Microtubule Nucleation Promoters Mto1 and Mto2 Regulate Cytokinesis in Fission Yeast

Abstract

AbstractMicrotubules 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-sensitivecps1-191strain (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 incps1-191cells do constrict slowly and that an S338N mutation in themto2gene is required with thebgs1D277Nmutation to reproduce thecps1-191phenotype. Complexes of Mto2 and Mto1 with γ-tubulin regulate microtubule assembly. Deletion of Mto1 along with thebgs1D277Nmutation also gives thecps1-191phenotype, which is not observed inmto2S338Normto1Δcells expressingbgs1+. Bothmto2S338Nandmto1Δcells 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 sensitizemto1Δandmto2S338Ncells to furrow ingression phenotypes.SummaryDundon and Pollard show that compromising the Mto1 or Mto2 regulators of the fission yeast γ-tubulin complex reduces or eliminates astral microtubules, exaggerates the effects of a D277N substitution in β-glucan synthase 1 (Cps1/Bgs1) on the rate of cytokinetic furrow formation, and increases Rho1-GTP at the cleavage site.