axoneme

GO:0005930 · Cytoskeleton · Filament · Proposed

A microtubule-based bundle with associated proteins that forms the core of a eukaryotic cilium or flagellum. [GO:0005930]

Has part: radial spoke (GO:0001534); axonemal nexin link (GO:0005931); axonemal central apparatus (GO:1990716); inner dynein arm (GO:0036156); outer dynein arm (GO:0036157); axonemal doublet microtubule (GO:0097545)

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

Taxonomic distribution

NCBITaxon:3055 Chlamydomonas reinhardtii — COMMON: The 9+2 motile axoneme has been structurally characterized in Chlamydomonas reinhardtii flagella. [DOI:10.1126/science.1128618]

Canonical examples

NCBITaxon:3055 Chlamydomonas reinhardtii — Green-algal model whose demembranated flagellar axonemes were rapidly frozen for cryoelectron tomography. [DOI:10.1126/science.1128618]

Functions

Chlamydomonas flagellar beating — In the Chlamydomonas 9+2 flagellar axoneme, outer-doublet microtubules, axonemal dyneins, radial spokes, central-pair structures, and nexin links form a scaffold for flagellar bending.
- DOI:10.1126/science.1128618 Nicastro et al. 2006 modeled force generation by dynein within the 9+2 axonemal microtubule scaffold.
- DOI:10.1083/jcb.200908067 Heuser et al. 2009 connected the nexin link with axonemal dynein regulation in Chlamydomonas.

Mechanism graphs

Dynein and regulatory complexes bend Chlamydomonas axonemes (FUNCTION)

In Chlamydomonas, dynein arms connect outer doublet microtubules to generate sliding forces; radial spokes, central-pair structures, and axonemal nexin links organize and coordinate the 9+2 flagellar axoneme.

Subject	Predicate	Object	Evidence
axonemal doublet microtubule	forms scaffold of	axoneme	`GO:0097545` GO defines the axonemal doublet microtubule as part of an axoneme. `DOI:10.1126/science.1128618` Nicastro et al. 2006 resolved the outer doublet microtubules of the Chlamydomonas axoneme by cryoelectron tomography.
inner dynein arm	projects from	axonemal doublet microtubule	`GO:0036156` GO identifies inner dynein arms as axonemal inner-arm structures on ciliary and flagellar outer doublets. `DOI:10.1126/science.1128618` Nicastro et al. 2006 visualized dynein-arm organization in 9+2 axonemes.
outer dynein arm	projects from	axonemal doublet microtubule	`GO:0036157` GO identifies the outer dynein arm as an axonemal outer-arm structure on ciliary and flagellar outer doublet microtubules. `DOI:10.1126/science.1128618` Nicastro et al. 2006 visualized dynein-microtubule organization in Chlamydomonas 9+2 axonemes.
radial spoke	projects toward	axonemal central apparatus	`GO:1990716` GO places the axonemal central apparatus within the 9+2 axoneme. `GO:0001534` GO defines the radial spoke as an axonemal complex that links outer doublets to the central-pair sheath. `DOI:10.1126/science.1128618` Nicastro et al. 2006 identified radial spokes and the central-pair region in the Chlamydomonas axoneme.
axonemal nexin link	links	axonemal doublet microtubule	`GO:0005931` GO identifies the axonemal nexin link as an axonemal complex that interconnects outer doublet microtubules. `DOI:10.1083/jcb.200908067` Heuser et al. 2009 identified the dynein regulatory complex as the axonemal nexin link.
inner dynein arm	drives	Chlamydomonas flagellar bending	`GO:0036156` GO states that inner and outer dynein arms have different functions in the generation of microtubule-based motility. `DOI:10.1126/science.1128618` Nicastro et al. 2006 interpreted the cryo-ET arrangement of axonemal dynein in a model for microtubule sliding force.
outer dynein arm	drives	Chlamydomonas flagellar bending	`GO:0036157` GO states that inner and outer dynein arms have different functions in the generation of microtubule-based motility. `DOI:10.1126/science.1128618` Nicastro et al. 2006 interpreted the axonemal dynein arrangement in a model for microtubule sliding force.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral groundings and boundaries for additional Chlamydomonas axoneme subcomplexes. The Chlamydomonas axoneme has many named regulatory, projection, and microtubule-associated complexes. This first record curates coarse substructure classes until their exact complex-level boundaries can be reviewed. Historical reassessment at git 0b7c77d1f1d0: The outer and inner dynein arm classes now have GO-backed boundaries in this axoneme record. The Chlamydomonas axoneme has additional named regulatory, projection, inner-arm isoform, and microtubule-associated complexes whose exact source-neutral groundings and record boundaries still need review. Historical reassessment at git 3304899aaa6f: The radial spoke and outer and inner dynein arm classes now have GO-backed boundaries in this axoneme record. The Chlamydomonas axoneme has additional named regulatory, projection, inner-arm isoform, and microtubule-associated complexes whose exact source-neutral groundings and record boundaries still need review. Historical reassessment at git e7aa953abdb8: The radial spoke, axonemal central apparatus, and outer and inner dynein arm classes now have GO-backed boundaries in this axoneme record. The Chlamydomonas axoneme has additional named regulatory, inner-arm isoform, and microtubule-associated complexes whose exact source-neutral groundings and record boundaries still need review. Historical reassessment at git 7102642edca7: The radial spoke, axonemal central apparatus, and outer and inner dynein arm classes now have GO-backed child-record boundaries. The Chlamydomonas axoneme has additional named regulatory and microtubule-associated complexes whose exact source-neutral groundings and record boundaries still need review. Historical reassessment at git 9f7ca79bbf4d: The radial spoke, axonemal central apparatus, outer and inner dynein arms, and axonemal nexin link now have GO-backed child-record boundaries. The Chlamydomonas axoneme has additional named regulatory and microtubule-associated complexes whose exact source-neutral groundings and record boundaries still need review. Historical reassessment at git 8b410f98eccd: The axonemal doublet microtubule, radial spoke, axonemal central apparatus, outer and inner dynein arms, and axonemal nexin link now have GO-backed child-record boundaries. The Chlamydomonas axoneme has additional named regulatory and microtubule-associated complexes whose exact source-neutral groundings and record boundaries still need review.

