axonemal central apparatus

GO:1990716 · Cytoskeleton · Multiprotein complex · Proposed

A 9+2 axonemal subassembly of the central microtubule pair, its projections, its tubule-bridging structures, and caps on the microtubule plus ends. [GO:1990716]

Part of: axoneme (GO:0005930)

Has part: axonemal central pair (GO:0097540); axonemal central bridge (GO:1990717); axonemal central pair projection (GO:1990718)

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

Taxonomic distribution

• NCBITaxon:3055 Chlamydomonas reinhardtii — COMMON: Chlamydomonas reinhardtii 9+2 flagellar axonemes contain a central apparatus with central singlet microtubules and associated projections. [DOI:10.1126/science.1128618]

Canonical examples

• NCBITaxon:3055 Chlamydomonas reinhardtii — Green-algal model whose demembranated flagellar axonemes were used to resolve central-pair organization by cryoelectron tomography. [DOI:10.1126/science.1128618]

Mechanism graphs

Central pair, bridge and projections organize the central apparatus (FUNCTION)

The Chlamydomonas axonemal central apparatus contains the central pair, the central bridge and central-pair projections.

Discussions

• CURATION_TODO (OPEN): Resolve exact source-neutral groundings for central-pair cap and named projection subcomplex classes. GO exactly identifies the axonemal central apparatus and the C1 and C2 axonemal microtubules, but no exact source-neutral term was verified for the broader central projection or bridge classes, central-pair caps, or named projection subcomplexes. Historical reassessment at git 0f8108780c5c: GO exactly identifies the axonemal central apparatus, axonemal central bridge, broad axonemal central-pair projection structures, and C1/C2 microtubules, but this pass leaves exact central-pair cap structures and named projection subcomplex boundaries for later curation. Historical reassessment at git 81057840432d: GO exactly identifies the axonemal central apparatus, axonemal central bridge, broad axonemal central-pair projection structures, and C1/C2 microtubules, but this pass leaves exact central-pair cap structures and finer named projection subcomplex boundaries for later curation. Historical reassessment at git 11903e2fbf98: GO exactly identifies the axonemal central pair, central bridge and broad central-pair projection structures, but this pass leaves exact central-pair cap structures and finer named projection subcomplex boundaries for later curation.

Evidence

• GO:1990716 Gene Ontology cellular-component term for the axonemal central apparatus.
• GO:0097540 Gene Ontology cellular-component term for the axonemal central pair.
• GO:1990717 Gene Ontology cellular-component term for the axonemal central bridge.
• GO:1990718 Gene Ontology cellular-component term for axonemal central pair projection structures.
• GO:0005930 Gene Ontology places the axonemal central apparatus within the axoneme.
• DOI:10.1126/science.1128618 Nicastro et al. 2006, 'The molecular architecture of axonemes revealed by cryoelectron tomography', Science.

Curation history

• 2026-09-23T10:14:16Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
• 2026-09-23T10:14:58Z codex · EXPANDED_RECORD — Added axoneme parthood, GO-grounded C1 and C2 axonemal microtubule components, label-only projection and bridge components, Chlamydomonas scope, GO and DOI evidence, a nonmechanistic central-apparatus architecture graph, and a central-pair projection grounding TODO.
• 2026-09-23T10:15:35Z codex · REFINE_CENTRAL_APPARATUS_TODO — Generalized the projection-subcomplex TODO so it does not name Chlamydomonas C1/C2 projection classes left unsupported by the current evidence set.
• 2026-09-23T10:24:59Z codex · ADDRESSED_REVIEW — Resolved PR #1380 review issues #1381 and #1382 by narrowing the central-pair projection edge to static parthood and splitting the bridge edge into explicit C1 and C2 endpoints.
• 2026-09-23T10:27:25Z codex · FIX_REVIEW_YAML_ALIASES — Resolved PR #1380 review issue #1383 by removing YAML anchors from duplicated central-pair bridge evidence.
• 2026-09-23T14:31:05Z codex · ADD_AXONEMAL_CENTRAL_BRIDGE_PART — Linked GO:1990717 as an axonemal central-apparatus substructure, replaced the label-only central-pair bridge component with a GO-grounded graph structure, and narrowed the remaining projection/cap TODO.
• 2026-09-23T14:31:44Z codex · FIX_CENTRAL_BRIDGE_TEXT — Fixed singular central-bridge edge descriptions and kept GO:1990717 has_part adjacent to central-apparatus parthood.
• 2026-09-23T14:32:58Z codex · GROUND_CENTRAL_PAIR_PROJECTIONS — Grounded the broad central-pair projections component to GO:1990718 and narrowed the residual central-apparatus TODO to central-pair caps and named projection subcomplexes.
• 2026-09-23T14:36:51Z codex · FIX_CENTRAL_PAIR_PROJECTION_GO_LABEL — Changed the GO:1990718 component and graph node label to the canonical axonemal central pair projection label and singularized the matching graph edge.
• 2026-09-23T15:12:48Z codex · ADD_AXONEMAL_CENTRAL_PAIR_PROJECTION_PART — Linked GO:1990718 as an axonemal central-apparatus substructure, replaced the broad central-pair projection component with a GO-grounded child structure node, and narrowed the remaining TODO.
• 2026-09-23T15:15:02Z codex · FIX_CENTRAL_PAIR_TODO — Removed stale wording that left GO:1990718 for a future record and retargeted the remaining TODO to central-pair caps plus named projection subcomplexes.
• 2026-09-23T15:30:41Z codex · ADDRESSED_REVIEW — Resolved PR #1404 review issue #1405 by keeping named projection subcomplex boundaries in the central-apparatus graph scope note.
• 2026-09-23T15:50:18Z codex · ADD_AXONEMAL_CENTRAL_PAIR_PART — Linked GO:0097540 as an axonemal central-apparatus substructure, replaced direct C1/C2 components with a GO-grounded central-pair child structure, and narrowed the parent graph to coarse child parthood.
• 2026-09-23T15:50:48Z codex · FIX_CENTRAL_PAIR_PARENT_TITLE — Renamed the central-apparatus graph title after the C1/C2 microtubule edges moved into the GO:0097540 axonemal central pair child record.
• 2026-10-11T08:09:51Z codex · ADDRESS_SAVED_REVIEW — Addressed #2195: Restored every distinct committed central-apparatus rationale and retained the current prompt, attachment, original date, OPEN status and child-structure graph.

Source: data/structures/cytoskeleton/axonemal_central_apparatus.yaml