We review studies on the polarity of developing cerebellar granule, showing that the centrosome localizes to the pole of the neuron that extrudes the nascent axon, and the Rho GTPase Cdc42 (cell division cycle 42) activates the mPar6alpha/Par3 (Par for partitioning defective) complex to coordinate actin dynamics in the growth cone. Subsequently, mPar6alpha signaling controls the migration of immature granule neurons down the Bergmann glial fibers into the internal granule cell layer in which they establish synaptic connections.