The Class V Myosin Myo2p Is Required for Fus2p Transport and Actin Polarization during the Yeast Mating Response

Department of Molecular Biology, Princeton University, Princeton, NJ 08544-1014, USA.
Molecular biology of the cell (Impact Factor: 4.47). 05/2009; 20(12):2909-19. DOI: 10.1091/mbc.E08-09-0923
Source: PubMed


Mating yeast cells remove their cell walls and fuse their plasma membranes in a spatially restricted cell contact region. Cell wall removal is dependent on Fus2p, an amphiphysin-associated Rho-GEF homolog. As mating cells polarize, Fus2p-GFP localizes to the tip of the mating projection, where cell fusion will occur, and to cytoplasmic puncta, which show rapid movement toward the tip. Movement requires polymerized actin, whereas tip localization is dependent on both actin and a membrane protein, Fus1p. Here, we show that Fus2p-GFP movement is specifically dependent on Myo2p, a type V myosin, and not on Myo4p, another type V myosin, or Myo3p and Myo5p, type I myosins. Fus2p-GFP tip localization and actin polarization in shmoos are also dependent on Myo2p. A temperature-sensitive tropomyosin mutation and Myo2p alleles that specifically disrupt vesicle binding caused rapid loss of actin patch organization, indicating that transport is required to maintain actin polarity. Mutant shmoos lost actin polarity more rapidly than mitotic cells, suggesting that the maintenance of cell polarity in shmoos is more sensitive to perturbation. The different velocities, differential sensitivity to mutation and lack of colocalization suggest that Fus2p and Sec4p, another Myo2p cargo associated with exocytotic vesicles, reside predominantly on different cellular organelles.

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    • "Focus formation could arise from highly focused upstream signaling by formin regulators like Cdc42. Another possibility is suggested by the observation that, as also seen in budding yeast (Sheltzer and Rose, 2009), myosin V was required for focus formation. Thus, one could envision a positive feedback focusing mechanism in which forminnucleated actin cables enable myosin V–mediated delivery of formins or their activators. "
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    ABSTRACT: During mating, yeast cells must perforate their rigid cell walls at the right place to allow cell-cell fusion. In this issue, Dudin et al. (2015; J. Cell Biol. image mating fission yeast cells with unprecedented spatiotemporal resolution. The authors find that when mating cells come into contact, they form aster-like actin structures that direct cell wall remodeling precisely to the point of contact. © 2015 McClure and Lew.
    Preview · Article · Mar 2015 · The Journal of Cell Biology
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    • "Further, the Cdc42-interacting protein Fus2, also necessary for cell wall digestion, displays a focused localization at the fusion site, which relies on both Fus1-and actin-based transport (Paterson et al., 2008; Sheltzer and Rose, 2009; Ydenberg et al., 2012). The precise role of the actin cytoskeleton has not been defined, though the formin Bni1, tropomyosin Tpm1, and type V myosin Myo2 are all required for cell fusion (Liu and Bretscher, 1992; Dorer et al., 1997; Sheltzer and Rose, 2009). The tight localization of fusion factors and vesicles suggests the existence of a specific mechanism to focalize cell wall digestion for fusion. "
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    ABSTRACT: Cell-cell fusion is essential for fertilization. For fusion of walled cells, the cell wall must be degraded at a precise location but maintained in surrounding regions to protect against lysis. In fission yeast cells, the formin Fus1, which nucleates linear actin filaments, is essential for this process. In this paper, we show that this formin organizes a specific actin structure-the actin fusion focus. Structured illumination microscopy and live-cell imaging of Fus1, actin, and type V myosins revealed an aster of actin filaments whose barbed ends are focalized near the plasma membrane. Focalization requires Fus1 and type V myosins and happens asynchronously always in the M cell first. Type V myosins are essential for fusion and concentrate cell wall hydrolases, but not cell wall synthases, at the fusion focus. Thus, the fusion focus focalizes cell wall dissolution within a broader cell wall synthesis zone to shift from cell growth to cell fusion. © 2015 Dudin et al.
    Full-text · Article · Mar 2015 · The Journal of Cell Biology
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    • "However, Fus2 and Fus1 play additive functions, as complete fusion block is only achieved in double mutants, which arrest at a pre-zygote stage with cell wall material separating the two partner cells [110,116]. Fus2 is probably transported to the fusion site along actin cables, as its localization depends on the polarisome and the type-V myosin Myo2 [112,118]. It functions late during fusion, blocking pairs with vesicles tightly clustered at the zone of fusion [110]. "
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    ABSTRACT: Many cells are able to orient themselves in a non-uniform environment by responding to localized cues. This leads to a polarized cellular response, where the cell can either grow or move towards the cue source. Fungal haploid cells secrete pheromones to signal mating, and respond by growing a mating projection towards a potential mate. Upon contact of the two partner cells, these fuse to form a diploid zygote. In this review, we present our current knowledge on the processes of mating signalling, pheromone-dependent polarized growth and cell fusion in Saccharomyces cerevisiae and Schizosaccharomyces pombe, two highly divergent ascomycete yeast models. While the global architecture of the mating response is very similar between these two species, they differ significantly both in their mating physiologies and in the molecular connections between pheromone perception and downstream responses. The use of both yeast models helps enlighten both conserved solutions and species-specific adaptations to a general biological problem.
    Full-text · Article · Mar 2013 · Open Biology
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