CN114540472B - Three-generation sequencing method - Google Patents

Three-generation sequencing method Download PDF

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CN114540472B
CN114540472B CN202210182810.8A CN202210182810A CN114540472B CN 114540472 B CN114540472 B CN 114540472B CN 202210182810 A CN202210182810 A CN 202210182810A CN 114540472 B CN114540472 B CN 114540472B
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陈路
林静雯
宋俊伟
唐超
徐梦莹
张丹
赵苑村
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West China Second University Hospital of Sichuan University
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Abstract

The invention particularly relates to a novel three-generation sequencing method. The method provided by the invention can improve the matching rate of the bar code and UMI, and simultaneously can improve the sequencing accuracy of DNA (for example, full-length cDNA), thereby being beneficial to obtaining correct information in practical application scenes. The method is suitable for various platforms based on single-cell sequencing and space transcriptome sequencing, is expected to solve the problems existing in the current stage of single-cell or space transcriptome full-length sequencing to a certain extent, and has wide application scenes.

Description

Three-generation sequencing method
Technical Field
The invention belongs to the field of gene sequencing, and particularly relates to a novel three-generation sequencing method.
Background
With the development of single-cell or space transcriptome sequencing technology, cell heterogeneity and cell-cell difference can be explored from the cell perspective by combining single-cell information, and tissue microenvironment and cell-cell interaction can be deeply understood by combining space position information. The current mature single Cell or space transcriptome sequencing means are to connect the two ends of the sequencing molecule (cDNA) with a bar code (CB, cell Barcode) for distinguishing single cells or a bar code (SB, spatial Barcode) for distinguishing space information, each cDNA is provided with a unique molecular identifier (UMI, unique Molecular Identifier), then break the cDNA by the next generation sequencing technology (NGS, next Generation Sequencing) and then carry out high throughput sequencing to obtain sequence information, and finally distinguish the sequence information of single cells or single space positions by CB or SB. Thus, obtaining accurate SB (or CB) and UMI is critical for spatial (or single cell) transcriptome sequencing.
However, NGS technology, because of its nature of having to interrupt cDNA, cannot obtain full-length information of the sequence, limits the differentiation of multiple isoforms (isoforms) of mRNA from the same gene due to alternative splicing (AS, alternative Splicing), and is not beneficial to mRNA post-transcriptional level regulation and transcript polymorphism studies. Currently, only two large sequencing platforms, namely oxford nanopore sequencing technology (ONT, oxford Nanopore Technologies) as a third generation sequencing technology and single molecule fluorescence sequencing (SMRT, single Molecule Real Time Sequencing) developed by pacific bioscience corporation (PacBio, pacific Biosciences), can achieve end-to-end (end-to-end) complete sequencing of full-length cDNA. The PacBIO's Iso-Seq workflow, as a gold standard for full-length cDNA sequencing, can produce about twenty thousand high quality full-length cDNA reads in one run cycle. The ONT can now produce millions of reads with a minion chip, and its strong flexibility, scalability and lower cost have become popular with laboratories, and have become the first tool for full-length transcriptome research.
However, ONT sequencing determines a relatively low sequencing accuracy due to the sequencing principle of the electrical signal of Kong Douqu nm, and the error rate can reach 5-25%, especially the errors of the homopolymer and the tandem repeat region (tandem repeats region). If full-length cDNA sequencing is required for single cell or spatial transcriptome libraries (library), CB or SB can not be accurately disassembled, and few reads can be made at the single cell or spatial location that can be correctly identified.
To solve this problem, volden et al first proposed the R2C2 method (Rolling Circle Amplification to Concatemeric Consensus) in 2018, namely by recombining a 200bp unrelated sequence to circularize the cDNA, generating a long tandem repeat (concatemer) by rolling circle amplification (RCA, rolling Circle Amplification) and performing ONT sequencing, and then mutually correcting the multiple-sequenced cdnas into consensus sequences (consensus) after disassembling the tandem repeat, thereby improving sequencing accuracy. Volden et al applied the R2C2 method to a commercial 10X Genomic single cell transcriptome platform (10 XR2C 2) in 2020, but its resolution of SB was only about 32.75% of all reads, while the match of SB and UMI was 15.86%. In addition, methods similar to R2C2 but different in application scenario have been developed in recent years, such as HiFRe for ultra-short DNA, circAID-p-seq for Phospho-RNA, TP53-specific CyclomicsSeq for circulating tumor DNA (ctDNA, circulating tumor DNA), and the like, which have proved to be widely used by the theory of correcting ONT by tandem repeats.
Meanwhile, another method for improving the matching rate of the bar code and the UMI is also provided. The methods of ScNaUmi-seq, scNapBar and the like are that the same single cell sequencing library is respectively subjected to second generation and ONT sequencing, and CB and UMI in the ONT data are identified and disassembled by taking the second generation data as reference guidance, so that ONT reads of accurate CB and UMI are obtained. However, the method can only improve the matching rate of the bar code and UMI, but can not improve the sequencing accuracy of cDNA, and the reads of the disassembled CB only account for 38.76% of all reads, and the matching rate of the disassembled CB and UMI is 29.45%, so that the problem that the matching rate of the bar code and UMI is not high can not be really solved.
Disclosure of Invention
In view of this, the present invention provides a nucleic acid sequencing method comprising: s1, cyclizing a nucleic acid sequence to be detected to obtain a cyclized nucleic acid sequence, wherein the nucleic acid sequence to be detected comprises a nucleic acid embedded sequence, a marker sequence and fixed sequences respectively positioned at two ends of the nucleic acid sequence to be detected, and the cyclized cyclizing mode comprises PLP; s2, performing rolling circle amplification by taking the circularized nucleic acid sequence as a template to obtain a rolling circle amplification product; s3, sequencing the rolling circle amplification product to obtain an original tandem repeat sequence; s4, based on the fixed sequence, performing first-round identification matching on the original tandem repeat sequence, and extracting a first sequence of an identification region; s5, based on the fixed sequence and the identification sequence, performing second-round identification matching on the original tandem repeat sequence, so as to correct the first identification region sequence and obtain a second identification region sequence; s6, based on the second sequence of the identification region, disassembling the original tandem repeat sequence to obtain one or more sub-read lengths, wherein the sub-read lengths comprise intermediates of the nucleic acid embedded sequence and the second sequence of the identification region; s7, performing multi-sequence comparison on the sub-read length, and extracting a first nucleic acid consensus sequence, wherein the first nucleic acid consensus sequence is taken as a sequencing result of the nucleic acid embedded sequence.
Further, the method further comprises: and before the second round of identification matching, comparing the original tandem repeat sequences based on the first sequence of the identification region, and extracting a second consensus sequence of the nucleic acid.
