A microtubule polymerase cooperates with the kinesin-6 motor and a microtubule cross-linker to promote bipolar spindle assembly in the absence of kinesin-5 and kinesin-14 in fission yeast

Mol Biol Cell. 2017 Dec 1;28(25):3647-3659. doi: 10.1091/mbc.E17-08-0497. Epub 2017 Oct 11.


Accurate chromosome segregation relies on the bipolar mitotic spindle. In many eukaryotes, spindle formation is driven by the plus-end-directed motor kinesin-5 that generates outward force to establish spindle bipolarity. Its inhibition leads to the emergence of monopolar spindles with mitotic arrest. Intriguingly, simultaneous inactivation of the minus-end-directed motor kinesin-14 restores spindle bipolarity in many systems. Here we show that in fission yeast, three independent pathways contribute to spindle bipolarity in the absence of kinesin-5/Cut7 and kinesin-14/Pkl1. One is kinesin-6/Klp9 that engages with spindle elongation once short bipolar spindles assemble. Klp9 also ensures the medial positioning of anaphase spindles to prevent unequal chromosome segregation. Another is the Alp7/TACC-Alp14/TOG microtubule polymerase complex. Temperature-sensitive alp7cut7pkl1 mutants are arrested with either monopolar or very short spindles. Forced targeting of Alp14 to the spindle pole body is sufficient to render alp7cut7pkl1 triply deleted cells viable and promote spindle assembly, indicating that Alp14-mediated microtubule polymerization from the nuclear face of the spindle pole body could generate outward force in place of Cut7 during early mitosis. The third pathway involves the Ase1/PRC1 microtubule cross-linker that stabilizes antiparallel microtubules. Our study, therefore, unveils multifaceted interplay among kinesin-dependent and -independent pathways leading to mitotic bipolar spindle assembly.

MeSH terms

  • Anaphase
  • Cathepsin A / metabolism
  • Chromosome Segregation / physiology*
  • Kinesins / metabolism
  • Kinesins / physiology*
  • Microtubule-Associated Proteins / metabolism
  • Microtubules / metabolism
  • Microtubules / physiology
  • Mitosis
  • Protein Binding
  • Schizosaccharomyces / metabolism
  • Schizosaccharomyces pombe Proteins / metabolism
  • Spindle Apparatus / metabolism
  • Spindle Apparatus / physiology*
  • Spindle Pole Bodies / metabolism


  • Alp7 protein, S pombe
  • Ase1 protein, S pombe
  • Cut7 protein, S pombe
  • Microtubule-Associated Proteins
  • PKL1 protein, S pombe
  • Schizosaccharomyces pombe Proteins
  • alp14 protein, S pombe
  • Cathepsin A
  • Kinesins