Chromatin-Mediated Alternative Splicing Regulates Cocaine Reward Behavior

Drugs of abuse are known to cause remodeling of neuronal cell populations that persists long after the drug is no longer present. It is well established that cocaine epigenetically regulates gene expression, yet mechanism(s) by which cocaine-induced epigenetic modifications regulate alternative splicing is largely unexplored.

We tested the hypothesis that H3K36me3 directly mediates alternative splicing in brain in the context of preclinical models of drug abuse. We first quantified concomitant splice-site enrichment of H3K36me3 and differential isoform expression in mouse brain tissue following cocaine intravenous self-administration (IVSA). We showed that cocaine IVSA led to enrichment of H3K36me3 at splice junctions of differentially spliced genes and that alternative splicing serves as a key transcriptional mechanism in three brain reward regions (NAC, PFC, and VTA). To validate that enrichment of H3K36me3 was causally linked to alternative splicing, we then overexpressed SET2 in the NAc. We processed infected tissue using single sample sequencing (S3EQ) to generate H3K36me3 ChIP- and RNA-seq data in order to identify H3K36me3-associated alternative splicing events. We found that SET2-driven enrichment of H3k36me3 was sufficient to increase alternative splicing in a subset of neuronal genes that were also mediated by cocaine self-administration.

Next, we tested if H3k36me3 enrichment was sufficient to alter cocaine behavior and found that SET2-mediated H3K36me3 enrichment in NAc increased cocaine seeking in both Conditioned Place Preference (CPP) and IVSA. In addition, we showed these effects can be rescued with a SET2 inhibitor. From these gene lists, we identified the splice factor, Srsf11, as highly enriched amongst both cocaine and SET2 spliced genes. Using CRISPR dcas9-SET2, we applied targeted epigenetic editing to establish that H3K36me3 functions directly in alternative splicing of Srsf11. Epigenetic editing of H3K36me3 at Srsf11 was sufficient to drive alternative splicing of Srsf11 and enhance cocaine CPP and IVSA.