Further, the identification sequence comprises a Unique Molecular Identifier (UMI) and/or a barcode, wherein the unique molecular identifier of the test nucleic acid sequence is uniquely determined, and the barcode of the test nucleic acid sequence provides information for identifying the test nucleic acid sequence.
Further, the barcode includes a spatial barcode and/or a cellular barcode.
Further, the first sequence of the identification region comprises a fixed sequence matching sequence matched with the fixed sequence, and 28-58bp which is directly connected with the fixed sequence matching sequence in the direction of the identification sequence.
Further, the S3 further comprises third generation sequencing the rolling circle amplification product and obtaining third generation sequencing data of the rolling circle amplification product.
Further, the third generation sequencing includes nanopore sequencing and/or single molecule fluorescence sequencing.
Further, the step S5 further comprises performing second generation sequencing on the nucleic acid sequence to be tested and obtaining second generation sequencing data of the nucleic acid sequence to be tested.
Further, the second generation sequencing includes one or more of ion semiconductor sequencing, pyrosequencing, sequencing by ligation, sequencing by synthesis, combined probe anchor sequencing by synthesis, and reversible end termination sequencing.
Further, the calibrating is to calibrate the first sequence of the identification region by using a reference sequence, wherein the reference sequence is from second generation sequencing data of the nucleic acid sequence to be tested.
Further, the S1 further comprises amplifying the test nucleic acid sequence to generate a library of the nucleic acid insert sequences, wherein the amplifying precedes the circularizing the test nucleic acid sequence.
Further, the nucleic acid insert sequence includes DNA.
Further, the nucleic acid insert sequence includes cDNA formed by reverse transcription of RNA in the biological sample.
Further, the nucleic acid first consensus sequence is highly accurate.
Further, the original tandem repeat sequences are aligned according to a guide tree algorithm.
Further, the alignment is optionally a profile-to-profile alignment.
Further, the sub-read lengths are subjected to multi-sequence comparison according to a dynamic programming algorithm.
Further, the biological sample includes one or more of a fresh tissue slice, a fresh single cell suspension, and extracted tissue RNA.
Further, the biological sample is derived from a tissue and/or organ of an organism.
Further, the biological sample comprises one or more of heart, kidney, liver, spleen, stomach, lung, ovary, breast, lymph node, tongue, brain, large intestine, small intestine, eye, skeletal muscle, testis, thyroid samples.
In another aspect, the present invention also provides a third generation sequencing system, comprising: the sequence information receiving module is used for receiving original tandem repeat sequence information of a nucleic acid sequence to be detected, wherein the nucleic acid sequence to be detected comprises a nucleic acid embedded sequence, an identification sequence and fixed sequences respectively positioned at two ends of the nucleic acid sequence to be detected, and the original tandem repeat sequence is obtained by rolling circle amplification by taking the cyclized nucleic acid sequence to be detected as a template; the first matching module is used for carrying out first round of identification matching on the original serial repeated sequence based on the fixed sequence, and extracting a first sequence of an identification area; the second matching module is used for carrying out second round of identification matching on the original tandem repeat sequence based on the fixed sequence and the identification sequence, so as to correct the first sequence of the identification region and obtain a second sequence of the identification region; the disassembly module is used for disassembling the original tandem repeat sequence based on the second sequence of the identification region to obtain one or more sub-read lengths, wherein the sub-read lengths comprise the nucleic acid embedded sequence and the second sequence of the identification region; and the comparison module is used for carrying out multi-sequence comparison on the sub-read length, extracting a first nucleic acid consensus sequence, wherein the first nucleic acid consensus sequence is taken as a sequencing result of the nucleic acid embedded sequence.
Further, the cyclizing means for cyclizing comprises PLP.
The comparison module may also be used to: and before the second round of identification matching, comparing the original tandem repeat sequences based on the first sequence of the identification region, and extracting a second consensus sequence of the nucleic acid.
Further, the identification sequence comprises a Unique Molecular Identifier (UMI) and/or a barcode, wherein the unique molecular identifier of the test nucleic acid sequence is uniquely determined, and the barcode of the test nucleic acid sequence provides information for identifying the test nucleic acid sequence.
Further, the barcode includes a spatial barcode and/or a cellular barcode.
Further, the first sequence of the identification region comprises a fixed sequence matching sequence matched with the fixed sequence, and 28-58bp which is directly connected with the fixed sequence matching sequence in the direction of the identification sequence.
Further, the original tandem repeat information of the nucleic acid sequence to be tested is obtained by third generation sequencing.
Further, the third generation sequencing includes nanopore sequencing and/or single molecule fluorescence sequencing.
Further, the sequence information receiving module can also be used for receiving second generation sequencing information of the nucleic acid sequence to be tested.
Further, the second generation sequencing includes one or more of ion semiconductor sequencing, pyrosequencing, sequencing by ligation, sequencing by synthesis, combined probe anchor sequencing by synthesis, and reversible end termination sequencing.
Further, the calibrating is to calibrate the first sequence of the identification region by using a reference sequence, wherein the reference sequence is from second generation sequencing information of the nucleic acid sequence to be tested.
Further, the nucleic acid insert sequence includes DNA.
Further, the nucleic acid insert sequence includes cDNA formed by reverse transcription of RNA in the biological sample.
Further, the nucleic acid first consensus sequence is highly accurate.
Further, the original tandem repeat sequences are aligned according to a guide tree algorithm.
Further, the alignment is optionally a profile-to-profile alignment.
Further, the sub-read lengths are subjected to multi-sequence comparison according to a dynamic programming algorithm.
Beneficial technical effects
At present, mature single cell or space transcriptome sequencing platforms are used for carrying out high throughput sequencing after a nucleic acid sequence to be sequenced is connected with random UMI and/or bar codes and then a nucleic acid sequence to be tested is broken by an NGS technology so as to obtain sequence information. Wherein, according to the difference of the sequencing objects, the bar code further comprises a bar code (Cell Barcode) for distinguishing single cells and a bar code (Spatial Barcode) for distinguishing Spatial information; while UMI is used to distinguish the same amplification product from different amplification products. Thus, obtaining accurate barcodes and UMI is critical to the practical application scenario of spatial (or single cell) transcriptome sequencing.
At present, a complete, mature, high-throughput and low-cost scheme capable of solving the full-length sequencing of single cells or space transcriptomes does not exist. There are a number of limitations in the prior art that expect to solve the above problems by single cell or spatial transcriptome platforms in combination with ONT sequencing platforms: for example, 10XR2C2 not only requires the introduction of extraneous sequences, reducing data validity, but also the bar code and UMI match rates are not high; the methods such as ScNaUmi-seq and ScNapBar also have the problem of low matching rate of bar codes and UMI, and the sequencing accuracy of cDNA cannot be really improved.
