scholarly journals Fission Yeast Aip3p (spAip3p) Is Required for an Alternative Actin-directed Polarity Program

2001 ◽  
Vol 12 (5) ◽  
pp. 1275-1291 ◽  
Author(s):  
Hui Jin ◽  
David C. Amberg
Keyword(s):  
Actin Cytoskeleton ◽  
Fission Yeast ◽  
Cell Polarity ◽  
Secretory Pathway ◽  
Budding Yeast ◽  
Microtubule Cytoskeleton ◽  
Interacting Protein ◽  
Sequencing Project ◽  
Polarized Cell Growth ◽  
Branch Formation

Aip3p is an actin-interacting protein that regulates cell polarity in budding yeast. The Schizosaccharomyces pombe-sequencing project recently led to the identification of a homologue of Aip3p that we have named spAip3p. Our results confirm that spAip3p is a true functional homologue of Aip3p. When expressed in budding yeast, spAip3p localizes similarly to Aip3p during the cell cycle and complements the cell polarity defects of anaip3Δ strain. Two-hybrid analysis shows that spAip3p interacts with actin similarly to Aip3p. In fission yeast, spAip3p localizes to both cell ends during interphase and later organizes into two rings at the site of cytokinesis. spAip3p localization to cell ends is dependent on microtubule cytoskeleton, its localization to the cell middle is dependent on actin cytoskeleton, and both patterns of localization require an operative secretory pathway. Overexpression of spAip3p disrupts the actin cytoskeleton and cell polarity, leading to morphologically aberrant cells. Fission yeast, which normally rely on the microtubule cytoskeleton to establish their polarity axis, can use the actin cytoskeleton in the absence of microtubule function to establish a new polarity axis, leading to the formation of branched cells. spAip3p localizes to, and is required for, branch formation, confirming its role in actin-directed polarized cell growth in bothSchizosaccharomyces pombe and Saccharomyces cerevisiae.

scholarly journals High Rates of Actin Filament Turnover in Budding Yeast and Roles for Actin in Establishment and Maintenance of Cell Polarity Revealed Using the Actin Inhibitor Latrunculin-A

1997 ◽  
Vol 137 (2) ◽  
pp. 399-416 ◽  
Author(s):  
Kathryn R. Ayscough ◽  
Joel Stryker ◽  
Navin Pokala ◽  
Miranda Sanders ◽  
Phil Crews ◽  
...  
Keyword(s):  
Cell Surface ◽  
Actin Cytoskeleton ◽  
Cell Polarity ◽  
Actin Filaments ◽  
Three Dimensional ◽  
Surface Growth ◽  
Interacting Protein ◽  
Capping Protein ◽  
Latrunculin A

We report that the actin assembly inhibitor latrunculin-A (LAT-A) causes complete disruption of the yeast actin cytoskeleton within 2–5 min, suggesting that although yeast are nonmotile, their actin filaments undergo rapid cycles of assembly and disassembly in vivo. Differences in the LAT-A sensitivities of strains carrying mutations in components of the actin cytoskeleton suggest that tropomyosin, fimbrin, capping protein, Sla2p, and Srv2p act to increase actin cytoskeleton stability, while End3p and Sla1p act to decrease stability. Identification of three LAT-A resistant actin mutants demonstrated that in vivo effects of LAT-A are due specifically to impairment of actin function and implicated a region on the three-dimensional actin structure as the LAT-A binding site. LAT-A was used to determine which of 19 different proteins implicated in cell polarity development require actin to achieve polarized localization. Results show that at least two molecular pathways, one actindependent and the other actin-independent, underlie polarity development. The actin-dependent pathway localizes secretory vesicles and a putative vesicle docking complex to sites of cell surface growth, providing an explanation for the dependence of polarized cell surface growth on actin function. Unexpectedly, several proteins that function with actin during cell polarity development, including an unconventional myosin (Myo2p), calmodulin, and an actin-interacting protein (Bud6/Aip3p), achieved polarized localization by an actin-independent pathway, revealing interdependence among cell polarity pathways. Finally, transient actin depolymerization caused many cells to abandon one bud site or mating projection and to initiate growth at a second site. Thus, actin filaments are also required for maintenance of an axis of cell polarity.

scholarly journals Regulation of cortical actin cytoskeleton assembly during polarized cell growth in budding yeast.

