Laminins have dramatic and varied actions on neurons in vitro. However, their in vivo function in brain development is not clear. Here we show that knockout of laminin ¿1 in the cerebral cortex leads to defects in neuritogenesis and neuronal migration. In the mutant mice, cortical layer structures were disrupted, and axonal pathfinding was impaired. During development, loss of laminin expression impaired phosphorylation of FAK and paxillin, indicating defects in integrin signaling pathways. Moreover, both phosphorylation and protein levels of GSK-3ß were significantly decreased, but only phosphorylation of AKT was affected in the mutant cortex. Knockout of laminin ¿1 expression in vitro, dramatically inhibited neurite growth. These results indicate that laminin regulates neurite growth and neuronal migration via integrin signaling through the AKT/GSK-3ß pathway, and thus reveal a novel mechanism of laminin function in brain development.

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