Molecular mechanisms of glial-guided neuronal migration.

The migration of young neurons from their site of origin in proliferative zones out into neuronal layers is a hallmark of cortical development. Neuroanatomic studies show that astroglial fibers provide the primary substrate for neuronal migration. In vitro studies on living cells provide evidence that migrating neurons express distinguishing cytologic features including the formation of a specialized junction at the site of neuron-glia contact and the extension of an active leading process in the direction of migration. Our in vitro functional assays point to a critical role for astrotactin in neuron-glia binding during the developmental periods of glial-guided cell migration and assembly in brain. Other receptor systems, including neural cell adhesion systems, cadherins, and integrins are expressed by granule cells but do not appear to contribute to neuron-glia binding or to glial-guided neuronal migration. A role for astrotactin in glial-guided migration and assembly is supported by our observation that astrotactin is expressed by neurons and not glial cells and by restricted spatiotemporal expression of astrotactin in vivo, wherein astrotactin is expressed by migrating neurons and by neurons during periods of assembly into neuronal layers in developing brain. Understanding the regulation of astrotactin expression and its role in migration will provide fundamental insights into the role of glial-guided migration in the histogenesis of the brain.