GO:0000915 actomyosin contractile ring assembly: Mechanism, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0000915 actomyosin contractile ring assembly describes the process that builds the actin-myosin ring responsible for cytokinesis.
• The ring is assembled from actin filaments, myosin II motors, and associated proteins such as anillin/Mid1 and septins.
• Rho GTPase signaling and formin-mediated actin nucleation are central to ring assembly and constriction.
• Temporal control by Plo1 kinase regulates myosin II recruitment to the division site.
• Cortical endoplasmic reticulum remodeling and IQGAP orthologues contribute to efficient ring assembly and closure.
• Defects in contractile ring assembly are linked to cytokinesis failure, which can drive aneuploidy and cancer.
Description
Actomyosin contractile ring assembly (GO:0000915) is the biological process that builds a ring of actin filaments, myosin II motors, and associated proteins at the cell equator to execute cytokinesis. This ring generates the force that constricts the plasma membrane and physically separates daughter cells, making it essential for genome stability and cell proliferation. Researchers study this process to understand fundamental cell division mechanisms and to identify therapeutic targets in diseases characterized by aberrant cytokinesis. The assembly is highly regulated in space and time, involving Rho GTPase signaling, formin-mediated actin nucleation, and myosin II recruitment. Recent work has also revealed contributions from cortical endoplasmic reticulum remodeling and septin assembly. Because cytokinesis failure can lead to aneuploidy and tumorigenesis, the molecular players of actomyosin ring assembly are of significant interest in cancer biology and regenerative medicine.
actomyosin contractile ring assembly At A Glance
| GO ID | GO:0000915 |
|---|---|
| GO term | actomyosin contractile ring assembly |
| Ontology | biological_process |
| Synonym | constriction ring assembly; contractile ring assembly; cytokinesis, actomyosin contractile ring assembly; cytokinesis, actomyosin contractile ring formation; cytokinesis, actomyosin ring biosynthesis; cytokinesis, actomyosin ring formation; cytokinesis, contractile ring assembly; myosin filament organization involved in cytokinetic actomyosin contractile ring assembly; myosin filament organization of constriction ring assembly; myosin filament organization of contractile ring assembly |
| Major function | Assembly of a ring composed of actin, myosin, and associated proteins that will function in cytokinesis |
| Related cellular component | Actomyosin contractile ring |
| Related molecular functions | Actin binding, myosin motor activity, GTPase activity |
| Key regulators | Rho GTPase, formins, Plo1 kinase, anillin/Mid1, septins |
What Is GO:0000915?
According to the Gene Ontology, GO:0000915 actomyosin contractile ring assembly is defined as the process of assembly of a ring composed of actin, myosin, and associated proteins that will function in cytokinesis. In other words, it encompasses all molecular events that build the contractile ring at the division site, from initial recruitment of components to the formation of a functional ring capable of constriction.
Why Is actomyosin contractile ring assembly Important in Cell Biology?
Actomyosin contractile ring assembly is fundamental to cytokinesis, the final step of cell division that ensures faithful segregation of genetic material. Defects in this process lead to cytokinesis failure, resulting in binucleated cells, aneuploidy, and genomic instability, which are hallmarks of cancer and developmental disorders. Understanding the molecular mechanisms of ring assembly provides insights into cell cycle regulation and offers potential targets for anticancer therapies. Moreover, the process is conserved from yeast to humans, making model organisms valuable for dissecting its components.
• Essential for cytokinesis and genome stability.
• Dysregulation leads to aneuploidy and cancer.
• Conserved mechanism from yeast to humans.
• Involves Rho GTPase signaling, a key drug target.
• Requires precise temporal control by kinases like Plo1.
• Cortical ER remodeling supports efficient ring assembly.
• Septins and IQGAP proteins contribute to ring closure.
• Provides targets for antiproliferative therapies.
• Model organisms (fission yeast, Aspergillus) enable genetic screens.
• Links to cell repair mechanisms beyond cytokinesis.
What Happens During actomyosin contractile ring assembly?
