Project

Adult neurogenesis is the process by which adult neural stem cells (NSCs) produce new neuronal and glial cells throughout an animal life. Studies in vertebrates have unveiled the crucial importance of this phenomenon for neural tissue homeostasis and proper brain function. Fundamentally, this process is a balance between maintaining a quiescent NSC pool and recruiting them into the neurogenesis cascade. Using the adult zebrafish anterior brain (telencephalon) as a model, we aim at deciphering the molecular mechanisms governing this balance. We identified a microRNA, miR-9, as a prominent quiescence enforcer. Unexpectedly, miR-9 concentrates into the nucleus of quiescent adult NSCs, together with Argonaute proteins (notably Ago2), effector proteins of microRNAs. This nuclear enrichment of Ago/miR-9 is not observed in embryonic or juvenile fish, being thus a signature of deep adult NSC quiescence. It is also observed in mouse NSCs. We wish to use nuclear miR-9/Ago2 as molecular entry points into the molecular mechanisms controlling this adult-specific deep NSC quiescence state. Within this frame, the present project aims to identify Ago2-bound nuclear targets. Through fractionation experiments, we could detect Ago proteins both in the nuclear soluble and in the chromatin-associated fractions of adult zebrafish NSCs. Thus, we built genetic tools to recover the nuclear Ago2-bound transcripts and genomic loci, ie. using CLIP-seq and DamID approaches, respectively. The enriched transcript sequences will be screened for potential miRNA-binding motifs. Putative genomic targets will be screened, in addition, for specific motifs and for their coincidence with defined functional regions (eg. coding or regulatory). The data will be cross-matched with the transcriptome and proteome of miR-9-positive versus –negative adult NSCs. Together, these data should help elaborate hypotheses on the molecular mode(s) of action of nuclear miR-9/AgAgo2 when controlling adult NSC quiescence.