Project description:Retinal ganglion cells (RGCs) relay visual information from the eye to the brain. RGCs are the first cell type generated during retinal neurogenesis. Loss of function of the transcription factor Atoh7, expressed in multipotent early neurogenic retinal progenitors leads to a selective and essentially complete loss of RGCs. Therefore, Atoh7 is considered essential for conferring competence on progenitors to generate RGCs. Despite the importance of Atoh7 in RGC specification, we find that inhibiting apoptosis in Atoh7-deficient mice by loss of function of Bax only modestly reduces RGC numbers. Single-cell RNA sequencing of Atoh7;Bax-deficient retinas shows that RGC differentiation is delayed but that the gene expression profile of RGC precursors is grossly normal. Atoh7;Bax-deficient RGCs eventually mature, fire action potentials, and incorporate into retinal circuitry but exhibit severe axonal guidance defects. This study reveals an essential role for Atoh7 in RGC survival and demonstrates Atoh7-dependent and Atoh7-independent mechanisms for RGC specification.
Project description:The retinal ganglion cell (RGC) competence factor ATOH7 is dynamically expressed during retinal histogenesis. ATOH7 transcription is controlled by a promoter-adjacent primary enhancer and a remote shadow enhancer (SE). Deletion of the ATOH7 human SE causes non‑syndromic congenital retinal non-attachment (NCRNA) disease, characterized by optic nerve aplasia and total blindness. We used genome editing to model NCRNA in mice. Deletion of the murine SE reduces Atoh7 mRNA >5-fold, but does not recapitulate optic nerve loss; however, SEdel/KO (knockout) trans heterozygotes have thin optic nerves. By analyzing Atoh7 mRNA and protein levels, RGC development and survival, and chromatin landscape effects, we show how the SE ensures robust Atoh7 transcriptional output. Combining SE deletion, KO and wild-type alleles in a genotypic series, we determined the amount of Atoh7 needed to produce a normal complement of adult RGCs, and the secondary consequences of graded reductions in Atoh7 dosage. Together these data reveal the workings of an evolutionary fail-safe, a duplicate enhancer mechanism hard-wired in the machinery of vertebrate retinal ganglion cell genesis.
Project description: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.
Project description: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.
Project description: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.
Project description: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.
Project description: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.
Project description: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.
Project description:The microarray analysis was designed to test the effects of HES5.3 siRNAs, Atoh7 siRNAs and nt siRNAs on gene expression in embryonic chick retina.