GO:0005826 actomyosin contractile ring: Components, Assembly and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0005826 actomyosin contractile ring is a cytoskeletal structure of actin filaments and myosin that assembles beneath the plasma membrane in the cell division plane.
• The ring constricts to drive cytokinesis in animal cells and many fungi, and its position is set perpendicular to the mitotic spindle axis.
• In budding yeast, the contractile ring forms at the mother-bud neck before mitosis, while in fission yeast it is associated with septation.
• Ring dynamics depend on actin and myosin turnover; myosin turnover controls contractile instability and ring stability.
• Ultrastructural analysis shows dynamic reorganization of actomyosin filaments within the contractile ring during constriction.
• Some organisms, such as protozoan parasites, can divide without a canonical contractile actomyosin ring, highlighting diversity in cytokinesis mechanisms.
Description
The actomyosin contractile ring (GO:0005826) is a transient cytoskeletal machine that assembles at the cell division plane and constricts to physically separate daughter cells during cytokinesis. It is composed primarily of actin filaments and myosin motors, and its position is determined by the mitotic spindle such that it forms perpendicular to the spindle axis. This structure is conserved across many eukaryotes, including animal cells and fungi, although variations exist in organisms that lack a canonical ring. Understanding the contractile ring is central to cell biology because it is the final mechanical step of cell division, and its failure leads to binucleation or aneuploidy. The ring also serves as a model for studying actomyosin network assembly, force generation, and mechanochemical regulation. In budding yeast, the ring forms at the mother-bud neck before mitosis, providing a genetically tractable system to dissect its assembly and constriction. In animal cells, the ring is located at the cleavage furrow and is tightly coupled to adhesion and membrane remodeling. Recent ultrastructural work has revealed the dynamic organization of actomyosin filaments within the ring, offering nanoscale insight into its architecture. Because the contractile ring is essential for proliferation, its components are potential targets in cancer and infectious disease research.
actomyosin contractile ring At A Glance
| GO ID | GO:0005826 |
|---|---|
| GO term | actomyosin contractile ring |
| Ontology | cellular_component |
| Synonym | actomyosin ring; CAR; constriction ring; contractile actomyosin ring; cytokinetic ring |
| Major function | Force generation for cytokinesis and cell division plane constriction |
| Location | Beneath the plasma membrane at the cleavage furrow in animal cells; at the mother-bud neck in budding yeast |
| Composition | Actin filaments and myosin motors, with associated regulatory proteins |
| Conservation | Present in many eukaryotes including animal cells and fungi; some protozoan parasites divide without a canonical ring |
What Is GO:0005826?
The actomyosin contractile ring is a cytoskeletal structure made of actin filaments and myosin that forms beneath the plasma membrane in a plane perpendicular to the spindle axis, marking the cell division plane. In animal cells, it is located at the cleavage furrow; in budding fungal cells such as mitotic S. cerevisiae, it forms at the mother-bud neck before mitosis. It is also known as the actomyosin ring, CAR, constriction ring, contractile actomyosin ring, or cytokinetic ring.
Why Is actomyosin contractile ring Important in Cell Biology?
The actomyosin contractile ring is essential for cytokinesis, the final step of cell division, and its proper assembly and constriction ensure faithful chromosome segregation and cell proliferation. Defects in ring formation or regulation can lead to failed cytokinesis, resulting in binucleated or aneuploid cells, which are hallmarks of cancer and developmental disorders. Because the ring is a dynamic actomyosin network, it also serves as a paradigm for understanding mechanochemical self-organization and force generation in cells. In budding and fission yeast, the ring is a genetically tractable model for dissecting the molecular machinery of cytokinesis. Moreover, some pathogens, such as protozoan parasites, have evolved alternative division strategies that bypass the canonical ring, making it a target for understanding divergent cell division. Research on the contractile ring thus spans cell biology, biophysics, and disease mechanisms.
• Drives cytokinesis and physical separation of daughter cells in animal cells and fungi.
• Its position is determined by the mitotic spindle, ensuring accurate division plane specification.
• Myosin turnover within the ring controls contractile instability and ring stability.
• Ultrastructural dynamics of actomyosin filaments are critical for constriction.
• In budding yeast, the ring forms at the mother-bud neck before mitosis, linking polarity and division.
• Fission yeast septation requires the contractile actomyosin ring for cell separation.
• Some protozoan parasites divide without a canonical contractile actomyosin ring, highlighting alternative mechanisms.
• The ring interfaces with adherens junctions and contractile actomyosin during entotic cell-in-cell formation.
