LRIG1 controls proliferation of adult neural stem cells by facilitating Tgfß and BMP signalling pathways

Adult Neural Stem Cells (aNSCs) in the ventricular-subventricular zone (V-SVZ) are largely quiescent. Here, we characterize the mechanism underlying the functional role of a cell-signalling inhibitory protein, LRIG1, in the control of aNSCs proliferation. Using constitutive Lrig1 knockout models, we show that Lrig1 ablation results in increased aNSCs proliferation with no change in neuronal progeny and that this hyperproliferation likely does not result from activation of the epidermal growth factor receptor (EGFR). Loss of LRIG1, however, does lead to impaired activation of canonical transforming growth factor beta (TGFβ) and bone morphogenic protein (BMP) signalling pathways. Biochemically, we show in vitro that LRIG1 is able to bind TGFβ/BMP receptors and the TGFβ1 ligand. Finally, we show that the consequences of these interactions are to facilitate SMAD phosphorylation and pathway activation. Collectively, these data suggest that, unlike in embryonic neural stem cells where EGFR is the primary mechanism of action, LRIG1 and TGFβ pathways positively work together to fulfill their inhibitory roles in aNSCs.