actomyosin contractile ring

GO:0005826 · Cytoskeleton · Filament · Proposed

A cytokinetic cytoskeletal ring composed of actin filaments, myosin, and accessory proteins that assembles beneath the plasma membrane and constricts during cell division. [GO:0005826]

Synonyms: contractile ring; cytokinetic actomyosin ring

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Essential	Role
actin filaments	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	act1	UNKNOWN	Filamentous actin tracks that assemble into the cytokinetic contractile ring. `DOI:10.1083/jcb.200602032` Wu et al. 2006 followed actin accumulation as fission-yeast cytokinesis nodes condensed into a contractile ring. `DOI:10.1002/cm.21052` Lee et al. 2012 review actin filaments as a central structural element of the fission-yeast contractile ring.
Myo2-family myosin-II motor	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	myo2	UNKNOWN	Myosin-II motor that contributes to contractile-ring force generation. `DOI:10.1083/jcb.200602032` Wu et al. 2006 tracked Myo2-positive nodes during fission-yeast contractile-ring assembly. `DOI:10.1002/cm.21052` Lee et al. 2012 review myosin II as a core fission-yeast contractile-ring protein.
Cdc12-family cytokinetic formin	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	cdc12	UNKNOWN	Cytokinetic formin retained in cytokinesis nodes and the assembled contractile ring; nucleates actin filaments during ring assembly and remains associated with their barbed ends. `DOI:10.1083/jcb.200602032` Wu et al. 2006, node-composition Results and Figure 2: functional Cdc12 reporters enter nodes that coalesce into a normally constricting ring. The Discussion describes formin retention at actin barbed ends. `DOI:10.1002/cm.21052` Lee et al. 2012 review Cdc12-mediated actin assembly in fission-yeast cytokinesis nodes and rings.

Taxonomic distribution

NCBITaxon:4896 Schizosaccharomyces pombe — COMMON: The actomyosin contractile ring is directly characterized in fission yeast; no broader fungal distribution is asserted in this first record. [DOI:10.1002/cm.21052]

Canonical examples

NCBITaxon:4896 Schizosaccharomyces pombe — Fission-yeast model in which cytokinetic nodes containing Myo2 and Cdc12 condense with actin into a medial contractile ring. [DOI:10.1083/jcb.200602032]

Functions

cytokinetic actomyosin constriction — The actomyosin contractile ring assembles at the division plane and constricts to help divide the fission-yeast cell during cytokinesis.
- DOI:10.1083/jcb.200602032 Wu and Pollard 2006 modeled assembly of the fission-yeast contractile ring from a broad band of nodes.
- DOI:10.1016/S1534-5807(03)00324-1 Wu et al. 2003 documented assembly and constriction of the fission-yeast contractile ring during cytokinesis.

Mechanism graphs

Cdc12 nodes assemble actin and Myo2 into the contractile ring (ASSEMBLY)

Fission-yeast cytokinesis nodes carrying Myo2 and Cdc12 condense through actin-dependent interactions to form the contractile ring.

Subject	Predicate	Object	Evidence
Cdc12-family cytokinetic formin	nucleates	actin filaments	`DOI:10.1083/jcb.200602032` Wu et al. 2006 modeled Cdc12 nodes as actin-nucleating precursors of the ring.
actin filaments	contributes to	actomyosin contractile ring	`DOI:10.1083/jcb.200602032` Wu et al. 2006 tracked actin during fission-yeast ring assembly.
Myo2-family myosin-II motor	contributes to	actomyosin contractile ring	`DOI:10.1083/jcb.200602032` Wu et al. 2006 tracked Myo2-containing nodes during contractile-ring formation.

Discussions

CURATION_TODO (OPEN): Resolve which Rng2, Cdc15, profilin, fimbrin, cofilin, and additional cytokinesis-node or actin-remodeling factors should be curated as contractile-ring constituents or associated assembly machinery. The fission-yeast contractile ring contains many node, nucleation, bundling, and remodeling proteins. This first record models actin, myosin II, and the Cdc12 formin until additional component boundaries are reviewed explicitly.

Evidence

GO:0005826 Gene Ontology cellular-component term for the actomyosin contractile ring.
DOI:10.1083/jcb.200602032 Wu and Pollard 2006, 'Assembly of the cytokinetic contractile ring from a broad band of nodes in fission yeast', Journal of Cell Biology.
DOI:10.1002/cm.21052 Lee, Coffman, and Wu 2012, 'Contractile-ring assembly in fission yeast cytokinesis: recent advances and new perspectives', Cytoskeleton.
DOI:10.1016/S1534-5807(03)00324-1 Wu et al. 2003, 'Spatial and temporal pathway for assembly and constriction of the contractile ring in fission yeast cytokinesis', Developmental Cell.

Curation history

2026-09-11T09:12:22Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-11T09:13:40Z codex · EXPANDED_RECORD — Added contractile-ring synonymy, actin, Myo2, and Cdc12 component classes, fission-yeast taxonomic scope, a cytokinetic-constriction function, DOI and GO evidence, a nonmechanistic node-condensation assembly graph, and a component-boundary TODO.
2026-09-11T09:21:29Z codex · ADDRESSED_REVIEW — Resolved PR #449 review issues #450 and #451 by adding constriction-specific Wu et al. 2003 evidence and by converting fission-yeast gene symbols to PomBase-style lowercase.
2026-10-11T07:14:19Z codex · ADDRESS_SAVED_REVIEW — Addressed #2189: Classified Cdc12 as a retained ring constituent with local primary localization evidence, preserving conservative family grounding, unknown essentiality and the accessory-component TODO.

Source: data/structures/cytoskeleton/actomyosin_contractile_ring.yaml