapped in plastic wrap, mounted on Whatman paper (3mm Chr) and exposed to x-ray film at -70°C with an intensifying screen.

Example 5 -Comparison Between Using Sets of Gene Specific Primers and oligo dT

³²P-labeled cDNA target were synthesized by M-MLV reverse transcriptase from a mixture 588 antisense gene-specific primers (B) or oligo dT(A) using placenta polyA+RNA as a template as described in Example 2. Primer extension products generated by reverse transcription were purified by gel filtration as described in Example 2 and hybridized separately with two cDNA arrays comprising 588 human genes under identical conditions as described in Example 4. Signals which can be detected by using cDNA target generated using the set of gene specific primers but can not be detected by using conventional target generated with oligo dT primers were observed. Note, the level of non-specific background detected as signal generated by membrane alone outside of the regions with immobilized probes generated by target generated using oligo dT primers was significantly higher in comparison with the background generated by the target generated by using the sets of gene specific primers.

Example 6 - Generation of cDNA array probe immobilized on glass slides.

50 cDNA fragments corresponding to 50 different human genes were amplified from plasmid clones containing corresponding cDNA fragments in 96 well plates using combination of vector primer ID No. 1376 and ID No. 1377 or sense and antisense gene- specific primers: ID No. 1+2, 3+4,5+6,7+8,.... 100+101 (from Table 1 of U.S. Patent Application No. 08/859,998, the disclosure of which is herein incorporated by reference). Amplification was conducted in a 400-μl volume containing 2 ng of plasmid DNA, 40 mM Tricine-KOH (pH 9.2 at 22 °C), 3.5 mM Mg(OAc)₂, 10 MM KOAc, 75 μg/ml BSA, 200 μM of each dATP, dGTP, dCTP and dTTP, 0.2 μM of each primers and 2 μl of KlenTaq Polymerase mix (CLONTECH). Temperature parameters of the PCR reactions were as follows: 1 min at 95 °C followed by 30 cycles of 95 °C for 15 sec and 68 °C for 2 min; followed by a 10-min final extension at 68 °C. PCR products were examined on 1.2% agarose/EtBr gels in 1 x TBE buffer. As a DNA size marker , a 1 Kb DNA Ladder was used, ds cDNA was then precipitated by addition of a 10% volume of 3M sodium acetate (pH 5-0) (about 40 μl) and 2.5 volumes of 96% ethanol (about 1 ml). After vortexing, the tube was immediately centrifuged at 14,000 r.p.m. in a microcentrifuge for 20 min. The pellet was washed with 80% ethanol without vortexing, centrifuged as above for 10 min, air dried, and dissolved in 10 μl of deionized water. Yield of ds cDNA after amplification step was about 20 μg. The ds cDNA was solved in 10 μl of distilled water, 10 μl of 1 M sodium carbonate buffer, pH 9.5, was added and the ds cDNA was denaturated by heating at 94°C for 5 min and cooled down. The treated glass slides were prepared as following: Glass slides were cleaned overnight in 25% solution of nitric acid at room temperature, washed 3 times by acetone, treated with 1% aminopropyl-trimethoxysilane for 3 hrs at room temperature, washed two times with acetone, heated at 120°C for 6 hrs and then treated with 0.2 % of para-phenylendiisothiocyanate (95:5 acetone-water solution) at room temperature for 3 hrs, then washed two times by acetone and dried in vacuum with desiccant. All cDNA probes were transferred in 384-well plate and printed on treated glass slides using 384 pin tool and Biomek 2000 (Beckman) robot. After printing, the arrays were incubated in wet chamber at 37°C overnight, then ultraviolet-cross linked to the surface by subjecting the slides to 30 mJ of energy (Stratagene Stratalinker). The arrays were washed with 1% of sodium borohydrate in 0.1 M NaOH, then washed 3 times in distilled water, dried in vacuum and stored with desiccant.

Example 7- Hybridization Cy3 -labeled cDNA Target (or Cy3/Cv5 labeled cDNA targets) with glass cDNA array

1. A solution of ExpressHyb (CLONTECH) and sheared salmon testes DNA (Sigma) was prepared as follows: a. 5 ml of ExpressHyb™ was prewarmed at 50-60°C. b. 0.5 mg of the sheared salmon testes DNA was heated at 95-100 °C for 5 min, and then chilled quickly on ice. c. Heat-denatured sheared salmon testes DNA was mixed with prewarmed ExpressHyb. 2. The glass cDNA array was placed in a hybridization container, and 1 ml of the solution prepared in step 1 above was added.

3. Prehybridization was conducted for 5 min with continuous agitation at 65 °C.

4. Labeled cDNA probe as prepared in example 3, step C13, above, (about 200 μl) was mixed with 2 μl ( 1 μg/μl) of human Cot- 1 DNA , and denaturated at 99 °C for 2 min.

5. The mixture prepared in Step 4 was added to the hybridization box from Step 3 and the two solutions were mixed together thoroughly. The container was sealed by sealing tape.

6. Hybridization was allowed to proceed overnight with continuous agitation at 65 °C. 7. The hybridization solution was carefully removed and discarded in an appropriate container, and replaced with 10 ml of Wash Solution 1 (2X SSC, 0.1% SDS). The array was washed for 10 min with continuous agitation at 65 °C. The step was repeated two times.

8. Additional 10-min washes were performed in 10 ml of Wash Solution 2 (0. 1 X SSC, 0.1% SDS) with continuous agitation at 65 °C.