Initiation and Rho GTPase Signaling
In simple terms: The cell decides where to build the ring by activating a molecular switch called Rho.
Assembly begins with the activation of the small GTPase Rho1 at the future division site. Rho1 controls the assembly of anillo-septin structures that facilitate contractile ring closure during cytokinesis. This signaling cascade recruits downstream effectors including formins and kinases that nucleate actin filaments and organize the ring.
Actin Nucleation by Formins
In simple terms: Formin proteins create long actin cables that form the ring's skeleton.
Formins are actin nucleators that generate unbranched actin filaments. Mechanoregulated inhibition of formin activity is critical for proper contractile actomyosin ring assembly, ensuring that filament elongation is coordinated with ring constriction. This regulation prevents premature or excessive actin polymerization that could disrupt ring architecture.
Myosin II Recruitment and Temporal Control
In simple terms: Myosin motors are brought in at the right time to generate contraction force.
Myosin II recruitment to the division site is temporally controlled by the Polo-like kinase Plo1, which regulates the Mid1/anillin complex. This ensures that myosin arrives after the actin scaffold is established, allowing for coordinated ring assembly and subsequent constriction. Disruption of this timing leads to defective rings.
Cortical ER Remodeling and Membrane Trafficking
In simple terms: Internal membranes are reorganized to supply materials for ring assembly.
Coordinated cortical endoplasmic reticulum (ER) remodeling facilitates actomyosin ring assembly by providing membrane and possibly lipids required for ring anchoring and constriction. This ER reorganization is an active process that couples membrane dynamics with cytoskeletal assembly.
Septin and IQGAP Contributions to Ring Closure
In simple terms: Additional proteins help the ring pinch off the cell.
Septins and IQGAP family proteins are recruited to the division site and are required for efficient constriction of the contractile actomyosin ring. In Aspergillus nidulans, the IQGAP orthologue SepG is essential for ring constriction, highlighting conserved roles for these proteins in ring closure.
Key Genes Involved in GO:0000915 actomyosin contractile ring assembly
The following genes and proteins are key players in actomyosin contractile ring assembly, as supported by published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| Rho1 | GTPase controlling anillo-septin assembly and ring closure | Central regulator; target for chemical inhibition |
| Plo1 | Kinase regulating myosin II recruitment via Mid1/anillin | Temporal control of ring assembly |
| Mid1/anillin | Scaffold protein recruiting myosin II | Essential for ring assembly; regulated by Plo1 |
| Formin (e.g., Cdc12) | Actin nucleation and filament elongation | Mechanoregulated inhibition ensures proper assembly |
| Myosin II (Myo2) | Motor protein generating contractile force | Force generation and ring constriction |
| Actin (Act1) | Structural component of the ring | Filament network for myosin binding |
| SepG (IQGAP orthologue) | Required for constriction of contractile actomyosin ring | Conserved role in ring closure |
| Septins | Filament-forming proteins at division site | Facilitate ring closure and stability |
| Cortical ER proteins | ER remodeling for ring assembly | Membrane-cytoskeleton coupling |
| Rho GTPase effectors | Downstream signaling for actin assembly | Potential drug targets |
| Anillin | Scaffold linking actin and myosin | Regulated by Plo1 |
| Polo-like kinase | Cell cycle kinase controlling ring timing | Conserved regulator |
| IQGAP | Scaffold protein for ring constriction | Model for fungal cytokinesis |
| Formin homology proteins | Actin nucleation | Mechanosensitive regulation |
| Myosin regulatory light chain | Regulates myosin II activity | Phosphorylation-dependent control |
| Actin depolymerizing factor | Turnover of actin filaments | Ring dynamics |
| Profilin | Actin monomer binding | Supports actin polymerization |
| Cofilin | Actin severing | Facilitates ring remodeling |
How Is actomyosin contractile ring assembly Regulated?
