Lineage tracing reveals atoh7 positive and negative retinal ganglion cell populations in the zebrafish retina

Purpose: Atoh7 is a transiently expressed developmental transcription factor that contributes to the generation of all seven major retinal cell types. Despite this broad lineage potential, Atoh7 is specifically required for retinal ganglion cell (RGC) formation and survival. In mice, a substantial proportion of RGCs arise from Atoh7-negative progenitors, suggesting potential nonautonomous roles for Atoh7 in RGC development. Although atoh7 function is conserved in zebrafish, the complete lineage, including the contribution to the RGC population, has not been fully defined. Here, we sought to determine the atoh7 retinal lineage in wild type and atoh7 mutant zebrafish. Methods: We generated atoh7:iCre transgenic zebrafish and paired them with the established ubi:Switch reporter to permanently label the atoh7 lineage. We validated transgene expression and lineage labeling using in vivo live imaging and immunohistochemistry in embryonic, larval, and adult retinas, as well as in select regions of the adult brain. Results: The atoh7:iCre;ubi:Switch system accurately recapitulated endogenous atoh7 onset, with reporter expression persisting into adulthood. We found that 79% of RGCs in wild-type retinas arise from atoh7-positive progenitors, a greater proportion than previously reported in mice. Additionally, mutant retinas displayed a significant increase in atoh7 lineage+/Pax6+ amacrine cells and an increased number of Prox1+ bipolar cells. We also identified atoh7 lineage positive cells in other central nervous system (CNS) regions. Conclusions: Our findings reveal both atoh7 lineage positive and negative retinal cell types in zebrafish, including RGCs, providing a platform to study survival and cell fate mechanisms of atoh7 lineage negative RGCs during retinal development.