How extracellular cues direct axon–dendrite polarization in mouse developing neurons is not fully understood. Here, we report that the radial glial cell (RGC)–cortical neuron interaction directs axon formation at the opposite side of the neuron from the contact site. N-cadherin accumulates at the contact site between the RGC and cortical neuron. Inhibition of the N-cadherin-mediated adhesion decreases this oriented axon formation in vitro, and disrupts the axon–dendrite polarization in vivo. Furthermore, the RGC–neuron interaction induces the polarized distribution of active RhoA at the contacting neurite and active Rac1 at the opposite neurite. Inhibition of Rho–Rho-kinase signaling in a neuron impairs the oriented axon formation in vitro, and prevents axon–dendrite polarization in vivo. Collectively, these results suggest that the N-cadherin-mediated radial glia–neuron interaction determines the contacting neurite as the leading process for radial glia-guided neuronal migration and directs axon formation to the opposite side acting through the Rho family GTPases.
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