Aiming at the problems, the invention provides a novel three-generation sequencing method. The method provided by the invention has the advantages that the nucleic acid sequence to be detected is subjected to lock probe cyclization, an irrelevant sequence is not introduced, the accidental occurrence of random looping is avoided, and the effectiveness of data is further improved. The method of the invention carries out two-round matching on the original tandem repeat sequence generated by the third generation sequencing: the first round is based on fixed sequences (10 and 12 in fig. 1) and allows for certain base insertions, deletions and mismatches, thereby extracting all potential identification sequences (barcodes and UMI, 14 and 18 in fig. 1) in the original tandem repeat sequence; the second round of matching the original tandem repeat sequence again based on the fixed sequence and the corrected identification sequences (10, 12 and 14 in fig. 1) improves the fault tolerance and the matching number and promotes the sequencing result of the nucleic acid embedded sequence to be more accurate; as a result, the two rounds of matching help to obtain highly accurate identification sequences (i.e., bar codes and UMIs). And according to the region of the second round of matching, the original tandem repeat sequence is disassembled into sub-read lengths, and the multiple sequences are aligned, so that the nucleic acid embedded sequence with high precision (20 in FIG. 1) is finally obtained.
In summary, the method provided by the invention improves the matching rate of UMI and bar code and the sequencing accuracy of DNA (e.g. full-length cDNA), which is helpful to obtain correct information (e.g. identification of space-specific isomers) in practical application scenarios. The method provided by the invention is suitable for various platforms based on single-cell sequencing and space transcriptome sequencing, and is expected to solve the problems existing in the full-length sequencing of single cells or space transcriptomes to a certain extent.
Terminology
As used herein, "nucleic acid sequence to be tested" refers to processing a nucleic acid sequence desired to be sequenced into a library-prepared linear DNA suitable for a sequencing platform (e.g., a second generation sequencing-based platform and a third generation sequencing-based platform). The nucleic acid sequence to be sequenced may be DNA or cDNA reverse transcribed from RNA. In some embodiments, the "test nucleic acid sequence" includes a nucleic acid insert sequence (i.e., a nucleic acid sequence to be sequenced), an identification sequence directly linked to the nucleic acid insert sequence, and a fixation sequence flanking the test nucleic acid sequence, wherein the fixation sequence is directly linked to the identification sequence. Thus, "tag sequence orientation" refers to the orientation of the immobilized sequence to the tag sequence to which it is directly attached.
As used herein, "immobilized sequence" refers to a linker sequence that is generated based on the sequencing platform used, and that is located at each end of the nucleic acid sequence to be tested. In some embodiments, the "fixed sequences" are "Read1" based on priming sequencing of a spatial transcriptome platform (Visium Spatial Gene Expression,10X Genomics corporation) and "Template Switch Oligonucleotides (TSOs)" for template switching. According to the actual requirements, the fixed sequence can also be a linker sequence based on other sequencing platforms.
The term "amplification" generally refers to any process in which a target nucleic acid or portion thereof is formed into one or more copies. The term "Rolling Circle Amplification (RCA)" refers to a nucleic acid amplification reaction that amplifies a circular nucleic acid template (e.g., a DNA circle) by a rolling circle mechanism; the rolling circle amplification reaction is initiated by hybridization of a primer to the circular nucleic acid template, which is then followed by extension of the primer by a nucleic acid polymerase, which is continually hybridized to the circular nucleic acid template to repeatedly replicate the sequence of the circular nucleic acid template. The rolling circle amplification reaction typically produces a tandem repeat sequence (concatamer) comprising tandem repeat units of a circular nucleic acid template sequence. In some embodiments, the "test nucleic acid sequence" may be formed into the corresponding circular nucleic acid template for the rolling circle amplification reaction by various circularization means (e.g., PLP, R2C2, BTA, CL, SL).
As used herein, "marker sequence" refers to a nucleotide sequence that is associated with the nucleic acid sequence desired to be sequenced for identifying the nucleic acid sequence to be tested. As used herein, "marker sequence" includes UMI and/or bar codes, with one end of the marker sequence being linked to a "fixed sequence" and the other end being linked to a "nucleic acid sequence desired to be sequenced". In some embodiments, "UMI" can be used to distinguish the same amplification product from different amplification products (e.g., each amplified nucleic acid sequence of interest to be sequenced will have a different random UMI, the same UMI representing that the amplification product is from the same nucleic acid sequence of interest to be sequenced). As used herein, "barcode" includes cellular barcodes and spatial barcodes. In some embodiments, a spatial barcode may comprise a nucleic acid sequence that provides information of the spatial location of the nucleic acid sequence for which sequencing is desired, such as coordinates of a sample, associated with the barcode. In some embodiments, the cell barcode may comprise a nucleic acid sequence that provides information for determining which of the desired sequenced nucleic acid sequences originated from which cell.
As used herein, "identification region first sequence" refers to the sequence that matches the fixed sequence in the original tandem repeat sequence, and 28-58bp directly linked to the sequence that matches the fixed sequence in the identification sequence direction; the "second sequence of the identification region" refers to a sequencing result of the "identification sequence" obtained by correcting the "first sequence of the identification region" in the original tandem repeat sequence by using the sequence information of the "fixed sequence" and the "identification sequence" in the second generation sequencing data of the "nucleic acid sequence to be tested" (the method provided by the invention regards the sequence information as correct sequence information).
As used herein, a "sample" may comprise a single cell, a plurality of cells, a tissue, an organ, a microorganism, or the like. The "sample" may also be DNA or RNA derived from a single cell, a plurality of cells, a tissue, an organ, a microorganism or the like.
As used herein, "cDNA (complementary DNA)" refers to DNA formed by reverse transcription of a stretch of RNA (typically mRNA, but not limited to mRNA). "full-length cDNA" means cDNA comprising at least the complete coding region of mRNA from which it is derived.
As used herein, "intermediate of nucleic acid insert sequences" refers to a sequence corresponding to a "nucleic acid insert sequence" in tandem repeat units of a circular nucleic acid template sequence of tandem repeat sequences. In view of errors caused by rolling circle amplification reactions, the intermediate product of the nucleic acid insert sequence may be identical to the "nucleic acid insert sequence" or may be identical to a portion of the "nucleic acid insert sequence".
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It will be apparent to those of ordinary skill in the art that the drawings in the following description are of some embodiments of the invention and that other drawings may be derived from these drawings without inventive faculty.
FIG. 1 is a workflow diagram of the method of the present invention;
FIG. 2 is a comparison of five self-looping methods;
FIG. 3 is a graph of performance effects of the method of the present invention;
FIG. 4 is a graph showing the improvement of isomer (isofine) accuracy by the method of the present invention;
FIG. 5 is an experimental diagram of the method of the present invention facilitating the identification of a new splice point;
FIG. 6 is a diagram of an experiment of the method of the invention to facilitate quantification of RNA editing sites;
FIG. 7 is a flow chart of a method for sequencing nucleic acid provided by the invention;
FIG. 8 is a functional block diagram of a third generation sequencing system provided by the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
As used in this specification, the term "about" is typically expressed as +/-5% of the value, more typically +/-4% of the value, more typically +/-3% of the value, more typically +/-2% of the value, even more typically +/-1% of the value, and even more typically +/-0.5% of the value.
