In situ combinatorial labeling of cellular molecules
Methods of uniquely labeling or barcoding molecules within a nucleus, a plurality of nuclei, a cell, a plurality of cells, and/or a tissue are provided. Kits for uniquely labeling or barcoding molecules within a nucleus, a plurality of nuclei, a cell, a plurality of cells, and/or a tissue are also provided. The molecules to be labeled may include, but are not limited to, RNAs and/or cDNAs.
1. A method of preparing tagged cDNA molecules for use in single-cell transcriptome analysis, the method comprising:
(a) fixing and permeabilizing a plurality of cells, wherein each of the plurality of fixed, permeabilized cells comprises RNA, and wherein the plurality of cells is fixed and permeabilized at a temperature below about 8° C.;
(b) dividing the plurality of cells into a first plurality of aliquots, wherein each aliquot of the first plurality of aliquots comprises more than one cell;
(c) reverse transcribing RNA molecules within the cells of the first plurality of aliquots to generate complementary DNA (cDNA) molecules, wherein the RNA molecules are reverse transcribed using reverse transcription (RT) primers each comprising:
(i) a poly (T) sequence or a random nucleotide sequence;
(ii) an RT primer barcode sequence,
wherein multiple distinct RT primer barcode sequences are present among the RT primers used in the first plurality of aliquots, and
wherein the RT primer barcode sequences present in each individual aliquot of the first plurality of aliquots are specific to the individual aliquot; and
(iii) a 5′ overhang comprising a 5′ overhang sequence located 5′ of the poly (T) or the random nucleotide sequence,
wherein the 5′ overhang sequence is the same in all of the RT primers used in the first plurality of aliquots, and
wherein following reverse transcription of the RNA, the 5′ overhang sequence is present at the 5′ end of each of the cDNA molecules;
(d) combining the cells from the first plurality of aliquots;
(e) dividing the combined cells from the first plurality of aliquots into a second plurality of aliquots, wherein each of the second plurality of aliquots comprises more than one cell;
(f) coupling nucleic acid tags to the cDNA molecules within cells of the second plurality of aliquots, thereby generating tagged cDNA molecules, wherein each of the nucleic acid tags comprises:
i) a tag barcode sequence; and
ii) a 3′ hybridization sequence located 3′ of the barcode sequence and/or a 5′ hybridization sequence located 5′ of the barcode sequence,
wherein multiple distinct tag barcode sequences are present among the nucleic acid tags used in the second plurality of aliquots, and
wherein the tag barcode sequences present in each individual aliquot of the second plurality of aliquots are specific to the individual aliquot;
(g) combining the cells from the second plurality of aliquots;
(h) lysing the combined cells from the second plurality of aliquots, thereby releasing the tagged cDNA molecules and forming a lysate in each sample of the plurality of samples; and
(i) isolating tagged cDNA molecules released during step (h) using a binding agent, such that the isolated tagged cDNA molecules are bound to the binding agent.
2. The method of claim 1 , wherein the lysing of step (h) is performed in the presence of a protease.
3. The method of claim 2 , wherein the protease is proteinase K.
4. The method of claim 1 , wherein a protease inhibitor is added to the lysate prior to or together with the binding agent.
5. The method of claim 1 , further comprising:
(j) conducting a template switch of the tagged cDNA molecules bound to the binding agent.
6. The method of claim 1 , wherein the combined cells from the second plurality of aliquots are divided into the plurality of samples prior to step (h), and wherein the method further comprises:
(k) amplifying the isolated tagged cDNA molecules using amplification primers,
wherein at least a portion of the amplification primers used in each of the plurality of samples comprise an index sequence,
wherein multiple distinct index sequences are present among the amplification primers used in the plurality of samples, and
wherein the index sequences present in each individual sample of the plurality of samples are specific to the individual sample.
7. The method of claim 6 , wherein the tagged cDNA molecules amplified in step (k) are present in an amplified cDNA solution, and further comprising:
(l) size selecting the tagged cDNA molecules amplified in step (k) by introducing a solid phase reversible immobilization (SPRI) bead solution to the amplified cDNA solution, wherein the ratio of SPRI bead solution to amplified cDNA solution is between about 0.9:1 and about 0:7:1.
8. The method of claim 1 , wherein the plurality of cells is fixed and permeabilized at about 4° C. or below about 4° C.
9. The method of claim 1 , wherein steps (e) through (g) are repeated one or more times, thereby generating repeatedly tagged cDNA molecules.
10. The method of claim 1 , wherein the coupling in step (f) comprises ligating a 3′ end of a nucleic acid tag to a 5′ end of a cDNA molecule.
11. The method of claim 10 , wherein the 3′ end of the nucleic acid tag is present within the 3′ hybridization sequence, and wherein the 3′ end of the nucleic acid tag is brought into proximity of the 5′ end of the cDNA molecule by being preannealed to a linker nucleic acid strand that is complementary to the 3′ hybridization sequence of the nucleic acid tag and to the 5′ overhang sequence of the RT primer.
12. The method of claim 1 , wherein the RT primers and/or nucleic acid tags are DNA molecules.
13. The method of claim 9 , wherein the nucleic acid tags that are coupled to the tagged or repeatedly tagged cDNA molecules during the last of the one or more times that steps (e) to (g) are repeated comprise one or more elements selected from the group consisting of a random nucleotide sequence to prevent counting of PCR duplicates, a capture agent, and a next-generation sequencing (NGS) adapter sequence.
14. The method of claim 13 , wherein the capture agent comprises biotin, and wherein the binding agent comprises streptavidin-coated magnetic beads.
15. The method of claim 1 , wherein the RT primer barcode sequences and/or the tag barcode sequences each comprise at least 8 nucleotides.
16. The method of claim 6 , wherein at least a portion of the amplification primers further comprise one or more elements selected from the group consisting of a flow-cell binding sequence, an NGS primer binding sequence, and an NGS adapter sequence.
17. The method of claim 6 , further comprising:
(m) sequencing the tagged cDNA molecules amplified in step (k).
18. The method of claim 17 , wherein the method further comprises:
(n) grouping the sequencing reads obtained in step (m) by any combination of two or more sequences selected from the group consisting of RT primer barcode sequence, tag barcode sequence, and index sequence.
19. The method of claim 1 , wherein the first plurality of aliquots comprises 96 aliquots distributed into the wells of a first 96-well plate, wherein the RT primers used in the first plurality of aliquots comprise 96 distinct RT primer barcode sequences, and wherein each of the 96 distinct RT primer barcode sequences is present in only one well of the first 96-well plate.
20. The method of claim 1 , wherein the second plurality of aliquots comprises 96 aliquots distributed into the wells of a second 96-well plate, wherein the nucleic acid tags used in the second plurality of aliquots comprise 96 distinct tag barcode sequences, and wherein each of the 96 distinct tag barcode sequences is present in only one well of the second 96-well plate.