Disruption of the single tropomyosin gene in yeast results in the disappearance of actin cables from the cytoskeleton

Epithelial junctions comprise two subdomains, the apical junctional complex (AJC) and the adjacent lateral membrane contacts (LCs), that span the majority of the junction. The AJC is lined with circumferential actin cables, whereas the LCs are associated with less-organized actin filaments whose roles are elusive. We found that DAAM1, a formin family actin regulator, accumulated at the LCs, and its depletion caused dispersion of actin filaments at these sites while hardly affecting circumferential actin cables. DAAM1 loss enhanced the motility of LC-forming membranes, leading to their invasion of neighboring cell layers, as well as disruption of polarized epithelial layers. We found that components of the WAVE complex and its downstream targets were required for the elevation of LC motility caused by DAAM1 loss. These findings suggest that the LC membranes are motile by nature because of the WAVE complex, but DAAM1-mediated actin regulation normally restrains this motility, thereby stabilizing epithelial architecture, and that DAAM1 loss evokes invasive abilities of epithelial cells.

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The novel proteins Rng8 and Rng9 regulate the myosin-V Myo51 during fission yeast cytokinesis

The Journal of Cell Biology ◽

10.1083/jcb.201308146 ◽

2014 ◽

Vol 205 (3) ◽

pp. 357-375 ◽

Cited By ~ 30

Author(s):

Ning Wang ◽

Libera Lo Presti ◽

Yi-Hua Zhu ◽

Minhee Kang ◽

Zhengrong Wu ◽

...

Keyword(s):

Fission Yeast ◽

Molecular Motors ◽

Coiled Coil ◽

Myosin V ◽

Contractile Ring ◽

Novel Proteins ◽

Ring Assembly ◽

Actin Cables ◽

Order Complexes

The myosin-V family of molecular motors is known to be under sophisticated regulation, but our knowledge of the roles and regulation of myosin-Vs in cytokinesis is limited. Here, we report that the myosin-V Myo51 affects contractile ring assembly and stability during fission yeast cytokinesis, and is regulated by two novel coiled-coil proteins, Rng8 and Rng9. Both rng8Δ and rng9Δ cells display similar defects as myo51Δ in cytokinesis. Rng8 and Rng9 are required for Myo51’s localizations to cytoplasmic puncta, actin cables, and the contractile ring. Myo51 puncta contain multiple Myo51 molecules and walk continuously on actin filaments in rng8+ cells, whereas Myo51 forms speckles containing only one dimer and does not move efficiently on actin tracks in rng8Δ. Consistently, Myo51 transports artificial cargos efficiently in vivo, and this activity is regulated by Rng8. Purified Rng8 and Rng9 form stable higher-order complexes. Collectively, we propose that Rng8 and Rng9 form oligomers and cluster multiple Myo51 dimers to regulate Myo51 localization and functions.

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The Cooh-Terminal Domain of Myo2p, a Yeast Myosin V, Has a Direct Role in Secretory Vesicle Targeting

The Journal of Cell Biology ◽

10.1083/jcb.147.4.791 ◽

1999 ◽

Vol 147 (4) ◽

pp. 791-808 ◽

Cited By ~ 184

Author(s):

Daniel Schott ◽

Jackson Ho ◽

David Pruyne ◽

Anthony Bretscher

Keyword(s):

Secretory Vesicle ◽

Restrictive Temperature ◽

Secretory Vesicles ◽

Tail Domain ◽

Myosin V ◽

Direct Role ◽

Rab Protein ◽

Polarized Delivery ◽

Actin Cables ◽

Type V

MYO2 encodes a type V myosin heavy chain needed for the targeting of vacuoles and secretory vesicles to the growing bud of yeast. Here we describe new myo2 alleles containing conditional lethal mutations in the COOH-terminal tail domain. Within 5 min of shifting to the restrictive temperature, the polarized distribution of secretory vesicles is abolished without affecting the distribution of actin or the mutant Myo2p, showing that the tail has a direct role in vesicle targeting. We also show that the actin cable–dependent translocation of Myo2p to growth sites does not require secretory vesicle cargo. Although a fusion protein containing the Myo2p tail also concentrates at growth sites, this accumulation depends on the polarized delivery of secretory vesicles, implying that the Myo2p tail binds to secretory vesicles. Most of the new mutations alter a region of the Myo2p tail conserved with vertebrate myosin Vs but divergent from Myo4p, the myosin V involved in mRNA transport, and genetic data suggest that the tail interacts with Smy1p, a kinesin homologue, and Sec4p, a vesicle-associated Rab protein. The data support a model in which the Myo2p tail tethers secretory vesicles, and the motor transports them down polarized actin cables to the site of exocytosis.

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Characterization of TPM1 disrupted yeast cells indicates an involvement of tropomyosin in directed vesicular transport.

