[Kinesin-14 leaps to pole position in bipolar spindle assembly]

Abstract

Formation of a mitotic spindle occurs almost effortlessly as cells cycle and is essential for chromosome segregation. Early in a cell cycle, the replication of centrosomes or spindle pole bodies at G1/S leaves mother and daughter poles in close association until forced apart into a bipolar arrangement at mitotic onset. Kinesin-like proteins (Klps) generate a variety of forces that contribute to the timing, formation and maintenance of spindle bipolarity. The ability of two key players, Kinesin-5 and Kinesin-14, to cross-link both parallel and anti-parallel microtubules has led to emphasis on spindle microtubule interactions in the spindle assembly mechanism. Recent identification of a Kinesin-14 binding site on gamma-tubulin, a ubiquitous component of microtubule organizing centers (MTOCs) at poles combined with the ability of changes to MTOC complexes to regulate bipolarity, now shifts an inquisitive eye to pole mechanisms and to the complexities evolving around MTOCs.