Chromosome Congression by Kinesin-5 Motor-Mediated Disassembly of Longer Kinetochore Microtubules

Abstract

Summary During mitosis, sister chromatids congress to the spindle equator and are subsequently segregated via attachment to dynamic kinetochore microtubule (kMT) plus-ends. A major question is how kMT plus-end assembly is spatially regulated to achieve chromosome congression. Here we find in budding yeast that the widely-conserved kinesin-5 sliding motor proteins, Cin8p and Kip1p, mediate chromosome congression by suppressing kMT plus-end assembly of longer kMTs. Of the two, Cin8p is the major effector and its activity requires a functional motor domain. In contrast, the depolymerizing kinesin-8 motor Kip3p plays a minor role in spatial regulation of yeast kMT assembly. Our analysis identified a model where kinesin-5 motors bind to kMTs, move to kMT plus ends, and upon arrival at a growing plus-end promote net kMT plus-end disassembly. In conclusion, we find that length-dependent control of net kMT assembly by kinesin-5 motors yields a simple and stable self-organizing mechanism for chromosome congression.

Kinesin-5–dependent Poleward Flux and Spindle Length Control inDrosophilaEmbryo Mitosis

“…In yeast cells the homotetrameric structure of kinesin-5 appears to be essential for mitosis (Hildebrandt et al, 2006), and in Drosophila embryos KLP61F displays dynamic properties consistent with an association with spindle MTs (Cheerambathur et al, 2008) and forms presumptive MT-MT cross-bridges (Sharp et al, 1999a). These results suggest that ensembles of multiple kinesin-5 motors could serve as dynamic cross-links that organize spindle MTs into bundles and drive a sliding filament mechanism that pushes apart antiparallel spindle MTs (Sharp et al, 1999a;Brust-Mascher et al, 2004), although alternative mechanisms of action for kinesin-5 motors have also been proposed (Kapoor and Mitchison, 2001;Tsai et al, 2006;Johansen and Johansen, 2007;Gardner et al, 2008).…”

“…In yeast cells the homotetrameric structure of kinesin-5 appears to be essential for mitosis (Hildebrandt et al, 2006), and in Drosophila embryos KLP61F displays dynamic properties consistent with an association with spindle MTs (Cheerambathur et al, 2008) and forms presumptive MT-MT cross-bridges (Sharp et al, 1999a). These results suggest that ensembles of multiple kinesin-5 motors could serve as dynamic cross-links that organize spindle MTs into bundles and drive a sliding filament mechanism that pushes apart antiparallel spindle MTs (Sharp et al, 1999a;Brust-Mascher et al, 2004), although alternative mechanisms of action for kinesin-5 motors have also been proposed (Kapoor and Mitchison, 2001;Tsai et al, 2006;Johansen and Johansen, 2007;Gardner et al, 2008).The most obvious and frequently observed consequence of loss of activity of kinesin-5 motors, induced by loss-offunction mutation, antibody inhibition, small molecule inhibition, or RNA interference, is the formation of abnormal monoastral spindles (Enos and Morris, 1990;Saunders and Hoyt, 1992;Sawin et al, 1992;Heck et al, 1993;Saunders et al, 1997;Cottingham et al, 1999;Mayer et al, 1999;Sharp et al, 1999b;Sharp et al, 2000a;Goshima and Vale, 2003). This suggests that kinesin-5 may normally contribute to spindle bipolarity by sliding apart interpolar (ip) MTs to drive spindle pole separation during mitotic spindle assembly, elongation and function.…”

“…In some respects, therefore, the manner in which kinesin-5 is deployed in Drosophila embryos resembles yeast more closely than S2 cells, again possibly reflecting the relative dominance of centrosomes and spindle pole bodies. In other respects the two systems may differ significantly; for instance, although kinesin-5 contributes to congression in Drosophila embryos and yeast, the proposed underlying mechanisms are very different ( Figure 6 and Gardner et al, 2008).…”

“…We do not want to extrapolate our sliding filament model for kinesin-5 function in Drosophila syncytial embryos (Figure 6) to other systems where the molecular mechanism of action of kinesin-5 may be different (e.g., Kapoor and Mitchison, 2001;Gardner et al, 2008). The slow, plus-end-directed motility of kinesin-5 was first observed using recombinant motor domain subfragments of Eg5 (Sawin et al, 1992), and subsequently, in elegant, pioneering work, full-length recombinant Eg5 was shown to cross-link and slide adjacent MTs (Kapitein et al, 2005).…”

“…In Caenorhabditis elegans, kinesin-5 was also found to exert a braking effect on the spindle midzone that governs the rate of spindle elongation mediated by cortical motors (Saunders et al, 2007). It is unclear if these findings are relevant to all spindles and if they all reflect the antiparallel MT sliding activity of kinesin-5, or if kinesin-5 functions differently in different systems as implied by the proposal that kinesin-5 functions as a MT depolymerase rather than a sliding motor to control chromosome congression in Saccharomyces cerevisiae (Gardner et al, 2008). To distinguish these possibilities, therefore, systematic studies of kinesin-5 function throughout mitosis are needed, but this is difficult because the most frequently observed effect of perturbing kinesin-5 function, spindle collapse, obscures later effects in mitosis.…”