The Journal of Cell Biology ◽

10.1083/jcb.118.2.285 ◽

1992 ◽

Vol 118 (2) ◽

pp. 285-299 ◽

Cited By ~ 93

Author(s):

H Liu ◽

A Bretscher

Keyword(s):

Cell Surface ◽

Secretory Pathway ◽

Synthetic Lethality ◽

Vesicular Transport ◽

Yeast Cells ◽

Carboxypeptidase Y ◽

Apparent Loss ◽

Abnormal Accumulation ◽

Late Step ◽

Actin Cables

Disruption of the yeast tropomyosin gene TPM1 results in the apparent loss of actin cables from the cytoskeleton (Liu, H., and A. Bretscher. 1989. Cell. 57:233-242). Here we show that TPM1 disrupted cells grow slowly, show heterogeneity in cell size, have delocalized deposition of chitin, and mate poorly because of defects in both shmooing and cell fusion. The transit time of alpha-factor induced a-agglutinin secretion to the cell surface is longer than in isogenic wild-type strains, and some of the protein is mislocalized. Many of the TPM1-deleted cells contain abundant vesicles, similar in morphology to late secretory vesicles, but without an abnormal accumulation of intermediates in the delivery of either carboxypeptidase Y to the vacuole or invertase to the cell surface. Combinations of the TPM1 disruption with sec13 or sec18 mutations, which affect early steps in the secretory pathway, block vesicle accumulation, while combinations with sec1, sec4 or sec6 mutations, which affect a late step in the secretory pathway, have no effect on the vesicle accumulation. The phenotype of the TPM1 disrupted cells is very similar to that of a conditional mutation in the MYO2 gene, which encodes a myosin-like protein (Johnston, G. C., J. A. Prendergast, and R. A. Singer. 1991. J. Cell Biol. 113:539-551). The myo2-66 conditional mutation shows synthetic lethality with the TPM1 disruption, indicating that the MYO2 and TPM1 gene products may be involved in the same, or parallel function. We conclude that tropomyosin, and by inference actin cables, may facilitate directed vesicular transport of components to the correct location on the cell surface.

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Yeast-to-hypha transition ofSchizosaccharomyces japonicusin response to natural stimuli

10.1101/481853 ◽

2018 ◽

Author(s):

Cassandre Kinnaer ◽

Omaya Dudin ◽

Sophie G Martin

Keyword(s):

Daughter Cell ◽

Constant Width ◽

Fungal Species ◽

Distribution Center ◽

Dimorphic Fungus ◽

Unique System ◽

Natural Stress ◽

Complete Cell ◽

Actin Cables ◽

Hyphal Tip

AbstractMany fungal species are dimorphic, exhibiting both unicellular yeast-like and filamentous forms.Schizosaccharomyces japonicus, a member of the fission yeast clade, is one such dimorphic fungus. Here, we first identify fruit extracts as natural, stress-free, starvation-independent inducers of filamentation, which we use to describe the properties of the dimorphic switch. During the yeast-to-hypha transition, the cell evolves from a bipolar to a unipolar system with 10-fold accelerated polarized growth but constant width, vacuoles segregated to the non-growing half of the cell, and hyper-lengthening of the cell. We demonstrate unusual features ofS. japonicushyphae: these cells lack a Spitzenkörper, a vesicle distribution center at the hyphal tip, but display more rapid cytoskeleton-based transport than the yeast form, with actin cables being essential for the transition.S. japonicushyphae also remain mononuclear and undergo complete cell divisions, which are highly asymmetric: one daughter cell inherits the vacuole, the other the growing tip. We show these elongated cells scale their nuclear size, spindle length and elongation rates but display altered division size controls. This establishesS. japonicusas a unique system that switches between symmetric and asymmetric modes of growth and division.

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From Function to Shape: A Novel Role of a Formin in Morphogenesis of the Fungus Ashbya gossypii

Molecular Biology of the Cell ◽

10.1091/mbc.e05-06-0479 ◽

2006 ◽

Vol 17 (1) ◽

pp. 130-145 ◽

Cited By ~ 52

Author(s):

Hans-Peter Schmitz ◽

Andreas Kaufmann ◽

Michael Köhli ◽

Pierre Philippe Laissue ◽

Peter Philippsen

Keyword(s):

Giant Cells ◽

Polar Growth ◽

Ashbya Gossypii ◽

Essential Factor ◽

Wild Type ◽

Actin Cable ◽

Lateral Branches ◽

Actin Cables ◽

Two Hybrid

Morphogenesis of filamentous ascomycetes includes continuously elongating hyphae, frequently emerging lateral branches, and, under certain circumstances, symmetrically dividing hyphal tips. We identified the formin AgBni1p of the model fungus Ashbya gossypii as an essential factor in these processes. AgBni1p is an essential protein apparently lacking functional overlaps with the two additional A. gossypii formins that are nonessential. Agbni1 null mutants fail to develop hyphae and instead expand to potato-shaped giant cells, which lack actin cables and thus tip-directed transport of secretory vesicles. Consistent with the essential role in hyphal development, AgBni1p locates to tips, but not to septa. The presence of a diaphanous autoregulatory domain (DAD) indicates that the activation of AgBni1p depends on Rho-type GTPases. Deletion of this domain, which should render AgBni1p constitutively active, completely changes the branching pattern of young hyphae. New axes of polarity are no longer established subapically (lateral branching) but by symmetric divisions of hyphal tips (tip splitting). In wild-type hyphae, tip splitting is induced much later and only at much higher elongation speed. When GTP-locked Rho-type GTPases were tested, only the young hyphae with mutated AgCdc42p split at their tips, similar to the DAD deletion mutant. Two-hybrid experiments confirmed that AgBni1p interacts with GTP-bound AgCdc42p. These data suggest a pathway for transforming one axis into two new axes of polar growth, in which an increased activation of AgBni1p by a pulse of activated AgCdc42p stimulates additional actin cable formation and tip-directed vesicle transport, thus enlarging and ultimately splitting the polarity site.

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