scholarly journals The F-BAR Cdc15 promotes contractile ring formation through the direct recruitment of the formin Cdc12

2015 ◽  
Vol 208 (4) ◽  
pp. 391-399 ◽  
Author(s):  
Alaina H. Willet ◽  
Nathan A. McDonald ◽  
K. Adam Bohnert ◽  
Michelle A. Baird ◽  
John R. Allen ◽  
...  
Keyword(s):  
Schizosaccharomyces Pombe ◽  
Binding Proteins ◽  
Molecular Mechanisms ◽  
Ring Formation ◽  
Scaffolding Protein ◽  
Actin Binding ◽  
Contractile Ring ◽  
Bar Domain ◽  
Medial Cortex ◽  
N Terminus

In Schizosaccharomyces pombe, cytokinesis requires the assembly and constriction of an actomyosin-based contractile ring (CR). Nucleation of F-actin for the CR requires a single formin, Cdc12, that localizes to the cell middle at mitotic onset. Although genetic requirements for formin Cdc12 recruitment have been determined, the molecular mechanisms dictating its targeting to the medial cortex during cytokinesis are unknown. In this paper, we define a short motif within the N terminus of Cdc12 that binds directly to the F-BAR domain of the scaffolding protein Cdc15. Mutations preventing the Cdc12–Cdc15 interaction resulted in reduced Cdc12, F-actin, and actin-binding proteins at the CR, which in turn led to a delay in CR formation and sensitivity to other perturbations of CR assembly. We conclude that Cdc15 contributes to CR formation and cytokinesis via formin Cdc12 recruitment, defining a novel cytokinetic function for an F-BAR domain.

scholarly journals N-terminal modification of actin by acetylation and arginylation determines the architecture and assembly rate of linear and branched actin networks

2020 ◽  
Author(s):  
Samantha M. Chin ◽  
Tomoyuki Hatano ◽  
Lavanya Sivashanmugam ◽  
Andrejus Suchenko ◽  
Anna S. Kashina ◽  
...  
Keyword(s):  
Cell Migration ◽  
Binding Proteins ◽  
Molecular Mechanisms ◽  
Leading Edge ◽  
Actin Dynamics ◽  
Actin Binding ◽  
Actin Network ◽  
Post Translational Modification ◽  
Actin Binding Proteins ◽  
N Terminus

AbstractThe great diversity in actin network architectures and dynamics is exploited by cells to drive fundamental biological processes, including cell migration, endocytosis and cell division. While it is known that this versatility is the result of the many actin-remodeling activities of actin-binding proteins, recent work implicates post-translational modification of the actin N-terminus by either acetylation or arginylation itself as an equally important regulatory mechanism. However, the molecular mechanisms by which acetylation and arginylation alter the properties of actin are not well understood. Here, we directly compare how processing, and modification of the N-terminus of actin affects its intrinsic polymerization dynamics and its remodeling by actin-binding proteins that are essential for cell migration. We find that in comparison to acetylated actin, arginylated actin reduces intrinsic as well as formin-mediated elongation and Arp2/3-mediated nucleation. By contrast, there are no significant differences in Cofilin-mediated severing. Taken together, these results suggest that cells can employ the differently modified actins to precisely regulate actin dynamics. In addition, unprocessed, or non-acetylated actin show very different effects on formin-mediated-elongation, Arp2/3-mediated nucleation, and severing by Cofilin. Altogether, this study shows that the nature of the N-terminus of actin can induce distinct actin network dynamics, which can be differentially used by cells to locally finetune actin dynamics at distinct cellular locations, such as at the leading edge.

scholarly journals Cooperation between tropomyosin and α-actinin inhibits fimbrin association with actin filament networks in fission yeast

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Jenna R Christensen ◽  
Kaitlin E Homa ◽  
Alisha N Morganthaler ◽  
Rachel R Brown ◽  
Cristian Suarez ◽  
...  
Keyword(s):  
Fission Yeast ◽  
Cellular Networks ◽  
Residence Time ◽  
Actin Filament ◽  
Binding Proteins ◽  
Actin Binding ◽  
Contractile Ring ◽  
Actin Networks ◽  
Filament Networks ◽  
Actin Patch

