axonemal microtubule

GO:0005879 · Cytoskeleton · Filament · Proposed

A microtubule in the axoneme of a eukaryotic cilium or flagellum; an axoneme contains nine modified doublet microtubules, which may or may not surround a pair of single microtubules. [GO:0005879]

Part of: axoneme (GO:0005930)

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

Taxonomic distribution

NCBITaxon:3055 Chlamydomonas reinhardtii — COMMON: Chlamydomonas flagellar axonemes contain a 9+2 axonemal microtubule scaffold with nine outer doublets and a central-pair region. [DOI:10.1126/science.1128618]

Canonical examples

NCBITaxon:3055 Chlamydomonas reinhardtii — Green-algal model whose 9+2 flagellar axonemal microtubule scaffold was resolved by cryoelectron tomography. [DOI:10.1126/science.1128618]

Functions

axonemal microtubule scaffold — In Chlamydomonas, specialized axonemal microtubules form the A/B outer doublets and C1/C2 central-pair singlets of the 9+2 flagellar axoneme.
- GO:0005879 GO:0005879 defines axonemal microtubules as microtubules in the axoneme of a eukaryotic cilium or flagellum.
- DOI:10.1016/j.cell.2019.09.030 Ma et al. 2019 resolved native Chlamydomonas axonemal doublet microtubules with A- and B-tubule protofilament walls.
- DOI:10.1002/cm.21094 Carbajal-Gonzalez et al. 2013 resolved the Chlamydomonas axonemal central pair with asymmetric C1 and C2 singlet microtubules.

Mechanism graphs

Axonemal microtubules build Chlamydomonas 9+2 axonemes (FUNCTION)

Chlamydomonas 9+2 flagellar axonemes contain A and B axonemal microtubules in each outer doublet and C1 and C2 axonemal microtubules in the central pair.

Subject	Predicate	Object	Evidence
A axonemal microtubule	is subtype of	axonemal microtubule	`GO:0097649` GO places the A axonemal microtubule under the axonemal microtubule class.
B axonemal microtubule	is subtype of	axonemal microtubule	`GO:0097650` GO places the B axonemal microtubule under the axonemal microtubule class.
C1 axonemal microtubule	is subtype of	axonemal microtubule	`GO:1990719` GO places the C1 axonemal microtubule under the axonemal microtubule class.
C2 axonemal microtubule	is subtype of	axonemal microtubule	`GO:1990720` GO places the C2 axonemal microtubule under the axonemal microtubule class.
A axonemal microtubule	is part of	axonemal doublet microtubule	`GO:0097649` GO places the A axonemal microtubule within the axonemal doublet microtubule.
B axonemal microtubule	is part of	axonemal doublet microtubule	`GO:0097650` GO places the B axonemal microtubule within the axonemal doublet microtubule.
C1 axonemal microtubule	is part of	axonemal central pair	`GO:1990719` GO places the C1 axonemal microtubule within the axonemal central pair.
C2 axonemal microtubule	is part of	axonemal central pair	`GO:1990720` GO places the C2 axonemal microtubule within the axonemal central pair.
axonemal microtubule	is part of	axoneme	`GO:0005879` GO defines axonemal microtubules as microtubules in the axoneme.

Discussions

INTERPRETATION (RESOLVED): Should tubulin protofilaments, MIPs or central-pair projections be duplicated as direct axonemal microtubule components? GO:0005879 denotes the shared axonemal microtubule class. Tubulin constituents are curated on the generic microtubule and axonemal-doublet records, while A/B-tubule, C1/C2, MIP and projection details remain on child records so this parent record does not collapse subtype-specific geometry.

Evidence

GO:0005879 Gene Ontology cellular-component term for the axonemal microtubule.
GO:0005881 Gene Ontology cellular-component parent term for cytoplasmic microtubules.
GO:0005930 Gene Ontology places axonemal microtubules within the axoneme.
GO:0097545 Gene Ontology cellular-component term for the axonemal doublet microtubule.
GO:0097649 Gene Ontology cellular-component term for the A axonemal microtubule.
GO:0097650 Gene Ontology cellular-component term for the B axonemal microtubule.
GO:0097540 Gene Ontology cellular-component term for the axonemal central pair.
GO:1990719 Gene Ontology cellular-component term for the C1 axonemal microtubule.
GO:1990720 Gene Ontology cellular-component term for the C2 axonemal microtubule.
DOI:10.1126/science.1128618 Nicastro et al. 2006, 'The molecular architecture of axonemes revealed by cryoelectron tomography', Science.
DOI:10.1016/j.cell.2019.09.030 Ma et al. 2019, 'Structure of the Decorated Ciliary Doublet Microtubule', Cell.
DOI:10.1002/cm.21094 Carbajal-Gonzalez et al. 2013, 'Conserved structural motifs in the central pair complex of eukaryotic flagella', Cytoskeleton.

Curation history

2026-09-23T23:48:50Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-23T23:49:41Z codex · EXPANDED_RECORD — Added cytoplasmic-microtubule parentage, axoneme parthood, Chlamydomonas scope, GO/DOI evidence, a nonmechanistic axonemal-microtubule topology graph, and a resolved child-boundary discussion.
2026-09-23T23:50:22Z codex · FIXED_CHLAMYDOMONAS_SCOPE_EVIDENCE — Replaced the outer-doublet-only Chlamydomonas taxonomy/example citation with Nicastro et al. 2006 evidence for the whole 9+2 axonemal microtubule scaffold.

Source: data/structures/cytoskeleton/axonemal_microtubule.yaml