Methods for extending polynucleotides
The invention is directed to methods for synthesizing oligonucleotides directly on biomolecules or cells living or fixed. In some embodiments, template-free enzymatic synthesis is implemented under biological conditions with successive cycles of (i) enzymatic addition of a 3′-O-blocked nucleoside triphosphate and (ii) enzymatic deblocking of the incorporated nucleotide to regenerate a free 3′ hydroxyl. The invention has applications in single-cell cDNA library construction and analysis.
1. A method of generating cDNA libraries each having an oligonucleotide label, the method comprising the steps of:
(a) capturing an mRNA by hybridizing the mRNA to capture oligonucleotides attached to one or more solid supports, wherein
the capture oligonucleotides are complementary to segments of the mRNA, and the capture oligonucleotides are attached to the one or more solid supports by 5′-ends and have 3′-ends with free 3′-O-hydroxyls;
(b) extending the 3′-ends of the capture oligonucleotides with a reverse transcriptase using the captured mRNAs as templates to form the cDNA libraries on the one or more solid supports; and
(c) synthesizing oligonucleotide labels on cDNAs of the one or more solid supports by template-free enzymatic synthesis;
wherein:
said step (a) of capturing includes capturing the mRNA of a single cell or single tissue on the one or more solid supports to form said cDNA libraries that are cell-specific or tissue-specific cDNA libraries, respectively;
said oligonucleotide labels are unique cell-specific or tissue-specific oligonucleotide barcodes; and
said one or more solid supports include binding compounds attached thereto for capturing predetermined non-nucleic acid ligands.
2. The method of claim 1 , wherein said step of synthesizing comprises synthesizing said unique cell-specific oligonucleotide barcodes by a split and mix synthesis method.
3. The method of claim 1 , wherein said binding compounds comprise one or more species of antibody each with a predetermined specificity for one of said predetermined non-nucleic acid ligands, each different species of antibody having attached a releasable oligonucleotide barcode from which the antibody can be identified.
4. The method of claim 3 wherein the method is used for uniquely barcoding cells, either living cells, fixed cells, or fixed and permeabilized cells.
5. The method of claim 3 wherein protein expression may be monitored using one or more protein-specific antibodies each linked to a distinct initiator that may be extended by enzymatic synthesis.
6. The method of claim 3 wherein mRNA expression may be monitored using mRNA-specific primers to generate cDNAs that may be extended.
7. The method of claim 3 , the method comprising:
(a) disposing on a tissue section under binding conditions a plurality of different types of antibodies, each different type of antibody being capable of specifically binding to a different one of a plurality of proteins,
each different type of antibody having a releasably attached antibody barcode, each antibody barcode comprising an initiator with a free 3′-hydroxyl;
(b) repeating for a plurality of cycles at predetermined positions on the tissue section the steps of:
(i) contacting the antibody barcodes having free 3′-O-hydroxyls with a 3′-O-blocked nucleoside triphosphate and a template-independent DNA polymerase so that the antibody barcodes are elongated by incorporation of a 3′-O-blocked nucleoside triphosphate to form 3′-O-blocked elongated fragments, and
(ii) enzymatically deblocking the elongated fragments to form elongated fragments having free 3′-hydroxyls, thereby synthesizing a different position tag onto the releasably attached antibody barcodes at each different position to form position tag-antibody barcode conjugates;
(c) releasing the position tag-antibody barcode conjugates; and
(d) sequencing the released position tag-antibody barcode conjugates to determine a spatial distribution of the plurality of proteins in the tissue section.