1995 ◽  
Vol 128 (4) ◽  
pp. 599-615 ◽  
Author(s):  
R Li ◽  
Y Zheng ◽  
D G Drubin
Keyword(s):  
Cell Growth ◽  
Actin Cytoskeleton ◽  
Actin Filaments ◽  
Budding Yeast ◽  
Yeast Cells ◽  
Actin Assembly ◽  
Cortical Actin ◽  
Polarized Cell Growth ◽  
Nucleation Activity

We have established an in vitro assay for assembly of the cortical actin cytoskeleton of budding yeast cells. After permeabilization of yeast by a novel procedure designed to maintain the spatial organization of cellular constituents, exogenously added fluorescently labeled actin monomers assemble into distinct structures in a pattern that is similar to the cortical actin distribution in vivo. Actin assembly in the bud of small-budded cells requires a nucleation activity provided by protein factors that appear to be distinct from the barbed ends of endogenous actin filaments. This nucleation activity is lost in cells that lack either Sla1 or Sla2, proteins previously implicated in cortical actin cytoskeleton function, suggesting a possible role for these proteins in the nucleation reaction. The rate and the extent of actin assembly in the bud are increased in permeabilized delta cap2 cells, providing evidence that capping protein regulates the ability of the barbed ends of actin filaments to grow in yeast cells. Actin incorporation in the bud can be stimulated by treating the permeabilized cells with GTP-gamma S, and, significantly, the stimulatory effect is eliminated by a mutation in CDC42, a gene that encodes a Rho-like GTP-binding protein required for bud formation. Furthermore, the lack of actin nucleation activity in the cdc42 mutant can be complemented in vitro by a constitutively active Cdc42 protein. These results suggest that Cdc42 is closely involved in regulating actin assembly during polarized cell growth.

scholarly journals Regulation of Cell Polarity by Microtubules in Fission Yeast

1998 ◽  
Vol 142 (2) ◽  
pp. 457-471 ◽  
Author(s):  
Kenneth E. Sawin ◽  
Paul Nurse
Keyword(s):  
Cell Cycle ◽  
Fission Yeast ◽  
Cell Polarity ◽  
High Frequency ◽  
Fluorescent Protein ◽  
Physiological Importance ◽  
Normal Transition ◽  
Branch Formation ◽  
Green Fluorescent

To investigate the role of microtubules in regulating cell polarity in Schizosaccharomyces pombe, we have developed a system in which normally cylindrical fission yeast synchronously form branched cells at high frequency upon treatment with the microtubule-depolymerizing drug thiabendazole (TBZ). Branching depends on both elevated temperature and cell cycle state and occurs at high frequency only when TBZ is added to cells that have not yet passed through New-End Take-Off (NETO), the normal transition from monopolar to bipolar growth. This suggests that microtubules may be of greatest physiological importance for the maintenance of cell shape at specific points in the cell cycle. The localization of three different proteins normally found at cell ends—cortical F-actin, tea1, and an ral3 (scd2)–green fluorescent protein (GFP) fusion—is disrupted by TBZ treatment. However, these proteins can eventually return to cell ends in the absence of microtubules, indicating that although their localization to ends normally depends on microtubules, they may recover by alternative mechanisms. In addition, TBZ induces a shift in ral3–GFP distribution from cell ends to the cell middle, suggesting that a protein complex containing ral3 may be part of the cue that specifies the position of branch formation.