In this specification, certain embodiments may be disclosed in a format that is within a certain range. It should be appreciated that such a description of "within a certain range" is merely for convenience and brevity and should not be construed as a inflexible limitation on the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all possible sub-ranges and individual numerical values within that range. For example, a rangeThe description of (c) should be taken as having specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as individual numbers within such ranges, e.g., 1,2,3,4,5, and 6. The above rule applies regardless of the breadth of the range.
Embodiment one: materials and methods
1.1 splints design and Synthesis
The design of the clamp plate of the PLP (Padlockprobe) cyclization mode (PLP) in the invention can be flexibly designed according to the fixed sequences at two ends of different cDNA libraries, mainly aiming at connecting the two ends of the cDNA library end to end through the clamp plate, two clamp plates with reverse complementarity are usually required to be designed so as to realize the respective cyclization of the positive and negative strands of the cDNA. Taking the full-length cDNA generated by the procedure of the space transcriptome platform (Visium Spatial Gene Expression,10X Genomics company) as an example, the fixed sequences at both ends are: read1:5'-CTACACGACGCTCTTCCGATCT-3'; TSO: 5'-AAGCAGTGGTATCAACGCAGAGTACATGGG-3'. The two opposite complementary sequences of the clamp are respectively: splint-top: 5'-AGATCGGAAGAGCGTCGTGTAGAAGCAGTGGTATCAACGCAGAGTACATGGG-3'; splint-bottom: 5'-CCCATGTACTCTGCGTTGATACCACTGCTTCTACACGACGCTCTTCCGA TCT-3'.
1.2 phosphorylation amplification of full Length library and product purification
1.2.1 full Length library phosphorylation amplification
The cDNA was amplified as in Table 1 and the PCR apparatus was cycled as in Table 2.
TABLE 1cDNA amplification System
Remarks: since the 3'-5' exonuclease activity of KAPAHiFi hot start DNA polymerase is not hot start, the system should be formulated on ice in order to prevent degradation of the cDNA template or primer during formulation.
TABLE 2 setting of PCR instruments
1.2.2 purification and quality control of the product
The amplified product was purified using 0.6XAMPure XP beads, and then dissolved in 20. Mu.L of nuclease-free water. The concentration of the product is measured by using a Qubit instrument, and the length of the product is checked by using a Qseq instrument or other nucleic acid quality tester, wherein the concentration is more than 20ng/uL, and the length is consistent with that before amplification (generally more than 1 kb).
1.3 Rolling circle amplification and product purification
1.3.1 cyclization of cDNA
The meaning of each number in fig. 1 is as follows:
10: read1, 12: TSO,14: bar code, 16: poly (dT) VN,18: UMI,20: nucleic acid embedded sequences.
As shown in step (1) of FIG. 1, 100ng of full-length cDNA was taken, the peak value of the fragment length measured by Qsep1 was taken as the average fragment length, the molar concentration was calculated according to the following formula, and the mixture was mixed with Splint (Splint-top and Splint-bottom) having the same molar number as the cDNA, and diluted to 10. Mu.L with nuclease-free water. Incubate on PCR instrument at 95℃for 2min and immediately cool on ice.
The ligation reaction solutions were prepared according to Table 3. After 1h of room temperature ligation, 2. Mu.L of Exo III was added: lambda Exo: exoi=1: 9: the 10-ratio mixed enzyme was incubated on a heating block at 37℃for 30min, and then the cyclized product was purified using 0.6XAMPure XP magnetic beads, and after purification, dissolved in 50. Mu.L of nuclease-free water.
TABLE 3 connection reaction solution preparation System
1.3.2 Rolling circle amplification
Amplification was initiated on circular DNA using phosphorothioate modified 3' -5' exonuclease digestion resistant random hexamers with the last two phosphodiester linkages at the 3' end as primers. The Equiphi 29 DNA polymerase is used as an amplification enzyme, and because of the strand displacement property, when the strand displacement property is used for extending one circle around a circular template and contacting with the 5 'end of a new synthesis strand of the polymerase, the 5' end can be displaced, and the synthesis of the new strand can be continued, so that the tandem repeat amplification of the single-stranded circular template is realized. And the newly synthesized single strand can still be combined with a random primer to trigger the synthesis of the reverse complementary strand.
The cyclized products were divided into 5 tubes (about 10. Mu.L each) and formulated as in Table 4.
TABLE 4 Table 4
Immediately after denaturation on a heated block at 95℃for 2min, the block was placed on ice and reagents as in Table 5 were added. The PCR instrument was incubated at 42℃for 2 hours, and then at 37℃overnight or 8 hours.
TABLE 5
1.3.3 debranching (debranching)
Random primer-primed amplification is performed with multiple parallel amplification sites, resulting in branched single-strand and double-strand hybrid complexes of amplified products, and a debranching Endonuclease such as T7 Endonuclease (I) that recognizes and cleaves branched DNA may be used.
Since the amplified product was a viscous long fragment of DNA, carefully combine 5 amplification tubes of the same sample into the same low adhesion 1.5mL centrifuge tube and add nuclease free water to 300. Mu.L, add 0.5 XSPRISECET magnetic beads, and mix well with the bottom of the flick tube. Mixing for 5min on a test tube mixer, standing on a magnetic rack for 2min, sucking the supernatant, washing with 80% ethanol twice, air drying, adding 90 μL of nuclease-free water to resuspend magnetic beads, adding 10 μLNEBuffer 2 and 5 μ L T7E1, mixing with a light elastic tube bottom, placing in a incubator at 37 ℃ together with the test tube mixer, mixing, incubating for 2-3h, and stopping reaction according to the dissipation condition of the clustered magnetic beads.
The centrifuge tube was immediately removed and placed on a magnetic rack for 2min, the supernatant was transferred to a new 1.5mL low-adhesion centrifuge tube, 0.5 XSPRISECECEX magnetic beads were added, the bottom of the flick tube was well mixed, and the purification procedure was as described above, dissolved in 15. Mu.L of nuclease-free water. 1. Mu.L of the sample was diluted with 9. Mu.L of nuclease-free water and then the concentration was measured by Qubit, and the remaining diluted sample was subjected to 0.8% agarose gel electrophoresis by adding 2. Mu.L of 6 Xloading Buffer. The concentration is more than 100ng/uL, and the length is more than 10 kb.
