GSE19409
Ligand-dependent dynamics of retinoic acid receptor binding during early neurogenesis
Among its many roles in development, retinoic acid determines the anterior-posterior identity of differentiating motor neurons by activating Retinoic Acid Receptor (RAR)-mediated transcription. RAR is thought to bind the genome constitutively, and only induce transcription in the presence of the retinoid ligand. However, little is known about where RAR binds to the genome or how it selects target sites. We tested the constitutive RAR binding model using the retinoic acid-driven differentiation of mouse embryonic stem cells into differentiated motor neurons.  We find that retinoic acid treatment results in widespread changes in RAR genomic binding, including novel binding to genes directly responsible for anterior-posterior specification, as well as the subsequent recruitment of the basal polymerase machinery. Finally, we discovered that the binding of transcription factors at the embryonic stem cell stage can accurately predict where in the genome RAR binds after initial differentiation. We have characterized a ligand-dependent shift in RAR genomic occupancy at the initiation of neurogenesis. Our data also suggests that enhancers active in pluripotent embryonic stem cells may be preselecting regions that will be activated by RAR during neuronal differentiation. Overall design: The differentiation of ventral motor neurons is induced by treating embryonic stem cell cultures with retinoic acid. Here, ChIP-seq is used to profile the genome-wide occupancy of RAR isofroms both immediately prior to and during exposure of the cells to retinoic acid. ChIP-seq is also used to profile the genomic occupancy of Pol2 with phosphorylated serine 5 (Pol2-S5P) and phosphorylated serine 2 (Pol2-S2P) after exposure to retinoic acid.