The fission yeast microtubule cytoskeleton

1998 ◽  
Vol 111 (12) ◽  
pp. 1603-1612 ◽  
Author(s):  
I.M. Hagan
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Cell Cycle ◽  
Fission Yeast ◽  
Sexual Differentiation ◽  
Model System ◽  
Model Systems ◽  
Genome Sequencing Project ◽  
Microtubule Cytoskeleton ◽  
Sequencing Project ◽  
The Impact

The Schizosaccharomyces pombe genome sequencing project (http://www.sanger.ac.uk/Projects/S_pombe/) is nearly complete, and this is likely to generate interest in fission yeast as a model system beyond its traditional strongholds in the study of the cell cycle and sexual differentiation. In many fields S. pombe will offer a useful complement to the more widely studied Saccharomyces cerevisiae, but in some areas the impact of S. pombe may well rival or exceed that of this budding yeast in terms of relevance to higher systems. Because of the considerable differences from the S. cerevisiae microtubule cytoskeleton, studying microtubules in S. pombe is likely to enhance the contribution of model systems to our understanding of the principles and practices of microtubule organisation in eukaryotes in general.

scholarly journals Opposing Roles for Actin in Cdc42p Polarization

2005 ◽  
Vol 16 (3) ◽  
pp. 1296-1304 ◽  
Author(s):  
Javier E. Irazoqui ◽  
Audrey S. Howell ◽  
Chandra L. Theesfeld ◽  
Daniel J. Lew
Keyword(s):  
Actin Cytoskeleton ◽  
Cell Polarity ◽  
Budding Yeast ◽  
Cortical Actin ◽  
Independent Manner ◽  
Actin Depolymerization ◽  
Cell Biol ◽  
Actin Cables ◽  
Unexpected Difference

In animal and fungal cells, the monomeric GTPase Cdc42p is a key regulator of cell polarity that itself exhibits a polarized distribution in asymmetric cells. Previous work showed that in budding yeast, Cdc42p polarization is unaffected by depolymerization of the actin cytoskeleton (Ayscough et al., J. Cell Biol. 137, 399–416, 1997). Surprisingly, we now report that unlike complete actin depolymerization, partial actin depolymerization leads to the dispersal of Cdc42p from the polarization site in unbudded cells. We provide evidence that dispersal is due to endocytosis associated with cortical actin patches and that actin cables are required to counteract the dispersal and maintain Cdc42p polarity. Thus, although Cdc42p is initially polarized in an actin-independent manner, maintaining that polarity may involve a reinforcing feedback between Cdc42p and polarized actin cables to counteract the dispersing effects of actin-dependent endocytosis. In addition, we report that once a bud has formed, polarized Cdc42p becomes more resistant to dispersal, revealing an unexpected difference between unbudded and budded cells in the organization of the polarization site.

scholarly journals Activation of polarized cell growth by inhibition of cell polarity

2018 ◽  
Author(s):  
Marco Geymonat ◽  
Anatole Chessel ◽  
James Dodgson ◽  
Hannah Punter ◽  
Felix Horns ◽  
...  
Keyword(s):  
Cell Growth ◽  
Fission Yeast ◽  
Cell Polarity ◽  
Rho Gtpase ◽  
Dependent Manner ◽  
Polarized Cell Growth ◽  
And Control ◽  
Polarity Factor ◽  
Pak Kinase

AbstractA key feature of cells is the capacity to activate new functional polarized domains contemporaneously to pre-existing ones. How cells accomplish this is not clear. Here, we show that in fission yeast inhibition of cell polarity at pre-existing domains of polarized cell growth is required to activate new growth. This inhibition is mediated by the ERM-related polarity factor Tea3, which antagonizes the activation of the Rho-GTPase Cdc42 by its co-factor Scd2. We demonstrate that Tea3 acts in a phosphorylation-dependent manner controlled by the PAK kinase Shk1 and that, like Scd2, Tea3 is direct substrate of Shk1. Importantly, we show that Tea3 and Scd2 compete for their binding to Shk1, indicating that their biochemical competition for Shk1 underpins their antagonistic roles in controlling polarity. Thus, by preventing pre-existing growth domains from becoming overpowering, Tea3 allows cells to redistribute their polarity-activating machinery to prospective sites and control their timing of activation.

