Ephrin signalling controls brain size by regulating apoptosis of neural progenitors

The mechanisms controlling brain size are central to developmental genetics, neurobiology and mammalian evolution. A new study shows that a class of signalling factors present in the developing brain, the ephrins, induces the death of the progenitor or stem cells that generate all neurons, and thereby control the final size of the cerebral cortex. When this ‘death signal’ is increased, brain size decreases, resulting in microcephaly. When it decreases, cortical size increases, leading to exencephalic brain overgrowth. This has implications for brain diseases, regeneration, and cancer.