Phosphorylation of the Myosin-II Light Chain Does Not Regulate the Timing of Cytokinesis in Fission Yeast (original) (raw)
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Role of Myosin Light Chain Phosphorylation in the Regulation of Cytokinesis
Cell Structure and Function, 2001
Phosphorylation of regulatory light chain (RMLC) of myosin II at Ser19/Thr18 is likely to play important roles in controlling the morphological changes seen during cell division of cultured mammalian cells. Phosphorylation of RMLC regulates the activity of myosin II, an essntial motor for cytokinesis, and phosphorylation of RMLC shows dramatic changes during mitosis. Two exzymes, myosin phosphatase and kinase, control phosphorylation of RMLC. Myosin phosphatase is activated during mitosis, apparently as a result of mitosis-specific phosphorylation of the myosin phosphatase targeting subunit (MYPT). This activation of myosin phosphatase is likely to result in RMLC dephosphorylation, causing the disassemly of stress fibers and focal adhesions during prophase. The phosphorylation of MYPT is lost in cyotokinesis, which would decrease myosin phosphatase activity. At the same time, ROCK (Rho-kinase) probably phosphorylates MYPT at its inhibitory sites, further decreasing the activity of myosin phosphatase. These changes in MYPT phosphorylation would raise RMLC phosphorylation, leading to the activation of myosin II for cyotokinesis. RMLC phosphorylation is also regulated by several RMLC kinases including ROCK (Rho-kinase), MLCK and citron kinase, all of which are localized at cleavage furrows. Future studies should examine whether these multiple kinases are redundant or whether they control distinct aspects of cell division.
Conservation of mitotic controls in fission and budding yeasts
Cell, 1989
In fission yeast, the initiation of mitosis is regulated by a control network that integrates the opposing activities of mitotic inducers and inhibitors. To evaluate whether this control system is likely to be conserved among eukaryotes, we have investigated whether a similar mitotic control operates in the distantly related budding yeast S. cerevisiae. We have found that the protein kinase encoded by the mitotic inhibitor gene weeI+ of fission yeast, which acts to delay mitosis, is able also to delay the initiation of mitosis when expressed in S. cerevisiae. The wee7+ activity is counteracted in S. cerevisiae by the gene product of M/HI, a newly identified gene capable of encoding a protein of MW 54,000, which is a structural and functional homolog of the cdc25+ mitotic inducer of fission yeast. Expression of weel+ in a mihf-strain prevents the initiation of mitosis. These data indicate that important features of the cdc25+-weel+ mitotic control network identified in S. pombe are conserved in S. cerevisiae, and therefore are also likely to be generally conserved among eukaryotic organisms.
Yeast myosin light chain, Mlc1p, interacts with both IQGAP and class II myosin to effect cytokinesis
2000
These data support a direct interaction between the two proteins and immunoprecipitation experiments confirm this prediction. Mlc1p is also shown to interact with the class II conventional myosin (Myo1p). All three proteins form a complex, however, the interaction between Mlc1p and Iqg1p can be separated from the Mlc1p/Myo1p interaction. Mlc1p localisation and maintenance at the bud neck is independent of actin, Myo1p and Iqg1p. It is proposed that Mlc1p therefore functions to recruit Iqg1p and in turn actin to the actomyosin ring and that it is also required for Myo1p function during ring contraction.
Molecular Biology of the Cell, 2001
Myo2 truncations fused to green fluorescent protein (GFP) defined a C-terminal domain essential for the localization of Myo2 to the cytokinetic actin ring (CAR). The localization domain contained two predicted phosphorylation sites. Mutation of serine 1518 to alanine (S 1518 A) abolished Myo2 localization, whereas Myo2 with a glutamic acid at this position (S 1518 E) localized to the CAR. GFP-Myo2 formed rings in the septation initiation kinase (SIN) mutant cdc7-24 at 25°C but not at 36°C. GFP-Myo2S 1518 E rings persisted at 36°C in cdc7-24 but not in another SIN kinase mutant, sid2-250. To further examine the relationship between Myo2 and the SIN pathway, the chromosomal copy of myo2 ϩ was fused to GFP (strain myo2-gc). Myo2 ring formation was abolished in the double mutants myo2-gc cdc7.24 and myo2-gc sid2-250 at the restrictive temperature. In contrast, activation of the SIN pathway in the double mutant myo2-gc cdc16-116 resulted in the formation of Myo2 rings which subsequently collapsed at 36°C. We conclude that the SIN pathway that controls septation in fission yeast also regulates Myo2 ring formation and contraction. Cdc7 and Sid2 are involved in ring formation, in the case of Cdc7 by phosphorylation of a single serine residue in the Myo2 tail. Other kinases and/or phosphatases may control ring contraction.