We previously discovered that competition between fission yeast actin binding proteins (ABPs) for binding F-actin facilitates their sorting to different cellular networks. Specifically, competition between endocytic actin patch ABPs fimbrin Fim1 and cofilin Adf1 enhances their activities, and prevents tropomyosin Cdc8’s association with actin patches. However, these interactions do not explain how Fim1 is prevented from associating strongly with other F-actin networks such as the contractile ring. Here, we identified α-actinin Ain1, a contractile ring ABP, as another Fim1 competitor. Fim1 competes with Ain1 for association with F-actin, which is dependent upon their F-actin residence time. While Fim1 outcompetes both Ain1 and Cdc8 individually, Cdc8 enhances the F-actin bundling activity of Ain1, allowing Ain1 to generate F-actin bundles that Cdc8 can bind in the presence of Fim1. Therefore, the combination of contractile ring ABPs Ain1 and Cdc8 is capable of inhibiting Fim1’s association with F-actin networks.

scholarly journals Separate roles of IQGAP Rng2p in forming and constricting the Schizosaccharomyces pombe cytokinetic contractile ring

2013 ◽  
Vol 24 (12) ◽  
pp. 1904-1917 ◽  
Author(s):  
Irene R. Tebbs ◽  
Thomas D. Pollard
Keyword(s):  
Ring Formation ◽  
Actin Binding ◽  
Deletion Mutants ◽  
Alternative Mechanism ◽  
Adapter Proteins ◽  
Contractile Ring ◽  
Systematic Analysis ◽  
Septum Formation ◽  
Normal Ring ◽  
Ring Constriction

Eukaryotic cells require IQGAP family multidomain adapter proteins for cytokinesis, but many questions remain about how IQGAPs contribute to the process. Here we show that fission yeast IQGAP Rng2p is required for both the normal process of contractile ring formation from precursor nodes and an alternative mechanism by which rings form from strands of actin filaments. Our work adds to previous studies suggesting a role for Rng2p in node and ring formation. We demonstrate that Rng2p is also required for normal ring constriction and septum formation. Systematic analysis of domain-deletion mutants established how the four domains of Rng2p contribute to cytokinesis. Contrary to a previous report, the actin-binding calponin homology domain of Rng2p is not required for viability, ring formation, or ring constriction. The IQ motifs are not required for ring formation but are important for ring constriction and septum formation. The GTPase-activating protein (GAP)–related domain is required for node-based ring formation. The Rng2p C-terminal domain is the only domain essential for viability. Our studies identified several distinct functions of Rng2 at multiple stages of cytokinesis.

scholarly journals Diversity from similarity: cellular strategies for assigning particular identities to actin filaments and networks

Open Biology ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 200157
Author(s):  
Micaela Boiero Sanders ◽  
Adrien Antkowiak ◽  
Alphée Michelot
Keyword(s):  
Mechanical Properties ◽  
Actin Cytoskeleton ◽  
Actin Filaments ◽  
Binding Proteins ◽  
Molecular Mechanisms ◽  
Competitive Binding ◽  
Actin Binding ◽  
Actin Isoforms ◽  
Actin Networks ◽  
Covalent Modifications

The actin cytoskeleton has the particularity of being assembled into many functionally distinct filamentous networks from a common reservoir of monomeric actin. Each of these networks has its own geometrical, dynamical and mechanical properties, because they are capable of recruiting specific families of actin-binding proteins (ABPs), while excluding the others. This review discusses our current understanding of the underlying molecular mechanisms that cells have developed over the course of evolution to segregate ABPs to appropriate actin networks. Segregation of ABPs requires the ability to distinguish actin networks as different substrates for ABPs, which is regulated in three different ways: (1) by the geometrical organization of actin filaments within networks, which promotes or inhibits the accumulation of ABPs; (2) by the identity of the networks' filaments, which results from the decoration of actin filaments with additional proteins such as tropomyosin, from the use of different actin isoforms or from covalent modifications of actin; (3) by the existence of collaborative or competitive binding to actin filaments between two or multiple ABPs. This review highlights that all these effects need to be taken into account to understand the proper localization of ABPs in cells, and discusses what remains to be understood in this field of research.

