Article

Immobile myosin-II plays a scaffolding role during cytokinesis in budding yeast

Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA 19104.
The Journal of Cell Biology (Impact Factor: 9.83). 01/2013; 200(3). DOI: 10.1083/jcb.201208030
Source: PubMed

ABSTRACT

Core components of cytokinesis are conserved from yeast to human, but how these components are assembled into a robust machine that drives cytokinesis remains poorly understood. In this paper, we show by fluorescence recovery after photobleaching analysis that Myo1, the sole myosin-II in budding yeast, was mobile at the division site before anaphase and became immobilized shortly before cytokinesis. This immobility was independent of actin filaments or the motor domain of Myo1 but required a small region in the Myo1 tail that is thought to be involved in higher-order assembly. As expected, proteins involved in actin ring assembly (tropomyosin and formin) and membrane trafficking (myosin-V and exocyst) were dynamic during cytokinesis. Strikingly, proteins involved in septum formation (the chitin synthase Chs2) and/or its coordination with the actomyosin ring (essential light chain, IQGAP, F-BAR, etc.) displayed Myo1-dependent immobility during cytokinesis, suggesting that Myo1 plays a scaffolding role in the assembly of a cytokinesis machine.

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Available from: Erfei Bi, May 13, 2014
    • "Mutants lacking myosin form a primary septum, which often grows toward the cell body rather than in a centripetal manner. The tail of Myo1 forms a scaffold for Hof1 and Inn1 and is sufficient to guide centripetal primary septum formation [12, 13]. Interestingly, deletion of Myo1 or just the motor domain results in formation of more than one primary septum [12], though how this translates into the formation of a single primary septum is not known. "
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    ABSTRACT: Cytokinesis is the final process in the cell cycle that physically divides one cell into two. In budding yeast, cytokinesis is driven by a contractile actomyosin ring (AMR) and the simultaneous formation of a primary septum, which serves as template for cell wall deposition. AMR assembly, constriction, primary septum formation and cell wall deposition are successive processes and tightly coupled to cell cycle progression to ensure the correct distribution of genetic material and cell organelles among the two rising cells prior to cell division. The role of the AMR in cytokinesis and the molecular mechanisms that drive AMR constriction and septation are the focus of current research. This review summarizes the recent progresses in our understanding of how budding yeast cells orchestrate the multitude of molecular mechanisms that control AMR driven cytokinesis in a spatio-temporal manner to achieve an error free cell division.
    No preview · Article · Feb 2016 · Seminars in Cell and Developmental Biology
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    • "The fact that CAR contraction fails in iqg1-1 is intriguing in the light of recent evidence demonstrating that the force generation required for contraction derives from actin disassembly and that Myo1 serves as a CAR scaffold but is not required for contractile force [53], [54]. Iqg1p was suggested to act as a cross-linker between actin filaments [55], a necessary function if contractile force is driven by filament disassembly, and the data presented here are consistent with that proposal. "
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    ABSTRACT: The late events of the budding yeast cell division cycle, cytokinesis and cell separation, require the assembly of a contractile actomyosin ring (CAR), primary and secondary septum formation followed by enzymatic degradation of the primary septum. Here we present evidence that demonstrates a role for the budding yeast amphiphysin complex, a heterodimer comprising Rvs167 and Rvs161, in CAR assembly and cell separation. The iqg1-1 allele is synthetically lethal with both rvs167 and rvs161 null mutations. We show that both Iqg1 and the amphiphysin complex are required for CAR assembly in early anaphase but cells are able to complete assembly in late anaphase when these activities are, respectively, either compromised or absent. Amphiphysin dependent CAR assembly is dependent upon the Rvs167 SH3 domain, but this function is insufficient to explain the observed synthetic lethality. Dosage suppression of the iqg1-1 allele demonstrates that endocytosis is required for the default cell separation pathway in the absence of CAR contraction but is unlikely to be required to maintain viability. The amphiphysin complex is required for normal, post-mitotic, localization of Chs3 and the Rho1 GEF, Rom2, which are responsible for secondary septum deposition and the accumulation of GTP bound Rho1 at the bud neck. It is concluded that a failure of polarity establishment in the absence of CAR contraction and amphiphysin function leads to loss of viability as a result of the consequent cell separation defect.
    Full-text · Article · May 2014 · PLoS ONE
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    ABSTRACT: F-BAR proteins are membrane-associated proteins thought to link the plasma membrane to the actin cytoskeleton in cellular processes such as cytokinesis and endocytosis. In the budding yeast Saccharomyces cerevisiae, the F-BAR protein Hof1 localizes to the division site in a complex pattern during the cell cycle, and plays an important role in cytokinesis. However, the mechanisms underlying its localization and function remain poorly understood. Here, we show that Hof1 contains three distinct targeting domains that contribute to cytokinesis differentially. The N-terminal half of Hof1 localizes to the bud neck and the sites of polarized growth during the cell cycle. The neck localization is mediated mainly by an interaction between the second coiled-coil region in the N-terminus and the septin Cdc10, whereas the localization to the sites of polarized growth is mediated entirely by the F-BAR domain. In contrast, the C-terminal half of Hof1 interacts with Myo1, the sole myosin-II heavy chain in budding yeast, and localizes to the bud neck in a Myo1-dependent manner from the onset to the completion of cytokinesis. We also show that the SH3 domain in the C-terminus plays an important role in maintaining the symmetry of Myo1 ring constriction during cytokinesis, and that Hof1 interacts with Chs2, a chitin synthase that is required for primary septum formation. Together, these data define a mechanism that accounts for the localization of Hof1 during the cell cycle, and suggest that Hof1 may function in cytokinesis by coupling actomyosin ring constriction to primary septum formation through interactions with Myo1 and Chs2.
    Full-text · Article · Mar 2013 · Molecular biology of the cell
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