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

我们选择性失活成年小鼠胰腺β细胞（β细胞，BCs）中通用转录因子TFIID（general transcription factor TFIID）的Taf4亚基。Taf4失活可快速下调β细胞功能相关关键基因的表达，进而引发血糖升高、血胰岛素水平降低、葡萄糖刺激的胰岛素分泌缺陷；长期而言，还会通过β细胞亚群的凋亡导致β细胞总量减少。但11周后，血糖与血胰岛素水平可趋于稳定，突变型小鼠能够长期存活。对分离获取的朗格汉斯岛（胰岛，Langerhans islets）开展批量RNA测序（bulk RNA-seq）、转座酶可及性测序（ATAC-seq）以及单细胞RNA测序（single cell RNA-seq）后发现，Taf4缺失引发的染色质可及性与基因表达大规模重塑，不仅存在于靶向的β细胞中，在α细胞和δ细胞中同样显著。Taf4缺失1周后，可观察到兼具β细胞、α细胞和/或δ细胞特征的混合细胞群，同时存在一类向α细胞转分化的细胞群体。该转分化过程与Mafb、Mafg、Bptf及Foxp1转录因子的协同作用密切相关。由此可见，Taf4对于维持β细胞的功能与细胞身份至关重要，我们还鉴定出了一批与β细胞转分化相关的全新因子。
总体实验设计：从野生型对照小鼠，或β细胞中Taf4已分别失活1周、5周的小鼠体内分离朗格汉斯岛，共制备3个单细胞RNA测序样本。