Notch signaling blockade links transcriptome heterogeneity in quiescent neural stem cells with reactivation routes...

In the vertebrate brain, neural stem cell (NSC) quiescence is necessary for stemness maintenance. Using single-cell RNA sequencing (scRNAseq) in the zebrafish adult telencephalon, we identified different molecular clusters of quiescent NSCs, interpreted to sign different quiescence depths. Here, we show that these clusters, when challenged in vivo with an inhibitor of Notch signaling, a major quiescence promoting pathway, unfold different behaviors. Notably, deeply quiescent NSCs with astrocytic features display a unique activation phenotype that combines the maintenance of astrocytic markers with the rapid up-regulation of activation and neuronal commitment genes, reminiscent to murine periventricular astrocytes activating upon lesion. In contrast, an NSC cluster predicted to be in the deepest quiescence state resists Notch blockade, and we demonstrate that the transcription factor Nr2f1b mediates this resistance to activation in vivo. These results together link the molecular heterogeneity of quiescent NSCs with bona fide biological properties and their molecular regulators.