Dynamic enhancer landscape in postmitotic motor neurons

Generic spinal motor neuron identity is specified by cooperative binding of selector transcription factors to motor neuron specific enhancers. Whether these enhancers remain active to maintain the motor neuron expression program following downregulation of selector factors in maturing motor neurons remains unknown. We demonstrate that enhancers established by selector genes are highly transient during motor neuron differentiation. The chromatin immunoprecipitation-exonuclease (ChIP-exo) assay reveals that Isl1 is anchored to nascent motor neuron enhancers through protein-protein interaction. Stage-specific recruitment of transcription factors correlates with active enhancer marks. The majority of genes contain distinct early and late enhancers suggesting that the motor neuron expression program is maintained by a dynamic regulatory landscape. Examination of ChIP-seq profiles of 5 transcription factors and 1 histone modification, chromatin accessibility profiles using ATAC-seq, and total RNA profiles during differentiation of mouse ES cell-derived spinal motor neurons by deep sequencing.