Microtubule nucleation promoters Mto1 and Mto2 regulate cytokinesis 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 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 mto2S338N mutation is required with the bgs1D277N mutation to reproduce the cps1-191 phenotype. Complexes of Mto2 and Mto1 with γ-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 mto1Δ cells expressing bgs1+. Both mto2S338N 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 mto2S338N cells to furrow ingression phenotypes. [Media: see text]

Involvement of Smi1 in cell wall integrity and glucan synthase Bgs4 localization during fission yeast cytokinesis

“…Genetic evidence also supported that Smi1 works with glucan synthases for septum synthesis and cell-wall integrity. smi1-1 was synthetic lethal with mutations in β-glucan synthases Bgs1 [bgs1-191 and bgs1-D277N (Liu et al, 1999;Dundon and Pollard, 2020)] and Bgs4 [cwg1-1 and cwg1-2 (Ribas et al, 1991;Muñoz et al, 2013)] at 30°C (Figure 2B and Table 1), and showed moderate genetic interaction with the α-glucan synthase Ags1 mutant mok1-664 (Katayama et al, 1999) (Table 1). In addition, smi1-1 had strong genetic interactions with mutations in the cell integrity pathway [protein kinase Cs pck1 and pck2-1 (Toda et al, 1993;Viana et al, 2013), and arrestin art1 (Davidson et al, 2015)], in glucan synthase regulators rga7 and rng10 (Nakano et al, 2001;Kim et al, 2010;Liu et al, 2016;Liu et al, 2019), and in the septum initiation network [mob1-M17 (Salimova et al, 2000)] (Figure 2B and Table 1).…”

“…Most of our results indicate that Smi1 mainly regulates Bgs4, and the smi1-1 phenotype more closely resembles that of Bgs4 than that of Bgs1 mutants. After culture at restrictive temperature, Bgs1 mutants display very slow or complete failure in actomyosin ring constriction (Liu et al, 1999;Dundon and Pollard, 2020), as well as multiseptation and ring sliding due to less efficient anchoring (Arasada and Pollard, 2014;Cortes et al, 2015). None of these characteristics were observed in the smi1-1 mutant, and ring kinetics was not affected in smi1-1 (Supplemental Figure S3).…”

The Multiple Functions of Rho GTPases in Fission Yeasts

“…Recent work has shown that the amount of active Rho1 at the division site is also influenced by astral microtubules. Rho1-GTP signal peaks during furrow ingression and cell separation, and this accumulation is enhanced in lack of function mutants in the gamma-tubulin complex linkers Mto1 and Mto2 [225]. Despite these initial pieces of evidence, it is still unclear which Rho1 regulators contribute to this hyperactivation, how microtubules are connected to these proteins, and, most importantly, how increased Rho1 accumulation influences furrow ingression.…”

Comparative Analysis of the Roles of Non-muscle Myosin-IIs in Cytokinesis in Budding Yeast, Fission Yeast, and Mammalian Cells

“…The PS in S. pombe consists of linear β-1,3-glucan synthesized by Bgs1/Cps1, hereafter Bgs1 (Cortes et al, 2007). Conditional inactivation of PS synthesis in the temperature-sensitive cps1-191 mutant does not prevent AMR assembly but attenuates its constriction (Liu et al, 1999;Dundon and Pollard, 2020). Thus, PS formation is required for efficient AMR constriction and furrow ingression.…”