Methods of detecting analytes
Localized detection of RNA in a tissue sample that includes cells is accomplished on an array. The array include a number of features on a substrate. Each feature includes a different capture probe immobilized such that the capture probe has a free 3′ end. Each feature occupies a distinct position on the array and has an area of less than about 1 mm 2 . Each capture probe is a nucleic acid molecule, which includes a positional domain including a nucleotide sequence unique to a particular feature, and a capture domain including a nucleotide sequence complementary to the RNA to be detected. The capture domain can be at a position 3′ of the positional domain.
1. A method for localized detection of RNA in a tissue section, the method comprising:
(a) providing an array comprising a plurality of features on a substrate, wherein each feature occupies a distinct position on the array, wherein a feature of the plurality of features comprises a plurality of capture probes immobilized thereon, and wherein the plurality of capture probes comprise a nucleic acid molecule having the following domains oriented 5′ to 3′:
(i) a first sequence comprising a positional domain comprising a nucleotide sequence unique to the feature; and
(ii) a second sequence comprising a capture domain comprising a nucleotide sequence complementary to the RNA to be detected;
(b) contacting the array with the tissue section and allowing at least one RNA of the tissue section to hybridize to the capture domain of the capture probe;
(c) generating a cDNA molecule, by extending the capture probe using the hybridized RNA as an extension template, such that the generated cDNA molecule comprises the nucleotide sequence of the positional domain;
(d) releasing the generated cDNA molecule, or a portion thereof, or a second strand complementary to the generated cDNA molecule, or a portion thereof, from the array, and
(e) identifying the nucleotide sequence of the positional domain in the released cDNA molecule, or the complement thereof; and
(f) correlating the nucleotide sequence of the positional domain with the distinct position on the array, thereby detecting the RNA in the tissue section.
2. The method of claim 1 , further comprising, between steps (c) and (d), a step of generating the second strand complementary to the generated cDNA molecule or the portion thereof.
3. The method of claim 1 , wherein step (d) comprises releasing the generated cDNA molecule, or a portion thereof, or the second strand complementary to the generated cDNA molecule, or a portion thereof, from the capture domain of the capture probe, by denaturation.
4. The method of claim 1 further comprising a step of amplifying the generated cDNA, or a portion thereof, the second strand complementary to the generated cDNA, or a portion thereof, released from the array.
5. The method of claim 1 , wherein the capture probe further comprises a cleavage domain 5′ of the positional domain.
6. The method of claim 5 , further comprising cleaving the cleavage domain of the capture probe, wherein cleaving comprises applying a cleavage enzyme that recognizes a nucleotide sequence in the cleavage domain and cleaves the generated cDNA molecule at a position that is 5′ to the positional domain, thereby releasing the generated cDNA molecule or the portion thereof, or the second strand or the portion thereof, from the feature on the array.
7. The method of claim 1 , wherein the RNA is selected from the list consisting of mRNA, tRNA, rRNA, viral RNA, small nuclear RNA (snRNA), small nucleolar RNA (snoRNA), microRNA (miRNA), small interfering RNA (siRNA), piwi-interacting RNA (piRNA), ribozymal RNA, antisense RNA and non-coding RNA.
8. The method of claim 7 , wherein the RNA is mRNA.
9. The method of claim 8 , wherein the capture domain of the capture probe hybridizes to a poly-A tail of mRNA.
10. The method of claim 9 , wherein the capture domain comprises a poly-T sequence.
11. The method of claim 1 , wherein the method further comprises a step of staining the tissue section prior to step (c).
12. The method of claim 1 , further comprising correlating the nucleotide sequence obtained in step (f) with an image of the tissue section, wherein the method includes a step of imaging the tissue section prior to step (c).
13. The method of claim 1 , wherein the capture probe of the plurality of capture probes has a free 3′ end.
14. The method of claim 1 , wherein the capture probe is immobilized on the substrate by a linker.
15. The method of claim 1 , wherein the array is a bead array and the capture probe is immobilized on beads of the bead array.
16. The method of claim 1 , wherein the array comprises at least 1,000 features.
17. The method of claim 1 , wherein the features of the array have an average diameter of about less than 100 micrometers, about less than 50 micrometers, about less than about 20 micrometers, or about less than 10 micrometers.
18. The method of claim 1 , wherein the substrate comprises one or more arrays.
19. The method of claim 18 , wherein the one or more arrays comprise different positional domains.
20. The method of claim 1 , wherein the capture probes further comprise a primer binding site.
21. The method of claim 1 , wherein the tissue section comprises a fixed or fresh-frozen tissue section.
22. The method of claim 21 , wherein the fixed tissue section is a formalin-fixed paraffin embedded tissue section.
23. The method of claim 1 , wherein the plurality of features comprises printed or photolithographically deposited features.
24. The method of claim 1 , wherein identifying the nucleotide sequence of the positional domain comprises sequencing.