1.4ONT library construction, on-machine sequencing and data pretreatment
Library preparation of rolling circle amplification products (as shown in step (2) of FIG. 1) was performed according to the standard procedure of ONT ligation sequencing kit (SQK-LSK 109), and no amplification bar codes were ligated at DNA repair, end repair and addition of ABarcode) and samples were mixed according to the nebiocalculoator in final amounts of 100fmol, finally sequencing adaptors were ligated, and the top mix was prepared.
And then loading the mixture of the upper machine into an ONT sequencing chip with qualified quality inspection, setting sequencing parameters in MinKNOW software, and sequencing for more than 48 hours. The electric signal (Fast 5 format) obtained by sequencing was subjected to base cleavage using Guppy to obtain the original tandem repeat sequence (Raw Concatemer Reads) (this step is not required if the "High base" and above base recognition pattern is used in MinKNow).
1.5 Generation of Consensus sequences (Consensu Read) with high precision (hereinafter referred to simply as the method of the invention)
First, the original tandem repeat sequence (Raw Concatemer Reads) is first matched in a pattern of "fixed sequence (TSO+Read1)", using the function matchPattern in R-packet biosystems (https:// bioconductor. Org/packages/biosystems), in a pattern that allows for certain base insertions, deletions and mismatches, given the high error rate of the original reads (as shown in FIG. 1, step (3)). If a read match is successful, then 28-58bp (preferably 35 bp) is cut from the matching region along the identification sequence direction to extract all potential barcodes and UMI sequences from the original tandem repeat sequence (Raw Concatemer Reads) (as shown in step (4) of FIG. 1). Wherein "Poly (dT) VN" plays a role in localization, i.e. whether the "bar code" and "UMI" are completely intercepted or not can be judged from whether the intercepted fragment contains a partial "Poly (dT) VN" sequence (i.e. repeated T bases).
Next, optionally, a profile-to-profile alignment is performed on the plurality of unaligned sequences according to a guide tree algorithm using the function AlignSeqs in the R-packet DECIPHER [12], and a Consensus sequence (Consensus Read) is extracted from the multiple sequence alignment (as shown in step (5) of fig. 1). Simultaneously, NGS pooling and sequencing was performed on the same cDNA, using the second generation data as a "standard" sequence to aid in correcting the barcode and UMI sequences obtained from the co-recognition (Consensus Calling) of each original tandem repeat to obtain the correct barcode and UMI (as shown in step (6) of fig. 1). Next, a second round of matching is performed on the original tandem repeat sequence again using the function matchPattern (as shown in step (7) of fig. 1) using the "fixed sequence+barcode sequence (tso+read1+barcode)" as the pattern (i.e., the extended match pattern). Compared with the first round of matching, the fault tolerance rate is improved due to the extension of the pattern of the fixed sequence and the bar code sequence, the matching number is more, and the consensus identification is more accurate. And the original tandem repeat sequence is disassembled into sub-reads (as shown in step (8) of fig. 1) using the second round of matched regions. Finally, the alignment Seqs is used for carrying out multi-sequence alignment on the sub-read length, and the consensus sequence is extracted into a cDNA sequence with high precision (namely, the consensus recognition is carried out again, as shown in the step (9) of FIG. 1). To this end, the original tandem repeat sequence was generated as the correct barcode and UMI and high precision cDNA sequence.
In some embodiments of the invention, a novel three-generation sequencing method is shown in fig. 7.
Embodiment two: comparison of five cyclization modes
This example first systematically compares PLP with four other full-length cDNA self-loop methods (as shown in FIG. 2 a), including R2C2[ reference 6] and stem-loop Structural Ligation (SL) used in PacBIO sequencing, double-stranded self-loops (BTA) using Blunt/TA ligase in INC-seq [ reference 13], and CircLigase ligase-mediated single-stranded self-loops (CL).
In the embodiment, standard sequences with the length of 597bp are uniformly used as initial cDNA, cyclization is carried out respectively by experimental procedures of respective cyclization methods, then the subsequent procedures of an R2C2 method are used for generating original tandem repeat sequences, the C3POa software (https:// gitub. Com/rvalden/C3 POa) is used for generating consensus sequences, and the sequence is compared with the standard sequences by the minimum 2 software (https:// gitub. Com/lh 3/minimum 2). Finally, these five methods were evaluated comprehensively by the generation efficiency (Consensus%), alignment (Mapped), alignment length (Mapped length), deletion mutation rate (Indels%) and base Mismatch rate (Mismatch%) of Consensus sequences.
The results show that PLP and R2C2 produced the largest number of original sequences and gave the highest consensus sequence generation efficiencies of 12.4% and 30.9%, respectively; after alignment of the consensus sequences generated by the five methods with the standard sequences, the BTA and PLP alignment were 99.5% and 99.3%, respectively, followed by SL (98.5%), R2C2 (98%) and CL (78.2%) (fig. 2 b). As shown in fig. 2c, in the comparison of the alignment lengths, the alignment lengths of BTA and PLP are significantly closer to the length of the standard sequence, and are expressed as: the comparison lengths are intensively distributed at the top end (the maximum width) of the corresponding violin diagram, and the comparison length corresponding to the median is obviously larger than that of the other three parts; while the lengths of R2C2, CL and SL are significantly shorter (the solid dots in the violin diagram represent the median, and the width represents the frequency). In comparison of consensus sequence accuracy (also understood as "precision"), the deletion mutation rate (fig. 2 d) and base mismatch rate (fig. 2 e) of PLP were the lowest, and were expressed as: in the corresponding violin diagram, the deletion mutation rate and the base mismatch rate corresponding to the median are the lowest, and are intensively distributed at the bottom (width is the largest) of the violin diagram (the solid point in the violin diagram represents the median, and the width represents the frequency). Among the five cyclization modes of PLP, R2C2, BTA, CL and SL, the three cyclization modes of BTA, CL and SL do not introduce clamping plate sequences to mediate the cyclization process, and belong to random cyclization, so that a certain contingency exists in the practical application scene. In summary, PLP shows the highest efficiency in generating high percentage consensus sequences and low percentage deletion mutations and base mismatches with the desired length.
Embodiment III: comparison of the inventive method with published data
This example focused on comparing the data set forth in the 10XR2C2 and ScNaUmi-seq articles, and comparing the ratio of reads produced by each process to the number of original reads (basal reads) to explore the efficiency of each technique.
