Two Related Kinesins,klp5⁺andklp6⁺, Foster Microtubule Disassembly and Are Required for Meiosis in Fission Yeast

Abstract

The kinesin superfamily of microtubule motor proteins is important in many cellular processes, including mitosis and meiosis, vesicle transport, and the establishment and maintenance of cell polarity. We have characterized two related kinesins in fission yeast, klp5 ϩ and klp6 ϩ , that are amino-terminal motors of the KIP3 subfamily. Analysis of null mutants demonstrates that neither klp5 ϩ nor klp6 ϩ , individually or together, is essential for vegetative growth, although these mutants have altered microtubule behavior. klp5⌬ and klp6⌬ are resistant to high concentrations of the microtubule poison thiabendazole and have abnormally long cytoplasmic microtubules that can curl around the ends of the cell. This phenotype is greatly enhanced in the cell cycle mutant cdc25-22, leading to a bent, asymmetric cell morphology as cells elongate during cell cycle arrest. Klp5p-GFP and Klp6p-GFP both localize to cytoplasmic microtubules throughout the cell cycle and to spindles in mitosis, but their localizations are not interdependent. During the meiotic phase of the life cycle, both of these kinesins are essential. Spore viability is low in homozygous crosses of either null mutant. Heterozygous crosses of klp5⌬ with klp6⌬ have an intermediate viability, suggesting cooperation between these proteins in meiosis.

Role and regulation of kinesin-8 motors through the cell cycle

“…Fission yeast cells lacking Klp5 or Klp6 display resistance to microtubule depolymerising agents, abnormally long spindle microtubules, defective chromosomes congression, a delay in anaphase onset and higher rates of chromosome mis-segregation (West et al 2001(West et al , 2002Garcia et al 2002). Importantly, cells expressing a motor defective Klp5-Klp6 complex display all of these phenotypes, indicating that motor activity is important for kinesin-8 function.…”

“…Members of the kinesin-8 family, which include the human Kif18A, Kif18B, budding yeast Kip3, fission yeast Klp5 and Klp6 and fruit fly Klp67A proteins, share a similar domain architecture with an N-terminal motor domain, neck linker region, coiled-coil domain that mediates dimerization and a C-terminal tail of variable length (West et al 2001;Unsworth et al 2008;Peters et al 2010;Su et al 2011) ( Table 1; Fig. 1).…”

“…During interphase fission yeast microtubule bundles, which are nucleated from MTOCs (microtubule organising centres) surrounding a centrally located nucleus, grow towards both cell ends to deposit factors that are required for the maintenance of cell polarity and to maintain the nucleus in the centre of the cell (Martin 2009;Chang and Nurse 1996;Tran et al 2000Tran et al , 2001. In the absence of the Klp5 or Klp6 motors some interphase Savoian et al (2004) Spindle length Gandhi et al (2004); Savoian and Glover (2010) Mitochondrial distribution Gandhi et al (2004) Central spindle stability and formation Gatt et al (2005) Spindle elongation Wang et al (2010) Homo sapiens KIF18A Chromosome congression Mayr et al (2007) Chromosome oscillation Stumpff et al (2008) West et al (2001) microtubules fail to pause at the cell end and continue to grow, resulting in long microtubules that bend around the cell cortex. This results in a defect in cell polarity particularly in elongated cells (West et al 2001).…”

“…In the absence of the Klp5 or Klp6 motors some interphase Savoian et al (2004) Spindle length Gandhi et al (2004); Savoian and Glover (2010) Mitochondrial distribution Gandhi et al (2004) Central spindle stability and formation Gatt et al (2005) Spindle elongation Wang et al (2010) Homo sapiens KIF18A Chromosome congression Mayr et al (2007) Chromosome oscillation Stumpff et al (2008) West et al (2001) microtubules fail to pause at the cell end and continue to grow, resulting in long microtubules that bend around the cell cortex. This results in a defect in cell polarity particularly in elongated cells (West et al 2001). Similarly loss of Kip3 in budding yeast interferes with productive interaction of cortical microtubules with the bud cell cortex (Gupta et al 2006), leading to defects in spindle positioning.…”

“…Fission yeast contains two proteins of the kinesin-8 family, Klp5 and Klp6, which form a complex (Garcia et al 2002) that binds to and regulates microtubules at all locations through the cell cycle (West et al 2001). Notably, however, full length heterodimeric Klp5-Klp6 are not processive motors in vitro (Grissom et al 2009;Erent et al 2012).…”