Spatial regionalization and heterochrony in the formation of adult pallial neural stem cells.

Little is known on the embryonic origin and related heterogeneity of adult neural stem cells (aNSCs). We use conditional genetic tracing, activated in a global or mosaic fashion by cell type-specific promoters or focal laser uncaging, coupled with gene expression analyses and Notch invalidations, to address this issue in the zebrafish adult telencephalon. We report that the germinal zone of the adult pallium originates from two distinct subtypes of embryonic progenitors and integrates two modes of aNSC formation. Dorsomedial aNSCs derive from the amplification of actively neurogenic radial glia of the embryonic telencephalon. On the contrary, the lateral aNSC population is formed by stepwise addition at the pallial edge from a discrete neuroepithelial progenitor pool of the posterior telencephalic roof, activated at postembryonic stages and persisting lifelong. This dual origin of the pallial germinal zone allows the temporally organized building of pallial territories as a patchwork of juxtaposed compartments.