Cdc42p and Fus2p act together late in yeast cell fusion

Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
Molecular biology of the cell (Impact Factor: 4.47). 02/2012; 23(7):1208-18. DOI: 10.1091/mbc.E11-08-0723
Source: PubMed


Cell fusion is the key event of fertilization that gives rise to the diploid zygote and is a nearly universal aspect of eukaryotic biology. In the yeast Saccharomyces cerevisiae, several mutants have been identified that are defective for cell fusion, and yet the molecular mechanism of this process remains obscure. One obstacle has been that genetic screens have mainly focused on mating-specific factors, whereas the process likely involves housekeeping proteins as well. Here we implicate Cdc42p, an essential protein with roles in multiple aspects of morphogenesis, as a core component of the yeast cell fusion pathway. We identify a point mutant in the Rho-insert domain of CDC42, called cdc42-138, which is specifically defective in cell fusion. The cell fusion defect is not a secondary consequence of ineffective signaling or polarization. Genetic and morphological data show that Cdc42p acts at a late stage in cell fusion in concert with a key cell fusion regulator, Fus2p, which contains a Dbl-homology domain. We find that Fus2p binds specifically with activated Cdc42p, and binding is blocked by the cdc42-138 mutation. Thus, in addition to signaling and morphogenetic roles in mating, Cdc42p plays a role late in cell fusion via activation of Fus2p.

Download full-text


Available from: Casey Ydenberg, May 14, 2014
  • Source
    • "For this, both a fusion-specific transmembrane protein Fus1 (unrelated to its fission yeast formin Fus1 namesake) as well as Spa2, a formin-binding factor, are required (Gammie et al., 1998). 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). "
    [Show abstract] [Hide abstract]
    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
  • Source
    • "It functions late during fusion, blocking pairs with vesicles tightly clustered at the zone of fusion [110]. Similar phenotype is observed for a specific cdc42 allele, which displays defects only in cell fusion [105]. Fus2, which contains a putative Rho-GEF domain, in fact binds GTP-Cdc42 directly, suggesting it acts as a Cdc42 effector for fusion [105]. "
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Spermidine is a naturally occurring polyamine involved in multiple biological processes, including DNA metabolism, autophagy and aging. Like other polyamines, spermidine is also indispensable for successful reproduction at several stages. However, a direct influence on the actual fertilization process, i.e., the fusion of an oocyte with a spermatocyte, remains uncertain. To explore this possibility, we established the mating process in the yeast Saccharomyces cerevisiae as a model for fertilization in higher eukaryotes. During human fertilization, the sperm capacitates and the acrosome reaction is necessary for penetration of the oocyte. Similarly, sexually active yeasts form a protrusion called "shmoo" as a prerequisite for mating. In this study, we demonstrate that pheromone-induced shmoo formation requires spermidine. In addition, we show that spermidine is essential for mating in yeast as well as for egg fertilization in the nematode Caenorhabditis elegans. In both cases, this occurs independently from autophagy. In synthesis, we identify spermidine as an important mating component in unicellular and multicellular model organisms, supporting an unprecedented evolutionary conservation of the mechanisms governing fertilization-related cellular fusion.
    Full-text · Article · Jan 2012 · Cell cycle (Georgetown, Tex.)
Show more