Classifications

• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
  • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
  • C12Q1/68—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving nucleic acids
  • C12Q1/6813—Hybridisation assays
  • C12Q1/6827—Hybridisation assays for detection of mutation or polymorphism
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
  • C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
  • C12Q1/68—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions involving nucleic acids
  • C12Q1/6813—Hybridisation assays
  • C12Q1/6834—Enzymatic or biochemical coupling of nucleic acids to a solid phase
  • C12Q1/6837—Enzymatic or biochemical coupling of nucleic acids to a solid phase using probe arrays or probe chips

Definitions

• the present invention relates to a DNA chip system for detecting a mutation in a target nucleic acid so that only the DNA carrying the mutation remains on the chip at the end of the method.
• the invention relates to a method in which an ⁇ S-phosphothioatedésoxynucleotide complementary to the mutation is added by means of a DNA polymerase to the 3 'end of the probe hybridized to the target nucleic acid and in which an exonuclease is added so that only the extended probes are not degraded.
• the presence or absence of the mutation is detected by direct or indirect measurement of the presence or absence of DNA at a given site on the chip.
• the chip comprises transistors of the ISFET type or piezoelectric transducers.
• Mutations in germ cells or in somatic lines can have dreadful consequences on the organism, for example by causing hereditary genetic diseases or the appearance of cancer.
• the effect of a mutation is closely linked to its location in DNA. In the case of a mutation in a coding region, the loss of the function of the coded protein can be observed. If the mutation is in a regulatory region, DNA expression can be abolished or increased.
• a mutation in a gene involved in cancer in the germ line does not necessarily mean that the individual concerned will actually contract a tumor, but only that the risk of it is increased.
• the objective underlying the present invention has been to develop a technique allowing the simultaneous determination of several nucleotides to be identified and therefore the diagnosis of mutations and polymorphisms of genes, or the identification of pathogenic microorganisms or genetically modified. More specifically, the problem lies in a compilation of different biochemical, electronic or optical techniques within the same device which would be particularly easy to use, which could generate signals with a low noise / signal ratio without requiring any processing. tedious and complicated interpretation. It is also important to provide the most integrated device possible and at low cost.
• DNA chips could solve the aforementioned problems, but as they are proposed in the state of the art, they have inherent limits which hamper their large-scale exploitation.
• a chip consists of a multitude of nucleic probes precisely fixed at defined locations on a solid support in the form of flat or porous surfaces made of different materials allowing such fixing.
• the choice of support was conditioned by its ability to allow the fixation of the probes.
• Materials such as glass, silicon or polymers are commonly used in the prior art.
• the probes are grafted onto these surfaces during a first step called “functionalization” in which an intermediate layer of reactive molecules is added to capture or fix the probes.
• Glass is a material of choice since it is inert, non-polar and mechanically stable. It has been used in a process for the in situ synthesis of oligonucleotides by photochemical addressing developed by the company Affymetrix.
• This technique consists in using a glass surface activated by the addition of silane carrying NH 2 or OH groups; Sheldon EL (1993) Clin. Chem. 39 (4), 718-719. Another method is to cover the glass surface with poly-L-lysine, deposit the probes and then perform the transplant by exposure to UN. Mention may also be made of polymers such as the polypyrroles developed by CIS Biointernational.
• the AD ⁇ from the samples is allowed to hybridize under predefined conditions.
• the basic composition of the duplex is an essential element influencing its stability which is closely dependent on the melting temperature (Tm).
• Tm melting temperature
• the mismatches cause a drop in Tm, which results in the elimination of nucleic acids which have not completely hybridized during the washing step.
• the length of the probes represents a significant technical difficulty when it is desired to detect many mutations simultaneously using different probes of different length.
• An alternative approach is to use the properties of semiconductor materials. For example, one can choose a solid support based on silicon (Si) covered with a dielectric (Si ⁇ 2) on which the probes are fixed. Under certain suitable polarization conditions, a current, sensitive to changes in the load of the semiconductor, normally flows from the source to the drain. Hybridization between the probes and the DNA of the sample leads to a modification of the charge density of the semiconductor at the Si / Si ⁇ 2 interface. This variation can be measured and makes it possible to detect the specific hybridization between probes and target nucleic acids; Souteyrand et al. (1995) Letter from the Chemical Sciences 54, 9-11. This technique is used by the IFOS laboratory of the isme Centrale de Lyon.
