Shootin1 Acts in Concert with KIF20B to Promote Polarization of Migrating Neurons

Shootin1 has been ascribed a role in regulating polarization of primary hippocampal neurons. To better understand the possible role of Shootin1 in the developing brain, we identified a member of the kinesin superfamily, KIF20B, as a novel Shootin1 interacting protein and a potential mediator of Shootin1 interaction with microtubules. KIF20B/Shootin1 binding was mapped to a 57 aa KIF20B sequence, which was used as a dominant-negative fragment. Direct interaction between that peptide (MBD) and Shootin1 was confirmed by surface plasmon resonance-based technology and the affinity was determined in the 10(-7) M range. The proteins are expressed in the developing brain and formed a complex in vivo based on coimmunoprecipitation experiments and coimmunostaining in primary neurons. In primary hippocampal neurons Kif20b knockdown reduced Shootin1 mobilization to the developing axon, as evidenced by immunostaining and fluorescence recovery after photobleaching analysis, suggesting that Shootin1 is a novel KIF20B cargo. shRNA targeting of Shootin1 reduced PIP3 accumulation in the growth cone, as did Kif20b shRNA. In the developing mouse brain, Kif20b knockdown or expression of the KIF20B minimal binding domain inhibited neuronal migration, and in vivo migration assays suggested that Shootin1/Kif20b acts in the same genetic pathway. Time-lapse imaging of multipolar cells in the subventricular zone revealed that downregulating levels of either Shootin1 or Kif20b hindered the transition from multipolar to bipolar cells. Collectively, our data demonstrate the importance of the Shootin1/KIF20B interaction to the dynamic process of pyramidal neuronal polarization and migration.