SOX2 maintains the quiescent progenitor cell state of postnatal retinal Müller glia

Within discrete regions of the developing mammalian central nervous system, small subsets of glia become specialized to function as neural stem cells. As a result of their self-renewal and neurogenic capacity, these cells later serve to replenish neurons and glia during persistent or injury-induced adult neurogenesis. SOX2, an HMG box transcription factor, plays an essential role in the maintenance of both embryonic and adult neural progenitors. It is unclear, however, which biological mechanisms regulated by SOX2 are required for neural stem cell maintenance. In this study, we address this question through genetic analysis of SOX2 function in differentiating postnatal Muller glia, a cell type that maintains neurogenic capacity in the adult retina. By utilizing molecular analysis and real-time imaging, we show that two progenitor characteristics of nascent Muller glia - their radial morphology and cell cycle quiescence - are disrupted following conditional genetic ablation of Sox2 in the mouse postnatal retina, leading to Muller cell depletion and retinal degeneration. Moreover, we demonstrate that genetic induction of the Notch signaling pathway restores Muller glial cell identity to Sox2 mutant cells, but does not secure their quiescent state. Collectively, these results uncouple the roles of SOX2 and the Notch signaling pathway in the postnatal retina, and uncover a novel role for SOX2 in preventing the depletion of postnatal Muller glia through terminal cell division.