• the chips intended for the analysis of mutations must be able to analyze using probes each base of an already known sequence or to detect mutations previously identified as being implicated in diseases such as cancer.
• these probes are described as comprising a part homologous to the wild type sequence and a modification (substitution, deletion, addition) localized in the middle of the sequence in order to standardize the hybridization conditions.
• the probes are organized in tetrads, sets of four elements in which one of the probes has in the central position the base homologous to the nucleotide found in the wild-type sequence; the other three probes containing the other three possible bases.
• This full analysis is described in Chee M. et al. (1996) Science 274, 610-613. According to this technique, a DNA chip has been developed to detect heterozygous mutations in the BRCA1 gene by measuring fluorescence.
• This system comprises approximately 10 5 oligonucleotides allowing the detection of substitutions and insertions of single bases, as well as long deletions of 1 to 5 nucleotides.
• the hybridization analysis system is based on two-color labeling (green with fluorescein and red with a combination of phycoerythrin and streptavidin); Hacia JG et al. (1996) Nature Genêt 14, 441-447.
• a DNA microarray system which is based on the specific hybridization of the probe (in this case serving as an oligonucleotide primer) with the target DNA, the extension la probe with selective addition of at least one oligonucleotide derivative to the 3 'end of the primer complementary to the target DNA; the primer thus elongated being resistant to digestion by an exonuclease, in particular by exonuclease III.
• the primer thus elongated being resistant to digestion by an exonuclease, in particular by exonuclease III.
• the DNA remains present at a given site on the chip only when the following conditions are met: a) hybridization between the probe and the target DNA of the sample, and b) presence of a complementary base in the Target DNA allowing the incorporation of the ⁇ S-phosphothioatedésoxynucleotide in the probe; which prevents its degradation by nuclease.
• the probe does not hybridize with the target DNA, there is elimination of the probe at a given site (microwell or other). Likewise, if the target DNA does not contain the complementary base of the given ⁇ S-phosphothioatedésoxynucleotide, the latter is not incorporated and the probe is then digested by the nuclease.
• This technique associated with an electronic solid support makes it possible to measure the difference in charge, conductance, resistance, impedance or any other effect of electrical variation, variation of field effect or any variation of mass causing an electrical variation.
• piezoelectric transducer on the solid support.
• a support can be a semiconductor system, in particular an ISFET system (Ion Sensitive Field Effect Transistor). This system therefore receives simple signals 0 (no DNA) or 1 (DNA) of the binary type which can be directly transmitted to a data processing system, in particular to a computer.
• the present invention relates to a method for detecting a mutation in position n in a target nucleic acid, characterized in that it comprises the following steps: a) hybridization of a probe linked in 5 'to a support solid of the DNA chip type with a target nucleic acid, the 3 ′ end of said probe hybridizing at most to nucleotide n-1 of the target nucleic acid, b) elongation of the probe hybridized in step a) by incorporation in the 5'-3 'direction of nucleotides complementary to said target nucleic acid by means of a reaction mixture comprising at least one nucleotide derivative resistant to degradation by an exonuclease and a DNA polymerase, c) digestion by said exonuclease so that only the probes extended in step b) are not degraded, washing, d) detection of the presence or absence of the mutation by direct or indirect measurement of the presence or absence of DNA.
• the key steps of this process are illustrated in the example presented in
• DNA polymerase means any natural or modified enzyme having polymerase activity. Mention may be made, for example, of pol exo- DNAs, in particular T7 or the klenow fragment.
• Exonuclease is understood to mean any natural or modified enzyme having an exonuclease activity. Mention may be made, for example, of exonuclease III.
• DNA polymerase having a pyrophophorolysis activity in the presence of a high concentration of pyrophosphate, this enzyme adds a pyrophosphate on the last phosphodiester bond and therefore releases the nucleotide at 3 '.
• This product is available from Promega under the brand READIT TM, and variants using a luciferase revealing system is available under the brand READase TM.
• the presence or absence of the mutation can be demonstrated, according to a first embodiment, by measuring the modification of a property of the solid support linked to the presence or to the absence of DNA.
• Another solution is to detect the presence or absence of the mutation by optical reading of the presence or absence of DNA.
