Underlying the intricate complexity of the vertebrate brain is a complicated set of developmental programs regulating proliferation and differentiation of the different regions and neuronal types. In the mammalian neocortex, two major types of progenitor cells have been characterised: apical progenitors (APs) that divide at the apical surface of the ventricular zone and basal progenitors (BPs) that divide in the subventricular zone. BPs can be further subdivided into different types, including intermediate progenitors expressing the Tbr2 marker and cells with stem cell-like properties: basal radial glial cells (bRGs). To date, bRGs have only been characterised in mammals, but the evolutionary origin of different BP populations is uncertain. Now, Tadashi Nomura and co-workers (p. 66) characterise a bRG-like population in the chicken pallium (a region of which is homologous to the mammalian neocortex). These cells share many properties with mammalian bRGs, including their morphology, position, orientation of mitoses and response to various genetic manipulations. The authors further show that this lineage is distinct from Tbr2+ progenitors, which in the chick – unlike in the mouse – appear to be non-proliferative. Furthermore, surveying a range of amniotes and amphibians suggests that BPs are quite widely distributed in vertebrates, suggesting they may be a more ancient evolutionary innovation than previously thought.
- © 2016. Published by The Company of Biologists Ltd