Actomyosin contractile ring assembly is regulated by multiple mechanisms. The Rho1 GTPase acts as a master switch, controlling anillo-septin assembly and downstream actin polymerization. Formin activity is mechanoregulated, meaning that tension or mechanical forces inhibit formin to prevent excessive actin assembly. Temporal control is exerted by the Polo-like kinase Plo1, which regulates the recruitment of myosin II through the Mid1/anillin complex. Additionally, cortical ER remodeling contributes to the spatial organization of the ring. These regulatory layers ensure that ring assembly occurs at the correct time and place, and that it is coordinated with other cell cycle events.
actomyosin contractile ring assembly and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| Rho1 | Cancer, cytokinesis failure | Knockout in cancer cell lines |
| Plo1 | Aneuploidy, developmental defects | Point mutation in fission yeast |
| Mid1/anillin | Cytokinesis defects | Knockout in HeLa cells |
| SepG (IQGAP) | Fungal pathogenesis | Knockout in Aspergillus nidulans |
| Formin | Cancer, cell division defects | Overexpression in mammalian cells |
Cancer and Aneuploidy
Failure of actomyosin contractile ring assembly leads to cytokinesis failure, resulting in binucleated cells and aneuploidy, which are hallmarks of cancer. Many cancer cells exhibit defective cytokinesis, and targeting the molecular components of ring assembly is a potential therapeutic strategy.
Developmental Disorders
Proper cytokinesis is essential during development. Mutations in genes involved in contractile ring assembly can cause developmental defects due to impaired cell division. Model organisms such as fission yeast have been instrumental in identifying these genes.
Fungal Pathogenesis
In pathogenic fungi like Aspergillus nidulans, the IQGAP orthologue SepG is required for constriction of the contractile actomyosin ring, making it a potential antifungal target. Understanding ring assembly in fungi can inform new treatments for fungal infections.
From actomyosin contractile ring assembly-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does gene X regulate ring assembly? | Knockout cell line (e.g., CRISPR KO) |
| How does point mutation affect ring constriction? | Point mutation knock-in |
| Where does protein localize during assembly? | Tagged knock-in (e.g., GFP) |
| Does overexpression cause defects? | Overexpression cell line |
| What is the temporal dynamics of assembly? | Live-cell imaging with tagged proteins |
| Which genes are essential for ring assembly? | CRISPR library screening |
How to Study the actomyosin contractile ring assembly Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Live-cell imaging | Dynamics of ring assembly and constriction | Visualizing GFP-tagged proteins |
| CRISPR knockout | Loss-of-function phenotype | Identifying essential genes |
| RNAi knockdown | Gene silencing effects | Transient depletion studies |
| Proteomics | Protein interactions and composition | Defining ring components |
| In vitro actin assays | Actin polymerization kinetics | Testing formin regulation |
| FRAP | Protein turnover in the ring | Measuring exchange rates |
| High-content screening | Phenotypic changes in cell division | Drug discovery |
Live-Cell Imaging
Live-cell fluorescence microscopy of tagged actin, myosin, and regulatory proteins allows real-time visualization of contractile ring assembly dynamics. This method reveals the order of recruitment and the kinetics of constriction.
Genetic Screens
Forward and reverse genetic screens in model organisms such as fission yeast and Aspergillus nidulans have identified key genes required for ring assembly. These screens can be combined with CRISPR libraries for high-throughput discovery.
Proteomics and Interactomics
Affinity purification coupled with mass spectrometry can identify protein-protein interactions within the contractile ring. This helps define the molecular architecture and regulatory networks.
Biochemical Assays
In vitro actin polymerization assays and myosin motor activity assays reconstitute aspects of ring assembly. These assays test the direct effects of regulatory proteins on actin and myosin.
How CRISPR Can Be Used to Study GO:0000915 actomyosin contractile ring assembly
Knockout
CRISPR knockout of genes such as Rho1, Plo1, or Mid1/anillin can reveal their essential roles in actomyosin contractile ring assembly. Knockout cell lines often exhibit cytokinesis failure, providing a platform to study the process.
Point Mutation
Introducing point mutations in genes like Plo1 or formins allows researchers to dissect specific domains or phosphorylation sites required for ring assembly. This approach can separate actin nucleation from regulatory functions.