Evidence

GO:0005930 Gene Ontology cellular-component term for the axoneme.
GO:0001534 Gene Ontology cellular-component term for the radial spoke.
GO:0005931 Gene Ontology cellular-component term for the axonemal nexin link.
GO:1990716 Gene Ontology cellular-component term for the axonemal central apparatus.
GO:0036156 Gene Ontology cellular-component term for the inner dynein arm.
GO:0036157 Gene Ontology cellular-component term for the outer dynein arm.
GO:0097545 Gene Ontology cellular-component term for the axonemal doublet microtubule.
DOI:10.1126/science.1128618 Nicastro et al. 2006, 'The molecular architecture of axonemes revealed by cryoelectron tomography', Science.
DOI:10.1083/jcb.200908067 Heuser et al. 2009, 'The dynein regulatory complex is the nexin link and a major regulatory node in cilia and flagella', Journal of Cell Biology.

Curation history

2026-09-11T09:32:19Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-11T09:33:06Z codex · EXPANDED_RECORD — Added Chlamydomonas axoneme substructures, species-level taxonomic scope, a motility function, GO and DOI evidence, a nonmechanistic axonemal motility graph, and a subcomplex-boundary TODO.
2026-09-11T09:41:19Z codex · ADDRESSED_REVIEW — Resolved PR #452 review issues #453 and #454 by broadening the GO:0005930 definition beyond motile 9+2 axonemes and narrowing motility function and graph text to Chlamydomonas flagellar evidence.
2026-09-23T08:55:37Z codex · ADD_OUTER_DYNEIN_ARM_PART — Linked GO:0036157 as an axoneme substructure and narrowed the subcomplex-boundary TODO to the remaining unresolved Chlamydomonas axoneme complexes.
2026-09-23T09:07:56Z codex · ADDRESSED_REVIEW — Resolved PR #1374 review issues #1375 and #1376 by narrowing the coarse axonemal dynein component to GO:0036156 inner dynein arms, adding GO:0036156 and GO:0036157 axoneme evidence, and keeping the outer dynein arm as a GO:0036157 has_part child.
2026-09-23T09:11:59Z codex · FIX_ID_LABEL — Changed the GO:0036156 axoneme component and graph node label from 'inner dynein arms' to the canonical 'inner dynein arm'.
2026-09-23T09:35:54Z codex · ADD_RADIAL_SPOKE_PART — Linked GO:0001534 as an axoneme substructure, replaced the label-only radial-spoke component with a GO-grounded graph structure, and narrowed the subcomplex-boundary TODO.
2026-09-23T09:45:34Z codex · FIX_RADIAL_SPOKE_GRAPH_PREDICATE — Changed the radial-spoke graph predicate from 'project toward' to 'projects toward' after the graph node became singular.
2026-09-23T10:14:58Z codex · ADD_AXONEMAL_CENTRAL_APPARATUS_PART — Linked GO:1990716 as an axoneme substructure, replaced the label-only central-pair-apparatus component with a GO-grounded graph structure, and narrowed the subcomplex-boundary TODO.
2026-09-23T10:46:20Z codex · ADD_INNER_DYNEIN_ARM_PART — Linked GO:0036156 as an axoneme substructure, replaced the inner-dynein-arm component with a GO-grounded graph structure, and narrowed the subcomplex-boundary TODO.
2026-09-23T10:47:12Z codex · REFINE_INNER_DYNEIN_ARM_GRAPH — Changed the inner-dynein-arm graph edge predicate from bridge to projects from after the inner dynein arm became a GO-backed structure.
2026-09-23T10:55:55Z codex · ADDRESSED_INNER_DYNEIN_ARM_REVIEW — Resolved PR #1384 review issue #1386 by moving inner-arm isoform follow-up to the new GO:0036156 child record and narrowing the axoneme subcomplex TODO.
2026-09-23T11:15:38Z codex · ADD_AXONEMAL_NEXIN_LINK_PART — Linked GO:0005931 as an axoneme substructure, replaced the label-only nexin-dynein regulatory complex component with a GO-grounded graph structure, and narrowed the axoneme subcomplex TODO.
2026-09-23T11:46:26Z codex · ADD_AXONEMAL_DOUBLET_MICROTUBULE_PART — Linked GO:0097545 as an axoneme substructure, replaced the label-only outer-doublet component with a GO-grounded graph structure, and narrowed the axoneme subcomplex TODO.
2026-09-23T11:47:13Z codex · REFINE_AXONEMAL_DOUBLET_GRAPH — Restored inner- and outer-arm dynein drive edges to the flagellar bending process and changed the outer-dynein-arm doublet edge from bridges to projects from.
2026-09-23T11:56:16Z codex · ADDRESSED_REVIEW — Resolved PR #1390 review issue #1392 by changing the singular axonemal doublet microtubule graph predicate to forms scaffold of.
2026-10-11T08:56:29Z codex · ADDRESS_SAVED_REVIEW — Addressed #2200: restored original and intermediate discussion rationales with revision context; preserved the current prompt, task lifecycle, original dates, scientific claims and child-record boundaries.

Source: data/structures/cytoskeleton/axoneme.yaml