In situ nucleic acid sequencing of expanded biological samples
The invention provides in situ nucleic acid sequencing to be conducted in biological specimens that have been physically expanded. The invention leverages the techniques for expansion microscopy (ExM) to provide new methods for in situ sequencing of nucleic acids as well as new methods for fluorescent in situ sequencing (FISSEQ) in a new process referred to herein as “expansion sequencing” (ExSEQ).
1. A method for in-situ sequencing of target nucleic acids present in a biological sample comprising the steps of:
a) linking target nucleic acids present in the biological sample with a small molecule linker or a nucleic acid adaptor capable of linking to a target nucleic acid and to a swellable material;
b) embedding the biological sample comprising the target nucleic acids and attached small molecule linker or nucleic acid adaptor in a swellable material wherein the small molecule linker or the nucleic acid adaptor is linked to the target nucleic acids present in the sample and to the swellable material,
c) digesting proteins present in the biological sample;
d) swelling the swellable material to form a first enlarged biological sample that is enlarged as compared to the biological sample;
e) re-embedding the first enlarged sample in a non-swellable material;
(f) modifying the target nucleic acids or the nucleic acid adaptor to form a nucleic acid adaptor useful for sequencing; and
(g) sequencing the nucleic acids present in the first enlarged sample.
2. The method of claim 1 , wherein biochemically modifying the target nucleic acids or the nucleic acid adapter comprises contacting the target nucleic acids or the nucleic acid adapter with reverse transcriptase.
3. The method of claim 1 , wherein the sequencing step of step (g) is fluorescence in situ sequencing.
4. The method of claim 1 , further comprising repeating steps (a) through (e) on the first enlarged sample to form a second enlarged sample prior to sequencing.
5. The method of claim 1 , wherein nucleic acid adaptors are linked to target nucleic acids via ligation to the target nucleic acid.
6. The method of claim 1 , wherein the small molecule linkers are attached to target nucleic acids via a chemical reactive group capable of covalently binding the target nucleic acid.
7. The method of claim 1 , further comprising the step of passivating the first swellable material after re-embedding the first enlarged sample in a non-swellable material.