Sbno1 and Usp8 Cooperate to Enhance Notch Signaling in Regulating Neural Stem Cells

The Notch signaling pathway is essential for the self-renewal, differentiation, and maintenance of neural stem cells (NSCs). While genetic studies in Drosophila have implicated Strawberry Notch in Notch signaling, the role of its vertebrate homologue, Sbno1, in mammalian NSCs remains largely unexplored. Here we show that Sbno1 interacts with Rbpj, the central transcriptional mediator of Notch, as well as with the deubiquitinating enzyme Usp8. Promoter analyses revealed that Sbno1 and Usp8 synergistically enhance expression of Hes5, a well-known Notch target in NSCs. Using in utero electroporation to overexpress or knock out Usp8 in embryonic cortical NSCs, we demonstrate that Usp8 is essential for NSC maintenance whereas loss of Sbno1 leads to NSC depletion and premature neuronal differentiation. Mechanistically, our results suggest that Sbno1 facilitates Usp8-mediated stabilization of the Notch intracellular domain and resolves R-loops at the Hes5 promoter, thereby promoting target gene expression. Together, these findings identify Sbno1 and Usp8 as critical, previously unrecognized regulators of Notch signaling in NSCs and provide the first in vivo evidence of their physiological roles in mammalian cortical development.