scholarly journals The Secretory Pathway Mediates Localization of the Cell Polarity Regulator Aip3p/Bud6p

2000 ◽  
Vol 11 (2) ◽  
pp. 647-661 ◽  
Author(s):  
Hui Jin ◽  
David C. Amberg
Keyword(s):  
Secretory Pathway ◽  
Cell Cortex ◽  
Homologous Region ◽  
Secretory Vesicles ◽  
Interacting Protein ◽  
Polarized Cell Growth ◽  
N Terminus ◽  
Actin Cables ◽  
Type V ◽  
Secretory Apparatus

Aip3p/Bud6p is a regulator of cell and cytoskeletal polarity inSaccharomyces cerevisiae that was previously identified as an actin-interacting protein. Actin-interacting protein 3 (Aip3p) localizes at the cell cortex where cytoskeleton assembly must be achieved to execute polarized cell growth, and deletion ofAIP3 causes gross defects in cell and cytoskeletal polarity. We have discovered that Aip3p localization is mediated by the secretory pathway. Mutations in early- or late-acting components of the secretory apparatus lead to Aip3p mislocalization. Biochemical data show that a pool of Aip3p is associated with post-Golgi secretory vesicles. An investigation of the sequences within Aip3p necessary for Aip3p localization has identified a sequence within the N terminus of Aip3p that is sufficient for directing Aip3p localization. Replacement of the N terminus of Aip3p with a homologous region from aSchizosaccharomyces pombe protein allows for normal Aip3p localization, indicating that the secretory pathway–mediated Aip3p localization pathway is conserved. Delivery of Aip3p also requires the type V myosin motor Myo2p and its regulatory light-chain calmodulin. These data suggest that one function of calmodulin is to activate Myo2p's activity in the secretory pathway; this function is likely the polarized movement of late secretory vesicles and associated Aip3p on actin cables.

scholarly journals Response of Fission Yeast to Toxic Cations Involves Cooperative Action of the Stress-Activated Protein Kinase Spc1/Sty1 and the Hal4 Protein Kinase

2005 ◽  
Vol 25 (10) ◽  
pp. 3945-3955 ◽  
Author(s):  
Ling-yu Wang ◽  
Koichi Shimada ◽  
Masayo Morishita ◽  
Kazuhiro Shiozaki
Keyword(s):  
Protein Kinase ◽  
Fission Yeast ◽  
Budding Yeast ◽  
Physiological Role ◽  
Mitogen Activated Protein Kinase ◽  
Cellular Resistance ◽  
Interacting Protein ◽  
Cooperative Action ◽  
Mitogen Activated Protein

ABSTRACT Stress-activated protein kinases (SAPKs), members of a mitogen-activated protein kinase (MAPK) subfamily, are highly conserved among eukaryotes. Studies of yeasts demonstrated that SAPKs play pivotal roles in survival responses to high osmolarity, oxidative stress, and heat shock. Here we report a novel physiological role of the fission yeast Spc1 SAPK in cellular resistance to certain cations, such as Na+, Li+, and Ca2+. Strains lacking Spc1 or its activator, Wis1 MAPK kinase, are hypersensitive to these cations. Spc1 positively regulates expression of sod2 + encoding a Na+/H+ antiporter through Atf1 and other transcription factors. In addition, we have identified a novel Spc1-interacting protein, Hal4, which is highly homologous to the budding yeast Sat4/Hal4 protein kinase. Like its budding yeast counterpart, the fission yeast Hal4 kinase is essential for cellular resistance to Na+, Li+, and Ca2+. The hal4-null phenotype is complemented by overexpression of the Trk1 potassium transporter or increased K+ in the growth medium, suggesting that Hal4 promotes K+ uptake, which consequently increases cellular resistance to other cations. Interestingly, the Spc1-Hal4 interaction appears to be required for cellular resistance to Ca2+ but not Na+ and Li+. We propose that Spc1 SAPK and Hal4 kinase cooperatively function to protect cells from the toxic cations.

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