Microtubule nucleation promoters Mto1 and Mto2 regulate cytokinesis in fission yeast.
Microtubules of the mitotic spindle direct cytokinesis in metazoans but this has not been documented in fungi. We report evidence that microtubule nucleators at the spindle pole body help coordinate cytokinetic furrow formation in fission yeast. The temperature-sensitive  cps1-191  strain (Liu  et al. , 1999) with a D277N substitution in β-glucan synthase 1 (Cps1/Bgs1) was reported to arrest with an unconstricted contractile ring. We discovered that contractile rings in  cps1-191  cells constrict slowly and that an  mto2 S338N   mutation is required with the  bgs1 D277N  mutation to reproduce the  cps1-191  phenotype. Complexes of Mto2 and Mto1 with γ-tubulin regulate microtubule assembly. Deletion of Mto1 along with the  bgs1 D277N   mutation also gives the  cps1-191  phenotype, which is not observed in  mto2 S338N   or  mto1Δ  cells expressing  bgs1  + . Both  mto2 S338N   and  mto1Δ  cells nucleate fewer astral microtubules than normal and have higher levels of Rho1-GTP at the division site than wild-type cells. We report multiple conditions that sensitize  mto1Δ  and  mto2 S338N   cells to furrow ingression phenotypes.
Dundon SER, Pollard TD