Quantitative analysis of a molecular model of mitotic control in fission yeast
Journal of Theoretical Biology, 1995
A wealth of information has accumulated about the physiology, genetics and molecular biology of the cell cycle in the fission yeast, Schizosaccharomyces pombe. From this information we have constructed a detailed molecular mechanism of M-phase control based on the modification of M-phase promoting factor (MPF) by a suite of protein kinases (e.g. Wee1 and Mik1 which inhibit MPF) and phosphatases (e.g. Cdc25 which activates MPF). In particular, we analyze the interphase checkpoint in S. pombe, where the wild-type cell confirms that S phase is complete and that the cell is large enough to finish the division cycle. In our model, incomplete DNA replication restrains the onset of M phase by inhibiting Cdc25 and activating Mik1, whereas increasing size biases the cell towards mitosis by down-regulating Wee1. By standard mathematical methods of chemical kinetics, we show that our model gives a quantitatively accurate account of the effects of hydroxyurea treatments, nutritional shifts and other perturbations of the division cycle of wild-type and mutant cells.
Tying the knot: linking cytokinesis to the nuclear cycle
Journal of cell science, 2000
For the survival of both the parent and the progeny, it is imperative that the process of their physical division (cytokinesis) be precisely coordinated with progression through the mitotic cell cycle. Recent studies in the budding yeast Saccharomyces cerevisiae and the fission yeast Schizosaccharomyces pombe are beginning to unravel the nature of the links between cytokinesis and the nuclear division cycle. The cyclin-dependent kinases and a novel surveillance mechanism that monitors cytokinesis and/or morphogenesis appear to play important regulatory roles in forging these links. It is becoming increasingly clear that the inactivation of the mitosis-promoting cyclin-dependent kinase, which marks the completion of the nuclear division cycle, is essential for actomyosin ring constriction and division septum assembly in both yeasts. Additionally, the spindle pole bodies are emerging as important transient locale for proteins that might play a key role in coupling the completion of mi...
Cyclin C influences the timing of mitosis in fission yeast
Molecular biology of the cell, 2017
The multiprotein Mediator complex is required for the regulated transcription of nearly all RNA polymerase II-dependent genes. Mediator contains the Cdk8 regulatory subcomplex, which directs periodic transcription and influences cell cycle progression in fission yeast. We here investigate the role of CycC, the cognate cyclin partner of Cdk8, in cell cycle control. Previous reports suggested that CycC interact with other cellular Cdks, but a fusion of CycC to Cdk8 reported here did not cause any obvious cell cycle phenotypes. We find that Cdk8 and CycC interactions are stabilized within the Mediator complex and the activity of Cdk8-CycC is regulated by other Mediator components. Analysis of mutant yeast strain reveals that CycC together with Cdk8 primarily affect M-phase progression, but that mutations that release Cdk8 from CycC control also affect timing of entry into S-phase.
Evidence that myosin does not contribute to force production in chromosome movement
Journal of Cell Biology, 1982
Antibody against cytoplasmic myosin, when microinjected into actively dividing cells, provides a physiological test for the role of actin and myosin in chromosome movement. Anti-Asterias egg myosin, characterized by Mabuchi and Okuno (1977, J. Cell Biol., 74:251), completely and specifically inhibits the actin activated Mg++ -ATPase of myosin in vitro and, when microinjected, inhibits cytokinesis in vivo. Here, we demonstrate that microinjected antibody has no observable effect on the rate or extent of anaphase chromosome movements. Neither central spindle elongation nor chromosomal fiber shortening is affected by doses up to eightfold higher than those require to uniformly inhibit cytokinesis in all injected cells. We calculate that such doses are sufficient to completely inhibit myosin ATPase activity in these cells. Cells injected with buffer alone, with myosin-absorbed antibody, or with nonimmune gamma-globulin, proceed normally through both mitosis and cytokinesis. Control gamm...
Nuclear Compartmentalization Is Abolished during Fission Yeast Meiosis
Current Biology, 2010
In eukaryotic cells, the nuclear envelope partitions the nucleus from the cytoplasm. The fission yeast Schizosaccharomyces pombe undergoes closed mitosis in which the nuclear envelope persists rather than being broken down, as in higher eukaryotic cells . It is therefore assumed that nucleocytoplasmic transport continues during the cell cycle . Here we show that nuclear transport is, in fact, abolished specifically during anaphase of the second meiotic nuclear division. During that time, both nucleoplasmic and cytoplasmic proteins disperse throughout the cell, reminiscent of the open mitosis of higher eukaryotes, but the architecture of the S. pombe nuclear envelope itself persists. This functional alteration of the nucleocytoplasmic barrier is likely induced by spore wall formation, because ectopic induction of sporulation signaling leads to premature dispersion of nucleoplasmic proteins. A photobleaching assay demonstrated that nuclear envelope permeability increases abruptly at the onset of anaphase of the second meiotic division. The permeability was not altered when sporulation was inhibited by blocking the trafficking of forespore-membrane vesicles from the endoplasmic reticulum to the Golgi. The evidence indicates that yeast gametogenesis produces vesicle transport-mediated forespore membranes by inducing nuclear envelope permeabilization.