Fig. 10

Summary of phenotypes of Kif20b mutant neurons seen in culture. A Normal cortical neurons transition from multipolar (Stage 2) to polarized with a single axon (Stage 3) properly when Kif20b is present. Kif20b may organize or stabilize microtubule arrays in the axon and growth cone, keeping the axon thin and limiting its branching, and preventing microtubule invasion of filopodia. Kif20b may also tether Shootin1 at the microtubule plus ends in the axonal growth cone, which reinforces axonal growth. Kif20b may thereby enhance stability and inhibit axon retraction. B When Kif20b is absent, some neurons fail to transition from stage 2 to stage 3. Those that do polarize show a variety of phenotypes: longer minor neurites, shorter axons with extra branches, wider axons and minor neurites, and longer filopodia. Microtubules appear more loosely organized and extend into more filopodia. Shootin1 enrichment in the growth cone is severely reduced