Tangentially Migrating Neurons Assemble a Primary Cilium that Promotes Their Reorientation to the Cortical Plate

In migrating neurons, the centrosome nucleates and anchors a polarized network of microtubules that directs organelle movements. We report here that the mother centriole of neurons migrating tangentially from the medial ganglionic eminence (MGE) assembles a short primary cilium and exposes this cilium to the cell surface by docking to the plasma membrane in the leading process. Primary cilia are built by intraflagellar transport (IFT), which is also required for Sonic hedgehog (Shh) signal transduction in vertebrates. We show that Shh pathway perturbations influenced the leading process morphology and dynamics of MGE cells. Whereas Shh favored the exit of MGE cells away from their tangential migratory paths in the developing cortex, cyclopamine or invalidation of IFT genes maintained MGE cells in the tangential paths. Our findings show that signals transmitted through the primary cilium promote the escape of future GABAergic interneurons from their tangential routes to colonize the cortical plate.