STRIPAK Members Orchestrate Hippo and Insulin Receptor Signaling to Promote Neural Stem Cell Reactivation

Abstract

Summary: Adult stem cells reactivate from quiescence to maintain tissue homeostasis and in response to injury. How the underlying regulatory signals are integrated is largely unknown. Drosophila neural stem cells (NSCs) also leave quiescence to generate adult neurons and glia, a process that is dependent on Hippo signaling inhibition and activation of the insulin-like receptor (InR)/PI3K/Akt cascade. We performed a transcriptome analysis of individual quiescent and reactivating NSCs harvested directly from Drosophila brains and identified the conserved STRIPAK complex members mob4, cka, and PP2A (microtubule star, mts). We show that PP2A/Mts phosphatase, with its regulatory subunit Widerborst, maintains NSC quiescence, preventing premature activation of InR/PI3K/Akt signaling. Conversely, an increase in Mob4 and Cka levels promotes NSC reactivation. Mob4 and Cka are essential to recruit PP2A/Mts into a complex with Hippo kinase, resulting in Hippo pathway inhibition. We propose that Mob4/Cka/Mts functions as an intrinsic molecular switch coordinating Hippo and InR/PI3K/Akt pathways and enabling NSC reactivation. : The integration of signals allowing stem cell reactivation from quiescence is unclear. Gil-Ranedo et al. identify STRIPAK members Mob4, Cka, and PP2A/Mts through reactivating versus quiescent neural stem cell (NSC) transcriptional profiling. Their findings suggest that Mob4/Cka/Mts functions as an intrinsic molecular switch coordinating Hippo and InR/PI3K/Akt pathways, enabling NSC reactivation. Keywords: neural stem cells, quiescence, reactivation, STRIPAK members, Hippo signaling, InR/PI3K/Akt signaling