Faculty Opinions recommendation of Rapid glucose depletion immobilizes active myosin V on stabilized actin cables.

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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Fission yeast tropomyosin specifies directed transport of myosin-V along actin cables

Molecular Biology of the Cell ◽

10.1091/mbc.e13-04-0200 ◽

2014 ◽

Vol 25 (1) ◽

pp. 66-75 ◽

Cited By ~ 35

Author(s):

Joseph E. Clayton ◽

Luther W. Pollard ◽

Maria Sckolnick ◽

Carol S. Bookwalter ◽

Alex R. Hodges ◽

...

Keyword(s):

Fission Yeast ◽

Actin Filaments ◽

Total Internal Reflection ◽

Single Molecules ◽

Myosin V ◽

Class V ◽

Physiological Relevance ◽

Actin Cables

A hallmark of class-V myosins is their processivity—the ability to take multiple steps along actin filaments without dissociating. Our previous work suggested, however, that the fission yeast myosin-V (Myo52p) is a nonprocessive motor whose activity is enhanced by tropomyosin (Cdc8p). Here we investigate the molecular mechanism and physiological relevance of tropomyosin-mediated regulation of Myo52p transport, using a combination of in vitro and in vivo approaches. Single molecules of Myo52p, visualized by total internal reflection fluorescence microscopy, moved processively only when Cdc8p was present on actin filaments. Small ensembles of Myo52p bound to a quantum dot, mimicking the number of motors bound to physiological cargo, also required Cdc8p for continuous motion. Although a truncated form of Myo52p that lacked a cargo-binding domain failed to support function in vivo, it still underwent actin-dependent movement to polarized growth sites. This result suggests that truncated Myo52p lacking cargo, or single molecules of wild-type Myo52p with small cargoes, can undergo processive movement along actin-Cdc8p cables in vivo. Our findings outline a mechanism by which tropomyosin facilitates sorting of transport to specific actin tracks within the cell by switching on myosin processivity.

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Capping protein insulates Arp2/3-assembled actin patches from formins

10.1101/647198 ◽

2019 ◽

Author(s):

Ingrid Billault-Chaumartin ◽

Sophie G. Martin

Keyword(s):

Cell Wall ◽

Sexual Reproduction ◽

Yeast Cells ◽

Self Organization ◽

Myosin V ◽

Capping Protein ◽

Dual Identity ◽

Fusion Defect ◽

Low Levels ◽

Actin Cables

AbstractHow actin structures of distinct identities and functions co-exist within the same environment is a critical self-organization question. Fission yeast cells have a simple actin cytoskeleton made of four structures: Arp2/3 assembles actin patches around endocytic pits; the formins For3, Cdc12 and Fus1 assemble actin cables, the cytokinetic ring during division, and the fusion focus during sexual reproduction, respectively. The focus concentrates the delivery of hydrolases by myosin V to digest the cell wall for cell fusion. We discovered that cells lacking capping protein (CP), a heterodimer that blocks barbed-end dynamics and associates with actin patches, exhibit a delay in fusion. Consistent with CP-formin competition for barbed-end binding, Fus1, F-actin and the linear filament marker tropomyosin hyper-accumulate at the fusion focus in absence of CP. However, myosin V and exocytic cargoes are diverted to ectopic foci and reduced at the fusion focus, which underlies the fusion defect. Remarkably, ectopic foci coincide with actin patches, which now contain low levels of Fus1. During mitotic growth, actin patches lacking CP similarly display a dual identity, as they accumulate the formins For3 and Cdc12 and are co-decorated by tropomyosin and the patch marker fimbrin. Thus, CP serves to protect Arp2/3-nucleated structures from formin activity.

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Microtubule-independent movement of the fission yeast nucleus

10.1101/2020.08.29.273409 ◽

2020 ◽

Author(s):

Sanju Ashraf ◽

David A. Kelly ◽

Kenneth E. Sawin

Keyword(s):

Fission Yeast ◽

Actin Polymerization ◽

Nuclear Movement ◽

Myosin V ◽

Nuclear Positioning ◽

Membrane Contact Sites ◽

Growing Cell ◽

Pulling Forces ◽

Associated Proteins ◽

Actin Cables

ABSTRACTMovement of the cell nucleus typically involves the cytoskeleton and either polymerization-based pushing forces or motor-based pulling forces. In fission yeast Schizosaccharomyces pombe, nuclear movement and positioning are thought to depend on microtubule polymerization-based pushing forces. Here we describe a novel, microtubule-independent, form of nuclear movement in fission yeast. Microtubule-independent nuclear movement is directed towards growing cell tips, and it is strongest when the nucleus is close to a growing cell tip, and weakest when the nucleus is far from that tip. Microtubule-independent nuclear movement requires actin cables but does not depend on actin polymerization-based pushing or myosin V-based pulling forces. Vesicle-associated membrane protein (VAMP)-associated proteins (VAPs) Scs2 and Scs22, which are critical for endoplasmic reticulum-plasma membrane contact sites in fission yeast, are also required for microtubule-independent nuclear movement. We also find that in cells in which microtubule-based pushing forces are present, disruption of actin cables leads to increased fluctuations in interphase nuclear positioning and subsequent altered septation. Our results suggest two non-exclusive mechanisms for microtubule-independent nuclear movement, which may help illuminate aspects of nuclear positioning in other cells.

