Filling an ARHGAP in our knowledge of human brain evolution

The human cerebral cortex has tripled in size since our divergence from a common ancestor with chimpanzees. This cortical expansion is driven by the increased proliferative capacity of radial glia (RG), a neural progenitor cell (NPC) population that generates cortical neurons. RG along the ventricular zone (VZ) produce neurons and also give rise to basal progenitors (BPs), which migrate to the embryonic subventricular zone (SVZ). Comparative studies suggest that the increased proliferative capacity of human NPCs involves cell-intrinsic mechanisms (Otani et al, 2016), and a number of human-specific genetic changes have recently been linked to NPC proliferation. In particular, overexpression studies in model organisms indicate that the human-specific gene ARHGAP11B is sufficient to increase BP abundance when introduced into the developing brain of non-human model organisms (Florio et al, 2015; Kalebic et al, 2018; Heide et al, 2020). However, studying human-specific mutations in a hominid genetic and developmental context, rather than in more divergent model organisms, could provide further insight into the evolutionary consequences and effect size of human mutations. Fischer et al (2022) now developed a novel organoid electroporation technique to establish the necessity and sufficiency of ARHGAP11B for BP proliferation in cells from humans and our closest living relative, chimpanzees (Fig 1).