Retinal regeneration has been mostly studied after widespread tissue injury, such as puncture wounds and light damage. However, it is not well understood how the retina regenerates at the cellular level following loss of specific cell types, as is often seen in retinal degenerative diseases. Here, Jeff Mumm and colleagues make use of transgenic zebrafish to selectively ablate retinal ganglion cells (RGCs) and identify genes that regulate RGC regeneration. The authors first profile the transcriptional changes associated with RGC loss and regeneration, using single-cell RNA sequencing and pseudotime analyses. They find that Müller glia (MG), the active progenitor in retinal regeneration, transcriptionally respond differently to different injury types. Then, they perform a CRISPR screen of 101 genes involved in MG response. Surprisingly, key genes previously associated with regeneration following widespread injury are not required for RGC regeneration. In fact, several mutants from the CRISPR screen display accelerated RGC regeneration following RGC-specific ablation. In particular, knocking out ascl1a, a gene previously identified as pro-regenerative in the zebrafish retina, increases the propensity of MG progenitor cells to differentiate into RGCs and enhances RGC regeneration. Overall, the findings highlight the importance of context in retinal injury and how the retina elicits different genetic responses to replace lost cells.
