Actin and fimbrin are required for the internalization step of endocytosis in yeast.

Kübler, Eric; Riezman, Howard

doi:10.1002/j.1460-2075.1993.tb05947.x

Cited by 333 publications

(299 citation statements)

References 45 publications

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“…However, because these cables are generally more difficult to visualize in S. pombe than in S. cerevisiae, it is also possible that we failed to detect a subtle role of Fim1p. sac6 mutants are also defective in the internalization of mating pheromone, suggesting that fimbrin is also involved in endocytosis in S. cerevisiae (Kü bler and Riezman, 1993). Thus, the mating defect of fim1 mutants may also be caused, at least in part, by a defect in endocytosis.…”

Section: Roles Of Fim1p In Polarized Growth and Sexual Differentiationmentioning

confidence: 99%

Roles of a Fimbrin and an α-Actinin-like Protein in Fission Yeast Cell Polarization and Cytokinesis

Bähler

Pringle

2001

MBoC

146

183

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Eukaryotic cells contain many actin-interacting proteins, including the ␣-actinins and the fimbrins, both of which have actin cross-linking activity in vitro. We report here the identification and characterization of both an ␣-actinin-like protein (Ain1p) and a fimbrin (Fim1p) in the fission yeast Schizosaccharomyces pombe. Ain1p localizes to the actomyosin-containing medial ring in an F-actindependent manner, and the Ain1p ring contracts during cytokinesis. ain1 deletion cells have no obvious defects under normal growth conditions but display severe cytokinesis defects, associated with defects in medial-ring and septum formation, under certain stress conditions. Overexpression of Ain1p also causes cytokinesis defects, and the ain1 deletion shows synthetic effects with other mutations known to affect medial-ring positioning and/or organization. Fim1p localizes both to the cortical actin patches and to the medial ring in an F-actin-dependent manner, and several lines of evidence suggest that Fim1p is involved in polarization of the actin cytoskeleton. Although a fim1 deletion strain has no detectable defect in cytokinesis, overexpression of Fim1p causes a lethal cytokinesis defect associated with a failure to form the medial ring and concentrate actin patches at the cell middle. Moreover, an ain1 fim1 double mutant has a synthetical-lethal defect in medial-ring assembly and cell division. Thus, Ain1p and Fim1p appear to have an overlapping and essential function in fission yeast cytokinesis. In addition, protein-localization and mutant-phenotype data suggest that Fim1p, but not Ain1p, plays important roles in mating and in spore formation. INTRODUCTIONThe actin cytoskeleton is involved in many processes in eukaryotic cells, including the polarization of cell growth and cytokinesis. These many roles involve the interaction of actin with a wide variety of actin-binding proteins, including proteins that can cross-link actin filaments into isotropic gels or bundles. Many actin cross-linking proteins have been purified and studied in vitro, but their functions in vivo remain poorly understood (reviewed by Matsudaira, 1994a;Otto, 1994;Furukawa and Fechheimer, 1997;Ayscough, 1998;Bartles, 2000).Among the actin cross-linking proteins, one of the best characterized is ␣-actinin. It was first isolated from rabbit skeletal muscle (Ebashi and Ebashi, 1965) and has subsequently been identified in both muscle and nonmuscle cells from a variety of animals, in Acanthamoeba, and in Dictyostelium (Furukawa and Fechheimer, 1997;Critchley and Flood, 1999). ␣-Actinin forms a homodimer of antiparallel polypeptides (Critchley and Flood, 1999;Djinovic-Carugo et al., 1999), with the actin-binding domain of each polypeptide close to the NH 2 terminus, followed by four spectrin-like repeats and two COOH-terminal EF-hand motifs. Skeletal muscle isoforms are localized to the Z-disk and are not regulated by Ca 2ϩ , whereas nonmuscle isoforms are localized to focal adhesions, stress fibers, and other structures and are typically regulated by C...

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Section: Roles Of Fim1p In Polarized Growth and Sexual Differentiationmentioning

confidence: 99%

Roles of a Fimbrin and an α-Actinin-like Protein in Fission Yeast Cell Polarization and Cytokinesis

Bähler

Pringle

2001

MBoC

146

183

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“…Endocytosis is required for recycling of plasma membrane lipids and trafficking proteins, and for uptake or down-regulation of cell surface receptors (reviewed in Smythe and Ayscough, 2006). In yeast, a requirement for a dynamic actin cytoskeleton at sites of endocytosis has been recognized for many years (Kü bler and Riezman, 1993;Raths et al, 1993). Several elegant studies using live imaging of fluorescently tagged proteins have allowed a clear idea of the main stages of the endocytic process to be elucidated (Kaksonen et al, 2003(Kaksonen et al, , 2005.…”

Section: Introductionmentioning

confidence: 99%

The WASP Homologue Las17 Activates the Novel Actin-regulatory Activity of Ysc84 to Promote Endocytosis in Yeast

