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Many retinal diseases lead to the loss of retinal neurons and cause visual impairment. The adult mammalian retina has little capacity for regeneration. By contrast, teleost fish functionally regenerate their retina following injury, and Müller glia (MG) are the source of regenerated neurons. The proneural transcription factor Ascl1 is upregulated in MG after retinal damage in zebrafish and is necessary for regeneration. Although Ascl1 is not expressed in mammalian MG after injury, forced expression of Ascl1 in mouse MG induces a neurogenic state in vitro and in vivo after NMDA (N-methyl-d-aspartate) damage in young mice. However, by postnatal day 16, mouse MG lose neurogenic capacity, despite Ascl1 overexpression. Loss of neurogenic capacity in mature MG is accompanied by reduced chromatin accessibility, suggesting that epigenetic factors limit regeneration. Here we show that MG-specific overexpression of Ascl1, together with a histone deacetylase inhibitor, enables adult mice to generate neurons from MG after retinal injury. The MG-derived neurons express markers of inner retinal neurons, synapse with host retinal neurons, and respond to light. Using an assay for transposase-accessible chromatin with high-throughput sequencing (ATAC–seq), we show that the histone deacetylase inhibitor promotes accessibility at key gene loci in the MG, and allows more effective reprogramming. Our results thus provide a new approach for the treatment of blinding retinal diseases.

Müller glia (MG) serve as sources for retinal regeneration in non-mammalian vertebrates. We find that this process can be induced in mouse MG, after injury, by transgenic expression of the proneural transcription factor Ascl1 and the HDAC inhibitor TSA. However, new neurons are generated only from a subset of MG. Identifying factors that limit Ascl1-mediated MG reprogramming could make this process more efficient. In this study, we test whether injury-induced STAT activation hampers the ability of Ascl1 to reprogram MG into retinal neurons. Single-cell RNA-seq shows that progenitor-like cells derived from Ascl1-expressing MG have a higher level of STAT signaling than do those cells that become neurons. Ascl1-ChIPseq and ATAC-seq show that STAT potentially directs Ascl1 to developmentally inappropriate targets. Using a STAT inhibitor, in combination with our previously described reprogramming paradigm, we found a large increase in the ability of MG to generate neurons.