β1 integrins in radial glia but not in migrating neurons are essential for the formation of cell layers in the cerebral cortex

Radial glial cells in the cerebral cortex serve as progenitors for neurons and glia and guide the migration of cortical neurons. The integrin alpha 3 beta 1 is thought to mediate interactions of migrating neurons with radial glial cells and to function as a receptor for the reelin signaling molecule. Here, we challenge this view and demonstrate that beta 1 integrins in migrating neurons are not essential for the formation of cell layers in the cerebral cortex. Cortical cell layers also form normally in mice deficient in the integrin alpha 3 beta 1. However, we provide evidence that beta 1 integrins in radial glia control the morphological differentiation of both glia and neurons. We conclude that beta 1 integrins in radial glia are required for the proper development of the cerebral cortex, whereas beta 1 integrins in migrating neurons are not essential for glial-guided migration and reelin signaling.