The lack of Emx2 causes impairment of Reelin signaling and defects of neuronal migration in the developing cerebral cortex

Neocorticogenesis in mice homozygous for an Emx2 null allele is the topic o f this article. The development of both main components of neocortex, primo rdial plexiform layer derivatives and cortical plate, was analyzed, paying special attention to radial migration of neurons forming the cortical plate . The products of the Reelin gene, normally playing a key role in orchestra ting radial migration of these neurons, display normal distribution at the beginning of the cortical neuronogenesis but are absent in the neocortical marginal zone of the mutant mice at the time when the cortical plate is lai d down. As a consequence, the development of radial glia is impaired, and n eurons making up the cortical plate display abnormal migration patterns. In addition, restricted defects along the rostrocaudal and the mediolateral a xes are present in the subplate, suggesting an Emx2-specific role in primin g the proper development of this layer.