LRIG1 is a gatekeeper to exit from quiescence in adult neural stem cells

Adult neural stem cells (NSCs) must tightly regulate quiescence and proliferation. Single cell analysis has suggested a continuum of cell states as NSCs exit quiescence. Here we capture and characterize in vitro primed quiescent NSCs and identify LRIG1 as an important regulator. We show that BMP-4 signaling induces a dormant non-cycling quiescent state (d-qNSCs), whereas combined BMP-4/FGF-2 signalling induces a distinct primed quiescent state poised for cell cycle re-entry. Primed quiescent NSCs (p-qNSCs) are defined by high levels of LRIG1 and CD9, as well as an interferon response signature, and can efficiently engraft into the adult subventricular zone (SVZ) niche. Genetic disruption of Lrig1 in vivo within the SVZ NSCs leads an enhanced proliferation. Mechanistically, LRIG1 primes quiescent NSCs for cell cycle re-entry and EGFR responsiveness by enabling EGFR protein levels to increase but limiting signaling activation. LRIG1 is therefore an important functional regulator of NSC exit from quiescence. We used 2 independent adult neural stem cells lines. They were derived from the SVZ (Subventricular zone) of young WT adult mice (6-8 weeks old). ANS4 (A4) and Bl6. The cells were used at passage less than 10 and were plated at low density for 3 days. We used 2 biological replicas per condition in each line. NSCs were treated in EGF/FGF, BMP4 (B) and BMP4+FGF2 (BF) for 3 days and after RNA was extracted using Quiagen kit.