9. Using forceps, the cDNA array was removed from the container, briefly washed in 0. 1XSSC and excess buffer was removed from surface by centrifugation in a Beckman CS-6R centrifuge at 2000 φm.

10. Glass arrays were scanned using a custom-built laser scanner equipped by green (Cy3 chanel) and red ( Cy5 chanel) solid state laser built in UCLA. Images were scanned at a resolution of 20 μm per pixel.

It is evident from the above results and discussion that the subject invention provides a rapid, high throughput means to simply and quickly obtain a broad-scale screening of gene expression in a variety of different samples. Only simple hybridization protocols need be employed with the subject arrays, and signals can be detected using any convenient and readily available detection device. Despite their simplicity, assays conducted with the subject arrays yield a large amount of information regarding the expression of numerous different and important genes in a particular sample at substantially the same time, and thus have use in many different types of applications, including drug discovery and characterization, disease research, and the like.

All publications and patent applications cited in this specification are herein incoφorated by reference as if each individual publication or patent application were specifically and individually indicated to be incoφorated by reference. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention.

Although the foregoing invention has been described in some detail by way of illustration and example for puφoses of clarity of understanding, it is readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. An array comprising a plurality of polynucleotide spots stably associated with the surface of a solid support, wherein a portion of said plurality of polynucleotide spots comprise a polynucleotide probe composition made up of unique polynucleotides and all of the unique polynucleotides on said array correspond to genes of a specific type.

2. The array according to Claim 1, wherein said polynucleotides of said array have an average length of from about 120 to 1000 nt.

3. The array according to Claims 1 or 2, wherein each of said unique polynucleotides does not cross hybridize with the polynucleotides of any other polynucleotide probe composition on the array.

4. The array according to Claims 1, 2 or 3, wherein said polynucleotide probe composition comprises a population of single stranded identical polynucleotides.

5. The array according to Claims 1 , 2 or 3, wherein said polynucleotide probe composition comprises a population of two different complementary single stranded polynucleotides.

6. The array according to any of the preceding claims, wherein the density of spots on said array does not exceed about 500/cm².

7. The array according to any of the preceding claims, wherein the number of spots on said array ranges from about 50 to 1000.

8. The array according to any of the preceding claims, wherein said array is selected from the group consisting of a human array, a mouse array, a cancer array, an apoptosis array, a human stress array, an oncogene/tumor suppressor array, a cell-cell interaction array, a cytokine and cytokine receptor array, a rat array, a blood array, a mouse stress array, and a neuroarray.

9. The array according to any of the preceding claims, wherein said solid support is flexible.

10. The array according to any of the preceding claims, wherein said solid support is rigid.

11. The array according to any of the preceding claims, wherein said polynucleotide probes of said array are those listed in a table selected from the group consisting of: Table 1 , Table 2, Table 3, Table 4, Table 5, Table 6, Table 7 and Table 8.

12. A method of preparing an array according to any of the preceding claims, said method comprising: enzymatically generating said unique polynucleotides; and stably associating said enzymatically-generated, complementary, unique polynucleotides on the surface of said solid support.

13. A set of a representative number of distinct gene specific primers comprising gene specific primers corresponding to at least twenty distinct genes.

14. The set of gene specific primers according to Claim 13, wherein at least two of the twenty distinct genes are from different gene functional classes.

15. The set of gene specific primers according to Claim 14, wherein the set comprises from 20 to 10,000 gene specific primers.

16. The set of gene specific primers according to Claims 13, 14 or 15, wherein the set comprises primers capable of amplifying at least a portion of the polynucleotides present on an array according to any of Claims 1 to 1 1.

17. The set of gene specific primers according to Claim 16, wherein the set comprises primers capable of amplifying at least 20 of the polynucleotides present on an array according to any of Claims 1 to 1 1.

18. A method for detecting expression of a gene using a hybridization assay, said method comprising: contacting at least one labeled target polynucleotide sample with an array according to any of Claims 1 to 11 under hybridization conditions sufficient to produce a hybridization pattern; and detecting said hybridization pattern.

19. The method according to Claim 18, wherein said method further comprises washing said array prior to said detecting step.

20. The method according to Claims 18 or 19, wherein said method further comprises preparing said labeled target polynucleotide sample.

21. The method according to Claim 20, wherein said preparation comprises: obtaining a sample of nucleic acids from a physiological source; and generating a population of labeled nucleic acids from the nucleic acids sample by using a set of a representative number of distinct gene specific primers according to any of Claims 13 to 17; whereby said labeled target polynucleotide sample is produced.

22. The method according to Claims 20 or 21, wherein said preparing comprises conjugating a detectable label to a functionalized target polynucleotide.

23. The method according to any of Claims 18 to 22, where said method further comprises: generating a second hybridization pattern; and comparing said hybridization patterns.

24. The method according to Claim 23, wherein said hybridization patterns are generated on the same array.

25. The method according to Claim 23, wherein the second hybridization patters are generated on different arrays.

26. A kit for use in a hybridization assay, said kit comprising: an array according to any of Claims 1 to 11.

27. The kit according to Claim 26, wherein said kit further comprises reagents for generating a labeled target polynucleotide sample.

28. The kit according to Claims 27, wherein said reagents comprise a set of a representational number of gene specific primers according to any of Claims 13 to 17.

29. A kit for use in detecting the differential expression of genes of a plurality of physiological sources, the kit comprising: a set of a representative number of distinct gene specific primers according to any of

Claims 13 to 17.