AP-1 transcription factors and the BAF complex mediate signal-dependent enhancer selection

Enhancer elements are regulatory sequences within genomes that direct the selective expression of genes so that genetically identical cells can differentiate and acquire the highly specialized forms and functions required to build a functioning animal. To differentiate, cells must select from among the ~10^6 enhancers encoded in the genome the thousands of enhancers that drive the gene programs that impart their distinct features. We used a genetic approach to identify transcription factors (TFs) required for enhancer selection in fibroblasts. This revealed that the broadly expressed, growth factor-inducible TFs Fos/Jun (AP-1) play a central role in enhancer selection. Fos/Jun selects enhancers together with cell type-specific TFs by collaboratively binding to nucleosomal enhancers and directing recruitment of the SWI/SNF (BAF) chromatin remodeling complex to establish accessible chromatin. These experiments demonstrate how environmental signals acting via Fos/Jun and BAF coordinate with cell type-specific TFs to select enhancer repertoires that enable differentiation during development. Overall design: Genome-wide maps of H3K27ac, H3K4me1/2, AP-1 transcription factors, Smarca4, and chromatin accessibility before and after serum stimulation for the indicated times in primary mouse embryonic fibroblasts.