Integrin α5β1 is necessary for regulation of radial migration of cortical neurons during mouse brain development

During cerebral cortex development, post-mitotic neurons interact with radial glial fibers and the extracellular environment to migrate away from the ventricular region and form a correct laminar structure. Integrin receptors are major mediators of cell-cell and cell-extracellular matrix interactions. Several integrin heterodimers are present during formation of the cortical layers. The alpha 5 beta 1 receptor is expressed in the neural progenitors of the ventricular zone during cerebral cortex formation. Using in utero electroporation to introduce short hairpin RNAs in the brain at embryonic day 15.5, we were able to inhibit acutely the expression of alpha 5 integrin in the developing cortex. The knockdown of alpha 5 integrin expression level in neural precursors resulted in an inhibition of radial migration, without perturbing the glial scaffold. Moreover, the same inhibitory effect on neuronal migration was observed after electroporation of a Cre recombinase expression plasmid into the neural progenitors of conditional knockout mice for alpha 5 integrin. In both types of experiments, the electroporated cells expressing reduced levels of alpha 5 integrin accumulated in the premigratory region with an abnormal morphology. At postnatal day 2, ectopic neurons were observed in cortical layer V, while a deficit of neurons was observed in cortical layer II-IV. We show that these neurons do not express a layer V-specific marker, suggesting that they have not undergone premature differentiation. Overall, these results indicate that alpha 5 beta 1 integrin functions in the regulation of neural morphology and migration during cortical development, playing a role in cortical lamination.