A cis-regulatory module underlies retinal ganglion cell genesis and axonogenesis [Set8.Bulk RNA-Seq P18 Cerebellum WT and Atoh7 remote Enhancer KO]
During retinogenesis, the proneural bHLH transcription factor Atoh7 is transiently expressed in retinal progenitor cells (RPCs) and is required for retinal ganglion cell (RGC) differentiation. In humans, a deletion in a distal non-coding regulatory region upstream of ATOH7 is associated with nonsyndromic congenital retinal nonattachment (NCRNA) disorder, characterized by optic nerve atrophy and complete blindness. Here we functionally interrogate the significance of the Atoh7 enhancer landscape to retinogenesis. We demonstrate that deletion of the enhancer structure upstream of Atoh7 in mice leads to RGC deficiency, optic nerve hypoplasia and blood vascular abnormalities, phenocopying inactivation of Atoh7 and recapitulating key features of NCRNA.  We further provide evidence that the loss of the Atoh7 remote enhancer impacts ipsilaterally-projecting RGCs and disrupts proper axonal projections to the brain targets.  Transcriptionally, deletion of the Atoh7 remote enhancer is associated with dysregulation of axonogenesis genes, including the derepression of the axon repulsive cue Robo3 which is normally epigenetically silenced in the developing retina. Our data provide novel insights into how Atoh7 enhancer elements function to promote RGC development and optic nerve formation and uncover a key role of Atoh7 in the transcriptional control of axon guidance molecules possibly via epigenetic mechanisms. Overall design: Bulk RNA-Seq P18 Cerebellum WT and Atoh7 remote Enhancer KO: Three independent replicates of the developing cerebellum from WT or mouse Atoh7 remote enhancer knockout at P18 were processed for RNA extraction and submitted for RNA-Seq.