Her6 and Prox1 are novel regulators of photoreceptor regeneration in the zebrafish retina

Damage to light-sensing photoreceptors (PRs) occurs in highly prevalent retinal diseases. As humans cannot regenerate new PRs, these diseases often lead to irreversible blindness. Intriguingly, animals, such as the zebrafish, have the ability to regenerate PRs efficiently and restore functional vision. Upon injury, mature Muller glia (MG) undergo reprogramming to adopt a stem cell-like state. This process is similar to cellular dedifferentiation, and results in the generation of progenitor cells, which, in turn, proliferate and differentiate to replace lost retinal neurons. In this study, we tested whether factors involved in dedifferentiation of Drosophila CNS are implicated in the regenerative response in the zebrafish retina. We found that hairy-related 6 (her6) negatively regulates of PR production by regulating the rate of cell divisions in the MG-derived progenitors. prospero homeobox 1 (prox1) is expressed in differentiated PRs, and likely promotes PR differentiation through phase separation. Interestingly, upon Her6 downregulation, Prox1 is precociously upregulated in the PRs, to promote PR differentiation; conversely, loss of Prox1 also induces a downregulation of Her6. Together, we identified two novel candidates of PR regeneration that cross regulate each other, and may be exploited to promote human retinal regeneration and vision recovery.