Neurobiology: building a bigger brain.

Abstract

An innovative approach to analysing the functions and gene-expression profiles of neural stem cells in developing human and mouse brains sheds light on the differences — and similarities — between the two species. See Letter p.264 The unique intellectual capabilities of humans are widely attributed to the expansion of the human neocortex in comparison to primates and other mammals. Recent reports implicated the elevated proliferative potential of radial glia, a type of neuronal precursor cell than spans the developing cerebral cortex, as a driver for neocortical expansion. Arnold Kriegstein and colleagues take this concept further by identifying evolutionary changes in radial glia gene expression that may have contributed to human neocortical expansion. They find that humans and mice exhibit highly conserved gene expression patterns amongst radial glia except for a few specific signalling pathways. PDGFD and its receptor, PDGFRβ, show distinct expression patterns and profiles in human cortex development that are absent in mice. Disrupting these paths in human brain slice cultures prevents normal cell cycle progression, whereas ectopic activation of these paths in mice enhances radial glia proliferation and dispersion, revealing one critical mechanism specific to human cortical development.