Expression of the mitotic kinesin Kif15 in postmitotic neurons: implications for neuronal migration and development.

Kif15 is a kinesin-related protein whose mitotic homologues are believed to crosslink and immobilize spindle microtubules. We have obtained rodent sequences of Kif15, and have studied their expression and distribution in the developing nervous system. Kif15 is indeed expressed in actively dividing fibroblasts, but is also expressed in terminally postmitotic neurons. In mitotic cells, Kif15 localizes to spindle poles and microtubules during prometaphase to early anaphase, but then to the actin-based cleavage furrow during cytokinesis. In interphase fibroblasts, Kif15 localizes to actin bundles but not to microtubules. In cultured neurons, Kif15 localizes to microtubules but shows no apparent co-localization with actin. Localization of Kif15 to microtubules is particularly good when the microtubules are bundled, and there is a notable enrichment of Kif15 in the microtubule bundles that occupy stalled growth cones and dendrites. Studies on developing rodent brain show a pronounced enrichment of Kif15 in migratory neurons compared to other neurons. Notably, migratory neurons have a cage-like configuration of microtubules around their nucleus that is linked to the microtubule array within the leading process, such that the entire array moves in unison as the cell migrates. Since the capacity of microtubules to move independently of one another is restricted in all of these cases, we propose that Kif15 opposes the capacity of other motors to generate independent microtubule movements within key regions of developing neurons.