Notch is Required for Neural Progenitor Proliferation During Embryonic Eye Regrowth

The ability of an organism to regrow tissues is regulated by various signaling pathways. One such pathway that has been studied widely both in the context of regeneration and development is the Notch signaling pathway. Notch signaling is required for development of the eye and regeneration of tissues in multiple organisms but it is unknown if Notch plays a role in the regulation of Xenopus laevis embryonic eye regrowth. We found that Notch1 is required for eye regrowth and regulates retinal progenitor cell proliferation. Chemical and molecular inhibition of Notch1 significantly decreased eye regrowth through reducing retinal progenitor cell proliferation without affecting retinal differentiation. Temporal inhibition studies showed that Notch function is required during the first day of regrowth. Interestingly, Notch1 loss-of-function phenocopied the effects of the inhibition of the proton pump, V-ATPase, where retinal proliferation but not differentiation was blocked during eye regrowth. Overexpression of a form of activated Notch1, the Notch intracellular domain (NICD) was sufficient to rescue loss of eye regrowth due to V-ATPase inhibition, suggesting that Notch acts downstream of V-ATPase. These findings highlight the importance of the Notch signaling pathway in eye regeneration and its role in inducing retinal progenitor cell proliferation in response to injury.