• optical reading means any measurement of absorption, transmission or emission of light which may possibly be at a specific wavelength (260 nm for example) either directly from DNA or from any marker molecule linked to the probe.
• This definition also includes any measurement of the fluorescence emitted by markers (fluorescein and / or phycoerythrin).
• nucleotide derivative means any nucleotide analog which resists degradation by a nuclease. Mention may be made, for example, of the ⁇ S-phosphothioatedesoxynucleotides such as ⁇ S-dATP, ⁇ S-dTTP, S-dCTP, ⁇ S-dGTP, ⁇ S-dUTP and ⁇ S-dITP. These nucleotide derivatives can be labeled in particular with a fluorescent label.
• a “probe” is defined as being a nucleotide fragment comprising for example from 10 to 100 nucleotides, in particular from 15 to 35 nucleotides, having a specificity of hybridization under determined conditions to form a hybridization complex with a target nucleic acid.
• the probes according to the invention whether specific or non-specific, can be immobilized, directly or indirectly, on a solid support and can carry a labeling agent allowing or improving their detection.
• the probe serves as a primer in the context of the invention since the objective is to incorporate a nucleotide modified in position n corresponding to the position of the mutation that is sought.
• the 3 ′ end of the probe therefore ends at the maximum and preferably at n ⁇ 1.
• the probe can be immobilized on a solid support by any suitable means, for example by covalence, by adsorption, or by direct synthesis on a solid support. These techniques are described in particular in patent application WO 92/10092.
• the probe can be marked by means of a marker chosen, for example, from radioactive isotopes, enzymes, in particular enzymes capable of acting on a chromogenic, fluorigenic or luminescent substrate (in particular a peroxidase or an alkaline phosphatase) or alternatively enzymes producing or using protons (oxidase or hydrolase); chromophoric chemical compounds, chromogenic, fluorigenic or luminescent compounds, nucleotitic base analogs, and ligands such as biotin.
• a marker chosen, for example, from radioactive isotopes, enzymes, in particular enzymes capable of acting on a chromogenic, fluorigenic or luminescent substrate (in particular a peroxidase or an alkaline
• the labeling of the probes according to the invention is carried out by elements selected from ligands such as biotin, avidin, streptavidin, dioxygenin, haptens, dyes, luminescent agents such as radioluminescent, chemiluminescent, bioluminescent agents, fluorescent, phosphorescent.
• ligands such as biotin, avidin, streptavidin, dioxygenin, haptens, dyes, luminescent agents such as radioluminescent, chemiluminescent, bioluminescent agents, fluorescent, phosphorescent.
• luminescent agents such as radioluminescent, chemiluminescent, bioluminescent agents, fluorescent, phosphorescent.
• Another possibility is to label the probe with a peptide comprising an epitope recognized by a given antibody. The presence of this antibody can be revealed by means of a second labeled antibody.
• step d) comprises the measurement of a variation of a physico-chemical, electrical, optical or mechanical characteristic of the solid support in particular chosen from the charge, the doping, the conductivity, the resistance, impedance or any other electrical variation effect, the field effect or any mass variation resulting in a field variation, the resonant frequency or electroacoustic admittance.
• the solid support consists of a DNA chip which may include a material selected from semiconductors, dielectrics and piezoelectric transducers or an or-prism structure.
• a group containing a metal atom can be grafted onto the probes, in particular a ferrocene group.
• any measure of the change in an optical property of the solid support related to the presence or absence of DNA on said support is meant any measure of the change in an optical property of the solid support related to the presence or absence of DNA on said support.
• This embodiment of the invention therefore includes the measurement of the refractive index of the support. It is possible to measure by this technique the internal and external reflection, for example of ellipsometry, of the evanescent waves comprising the measurement of the SPR (surface plasmon resonance), Brewster's angle of refraction, critical angle of reflection, FTR (frustrated total reflection), or STIR (scattered total internai reflection).
• SPR surface plasmon resonance
• FTR frustrated total reflection
• STIR sintered total internai reflection
• step d) consists in measuring the quantity of light transmitted, absorbed or emitted.
• the support is made of a transparent material, in particular glass.
• the techniques for attaching the probes to the glass are well known to those skilled in the art. One can for example measure the fluorescence of the previously marked probes and carry out the optical reading with a CCD camera.
