Loss of Kinesin Kif20b Alters Axon Stability on Different Substrates, and can be rescued by Treatment with SirTubulin

Kinesin-6 family member, Kif20b, is a microtubule motor with a known role in microtubule bundling and neuron morphogenesis. We have previously reported that the loss of Kif20b causes microcephaly. When neurons from brains of mutant embryos are grown in vitro on poly-L-lysine (PLL) they have decreased neuron polarization. Interestingly, neurons that are able to polarize have wider, shorter axons that retract more often. We hypothesize that these phenotypes are due to less densely packed and more dynamic microtubules along with localization changes of Shootin1, which has been implicated in polarization and axon outgrowth. Shootin1 connects the actin cytoskeleton to the cell adhesion molecule L1 and has been shown to interact with Kif20b in the brain. Therefore, we predicted that when grown on the L1 substrate, Kif20b-/- neurons would have altered Shootin1 localization and would maintain the shorter axon phenotype. We tested the first part of this hypothesis by measuring the intensity of Shootin1 in the axons of neurons grown on both PLL and L1. Surprisingly, Kif20b-/- neurons plated on L1 grew significantly longer axons than controls. We tested this overgrowth phenotype by growing Kif20b-/- neurons on a different substrate that is known to increase axon outgrowth, Laminin, which is an important protein for cell attachment and differentiation as well as cell shape. On laminin, Kif20-/- neurons were not significantly longer than controls. Therefore, the increased axon length phenotype is unique to Kif20b-/- neurons on L1.