Neuroblasts across the brain fell into two general categories represented by two subtrees in the dendrogram (labeled “NBL” in Figure 1D). The first category expressed Igfbpl1 and was either GABAergic (OBNBL3) or did not express any clear neurotransmitter phenotype. These neuroblasts were found in the rostral migratory stream (SZNBL and OBNBL3), dentate gyrus (DGNBL2), and habenula (DETPH). The second category expressed the T-box transcription factor Eomes (also known as Tbr2) and the vesicular glutamate transporter (Slc17a7, also known as VGLUT1) and thus was glutamatergic. These neuroblasts were found in the olfactory bulb (OBNBL1, OBNBL2), cerebellum (CBNBL), and septum (SEPNBL). However, Eomes and Igfbpl1 overlapped in some populations (DGNBL1 and to some extent SZNBL), indicating that these categories of neuroblasts may represent sequential stages of neuronal maturation rather than divergent cell types. Eomes-expressing neuroblasts, with a generally less mature neurotransmitter phenotype, may then represent early stages of neuronal differentiation, whereas Igfbpl1 spans both early and later stages, as was already shown in the dentate gyrus (Hochgerner et al., 2018).
