Although most neuronal types were already mature at the age investigated (postnatal days 20–30), we observed signs of ongoing neurogenesis in several regions (Figure 2). As expected, we detected the two regions that maintain adult neurogenesis in the mouse: the subventricular zone along the striatum and the dentate gyrus subgranular zone. In the subventricular zone, radial glia-like cells (RGSZ) and cycling neuronal intermediate progenitor cells (SZNBL) were linked to more mature and presumably migrating neuroblasts along the rostral migratory stream and in the olfactory bulb (OBNBL3). In the subgranular zone of the dentate gyrus, radial glia-like cells (RGDG), neuroblasts (NBDG), and immature granule cells (DGNBL1 and DGNBL2) would give rise to mature granule cells (DGGC), as recently described in detail (Hochgerner et al., 2018). The radial glia-like cells (RGSZ and RGDG), which are the stem cells of both lineages, expressed Riiad1 (shared with ependymal cells; Figure 2D) and were more similar to astrocytes than to any neuroblast. Each local neurogenic niche was further marked by specific genes (Figure S2; e.g., the transcription factors Tfap2c in RGDG and Urah in RGSZ).