• Defects in ring function are associated with failed cytokinesis and aneuploidy, relevant to cancer.
• The ring is a model system for studying actomyosin network assembly and mechanochemistry.
Core Biology of the actomyosin contractile ring
Assembly and Positioning
In simple terms: The ring is built at the right place and time to divide the cell.
The actomyosin contractile ring assembles beneath the plasma membrane in a plane perpendicular to the spindle axis, which defines the cell division plane. In animal cells, the ring forms at the cleavage furrow, while in budding yeast it assembles at the mother-bud neck before mitosis. Positioning is tightly coupled to the mitotic spindle and cell polarity cues, ensuring that division occurs at the correct location. The ring is composed of actin filaments and myosin motors, which are recruited to the division site.
Constriction and Force Generation
In simple terms: The ring squeezes the cell like a drawstring to pinch it in two.
Once assembled, the contractile ring constricts through the sliding of actin filaments by myosin motors, generating force that invaginates the plasma membrane. This constriction is dynamic and requires continuous actin and myosin turnover. Myosin turnover controls actomyosin contractile instability, and perturbations in turnover can lead to ring instability. Ultrastructural analysis has revealed the dynamic reorganization of actomyosin filaments during constriction.
Structure and Composition
In simple terms: The ring is made of actin cables and myosin motors that work together.
The contractile ring is a cytoskeletal structure composed of actin filaments and myosin. In addition to actin and myosin, the ring contains associated proteins that regulate filament assembly, crosslinking, and motor activity. The ring is located beneath the plasma membrane and is linked to the membrane during constriction. In budding yeast, the ring forms at the mother-bud neck and is composed of actomyosin filaments.
Molecular Regulation
In simple terms: Many proteins control when and how the ring contracts.
The assembly and constriction of the contractile ring are regulated by signaling pathways that control actin polymerization and myosin activity. Myosin turnover is a key determinant of contractile instability and ring stability. The physical stability of the contractile actomyosin ring has been modeled, highlighting the interplay between motor activity and filament dynamics. In fission yeast, septation is coordinated with the contractile actomyosin ring to ensure proper cell separation.
Diversity and Alternative Division Modes
In simple terms: Not all cells use a contractile ring to divide.
While the actomyosin contractile ring is conserved in many eukaryotes, some protozoan parasites divide without a canonical contractile actomyosin ring, using alternative mechanisms. This diversity highlights the evolutionary plasticity of cytokinesis. In animal cells, the ring interfaces with adherens junctions and contractile actomyosin during entotic cell-in-cell formation, a process distinct from cytokinesis.
Key Genes Involved in GO:0005826 actomyosin contractile ring
The following genes and proteins are core components or regulators of the actomyosin contractile ring, based on published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| ACTB | Actin filament subunit | Core structural component of the contractile ring |
| MYH9 | Non-muscle myosin heavy chain | Motor protein driving ring constriction |
| MYL6 | Myosin light chain | Regulates myosin activity in the ring |
| RhoA | Small GTPase | Regulates actomyosin assembly and contractility |
| ROCK1 | Rho kinase | Phosphorylates myosin light chain to activate contraction |
| Citron kinase | Serine/threonine kinase | Localizes to the cleavage furrow and regulates cytokinesis |
| Anillin | Actin-binding protein | Scaffolds the contractile ring and links to the membrane |
| Septins | GTP-binding proteins | Organize the ring and coordinate with the plasma membrane |
| Formins | Actin nucleators | Promote actin filament assembly in the ring |
| Profilin | Actin monomer binding | Regulates actin polymerization dynamics |
| Cofilin | Actin severing protein | Promotes actin turnover in the ring |
| Myosin phosphatase | Enzyme | Dephosphorylates myosin light chain to modulate contraction |
| IQGAP | Scaffold protein | Links actin and myosin and regulates ring assembly |
| Ena/VASP | Actin elongation factors | Regulate actin filament elongation at the ring |
| PLC1 | Phospholipase C | Involved in septation and ring regulation in fission yeast |
| Mid1 | Anillin-like protein | Positions the contractile ring in fission yeast |
| Cdc12 | Formin | Nucleates actin for the contractile ring in fission yeast |
How Is actomyosin contractile ring Regulated?
