TheAtoh7remote enhancer provides transcriptional robustness during retinal ganglion cell development

Abstract

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 nonsyndromic congenital retinal nonattachment (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 messenger RNA (mRNA) fivefold but does not recapitulate optic nerve loss; however, SEdel/knockout (KO) trans heterozygotes have thin optic nerves. By analyzing Atoh7 mRNA and protein levels, RGC development and survival, and chromatin landscape effects, we show that the SE ensures robust Atoh7 transcriptional output. Combining SE deletion and 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 that is hard-wired in the machinery of vertebrate retinal ganglion cell genesis.

Dynamic Polarization of Rab11a Modulates Crb2a Localization and Impacts Signaling to Regulate Retinal Neurogenesis

“…Studies using frog and chick retinas suggest a negative feedback loop where Notch pathway activation and Atoh7 provide instructive signals for proliferation or cell cycle exit (Agathocleous et al, 2009 ). Recent data further suggest that Notch signaling activates Hes gene expression and can lengthen the cell cycle to allow the accumulation of higher levels of Atoh7, essential to ganglion cell genesis and cell cycle exit (Chiodini et al, 2013 ; Miesfeld et al, 2018b , 2020 ). While it is clear that the activity of these transcription factors is instructive for cell fate decisions, less is known about the mechanisms that link cellular features and signaling to the heterogeneity of transcription factor expression and activity within individual RPCs prior to cell fate commitment.…”

Atoh7-independent specification of retinal ganglion cell identity

“…6, B to E , and table S5). We also observed strong enrichment of Atoh7 binding within the Atoh7 proximal promoter and distal enhancer sequences ( 14 ), suggestive of autoregulation of Atoh7 expression ( Fig. 6D ).…”

“…Atoh7 -deficient mice and zebrafish lack upward of 95% of RGCs ( 1 , 8 , 10 , 11 ) and likewise lack any visible optic nerve or functional connections from the retina to the brain ( 12 , 13 ). Human mutations in ATOH7 or its cis-regulatory regions have been associated with optic nerve agenesis or hypoplasia ( 4 , 6 , 14 ) and increased susceptibility to glaucoma ( 15 , 16 ). Atoh7 deficiency also disrupts the development of retinal vasculature in both mice and humans, likely as an indirect result of the loss of RGCs ( 17 , 18 ).…”

Risk Factors for Retinal Ganglion Cell Distress in Glaucoma and Neuroprotective Potential Intervention

“…During the embryonic phase, by way of Sonic Hedgehog (SHH), RGCs exert a control over different downstream molecular events, including the laminar organization of the retina, the size of successive cell populations, the development of optic stalk neuro-epithelial cells and their morphogenesis [ 12 , 13 , 14 , 15 ]. In the advanced stages of development, the RGC axons of the optic nerve, which form the retinal nerve fiber layer, are closely involved with the migrating astrocytes.…”