PROJECT SUMMARY The colon is a responsive tissue, and the epithelium replaces itself every 3-4 days. The colon has dedicated stem cells that divide for self-renewal and differentiation into specialized cell types. Differentiated colon cells perform distinct functions including water absorption and mucus secretion. In many tissues, differentiation is driven by epigenetic mechanisms including histone modifications. Methylation of histone H3 at lysine 36 (H3K36) is associated with gene bodies at sites of transcriptional activity. H3K36 methylation contributes to differentiation and stem cell maintenance in rapidly renewing tissues including blood and testes. Based on preliminary data, I hypothesize that H3K36 methylation governs cell fate decisions and reinforces cell identity in colon epithelial cells, specifically colonocyte and goblet cell lineages. To address this hypothesis, I will pursue two specific aims. First, I plan to characterize the H3K36 methylation signature in colon epithelial cells. Second, I will determine the functional role of H3K36 methylation in colon cell identity. Although, establishing a direct connection between specific histone modifications and cellular processes is challenging due to redundancies in the system, I can overcome this obstacle by taking advantage of a lysine (K)-to-methionine (M) mutation first discovered in cancer patients to precisely suppress H3K36 methylation. I will combine multiple cutting-edge tools to specifically trace and manipulate H3K36 methylation in mice and organoid model systems to advance the understanding of chromatin and lineage specification in the colon. I will also utilize novel sorting protocols to purify distinct colon cell populations for comparative epigenetic and transcriptional analysis. Collectively, this work is significant because it will establish the role of H3K36 methylation in controlling cell-type specific gene expression and lineage decisions in the colon. Revealing the role histone modifications play in colon homeostasis is the first step to understanding how these regulatory mechanisms break down in diseases such as colitis/cancer and could impact human health.