For the more short-lived intermediate progenitors (Tbr2+), 14.6 ± 1.1% of Tbr2+ cells (Type 2a cells, 100 Tbr2+ cells from 3 animals) were double labeled with pimonidazole.
The distinct types of projection neurons are produced in the dorsolateral telencephalon (pallium) of the embryo from multipotent neural stem cells (NSCs) known as radial glia (RG), and from more restricted progenitors, the intermediate progenitors (IPs).
Based on the distribution of Tbr2 expressing cells in the developing cortex, the observation that Tbr2 expression follows the known developmental gradient (rostral-lateral first to caudo-medial last) is consistent with the possibility that early VZ progenitors are less likely to generate intermediate progenitors and more likely to produce additional radial progenitors.
We found that both proteins displayed more nuclear expression in NSCs and the intermediate progenitors, RGs and N/OPs, while being differentially distributed to the nucleus and cytoplasm of all neuronal subtypes examined (Figures S2, S3, S4).
Genotypes not present in the progenitor or evolved strain, but that occur in one or more intermediate strain, are classified as transient.
Because the human brain requires orders of magnitude more neurons than those of rodents it seems plausible that hNPCs would rely to a greater degree on intermediate progenitors to amplify neuron production in lieu of direct neurogenesis via RG asymmetric division.
Several intermediate progenitors have been identified that have the potential to give rise to different subsets of ILCs.
Moreover, Tbr2 appears to define intermediate progenitors, as conditional deletion of Tbr2 results in loss of intermediate progenitors, while overexpression can convert radial glia into intermediate progenitors [16].
In contrast to radial progenitors, intermediate progenitors are multipolar and lack ventricular contacts [9].
In contrast to radial progenitors, intermediate progenitors appear to divide symmetrically, producing either pairs of neurons or intermediate progenitors [9], [12].
