Abstract
Purpose :
Diseases and damage to the retina lead to losses in retinal neurons and eventual visual impairment. Although some vertebrates, particularly fish and amphibians have the capacity to regenerate new retinal neurons, the mammalian retina lacks regenerative capabilities, making vision loss permanent. We have previously shown that induced expression of Ascl1 in retinal Müller glia (MG) stimulates neurogenesis in the mouse retina, similar to what happens naturally in fish; however, this treatment only generates inner retinal neurons, and not rod or cone photoreceptors. We hypothesized that loss in chromatin accessibility for enhancers of photoreceptor-specific genes might restrict the potential of MG to generate photoreceptors.
Methods :
We carried out ATAC sequencing of the retinal progenitors and mature Müller glia to analyze differences between these cells. We also compared the MG and progenitor ARs to those of ATACseq in rods, cones and bipolar cells, to determine whether chromatin accessibility correlates with the bias in MG to generate inner retinal neurons after Ascl1 over-expression.
Results :
We find that progenitors and MG have similar patterns of chromatin accessibility, with approximately 60% of the accessible regions (ARs) shared between these cell types. Approximately 30% of the ARs are unique to progenitors (not in MG), and these are associated with developmental genes (eg. GO: developmental process). The unique progenitor peaks are also enriched in predicted motifs for proneural transcription factors (eg. Sox2/bHLH). Shared ARs are associated with cell cycle genes and related predicted motifs. When comparing MG and progenitors to retinal neurons, the shared ARs are strikingly similar, but patterns in bipolar cell-specific ARs indicate that bHLH pioneering activity may drive that fate above other neurons via the Otx2 gene network.
Conclusions :
Overall, our analysis indicates a loss of neurogenic gene expression and motif accessibility during glial maturation that may prevent efficient reprogramming, and a tendency for bipolar neurons to be generated with Ascl1 expression in MG.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.