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A Type V Myosin (Myo2p) and a Rab-like G-Protein (Ypt11p) Are Required for Retention of Newly Inherited Mitochondria in Yeast Cells during Cell Division

Molecular Biology of the Cell ◽

10.1091/mbc.e04-01-0053 ◽

2004 ◽

Vol 15 (9) ◽

pp. 3994-4002 ◽

Cited By ~ 87

Author(s):

Istvan R. Boldogh ◽

Sharmilee L. Ramcharan ◽

Hyeong-Cheol Yang ◽

Liza A. Pon

Keyword(s):

Yeast Cells ◽

Mitochondrial Morphology ◽

Temperature Sensitive ◽

Myosin V ◽

Binding Partner ◽

Mitochondrial Movement ◽

Mitochondrial Motility ◽

Mother Cells ◽

Actin Cables ◽

Type V

Two actin-dependent force generators contribute to mitochondrial inheritance: Arp2/3 complex and the myosin V Myo2p (together with its Rab-like binding partner Ypt11p). We found that deletion of YPT11, reduction of the length of the Myo2p lever arm (myo2-Δ6IQ), or deletion of MYO4 (the other yeast myosin V), had no effect on mitochondrial morphology, colocalization of mitochondria with actin cables, or the velocity of bud-directed mitochondrial movement. In contrast, retention of mitochondria in the bud was compromised in YPT11 and MYO2 mutants. Retention of mitochondria in the bud tip of wild-type cells results in a 60% decrease in mitochondrial movement in buds compared with mother cells. In ypt11Δ mutants, however, the level of mitochondrial motility in buds was similar to that observed in mother cells. Moreover, the myo2-66 mutant, which carries a temperature-sensitive mutation in the Myo2p motor domain, exhibited a 55% decrease in accumulation of mitochondria in the bud tip, and an increase in accumulation of mitochondria at the retention site in the mother cell after shift to restrictive temperatures. Finally, destabilization of actin cables and the resulting delocalization of Myo2p from the bud tip had no significant effect on the accumulation of mitochondria in the bud tip.

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Microtubule-independent movement of the fission yeast nucleus

Journal of Cell Science ◽

10.1242/jcs.253021 ◽

2021 ◽

pp. jcs.253021

Author(s):

Sanju Ashraf ◽

Ye Dee Tay ◽

David A. Kelly ◽

Kenneth E. Sawin

Keyword(s):

Fission Yeast ◽

Actin Polymerization ◽

Nuclear Movement ◽

Myosin V ◽

Nuclear Positioning ◽

Membrane Contact Sites ◽

Growing Cell ◽

Pulling Forces ◽

Associated Proteins ◽

Actin Cables

Movement of the cell nucleus typically involves the cytoskeleton and either polymerization-based pushing forces or motor-based pulling forces. In fission yeast Schizosaccharomyces pombe, nuclear movement and positioning are thought to depend on microtubule polymerization-based pushing forces. Here we describe a novel, microtubule-independent, form of nuclear movement in fission yeast. Microtubule-independent nuclear movement is directed towards growing cell tips, and it is strongest when the nucleus is close to a growing cell tip, and weakest when the nucleus is far from that tip. Microtubule-independent nuclear movement requires actin cables but does not depend on actin polymerization-based pushing or myosin V-based pulling forces. Vesicle-associated membrane protein (VAMP)-associated proteins (VAPs) Scs2 and Scs22, which are critical for endoplasmic reticulum-plasma membrane contact sites in fission yeast, are also required for microtubule-independent nuclear movement. We also find that in cells in which microtubule-based pushing forces are present, disruption of actin cables leads to increased fluctuations in interphase nuclear positioning and subsequent altered septation. Our results suggest two non-exclusive mechanisms for microtubule-independent nuclear movement, which may help illuminate aspects of nuclear positioning in other cells.

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Nonmedially assembled F-actin cables incorporate into the actomyosin ring in fission yeast

The Journal of Cell Biology ◽

10.1083/jcb.201209044 ◽

2012 ◽

Vol 199 (5) ◽

pp. 831-847 ◽

Cited By ~ 71

Author(s):

Junqi Huang ◽

Yinyi Huang ◽

Haochen Yu ◽

Dhivya Subramanian ◽

Anup Padmanabhan ◽

...

Keyword(s):

De Novo ◽

Actin Dynamics ◽

Actin Assembly ◽

Animal Cells ◽

Myosin V ◽

Contractile Ring ◽

Division Site ◽

Ring Assembly ◽

Actin Cables

In many eukaryotes, cytokinesis requires the assembly and constriction of an actomyosin-based contractile ring. Despite the central role of this ring in cytokinesis, the mechanism of F-actin assembly and accumulation in the ring is not fully understood. In this paper, we investigate the mechanism of F-actin assembly during cytokinesis in Schizosaccharomyces pombe using lifeact as a probe to monitor actin dynamics. Previous work has shown that F-actin in the actomyosin ring is assembled de novo at the division site. Surprisingly, we find that a significant fraction of F-actin in the ring was recruited from formin-Cdc12p nucleated long actin cables that were generated at multiple nonmedial locations and incorporated into the ring by a combination of myosin II and myosin V activities. Our results, together with findings in animal cells, suggest that de novo F-actin assembly at the division site and directed transport of F-actin cables assembled elsewhere can contribute to ring assembly.

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