scholarly journals Molecular mechanism of myosin-II assembly at the division site in Schizosaccharomyces pombe

2000 ◽  
Vol 113 (10) ◽  
pp. 1813-1825 ◽  
Author(s):  
F. Motegi ◽  
K. Nakano ◽  
I. Mabuchi
Keyword(s):  
Schizosaccharomyces Pombe ◽  
Myosin Ii ◽  
Loss Of Function ◽  
Contractile Ring ◽  
Actin Ring ◽  
Medial Region ◽  
Division Site ◽  
Medial Cortex ◽  
Actin Cables ◽  
Mutant Cells

Schizosaccharomyces pombe cells divide by virtue of the F-actin-based contractile ring (F-actin ring). Two myosin-II heavy chains, Myo2 and Myp2/Myo3, have been localized to the F-actin ring. Here, we investigated the mechanism of myosin-II assembly at the division site in S. pombe cells. First, we showed that Cdc4, an EF-hand protein, appears to be a common myosin light chain associated with both Myo2 and Myo3. Loss of function of both Myo2 and Myo3 caused a defect in F-actin assembly at the division site, like the phenotype of cdc4 null cells. It is suggested that Myo2, Myo3 and Cdc4 function in a cooperative manner in the formation of the F-actin ring during mitosis. Next, we investigated the dynamics of myosin-II during mitosis in S. pombe cells. In early mitosis when accumulation of F-actin cables in the medial region was not yet observed, Myo2 was detected primarily as dots widely located in the medial cortex. Myo2 fibers also became visible following the appearance of the dots. The Myo2 dots and fibers then fused with each other to form a medial cortical network. Some Myo2 dots appeared to be localized with F-actin cables which are also accumulated in the medial region. Finally these structures were packed into a thin contractile ring. In mutant cells that cannot form the F-actin ring such as cdc3(ts), cdc8(ts) and cdc12(ts), Myo2 was able to accumulate as dots in the medial cortex, whereas no accumulation of Myo2 dots was detected in cdc4(ts) cells. Moreover, disruption of F-actin in the cell by applying latrunculin-A did not affect the accumulation of Myo2 dots, suggesting that F-actin is not required for their accumulation. A truncated Myo2 which lacks putative Cdc4-binding sites (Myo2dIQs) was able to rescue myo2 null cells, myo3 null cells, cdc4(ts) mutant cells and cdc4 null cells. The Myo2dIQs could assemble into a normal-shaped ring in these cells. Therefore, its assembly at the division site does not require the function of either Cdc4 or Myo3.

scholarly journals Cdk1-dependent phosphoinhibition of a formin-F-BAR interaction opposes cytokinetic contractile ring formation

2018 ◽  
Vol 29 (6) ◽  
pp. 713-721 ◽  
Author(s):  
Alaina H. Willet ◽  
K. Adam Bohnert ◽  
Kathleen L. Gould
Keyword(s):  
Schizosaccharomyces Pombe ◽  
Binding Site ◽  
Chromosome Segregation ◽  
Binding Motif ◽  
Contractile Ring ◽  
General Role ◽  
Bar Domain ◽  
Mitotic Kinase ◽  
M Phase ◽  
Direct Binding

