The TFIID subunit TAF4 is required for pancreatic beta cell function and identity [single-cell RNA-seq]

We selectively inactivated the Taf4 subunit of general transcription factor TFIID in adult murine pancreatic beta cells (BCs). Taf4 inactivation rapidly diminishes expression of critical genes involved in BC function leading to increased glycaemia, lowered blood insulin levels, defective glucose-stimulated insulin secretion and in the longer term reduced BC mass through apoptosis of a subpopulation of BCs. Nevertheless, glycaemia and blood insulin levels are stabilised after 11 weeks with mutant animals showing long term survival. Bulk RNA-seq and ATAC-seq and single cell RNA-seq on isolated Langerhans islets show that Taf4 loss leads to major remodelling of chromatin accessibility and gene expression not only in targeted BCs, but also alpha and delta cells. One week after Taf4-loss cells with mixed BC, alpha and/or delta cell identities were observed as well as a population trans-differentiating into alpha cells. Trans-differentiation was associated with the concerted action of the Mafb, Mafg, Bptf and Foxp1 transcription factors. Taf4 is therefore essential for BC function and identity and we identify a novel set of factors associated with BC trans-differentiation. Three single cell RNA-seq samples from isolated Langerhans islets from wild-type control mice or mice where Taf4 has been inactivated in beta cells for 1 or 5 weeks.