After correction of the original tandem repeat sequence to a consensus sequence, as shown in Table 6, in a comparison of the number of reads with linker sequences (also known as "fixed sequences") at Both ends to the number of original reads (Both-end reads%), 7 replicates of the method of the invention (in PLP circularization) produced more than 60% reads, but 8 replicates in ScaNaUmi-seq produced an average of 57% reads, whereas 2 replicates of 10XR2C2 produced only about 32.1% and 33.4% reads. Next, on the basis of having a linker sequence, the ratio of reads number of matching correct bar codes to original reads number (Both-end Barcode reads%) was compared, and the inventive method was based on the principle of finding Both ends of the linker while matching correct bar codes, so that the ratio was unchanged from the previous step (i.e. the ratio of reads number of matching correct bar codes to original reads number), whereas 8 replicates of the scanami-seq were reduced to an average of 38.76%, and 2 replicates of 10XR2C2 were reduced to 21.66% and 21.63%, respectively. Finally, on the basis of the correct bar code with the linker sequence, the ratio of the number of reads matching the correct UMI to the number of original reads (Both-end Barcode & UMI reads%) was compared, 7 replicates of the method of the invention gave an average of 36.43% reads, whereas 8 replicates in the ScNaUmi-seq were 29.45% on average, and 2 replicates of 10XR2C2 were 16.10% and 15.83%.
TABLE 6 comparison of the number of reads for each procedure
In addition, this example also compares the same cDNA sample with the R2C2 method. The sub-read coverage (sub-read coverage) represents the number of sub-reads contained in a tandem repeat sequence. As shown in fig. 3a, the method of the present invention (cyclization in PLP) has a coverage of greater than 10 sub-read lengths and about 30% higher than R2C2 compared to the R2C2 method, which indicates that the cycle number of rolling circle amplification of the method of the present invention is significantly greater than R2C2 and thus the success rate of mutual correction between sub-read lengths is higher. Next, ONT sequencing was performed on the same cDNA sample and the data processing flow of ScNapBar [ reference 11] was run, with only 18.5% reads matching the correct barcode. Theoretically, the splint sequence of the method of the present invention (in PLP cyclization) does not introduce an unrelated sequence, whereas R2C2 requires the introduction of a 200bp unrelated sequence to reconstruct the loop, so the sequencing cost of the method of the present invention is lower and the availability of reads is higher.
In summary, the inventive method exhibits a greater capacity and higher efficiency of reads production than 10XR2C2, scNaUmi-seq and ScNapBar in the treatment of the respective processes; higher correction success rate than R2C2 and more efficient reads yield pattern.
Embodiment four: performance effects of the inventive method
In this example, direct ONT sequencing and the method of the invention (in PLP circularization) were performed on the same cDNA sample, respectively, and the effect of the sub-read length coverage on the base quality of the consensus sequence was evaluated. The reads sequenced by ONT showed a deletion mutation rate of 1.57% and a base mismatch rate of 3.37%, whereas the consensus sequences of the method of the invention (in PLP circularization) had lower deletion mutations and base mismatches, reaching 0.84% deletion mutations and 1.8% base mismatches with coverage of greater than 10 sub-reads. The Base Quality (BQ) value is an important index for measuring the sequencing quality, and the higher the quality value is, the smaller the probability of the detected error of the base is represented, and the calculation formula is Q= -10lgP (Q represents the quality value and P represents the probability of the detected error). Notably, as the number of sub-reads increases, the deletion mutation rate and base mismatch rate of the method of the present invention (cyclized in PLP) decrease and are concentrated at the bottom of the corresponding violin plot (maximum width) and lighter in color (corresponding base mass value greater than 20), indicating that both the deletion mutation rate and base mismatch rate of the method of the present invention (cyclized in PLP) are concentrated at lower values and that the probability of base being misdetected is low. In addition, the accuracy of the single consensus sequence measured was highly correlated with the average Base Quality (BQ) score of its base raw reads, further indicating that the method of the present invention is capable of obtaining high accuracy consensus sequences (as shown in FIGS. 3b-3 c).
In addition, this example compares the identity between the method of the invention (in PLP circularization) and the NGS (second generation sequencing, next-generation sequencing) barcodes. The minimum edit distance (Levenshtein distance) between the barcodes that can be matched in the consensus sequence of the method (in PLP cyclization) and the barcodes measured by NGS is calculated separately, namely: on the premise of aligning the same gene, reads from the method of the invention (cyclized in PLP) are tolerant of error bases (errors include deletions, insertions, substitutions) compared to NGS with the same barcode. To investigate the effect of edit distance on barcode resolution, the percentage of genes from the method of the invention (cyclization in PLP) reads and NGS with the same barcode, aligned with the same gene, were calculated. Specifically, when barcodes are perfectly matched, i.e., edit distance = 0, about 80% of genes are correctly aligned; when the edit distance is greater than 3, the percentage of correctly matched genes is significantly lower than the perfect match ("edit distance=0" corresponding percentage) (fig. 3 d). Thus, choosing an edit distance less than 3 as a reliable condition, the method of the present invention can produce reads of about 65% of correctly matched barcodes (FIG. 3 e) and about 34.49% of correctly matched UMI (FIG. 3 f).
Fifth embodiment: analysis and study of the four regions of the mouse brain at the spatial level by the method of the invention (cyclization in PLP)
In this example, the method of the present invention was applied to a 10×genomic spatial transcriptome platform, and analysis and study on the spatial level were performed on four regions of the mouse brain (according to actual requirements, the method provided by the present invention may also be applied to single-cell sequencing). The method of the invention (cyclisation in PLP) facilitates the identification of spatially specific isomers (isoforms), i.e. applying stringent filtration conditions that retain only more than 3 of the unannotated isomers of reads (i.e. the new isomers are only detected 3 times and only retained), a total of 15,318 unique isomers are detected, including 609 new isomers in the known genes and 66 new isomers in the intergenic region.
The experimenter also identified 226 spatially specific isoforms, such as two isoforms of the Rps24 gene (Rps 24-205 (ensmest 00000223999) and Rps24-202 (ensmest 00000169826)), whose alternative splicing type is exon Skipping (SE, fig. 4a, 4 b). The two transcripts were identified in ONT sequencing and reads based on the method of the invention, which showed significantly lower deletion mutation rates (p=2e-16) and base mismatch rates (p=2e-16) (as shown in FIGS. 4a, 4c, where the black dots represent mismatches in FIG. 4 a). In forebrain coronal section (WTA), transcript ensust 00000223999 was most expressed in the subventricular zone (SVZ), while transcript ensust 00000169826 (with skipped exons) was most expressed in White Matter (WM) (fig. 4 d).
Furthermore, the experimenters found that Rtn1 showed high expression in Granulosa Cells (GC), bergmann glial cell/purkinje cell layer (BG/PC) and Molecular Layer (ML) of cerebellar coronal (WTD) sections (fig. 4e, 4 g). Whereas the experimenter found that the Rtn1 gene has a pair of spatially specific subtype switches, the short and long isoforms between the cerebellar regions have selective transcription initiation sites (TSS, fig. 4 f), and the long and short isoforms have a preference, expressed in: the long isomer (Rtn 1-202) was expressed in the Molecular Layer (ML) region and the short isomer (Rtn 1-201, rtn 1-203) was expressed in Granulosa Cells (GC) (FIG. 4 e). The pattern was further verified by single molecule RNA fluorescence in situ hybridization (smRNA-FISH) using separate probes designed for the short and long isomers, and the short isomer (red fluorescence) was found to co-localize in GC, while the long isomer (yellow fluorescence) was co-localized in ML (fig. 4 h). These results indicate that the method of the invention (which improves the accuracy of the cDNA sequence) helps to identify spatially specific isomers.