In Schizosaccharomyces pombe, cytokinesis requires the assembly and constriction of an actomyosin-based contractile ring (CR). A single essential formin, Cdc12, localizes to the cell middle upon mitotic onset and nucleates the F-actin of the CR. Cdc12 medial recruitment is mediated in part by its direct binding to the F-BAR scaffold Cdc15. Given that Cdc12 is hyperphosphorylated in M phase, we explored whether Cdc12 phosphoregulation impacts its association with Cdc15 during mitosis. We found that Cdk1, a major mitotic kinase, phosphorylates Cdc12 on six N-terminal residues near the Cdc15-binding site, and phosphorylation on these sites inhibits its interaction with the Cdc15 F-BAR domain. Consistent with this finding, a cdc12 mutant with all six Cdk1 sites changed to phosphomimetic residues (cdc12-6D) displays phenotypes similar to cdc12-P31A, in which the Cdc15-binding motif is disrupted; both show reduced Cdc12 at the CR and delayed CR formation. Together, these results indicate that Cdk1 phosphorylation of formin Cdc12 antagonizes its interaction with Cdc15 and thereby opposes Cdc12’s CR localization. These results are consistent with a general role for Cdk1 in inhibiting cytokinesis until chromosome segregation is complete.

Identification and characterisation of Xenopus moesin, a Src substrate in Xenopus laevis oocytes

Zygote ◽  
1999 ◽  
Vol 7 (2) ◽  
pp. 113-122 ◽  
Author(s):  
Judith M. Thorn ◽  
Norris A. Armstrong ◽  
Leigh A. Cantrell ◽  
Brian K. Kay
Keyword(s):  
Xenopus Laevis ◽  
Tyrosine Kinase ◽  
Actin Filaments ◽  
Binding Proteins ◽  
Molecular Mechanisms ◽  
Actin Binding ◽  
Xenopus Laevis Oocytes ◽  
Cortical Actin ◽  
Actin Binding Proteins ◽  
Src Tyrosine Kinase

The cortical actin cytoskeleton, consisting of actin filaments and actin binding proteins, immediately underlies the inner surface of the plasma membrane and is important both structurally and in relaying signals from the surface to the interior of the cell. Signal transduction processes, initiated in the cortex, modulate numerous cellular changes ranging from modifications of the local cytoskeleton structure, the position in the cell cycle, to cell behaviour. To examine the molecular mechanisms and events associated with cortical changes. We have investigated targets of the protein tyrosine kinase, Src, which is associated with the cortical cytoskeleton, in Xenopus laevis oocytes. When a mRNA encoding an activated form of Src tyrosine kinase (d-Src) is injected into oocytes several changes are observed: proteins are phosphorylated, the rate at which progesterone matures an oocyte to an egg is accelerated, and the cortex at the site of injection appears to contract. Previous studies have implicated actin filaments in the Src-stimulated cortical rearrangements. In this study we identify two actin binding proteins – cortactin and moesin – as Src substrates in Xenopus oocytes that are Src substrates. We cloned and characterised the cDNA encoding one of those, Xenopus moesin, a member of the ezrin/radixin/moesin (ERM) family of actin binding proteins. In addition, we have determined that moesin is recruited to the cortex at the site of Src mRNA injection.

scholarly journals Regulation of contractile ring formation and septation in Schizosaccharomyces pombe

2015 ◽  
Vol 28 ◽  
pp. 46-52 ◽  
Author(s):  
Alaina H Willet ◽  
Nathan A McDonald ◽  
Kathleen L Gould
Keyword(s):  
Schizosaccharomyces Pombe ◽  
Ring Formation ◽  
Contractile Ring

High resolution spot scan imaging of frozen, hydrated actin bundles with 400kV electrons

1992 ◽  
Vol 50 (1) ◽  
pp. 512-513
Author(s):  
J. Jakana ◽  
M.F. Schmid ◽  
P. Matsudaira ◽  
W. Chiu
Keyword(s):  
High Resolution ◽  
Binding Proteins ◽  
Actin Binding ◽  
Eukaryotic Cells ◽  
Dimensional Structure ◽  
Structural Basis ◽  
Actin Bundle ◽  
Actin Bundles ◽  
3 Dimensional ◽  
Macromolecular Assembly

Actin is a protein found in all eukaryotic cells. In its polymerized form, the cells use it for motility, cytokinesis and for cytoskeletal support. An example of this latter class is the actin bundle in the acrosomal process from the Limulus sperm. The different functions actin performs seem to arise from its interaction with the actin binding proteins. A 3-dimensional structure of this macromolecular assembly is essential to provide a structural basis for understanding this interaction in relationship to its development and functions.

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