Genome-wide characterization of Six1 binding in embryo and cochlea

Otic ectoderm gives rise to almost all cell types of the inner ear; however, the mechanisms that link transcription factors, chromatin, lineage commitment and differentiation capacity are largely unknown. Here we show that Brg1 chromatin-remodeling factor is required for specifying neurosensory lineage in the otocyst and for inducing hair and supporting cell fates in the cochlear sensory epithelium. Brg1 interacts with the critical neurosensory-specific transcription factors Eya1/Six1, both of which simultaneously interact with BAF60a or BAF60c. Chromatin immunoprecipitation-sequencing (ChIP-seq) and ChIP assays demonstrate Brg1 association with discrete regulatory elements at the Eya1 and Six1 loci. Brg1-deficiency leads to markedly decreased Brg1 binding at these elements and loss of Eya1 and Six1 expression. Furthermore, ChIP-seq reveals Brg1-bound promoter-proximal and distal regions near genes essential for inner ear morphogenesis and cochlear sensory epithelium development. These findings uncover essential functions for chromatin-remodeling in the activation of neurosensory fates during inner ear development. Overall design: Six1 is a critical transcription factor for specifying cell fates in multiple organs and shares common DNA-binding sites with Six2/4/5. However, its molecular function in defining the specificity of Six1-DNA interactions and in instructing cell fates is poorly understood. We performed Six1 ChIP-seq analyses in E10.5 mouse embryos and E13.5 cochleae to map genome-wide CRMs through which Six1 and its interacting TFs function in a combinatorial fashion to control the network of gene regulation necessary for proper development. Genome-wide characterization has identified a robust set of Six1 targets in embryos and auditory sensory epithelium, including genes participating in Wnt/Notch/Shh/Fgf signaling pathways and regulators critical for auditory hair cell formation. Our data provide insights into how Six1 acts in multiple regulatory networks operating in distinct cell types at different stages. Genome-wide Six1 binding feature was characterized in whole embryo and cochlea using ChIP-seq. Please note that both Series and sample records have been updated on Dec 9th, 2020.