• an ⁇ S-phosphothioatedésoxynucleotide such as ⁇ S-dATP, ⁇ S-dTTP, ⁇ S-dCTP, ⁇ S-dGTP, ⁇ S-dUTP or ⁇ S-dITP is incorporated at the 3 ′ end of the probe.
• This can be done for example by LCR, or preferably by asymmetric PCR, the probe then serving as a primer being in each case chemically coupled at its 5 ′ end to the solid phase at a predetermined site.
• the ⁇ S-phosphothioatedésoxynucleotides can be easily incorporated into polynucleotides by all the polymerases and reverse transcriptases tested, which makes it possible to use DNA polymerases at a more advantageous cost price than in other detection of mutations.
• the prior fixing of the probes at a specific site on the chip can be carried out by microfluidic addressing techniques developed by the company Orchid or photochemical techniques by the company Aff ⁇ métrix or even electro-addressing by Cis-Bio international, said techniques being within reach of the skilled person.
• the target DNA is hybridized with a probe so that its 3 'end ends immediately before the nucleotide to be identified.
• An ⁇ S- phosphothioatedésoxynucleotide is added to the 3 'end of the probe by means of a DNA polymerase and is therefore complementary to the nucleotide to be identified.
• Step b) can be carried out in parallel on 4 sites (in tetrads) for each probe, with the addition of a reaction mixture comprising a different ⁇ S- phosphothioated deoxynucleotide per site. It is thus possible to detect a mutation at a given position in the target DNA whatever the nature of the basic substitution.
• the method according to the invention is particularly intended for the detection of mutations in genes involved in diseases. Mention may in particular be made of hereditary genetic diseases, in particular hemochromatosis, sickle cell anemia, ⁇ and ⁇ thalassemia, cystic fibrosis, hemophilia, and mutations in the genes involved in cancer, for example in the Ras, p53, BRCA1 genes. An exhaustive list of mutations in these genes is given on the following website: ftp: // ncbi .nlm .nih. O v / repository / OMIM / morbidmap
• the method according to the invention is useful when studying the polymorphism of genes or of any genetic region and for the detection and / or identification of genetically modified organisms (GMOs).
• GMOs genetically modified organisms
• Such a method may include a system for detecting the presence or absence of DNA at a given site of a chip, in particular a piezoelectric transducer, a field effect transducer, an optical density reader or fluorescence. It can be coupled to a data processing system, in particular to a computer.
• kits comprising a DNA chip on which probes are fixed and at least one of the elements chosen from: a batch of 4 reaction mixtures each comprising a different ⁇ S- phosphothioatedésoxynucleotide selected from ⁇ S-dATP, ⁇ S-dTTP, ⁇ S-dCTP and ⁇ S-dGTP, a DNA polymerase, an exonuclease, in particular exonuclease III, a batch of solutions for dissolve the DNA polymerase and / or the exonuclease in the case where these enzymes are in the form of lyophilized powder.
• the chips of this kit comprise a solid support of the ISFET, ENFET type.
• This kit is intended for the detection of gene mutations implicated in diseases, in particular in hereditary genetic diseases and in cancer. It can also be used for genetic typing and the study of gene polymorphism (for the detection of SNPs (Single Nucleotide Polymorphism)) and for the detection and / or identification of genetically modified organisms (GMOs).
• GMOs genetically modified organisms
• Figure 1 schematic representation of a particular mode of implementation method according to the invention. a) hybridization of a probe linked in 5 ′ to a solid support of the DNA chip type with a target nucleic acid, the 3 ′ end of said probe hybridizing to nucleotide n-1 of the nucleic acid target, b) incorporation in the 5 '-3' direction of an ⁇ S-dATP c) digestion with exonuclease III so that only the probes elongated in step b) are not degraded and washed, d) detection the presence or absence of the mutation by direct or indirect measurement of the presence or absence of DNA.
• Figure 2 classic structure of a support of the Metal-Oxide-Semiconductor (MOS) type.
• MOS Metal-Oxide-Semiconductor
• Figure 4 principle of the chips according to the invention with a series of tetrads for the detection of mutations in the hemochromatosis gene.
• Example 1 particular embodiment of the invention
• Target DNA comprising a DNA fragment which contains a T— »G mutation at position n to be identified, is added to the surface of the chip. Said DNA fragment hybridizes to the complementary oligonucleotide probe labeled with FITC (fluorescein isothiocyanate) immobilized at a site defined on the support of the chip.
