SMNDC1 links chromatin remodeling and splicing to regulate pancreatic hormone expression

Insulin expression is restricted to the pancreatic beta cells, which are physically or functionally depleted in diabetes. Identifying targetable pathways repressing insulin in non-beta cells, particularly in the developmentally related glucagon-secreting alpha cells, is an important aim of regenerative medicine. Here, we performed an RNA interference screen in the murine alpha cell line, alphaTC1, to identify silencers of insulin expression. We discovered that knockdown of the splicing factor Smndc1 (Survival Motor Neuron Domain Containing 1) triggered a global repression of alpha cell gene-expression programs in favor of increased beta cell markers. Mechanistically, Smndc1 knockdown upregulated the key beta cell transcription factor Pdx1, by modulating the activities of the BAF and Atrx families of chromatin remodeling complexes. SMNDC1’s repressive role was conserved in human pancreatic islets, its loss triggering enhanced insulin secretion and PDX1 expression. Our study identifies Smndc1 as a key factor connecting splicing and chromatin remodeling to the control of insulin expression in human and mouse islet cells.