Hedgehog signaling promotes basal progenitor expansion and the growth and folding of the neocortex.

During evolution, the neocortex has expanded dramatically and folded in certain species, providing superior sensorimotor and cognitive abilities. Expansion of neural progenitors called bRGs and IPCs plays key roles in expansion and folding of the neocortex. Using mouse models, comparative genomics and human cerebral organoids, this study shows that Shh signaling expands bRG and IPC populations, leading to neocortical expansion and folding.