Next, the experimenter extracted a large number of splice junctions (splice junctions) from long reads and explored the size of the unexplored splice junctions. Almost all introns are considered to contain two highly conserved dinucleotides; and splice junctions refer to motifs (motif) on both sides of the cleavage and recombination sites, the junction on the left side (5 'end) of the intron being called donor (donor) and the junction on the right side (3' end) of the intron being called acceptor (receptor). Following cleavage of the 5' end of the intron sequence, the donor splice site is exactly GT; the acceptor splice site is just AG (i.e., GT-AG canonical splice motif (canonical splice site motif)) prior to cleavage of the 3' end of the intron sequence; furthermore, non-canonical splice motifs such as GC-AG, AT-AC, GG-AG, GT-TG, GT-CG, CT-AG, etc. can be observed. When the classical dinucleotides requiring support of AT least 2 reads and using only GT-AG, GC-AG and AT-AC were used as filtration conditions, a total of 53,305 annotations (90.45%) and 5,631 new splice points (9.55%) were detected (fig. 5a, 5 b). To evaluate whether these new splice points were merely noise from ONT sequencing, the experimenter downloaded a public Expressed Sequence Tag (EST)/mRNA dataset, and found 1,098 (19.5%) new and validated splice points ("validated"), indicating that these validated splice points were not due to ONT sequencing errors. Whether the donor and acceptor sites are annotated in Ensembl v93 based on the new splice point fall into four classes: 745 (13.23%) junction donor sites and acceptor sites were both annotated, but no splice mode was annotated; both the donor site and the acceptor site of 3,300 (58.6%) splice events have a splice pattern; 794. the individual (14.1%) and 792 (14.06%) splice sites included the unannotated splice donor or acceptor (fig. 5 a).
To further characterize the 5,631 observed new splice sites, the experimenter studied the extent of their splice site probability score (splice site probability scores), conservation score (conservation scores) and splice site motif (motif). First, the experimenter observed a low level of confusion for "annotation", "verification", and a high level of confusion for new and unverified ("new") (fig. 5 b). Notably, when comparing splice site probability scores between ONT sequencing and the methods of the invention, both at the acceptor (p=4.2×10 -8 T-test) or donor (p=4.2×10 -8 T-test) the probability score for splice sites of new junctions identified by the method of the invention is higher than for ONT sequencing (as shown in fig. 5c, the ordinate indicates the maximum entropy of splice sites). Next, the conserved scores of splice sites are revealed (present implementationExamples sequence conservation scoring using PhastCons): the "annotation" sites are highly conserved, "verify", "new" also have a similar pattern and differ from the random sequence (mm 10) (fig. 5 d), indicating that the identified new splice points are highly conserved in vertebrates. The experimenter then also found that annotation, validation and new (novel) splice points had high coding potential in both acceptor and donor, and the coding capacity ranged from high to low (fig. 5 e). The experimenter found that "validation" (94.83%) had a close proportion of canonical splice motif GT-AG compared to the annotation site (99.26%), while "new" (figure 5 f) had a certain difference. The experimenter revealed an unexplained exon skipping pattern in the Ttr gene, and the new isomer 18:20666587-20673630 exhibited a narrower expression pattern than the Ttr gene, but co-located with the annotated isomer ensmest 00000075312 (fig. 5g, 5 h), indicating that both isomers were expressed in the same spatial region. In summary, the methods provided herein are capable of identifying a number of novel splice junctions with high splice scores and high conservation.
To study the spatial distribution of RNA editing in mouse brain, the experimenter identified 13,397 and 8,533 RNA editing sites, respectively, from short reads (also known as illumine technology in "second generation sequencing") and long reads (long reads, also known as ONT technology in "third generation sequencing"), respectively (as shown in fig. 6 a). It was found by REDIPortal [ reference 14] annotation that most of these sites are located in the Alu region and are prone to A-to-I (adenosin-to-inosine) editing patterns. For the RNA editing sites found by both of the above techniques (i.e., long read long ONT technique and short read long illumine technique), the RNA editing level has a high correlation (Pearson correlation coefficient > 0.96). Notably, the experimenter found that the difference in RNA editing levels of the method of the invention and illumine was significantly lower compared to the difference between ONT sequencing and illumine (p=0.016, wilcox test, as shown in fig. 6 b). For example, the method of the present invention accurately identified RNA edits in the poly-T region of chr11:75599645 of Pitpna and chr10:86731780 of Ttc41 (in a PLP circularized fashion), whereas ONT 1D was not accurately identified (as distinct from illuminea) (FIG. 6 c), indicating that the method of the present invention improved the accuracy of quantification of RNA edits. Next, the experimenter determined spatially specific RNA editing sites in forebrain coronal sections (fig. 6 d). For example, chr10:86731780 of Ttc41 is specific in the cortical layer (CTX, cotex) (fig. 6e, 6 f), whereas 16:51669711 of the new isomer occurs only in the White Matter (WM) region (fig. 6e, 6 g). Notably, 11:86630507 of Vmp1 is distributed in most areas except the dermis (CTX, cotex) and hypothalamus (HT, hypothamus) (fig. 6e, 6 h). In summary, using the methods provided herein, the experimenters identified spatially specific RNA editing sites, indicating that the methods of the invention facilitate quantification of RNA editing sites.
In summary, this example analyzes the isoforms and RNA editing panoramas of four regions of the mouse brain by applying the method of the present invention to spatial transcriptome sequencing, and identifies multiple genes that alternatively splice isoforms or RNA editing in a spatially specific manner.
Example six:
based on the third generation sequencing method, the invention further provides a third generation sequencing system 100, and the third generation sequencing system is described below with reference to the specific drawings and the embodiments.
FIG. 8 is a functional block diagram of a third generation sequencing system according to the present invention, and specifically, the third generation sequencing system 100 of the present embodiment includes:
a sequence information receiving module: the method comprises the steps of receiving original tandem repeat sequence information of a nucleic acid sequence to be detected, wherein the original tandem repeat sequence information of the nucleic acid sequence to be detected is obtained through third generation sequencing, and the third generation sequencing comprises nanopore sequencing and/or single-molecule fluorescence sequencing; and can also be used for receiving second generation sequencing information of the nucleic acid sequence to be tested, wherein the second generation sequencing comprises one or more of ion semiconductor sequencing, pyrosequencing, ligation sequencing, sequencing by synthesis, combined probe anchor point sequencing by synthesis and reversible end termination sequencing. The original tandem repeat sequence is obtained by rolling circle amplification by taking the cyclized nucleic acid sequence to be detected as a template.