Robertson¹,

Allwood²,

Smith³

et al. 2009

MBoC

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Actin plays an essential role in many eukaryotic cellular processes, including motility, generation of polarity, and membrane trafficking. Actin function in these roles is regulated by association with proteins that affect its polymerization state, dynamics, and organization. Numerous proteins have been shown to localize with cortical patches of yeast actin during endocytosis, but the role of many of these proteins remains poorly understood. Here, we reveal that the yeast protein Ysc84 represents a new class of actin-binding proteins, conserved from yeast to humans. It contains a novel N-terminal actin-binding domain termed Ysc84 actin binding (YAB), which can bind and bundle actin filaments. Intriguingly, full-length Ysc84 alone does not bind to actin, but binding can be activated by a specific motif within the polyproline region of the yeast WASP homologue Las17. We also identify a new monomeric actin-binding site on Las17. Together, the polyproline region of Las17 and Ysc84 can promote actin polymerization. Using live cell imaging, kinetics of assembly and disassembly of proteins at the endocytic site were analyzed and reveal that loss of Ysc84 and its homologue Lsb3 decrease inward movement of vesicles consistent with a role in actin polymerization during endocytosis.

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“…Cortical actin patches contain many of the actin-associated proteins common to all eukaryotes (Goode and Rodal, 2001) and are composed of actin filaments that undergo rapid turnover (Ayscough et al, 1997). Actin is essential for yeast endocytosis (Kubler and Riezman, 1993). A number of recent studies suggest that actin participates directly in endocytosis via a dynamic, highly regulated pathway, but the precise function of actin in endocytosis is not understood (Engqvist-Goldstein and Drubin, 2003;Kaksonen et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Actin and Septin Ultrastructures at the Budding Yeast Cell Cortex

Rodal

Kozubowski

Goode

et al. 2005

MBoC

174

162

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Budding yeast has been a powerful model organism for studies of the roles of actin in endocytosis and septins in cell division and in signaling. However, the depth of mechanistic understanding that can be obtained from such studies has been severely hindered by a lack of ultrastructural information about how actin and septins are organized at the cell cortex. To address this problem, we developed rapid-freeze and deep-etch techniques to image the yeast cell cortex in spheroplasted cells at high resolution. The cortical actin cytoskeleton assembles into conical or mound-like structures composed of short, cross-linked filaments. The Arp2/3 complex localizes near the apex of these structures, suggesting that actin patch assembly may be initiated from the apex. Mutants in cortical actin patch components with defined defects in endocytosis disrupted different stages of cortical actin patch assembly. Based on these results, we propose a model for actin function during endocytosis. In addition to actin structures, we found that septin-containing filaments assemble into two kinds of higher order structures at the cell cortex: rings and ordered gauzes. These images provide the first high-resolution views of septin organization in cells. INTRODUCTIONBudding yeast has been used for over 20 yr as a model organism to study cytoskeletal function because the genes encoding many components of the cytoskeleton are conserved and because yeast cells are readily amenable to parallel genetic, biochemical, and cell biological analyses. Despite rapid advances in defining the components of the yeast cytoskeleton, its ultrastructure has been difficult to image at the resolution of the electron microscope, with the exception of microtubules (O'Toole et al., 1999). This may be due to the low abundance of the cytoskeleton in yeast relative to mammalian cells, to the presence of a cell wall that complicates extraction procedures, and to high ribosome density in the yeast cytoplasm. As a result, there has been a conspicuous deficit in our understanding of the higher order organization of actin and septin polymers in vivo (Pruyne and Bretscher, 2000). Thus, although it is possible to rapidly identify and mutate cytoskeletal proteins in yeast, there is no method by which to examine the ultrastructural consequences of these mutations. This gap could be filled by developing an approach to image the yeast cytoskeleton at high resolution.The yeast actin cytoskeleton is organized into three distinct structures: motile cortical patches that are polarized in the growing bud, actin cables that run along the motherdaughter cell axis, and a contractile cytokinetic ring at the neck of dividing cells (reviewed in Pruyne and Bretscher, 2000). Cortical actin patches contain many of the actin-associated proteins common to all eukaryotes (Goode and Rodal, 2001) and are composed of actin filaments that undergo rapid turnover (Ayscough et al., 1997). Actin is essential for yeast endocytosis (Kubler and Riezman, 1993). A number of recent studies suggest that act...

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Actin and fimbrin are required for the internalization step of endocytosis in yeast.

Cited by 333 publications

References 45 publications

Roles of a Fimbrin and an α-Actinin-like Protein in Fission Yeast Cell Polarization and Cytokinesis

Roles of a Fimbrin and an α-Actinin-like Protein in Fission Yeast Cell Polarization and Cytokinesis

The WASP Homologue Las17 Activates the Novel Actin-regulatory Activity of Ysc84 to Promote Endocytosis in Yeast

Actin and Septin Ultrastructures at the Budding Yeast Cell Cortex

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