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Abstract

Adult neural stem cells (NSCs) in the subventricular zone (SVZ) of the lateral ventricles remain largely quiescent. Unravelling the mechanism regulating lineage progression from NSCs to newborn neurons is critical for understanding tissue homeostasis and aging. Extrinsic and intrinsic factors regulate NSC self-renewal and differentiation. In this study, I analyse the effects of one extrinsic and one intrinsic factor in NSC regulation. In both analyses, I investigate the effect of the regulators on the so-called apical NSCs, because they display an apical membrane and apical/basal polarity, and basal NSCs, which lack an apical attachment. Focusing on the neurotransmitter γ-aminobutyric acid (GABA) as an extrinsic regulator of NSC activation, I show that activation of GABA type A receptors (GABAARs) on adult NSCs induces cell swelling and cell cycle entry by recruiting the epidermal growth factor receptor (EGFR). Although apical and basal NSCs underwent swelling upon GABAAR activation, increased EGFR phosphorylation and cell cycle entry was only observed in in the latter, which also displayed higher Egfr transcripts than apical NSCs. Underscoring the importance of EGFR signalling in proliferation, pharmacological blockade of EGFR prevented NSC proliferation. In addition, I show that activation of GABAARs also promotes a decrease in the expression of the cell adhesion receptor β1Integrin, both in basal and apical NSCs and loss of the epithelial marker Prominin1 in apical NSCs. As an intrinsic regulator of NSC activation, I have studied the role of the orphan nuclear receptor TLX and its interaction with NOTCH signalling. This analysis revealed that lack of Tlx leads to the overexpression of Hes1 and increases NOTCH activation in apical NSCs, suggesting that this may contribute to impaired neurogenesis. Indeed, downregulation of Hes1 in the apical SVZ restored neurogenesis and increased proliferation. Interestingly, this effect was mostly noted in basal NSCs, highlighting a non-cell autonomous regulatory mechanism mediated by NOTCH signalling. Thus, altogether my results show that GABA and TLX-HES1 interaction both play an important role in the regulation of adult NSC quiescence, being both essentials for proper NSC activation and apical-basal lineage progression.