A first matching module: and the method is used for carrying out first round of identification matching on the original tandem repeat sequence based on the fixed sequence, and extracting an identification region first sequence.
And a second matching module: and the method is used for carrying out second round of identification matching on the original tandem repeat sequence based on the fixed sequence and the identification sequence, so as to correct the first identification region sequence and obtain a second identification region sequence. It should be noted that the first matching module and the second matching module may be integrated into one matching module.
And (3) disassembling the module: and the method is used for disassembling the original tandem repeat sequence based on the identification region second sequence to obtain one or more sub-read lengths, wherein the sub-read lengths comprise intermediates of the nucleic acid embedded sequence and the identification region second sequence.
Comparison module: the method comprises the steps of performing multi-sequence comparison on the sub-read length, and extracting a first nucleic acid consensus sequence which is regarded as a sequencing result of the nucleic acid embedded sequence; and the method can be used for comparing the original tandem repeat sequences based on the first sequence of the identification region before the second round of identification matching, and extracting a second consensus sequence of the nucleic acid. It should be noted that the disassembling module and the comparing module may be integrated into one analyzing module.
In a specific embodiment, the sequence information receiving module transmits the received original tandem repeat sequence information of the nucleic acid sequence to be detected to the first matching module for the first round of identification matching; the first matching module transmits the extracted first sequence information of the identification area to the second matching module; the sequence information receiving module transmits the received second generation sequencing information of the nucleic acid sequence to be detected to the second matching module; the second matching module performs second round of identification matching on the original tandem repeat sequence, corrects the first sequence of the identification region, and transmits the obtained second sequence information of the identification region to the disassembly module; the disassembly module disassembles the original tandem repeat sequence based on the second sequence of the identification area to obtain one or more sub-read lengths, and transmits the sub-read length information to the comparison module; and the comparison module performs multi-sequence comparison on the sub-read length, extracts a first nucleic acid consensus sequence, and the first nucleic acid consensus sequence is regarded as a sequencing result of the nucleic acid embedded sequence. In addition, the first matching module may further transmit the extracted first sequence information of the identification region to the alignment module; and the comparison module is used for comparing the original tandem repeat sequences based on the first sequence of the identification region before the second round of identification matching, and extracting a second consensus sequence of the nucleic acid.
The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to the above-described embodiments, which are merely illustrative and not restrictive, and many forms may be made by those having ordinary skill in the art without departing from the spirit of the present invention and the scope of the claims, which are to be protected by the present invention.
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Claims (14)

1. A method of nucleic acid sequencing comprising:
s1, cyclizing a nucleic acid sequence to be detected to obtain a cyclized nucleic acid sequence, wherein the nucleic acid sequence to be detected comprises a nucleic acid embedded sequence, an identification sequence and fixed sequences respectively positioned at two ends of the nucleic acid sequence to be detected, the cyclizing mode of cyclizing comprises lock probe cyclizing, the nucleic acid embedded sequence is a nucleic acid sequence expected to be sequenced, the identification sequence comprises a unique molecular identifier and/or a bar code, and the fixed sequences are joint sequences generated by a sequencing platform;
s2, performing rolling circle amplification by taking the circularized nucleic acid sequence as a template to obtain a rolling circle amplification product;
s3, performing third-generation sequencing on the rolling circle amplification product to obtain an original tandem repeat sequence;
S4, carrying out first round of identification matching on the original tandem repeat sequence based on the fixed sequence, and extracting an identification region first sequence, wherein the identification region first sequence comprises a fixed sequence matching sequence matched with the fixed sequence and 28-58 bp directly connected with the fixed sequence matching sequence in the direction of the identification sequence;
s5, comparing the original tandem repeat sequences based on the first sequence of the identification region, extracting a second nucleic acid consensus sequence, and correcting the second nucleic acid consensus sequence by using a reference sequence to obtain a second sequence of the identification region, wherein the reference sequence is from second generation sequencing data of the nucleic acid sequence to be detected, and the second sequence of the identification region is regarded as a correct identification sequence;
s6, performing second round of identification matching on the original tandem repeat sequence based on the fixed sequence and the identification region second sequence, and disassembling the original tandem repeat sequence based on the identification region second sequence to obtain one or more sub-read lengths, wherein the sub-read lengths comprise intermediate products of the nucleic acid embedded sequences and the identification region second sequence, and the intermediate products of the nucleic acid embedded sequences are sequences corresponding to the nucleic acid embedded sequences in the original tandem repeat sequence;
S7, performing multi-sequence comparison on the sub-read length, and extracting a first nucleic acid consensus sequence, wherein the first nucleic acid consensus sequence is taken as a sequencing result of the nucleic acid embedded sequence.
2. The method of claim 1, wherein the unique molecular identifier of the test nucleic acid sequence is uniquely determined and the barcode of the test nucleic acid sequence provides information for identifying the test nucleic acid sequence.
3. The method of claim 1, wherein the barcode comprises a spatial barcode and/or a cellular barcode.
4. The method of claim 1, wherein S3 further comprises third generation sequencing the rolling circle amplification product and obtaining third generation sequencing data for the rolling circle amplification product, the third generation sequencing comprising nanopore sequencing and/or single molecule fluorescence sequencing.
5. The method of claim 1, wherein S5 further comprises performing a second generation sequencing of the test nucleic acid sequence and obtaining second generation sequencing data of the test nucleic acid sequence, the second generation sequencing comprising one or more of ion semiconductor sequencing, pyrosequencing, sequencing by ligation, sequencing by synthesis, combined probe anchor point sequencing by synthesis, and reversible end termination sequencing.
6. The method of claim 1, wherein S1 further comprises amplifying the test nucleic acid sequence to generate a library of the nucleic acid embedded sequences, wherein the amplifying precedes the circularizing the test nucleic acid sequence.
7. The method of claim 1, wherein the nucleic acid insert comprises DNA.
8. The method of claim 7, wherein the DNA comprises cDNA formed by reverse transcription of RNA in the biological sample.
9. The method of claim 1, wherein the first consensus sequence of nucleic acids is highly accurate.
10. The method of claim 1, wherein the original tandem repeat sequence is aligned in S5 according to a guide tree algorithm.
11. The method of claim 10, wherein the alignment is a profile-to-profile alignment.
12. The method of claim 1, wherein the sub-read lengths are aligned in multiple sequences according to a dynamic programming algorithm.
13. The method of claim 8, wherein the biological sample comprises one or more of a fresh tissue section, a fresh single cell suspension, and extracted tissue RNA.
14. The method of claim 13, wherein the biological sample is derived from a tissue and/or organ of an organism, the biological sample comprising one or more of a heart, kidney, liver, spleen, stomach, lung, ovary, breast, lymph node, tongue, brain, large intestine, small intestine, eye, skeletal muscle, testis, thyroid sample.
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