Kavli Affiliate: Seth Blackshaw
| Authors: Nguyet Le, Trieu-Duc Vu, Isabella Palazzo, Ritvik Pulya, Yehna Kim, Seth Blackshaw and Thanh Hoang
| Summary:
Neurogenic competence is actively repressed in mature mammalian Muller glial cells, and previous studies have predicted that this is in part mediated by active Notch signaling. To determine whether global loss of Notch signaling could induce reprogramming of, we selectively deleted the common Notch transcriptional mediator Rbpj in adult mouse Muller glia while simultaneously tracing the fate of Muller glia-derived cells. We observed that Rbpj-deficient Muller glia directly transdifferentiate into bipolar and amacrine cells in the absence of injury, but also observed that this effect was significantly enhanced by NMDA-dependent excitotoxic injury. We found that Muller glia-specific loss of function of Notch1 and Notch2 phenocopied this injury-induced induction of neurogenic competence. Integrated multiomic and Cut&Tag analysis revealed that Rbpj directly activates Notch effectors and mature Muller glial-specific genes, and indirectly represses expression of neurogenic bHLH factors. Moreover, we find that combined loss of function of Rbpj and Nfia/b/x leads to a near-complete conversion of Muller glia to neurons in the absence of proliferation, leading to a severe disruption of retinal structure as the result of Muller glia depletion. Finally, however, we show that induction of Muller glial proliferation by AAV-mediated overexpression of dominant-active Yap both preserves retinal structure and supports efficient levels of Muller glia-derived neurogenesis in both Rbpj- and Nfia/b/x/Rbpj-deficient Muller glia. These findings demonstrate that, like in zebrafish, Notch signaling actively represses neurogenic competence in mammalian Muller glia, and imply that inhibition of Notch signaling in combination with Nfia/b/x loss of function and overexpression of activated Yap, could be an effective component of regenerative therapies for degenerative retinal diseases.