GSE111264
A non-canonical BRD9-containing BAF chromatin remodeling complex regulates naïve pluripotency in mouse embryonic stem cells
The mammalian BRG1-associated factors (BAF) complex is a multi-subunit chromatin remodeling complex that is an important component of the embryonic stem cell (ESC) transcriptional regulatory network. However, the role of individual subunits in BAF complex targeting and function needs to be elucidated. Here, we find that the Bromodomain containing protein 9 (BRD9) and Glioma tumor suppressor candidate region gene 1 (GLTSCR1; also known as BICRA) or its paralog GLTSCR1-like (also known as BICRAL) define a smaller, non-canonical BAF complex (GBAF for GLTSCR1/1L-containing BAF complex) in mouse ESCs that is distinct from the canonical embryonic stem cell BAF (esBAF) and the polybromo-associated BAF (PBAF) complexes. GBAF lacks several esBAF subunits, including BAF47, BAF57 and ARID1A. We demonstrate that GBAF and esBAF complexes are targeted to different features of the genome and are co-bound with different sets of pluripotency transcription factors. Specifically, GBAF complexes co-localize with key regulators of naïve pluripotency, KLF4 and Sp5, on the genome. Consistent with this, we provide evidence that GBAF's specific function is to regulate the transcription of genes involved in the maintenance of naïve pluripotency, including Nanog and Prdm14. Additionally, we show that BRD9 is displaced from chromatin by the selective BRD9 bromodomain inhibitor, I-BRD9, and that this leads to changes in target gene expression. The function of the GBAF complex in ESCs is highly correlated with the function of BRD4, consistent with an association between GBAF complexes and BRD4. We find that GBAF complexes are directly recruited to chromatin by BRD4 in a bromodomain-dependent fashion and we identify a set of I-BRD9- and JQ1-sensitive BRD9 binding sites that determine the functional similarity between these epigenetic regulators. Together, our results demonstrate functionally specific roles for BAF complex assemblies in maintaining the transcriptional network of pluripotency, highlighting the biological importance of complex heterogeneity. Overall design: ChIP-Seq of BRD9, BRG1, ARID1A and BRD4 in v6.5 mouse embryonic stem cells (mESCs), RNA-Seq of control or Brd9 knocked down populations in v6.5 mESCs, RNA-Seq of DMSO or I-BRD9-treated mESCs at 24 or 48 hour timepoints, RNA-Seq of control or ARID1A knockout populations using Arid1af/f:CreERT2 ESCs.