• FITC fluorescein isothiocyanate
• an incorporated phosphothioatedésoxynucleotide ( ⁇ SdATP) is found in position complementary to the nucleotide T in position n. If the phosphothioatedésoxynucleotide which is in the reaction mixture is not complementary to the nucleotide to be identified (different from ⁇ SdATP), the probe is not extended in 3 '.
• Exonuclease III then degrades all the probes which have not been extended by a phosphothioatedésoxynucleotide. Detection is then carried out by binding an anti-FITC conjugate conjugated to peroxidase. Once the enzyme-substrate reaction has been carried out, a strong measurement signal therefore indicates whether the nucleotide to be identified (T) is complementary to the phosphothioatedésoxynucleotide ( ⁇ SdATP) which was added to the reaction mixture for the reaction with the polymerase.
• T nucleotide to be identified
• ⁇ SdATP phosphothioatedésoxynucleotide
• Example 2 Use of an ISFET or ENFET type support (Jaffrezic-Renault N., Microsensors and Microtechnics 225-235).
• Figure 3A (taken from Jaffrezic-Renault) schematically represents the ISFET structure. This derives from the MOSFET structure (see Figure 2; Jaffrezic-Renault) in the sense that the metal grid is replaced by the electrolytes and the reference electrode.
• Vj is a function of the chemical characteristic of the solution ( ⁇ 0 is the potential difference between the sensitive membrane and the solution).
• ⁇ 0 is the potential difference between the sensitive membrane and the solution.
• the drain current is kept constant and the voltage variation VQ which is proportional to ⁇ 0 is measured .
• the membrane sensitive to pH consists of thin layers of Al O 3 , Ta 2 O 5 , If 3 N 4 .
• Other membranes sensitive to K + , Na + , Ag + , F “ , Br “ , I “ , Ca 2 + and NO 3 " ions are also available.
• Example 3 Use of a solid support of the piezoelectric transducer type.
• Certain materials such as Si0 2 , TiO Ba, LiNbO 3 and piezoelectric polymers (PVF2) have the property of being deformed when a physical stress is applied; Perrot H. and Hoummady M., Piezoelectric transducers. A measurable electrical potential then appears due to the pressure exerted by the mass of DNA molecules. This measurement can be the resonant frequency or the admittance around the resonant frequency.
• the DNA is in a liquid medium. Therefore, one can also measure the electroacoustic admittance or conductivity which depends in particular on the density and viscosity of the solution containing the electrolytes. We can thus detect a difference of 100 pg in liquid medium.
• the point mutations designated HHP-1, HHP-19 and HHP-29 in US 5,753,438 can be detected by means of the method according to the invention using a probe whose 3 'end ends at n-1 of the position of the mutation:
• the following probe can be used: 5'TATATAGATATTAGATATAAAGAA3 '(SEQ ID N ° 4)
• the following probe can be used: 5 ⁇ ACCCCTAAAATATCTAAAAT3' (SEQ ID # 5)
• the four ohgonucleotides SED ID No. 6 to 9 can be used for the identification of the nucleotide which is located immediately after the 3 'end of these ohgonucleotides.
• a tetrad system can be provided for this purpose (see Figure 4).
• Example 5 detection of mutations in genes involved in cancer.
• the detection method according to the invention with a chip comprising specific probes for each of the above mutations therefore appears essential to guarantee a patient an exact diagnosis.
• WO 91/13075 presents probes making it possible to detect point mutations in codon 12 of K-ras.
• the following probes can be grafted onto the chip and therefore guarantee complete detection of all possible mutations:
• This work aims to determine the genetic polymorphism of DNA through the use of a new biochip technique.
• This technique consists in the gene amplification of interest, the hybridization of the amplification products obtained on a solid support (substrate) previously prepared by fixing a probe covalently, extension of the probe with a modified nucleotide, revelation degradation or protection of the probe.
• the size of the amplification fragments expected in each case is approximately 100 bp
• the amplifications obtained are checked on 1.5% agarose gel
• the probes used for C282Y and H63D are those described in Example 4: two probes for each genotype to be determined.
• the probes are fixed following a chemical modification of the surface allowing the reactivity of the 5 'ends of the probe ohgonucleotides.
• the measurement of the fluorescence emission due to Cy3 is carried out (reading on a scanner for example) on each pad / chip.

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