title: Fission yeast IQGAP maintains F-actin-independent localization of myosin-II in the contractile ring.
abstract: During cytokinesis in many eukaryotic cells, myosin-II concentrates at the equatorial cortex with actin filaments (F-actin) and is supposed to generate forces to divide the cell into two, which is called the contractile ring (CR) hypothesis. Several lines of evidence indicate that the myosin-II is recruited independently of F-actin and interacts specifically with the equatorial F-actin. Molecular details of these mechanisms are still unknown. We used the fission yeast Schizosaccharomyces pombe to investigate the regulation of myosin-II localization. We demonstrate that the CR myosin-II was composed of F-actin-dependent and -independent fractions by simultaneously observing F-actin and myosin. The F-actin-independent fraction was visualized as cortical dots in the absence of F-actin. IQGAP Rng2, an indispensable element of CR, was implicated in maintenance of the F-actin-independent fraction of myosin-II, whereas anillin Mid1 was required for assembly but not for maintenance of the fraction. In the CR of the rng2 mutant, myosin-II was less concentrated, unstable, and nonhomogeneous, which often resulted in cytokinesis failure. These results suggest that Rng2 tethers myosin-II to the cortex along the CR independently of F-actin to provide a sufficient concentration. The robust localization of myosin-II would ensure successful cytokinesis.
authors: Department of Biological Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki, 305-8577, Japan.
authors: Masak
authors: M
authors: Takaine
authors: Osamu
authors: O
authors: Numata
authors: Kentaro
authors: K
authors: Nakano
mesh_terms: D000199:Actins / Q000378:metabolism*; D003285:Contractile Proteins / Q000378:metabolism; D024462:Myosin Type II / Q000378:metabolism*; D012568:Schizosaccharomyces / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism
chemical_list: D000199:Actins; D003285:Contractile Proteins; C489694:Mid1 protein, S pombe; D029702:Schizosaccharomyces pombe Proteins; D024462:Myosin Type II