Knock-in
Knock-in of fluorescent tags (e.g., GFP) into endogenous loci enables real-time tracking of protein localization during ring assembly. This is crucial for understanding spatiotemporal dynamics.
Overexpression
Overexpression of formins or myosin II can cause aberrant ring assembly, helping to identify dosage-sensitive components. This approach can also rescue knockout phenotypes.
How EDITGENE Supports actomyosin contractile ring assembly Research
Researchers studying actomyosin contractile ring assembly-related genes often need to determine whether a candidate gene is causally involved in the process or merely correlated with it. EDITGENE provides a comprehensive suite of CRISPR-based services to enable such functional studies.
Contact EDITGENE today to design your custom CRISPR model for actomyosin contractile ring assembly research.
Frequently Asked Questions About actomyosin contractile ring assembly
What is actomyosin contractile ring assembly?
It is the biological process (GO:0000915) of building a ring of actin, myosin, and associated proteins that functions in cytokinesis.
What genes are involved in actomyosin contractile ring assembly?
Key genes include Rho1, Plo1, Mid1/anillin, formins, myosin II, actin, septins, and IQGAP proteins.
How is the contractile ring assembled?
Assembly involves Rho GTPase signaling, formin-mediated actin nucleation, myosin II recruitment, and septin assembly.
What is the role of Rho1 in contractile ring assembly?
Rho1 controls anillo-septin assembly to facilitate contractile ring closure during cytokinesis.
How does Plo1 regulate ring assembly?
Plo1 kinase temporally controls myosin II recruitment by regulating the Mid1/anillin complex.
What happens if contractile ring assembly fails?
Failure leads to cytokinesis defects, aneuploidy, and potentially cancer.
Which model organisms are used to study contractile ring assembly?
Fission yeast (Schizosaccharomyces pombe) and Aspergillus nidulans are common models.
What methods are used to study actomyosin contractile ring assembly?
Live-cell imaging, genetic screens, proteomics, and in vitro actin assays are widely used.
How can CRISPR help study contractile ring assembly?
CRISPR knockout, point mutation, knock-in, and overexpression models allow functional dissection of genes involved.
What diseases are linked to defective contractile ring assembly?
Cancer, developmental disorders, and fungal infections are associated with defects in this process.
Conclusion
Actomyosin contractile ring assembly (GO:0000915) is a highly regulated process essential for cytokinesis and genome stability. Its molecular components, including Rho GTPase, formins, Plo1, and myosin II, are conserved and have been extensively studied in model organisms. Defects in this process contribute to aneuploidy and cancer, making it a compelling area for therapeutic intervention. Continued research using advanced CRISPR models and imaging techniques will further elucidate the mechanisms and identify new targets.
References
- 1. Zhang D et al.. 2022. Coordinated cortical ER remodeling facilitates actomyosin ring assembly.. Curr Biol 32(12):2694-2703.e4 PMID: 35609605
- 2. Dekraker C et al.. 2018. Regulation and Assembly of Actomyosin Contractile Rings in Cytokinesis and Cell Repair.. Anat Rec (Hoboken) 301(12):2051-2066 PMID: 30312008
- 3. Zimmermann D et al.. 2017. Mechanoregulated inhibition of formin facilitates contractile actomyosin ring assembly.. Nat Commun 8(1):703 PMID: 28951543
- 4. Carim SC et al.. 2023. The Rho1 GTPase controls anillo-septin assembly to facilitate contractile ring closure during cytokinesis.. iScience 26(6):106903 PMID: 37378349
- 5. Almonacid M et al.. 2011. Temporal control of contractile ring assembly by Plo1 regulation of myosin II recruitment by Mid1/anillin.. Curr Biol 21(6):473-9 PMID: 21376600
- 7. Hill TW et al.. 2020. The Aspergillus nidulans IQGAP orthologue SepG is required for constriction of the contractile actomyosin ring.. Fungal Genet Biol 144:103439 PMID: 32768603
- 8. Laporte D et al.. 2010. Mechanisms of contractile-ring assembly in fission yeast and beyond.. Semin Cell Dev Biol 21(9):892-8 PMID: 20708088
