Astral Microtubules Regulate Formation of the Cytokinetic Cleavage Furrow in Fission Yeast

Abstract

Microtubules of the mitotic spindle direct cytokinesis in metazoans but this has not been documented in fungi. We report evidence that astral microtubules help coordinate cytokinetic furrow formation in fission yeast. The temperature-sensitive cps1-191 strain (Liu et al., 1999) with a D277N substitution in {beta}-glucan synthase 1 (Cps1/Bgs1) was reported to arrest with an unconstricted contractile ring. We discovered that contractile rings in cps1-191 cells do constrict slowly and that an S338N mutation in the mto2 gene is required with the bgs1D277N mutation to reproduce the cps1-191 phenotype. Complexes of Mto2 and Mto1 with {gamma}-tubulin regulate microtubule assembly. Deletion of Mto1 along with the bgs1D277N mutation also gives the cps1-191 phenotype, which is not observed in mto2S338N or mto1{Delta} cells expressing bgs1+. Both mto2S338N and mto1{Delta} 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 mto1{Delta} and mto2S338N cells to furrow ingression phenotypes. SummaryDundon and Pollard show that compromising the Mto1 or Mto2 regulators of the fission yeast {gamma}-tubulin complex reduces or eliminates astral microtubules, exaggerates the effects of a D277N substitution in {beta}-glucan synthase 1 (Cps1/Bgs1) on the rate of cytokinetic furrow formation, and increases Rho1-GTP at the cleavage site.