The actomyosin contractile ring is regulated by RhoA signaling, which activates formins and ROCK to promote actin polymerization and myosin contractility. Myosin turnover is a critical parameter that controls contractile instability and ring stability; altering turnover can lead to either stable or oscillatory contraction. Physical models of the contractile actomyosin ring highlight the interplay between motor activity, filament turnover, and mechanical tension in determining ring dynamics. In fission yeast, septation is coordinated with the contractile actomyosin ring through signaling pathways that ensure proper cell separation. Ultrastructural studies reveal that actomyosin filaments within the ring undergo dynamic reorganization during constriction, which is likely regulated by actin-binding proteins and motors.
actomyosin contractile ring and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| MYH9 | Cancer, cytokinesis failure | Knockout cell lines and xenografts |
| RhoA | Cancer, cell proliferation | Point mutation and overexpression models |
| Anillin | Aneuploidy, tumorigenesis | Knock-in tagged lines for live imaging |
| Citron kinase | Developmental disorders, cytokinesis | Knockout mouse models |
| Septins | Cancer, neurodegenerative disease | Knockout and overexpression cell models |
Cancer and Aneuploidy
Defects in contractile ring assembly or constriction can lead to failed cytokinesis, resulting in binucleated cells and aneuploidy, which are hallmarks of cancer. The mechanical ring interfaces between adherens junctions and contractile actomyosin during entotic cell-in-cell formation, a process relevant to tumor cell cannibalism. Understanding ring regulation may reveal vulnerabilities in cancer cells that rely on aberrant cytokinesis.
Developmental Disorders
Proper contractile ring function is essential for embryonic development, as it ensures accurate cell division and tissue morphogenesis. Mutations in genes encoding ring components or regulators could disrupt cytokinesis and contribute to developmental abnormalities. Studies in model organisms such as ascidians have shed light on actomyosin dynamics during notochord elongation, a morphogenetic process dependent on actomyosin contractility.
Infectious Disease
Some protozoan parasites divide without a canonical contractile actomyosin ring, making their division machinery a potential target for antiparasitic drugs. Understanding how these organisms bypass the ring could inform new therapeutic strategies.
From actomyosin contractile ring-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of a ring component block cytokinesis? | CRISPR knockout cell lines |
| How does a point mutation affect myosin motor activity? | CRISPR point mutation knock-in |
| Where does a protein localize during ring constriction? | Endogenous fluorescent knock-in tagging |
| Does overexpression of a regulator alter ring dynamics? | Inducible overexpression cell lines |
| What genes are essential for ring assembly? | Genome-wide CRISPR library screening |
| How does a disease-associated variant affect ring function? | Patient-derived iPSCs with isogenic controls |
How to Study the actomyosin contractile ring Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Live-cell confocal microscopy | Ring assembly and constriction dynamics | Visualizing actomyosin dynamics |
| Electron microscopy | Ultrastructure of actomyosin filaments | Nanoscale architecture of the ring |
| CRISPR knockout screening | Genes essential for ring function | Identifying novel regulators |
| Proteomics | Protein composition of the ring | Discovering new ring components |
| Phosphoproteomics | Signaling events regulating contraction | Mapping myosin regulation |
| Optical tweezers | Mechanical forces generated by the ring | Quantifying contractility |
| Computational modeling | Predictive behavior of actomyosin networks | Simulating ring dynamics |
Live-Cell Imaging
Live-cell fluorescence microscopy of tagged actomyosin components allows visualization of ring assembly, constriction, and disassembly in real time. Ultrastructural analysis by electron microscopy provides nanoscale detail of filament organization within the ring.
Proteomics and Interactomics
Affinity purification coupled with mass spectrometry can identify proteins that co-purify with contractile ring components, revealing the composition and interaction network of the ring. Phosphoproteomics can uncover signaling events that regulate myosin and actin dynamics.
Genetic Screens
Genome-wide CRISPR knockout or RNAi screens can identify genes required for cytokinesis and contractile ring function. Such screens are powerful for discovering novel regulators and potential drug targets.
Biophysical Measurements
Force measurements using optical tweezers or micropatterning can quantify the mechanical output of the contractile ring. Computational modeling of actomyosin networks helps interpret experimental data and predict ring behavior.
How CRISPR Can Be Used to Study GO:0005826 actomyosin contractile ring
Knockout
CRISPR knockout of genes encoding contractile ring components, such as MYH9 or RhoA, can abolish cytokinesis and cause binucleation, providing direct evidence of their essential roles. Knockout cell lines are valuable for studying the consequences of ring loss on proliferation and genome stability.
Point Mutation
CRISPR point mutation knock-in can introduce disease-associated or functional variants into genes like MYH9 to dissect how specific residues affect motor activity and ring constriction. Such models are crucial for understanding the molecular basis of cytokinesis defects.
