The Kinesin-13 Proteins Kif2a, Kif2b, and Kif2c/MCAK Have Distinct Roles during Mitosis in Human Cells

Abstract

The human genome has three unique genes coding for kinesin-13 proteins called Kif2a, Kif2b, and MCAK (Kif2c). Kif2a and MCAK have documented roles in mitosis, but the function of Kif2b has not been defined. Here, we show that Kif2b is expressed at very low levels in cultured cells and that GFP-Kif2b localizes predominately to centrosomes and midbodies, but also to spindle microtubules and transiently to kinetochores. Kif2b-deficient cells assemble monopolar or disorganized spindles. Chromosomes in Kif2b-deficient cells show typical kinetochore-microtubule attachments, but the velocity of movement is reduced approximately 80% compared with control cells. Some Kif2b-deficient cells attempt anaphase, but the cleavage furrow regresses and cytokinesis fails. Like Kif2a-deficient cells, bipolar spindle assembly can be restored to Kif2b-deficient cells by simultaneous deficiency of MCAK or Nuf2 or treatment with low doses of nocodazole. However, Kif2b-deficient cells are unique in that they assemble bipolar spindles when the pole focusing activities of NuMA and HSET are perturbed. These data demonstrate that Kif2b function is required for spindle assembly and chromosome movement and that the microtubule depolymerase activities of Kif2a, Kif2b, and MCAK fulfill distinct functions during mitosis in human cells.

Bipolar, anastral spindle development in artificially activated sea urchin eggs

“…Finally, the Kif2a staining of the poles of control spindles and mini-spindles (Fig. 9) is consistent with its localization in other cells and with its essential function as a MT depolymerase involved with bipolar spindle assembly and chromosome movement (Ganem and Compton, 2004;Manning et al, 2007).…”

“…These kinesins do not appear to be motors but instead act as MT depolymerizers that impact spindle MT dynamics. Kif2a and 2b have been shown to be essential for bipolar spindle assembly and chromosome movement in mammalian cells and localize to the spindle pole and kinetochores (Ganem and Compton, 2004;Manning et al, 2007). In the control fertilized embryos, Kif2a labels the spindle with a concentration at the poles (Fig.…”

The perpetual movements of anaphase

“…Amongst the kinesin-13 proteins in human cells, only Kif2b and MCAK (Kif2c) localize to centromeres/kinetochores [69,168,169], but MCAK is not required for anaphase A [61].…”

“…Interestingly, chromosome velocities in monopolar spindles that form after Kif2b RNAi are severely reduced [168]. Spindle bipolarity after Kif2b RNAi can be restored by simultaneous knockdown of MCAK, with chromosomes moving towards the poles in anaphase at ~0.6 μm/min, which represents a two-third reduction in their normal…”

“…Kif2b is no longer detectable at kinetochores during anaphase, possibly due to its low abundance [168]. Finally, it has been reported that Katanin, a AAA ATPase that severs microtubules, is also important for the pac-man activity at kinetochores in Drosophila S2 cells [170].…”