Laminin/β1 integrin signal triggers axon formation by promoting microtubule assembly and stabilization

In this study, the authors present several lines of evidence implicating the indispensable role of laminin in promoting neural polarization through integrin b1 (Itgb1) mediated microtubule assembly and stabilization. Laminin coated substrates (either in stripes or gradient) could initiate directional axon growth in undifferentiated neurites of both cultured hippocampal neurons and cortical slices in an Itgb1 dependent manner. Impairing endogenous laminin function either by treatment with exogenous laminins or by abolishing Itgb1 signaling using siRNA, resulted in defective axonal formation. Conditional knock out mice with abrogated Itgb1 expression in dorsal telencephalic progenitors displayed defective expression/activity of neuronal polarity related proteins, SAD and LKB1 kinases in addition to abnormal axonal development of cortical pyramidal neurons. These results not only identify laminin/ integrin b1 signaling as a crucial step in axon initiation and development but also link extracellular matrix adhesion to cytoskeleton remodeling that occurs during neuronal polarization.