Knock-in
Knock-in of fluorescent tags (e.g., GFP) into endogenous loci allows real-time visualization of ring proteins at physiological expression levels. This approach is ideal for studying the dynamic localization of actomyosin components during constriction.
Overexpression
CRISPR activation or inducible overexpression of regulators such as RhoA or formins can perturb ring dynamics and contractility, revealing dose-dependent effects on cytokinesis. Overexpression models are useful for testing whether increased activity of a component drives ring instability.
How EDITGENE Supports actomyosin contractile ring Research
Researchers studying actomyosin contractile ring-related genes often need to determine whether a candidate gene is causally involved in ring assembly, constriction, or cytokinesis. EDITGENE provides a comprehensive suite of CRISPR services to enable such functional studies in relevant cell models.
Contact EDITGENE today to design your custom CRISPR model for actomyosin contractile ring research.
Frequently Asked Questions About actomyosin contractile ring
What is the actomyosin contractile ring?
The actomyosin contractile ring (GO:0005826) is a cytoskeletal structure composed of actin filaments and myosin that forms beneath the plasma membrane in the cell division plane and constricts to drive cytokinesis.
What genes are involved in the actomyosin contractile ring?
Key genes include ACTB, MYH9, RhoA, ROCK1, Anillin, and septins, among others.
Where is the contractile ring located?
In animal cells, it is at the cleavage furrow; in budding yeast, it forms at the mother-bud neck before mitosis.
How does the contractile ring constrict?
Constriction is driven by myosin motor activity sliding actin filaments, and it requires continuous actin and myosin turnover.
What happens if the contractile ring fails?
Failure of ring assembly or constriction leads to failed cytokinesis, resulting in binucleated or aneuploid cells.
Is the contractile ring conserved across species?
It is present in many eukaryotes including animal cells and fungi, but some protozoan parasites divide without a canonical ring.
What is the role of myosin in the contractile ring?
Myosin is the motor protein that generates force for ring constriction, and its turnover controls contractile instability.
How can I study the contractile ring in the lab?
Common methods include live-cell imaging of tagged proteins, CRISPR knockout screens, proteomics, and biophysical measurements.
What diseases are linked to contractile ring defects?
Defects are associated with cancer, aneuploidy, and developmental disorders due to failed cytokinesis.
What CRISPR models are available for contractile ring research?
EDITGENE offers knockout, point mutation, knock-in, overexpression, and library screening services for genes involved in the contractile ring.
Conclusion
The actomyosin contractile ring (GO:0005826) is a fundamental cytoskeletal machine that drives cytokinesis in many eukaryotes. Its assembly, constriction, and regulation involve a complex interplay of actin, myosin, and associated proteins, with critical roles in development and disease. Research using CRISPR models and advanced imaging continues to reveal the mechanistic details of this dynamic structure. EDITGENE provides comprehensive CRISPR services to support functional studies of contractile ring genes, from knockout to library screening.
References
- 1. Hammarton TC. 2019. Who Needs a Contractile Actomyosin Ring? The Plethora of Alternative Ways to Divide a Protozoan Parasite.. Front Cell Infect Microbiol 9:397 PMID: 31824870
- 2. Arima T et al.. 2023. Dynamics of actomyosin filaments in the contractile ring revealed by ultrastructural analysis.. Genes Cells 28(12):845-856 PMID: 37844904
- 3. Lu Q et al.. 2019. Ascidian notochord elongation.. Dev Biol 448(2):147-153 PMID: 30458170
- 4. Wang M et al.. 2020. Mechanical Ring Interfaces between Adherens Junction and Contractile Actomyosin to Coordinate Entotic Cell-in-Cell Formation.. Cell Rep 32(8):108071 PMID: 32846129
- 5. Thiyagarajan S et al.. 2022. Myosin turnover controls actomyosin contractile instability.. Proc Natl Acad Sci U S A 119(43):e2211431119 PMID: 36264833
- 6. Satterwhite LL et al.. 1992. Cytokinesis.. Curr Opin Cell Biol 4(1):43-52 PMID: 1313686
- 7. Cortés JC et al.. 2016. Fission yeast septation.. Commun Integr Biol 9(4):e1189045 PMID: 27574536
- 8. Chatterjee M et al.. 2022. Dynamics and Stability of the Contractile Actomyosin Ring in the Cell.. Phys Rev Lett 128(6):068102 PMID: 35213206
