intraconoid microtubule

GO:0033289 · Cytoskeleton · Filament · Proposed

A microtubule located such that it threads through the conoid and projects through the polar ring. [GO:0033289]

Part of: apical complex (GO:0020007)

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
alpha- and beta-tubulins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			ESSENTIAL	Tubulin subunits that polymerize into the two conventional intraconoid microtubules threading through the Toxoplasma conoid. `GO:0005874` Gene Ontology defines microtubules as polymeric tubulin tubes. `DOI:10.1371/journal.ppat.0020013` Hu et al. 2006 grouped the two Toxoplasma intraconoid microtubules with conventional alpha/beta-tubulin microtubules.

NCBITaxon:5811 Toxoplasma gondii — COMMON: Toxoplasma tachyzoites have two intraconoid microtubules running through the center of the conoid at the apical complex. [DOI:10.1371/journal.ppat.0020013]

NCBITaxon:5811 Toxoplasma gondii — Apicomplexan model in which the conoid fibers, the two intraconoid microtubules, and the subpellicular microtubules were described as distinct apical-complex cytoskeletal elements. [DOI:10.1371/journal.ppat.0020013]

conoid-center microtubule scaffold — The two intraconoid microtubules provide conventional tubulin filaments that run through the center of the Toxoplasma conoid.
- DOI:10.1371/journal.ppat.0020013 Hu et al. 2006 described a pair of Toxoplasma intraconoid microtubules that pass through the center of the conoid.

Alpha- and beta-tubulins polymerize into a pair of conventional intraconoid microtubules that run through the center of the Toxoplasma conoid.

Subject	Predicate	Object	Evidence
alpha- and beta-tubulins	polymerize into	intraconoid microtubule	`GO:0005874` Gene Ontology defines microtubules as polymeric tubulin tubes. `DOI:10.1371/journal.ppat.0020013` Hu et al. 2006 distinguished Toxoplasma intraconoid microtubules as conventional alpha/beta-tubulin microtubules.
intraconoid microtubule	threads through	conoid	`DOI:10.1371/journal.ppat.0020013` Hu et al. 2006 placed the two intraconoid microtubules inside the Toxoplasma conoid.
intraconoid microtubule	is part of	apical complex	`GO:0020007` Gene Ontology models the intraconoid microtubule as part of the apical complex.

CURATION_TODO (OPEN): Resolve the filament-end organizers and accessory proteins that place the two intraconoid microtubules within the conoid. This first record captures the mature topology of the two Toxoplasma intraconoid microtubules but leaves filament-end organizers, polar-ring linkers and assembly timing out until candidate proteins are localized directly to the intraconoid microtubule boundary.
INTERPRETATION (RESOLVED): Keep the conventional intraconoid microtubules distinct from the unusual ribbon-like tubulin fibers that form the conoid. Hu et al. distinguished the two intraconoid microtubules from the conoid fibers, whose tubulin protofilaments form a ribbon polymer rather than a closed microtubule tube. This record therefore curates only the two conventional intraconoid microtubules.
INTERPRETATION (RESOLVED): Do not infer a specific anterior-ring endpoint from the generic GO polar-ring wording. GO:0033289 describes projection through a polar ring without selecting a ring identifier or filament endpoint. The earlier graph added distal ends and GO:0020031, the anterior conoid-fiber-origin ring. Historical schematic terminology is not enough to establish that precise edge; modern studies distinguish preconoidal rings from the fixed APR.

GO:0033289 Gene Ontology cellular-component term for the intraconoid microtubule.
GO:0005874 Gene Ontology places intraconoid microtubules under the microtubule class.
GO:0020007 Gene Ontology models intraconoid microtubules as part of the apical complex.
DOI:10.1083/jcb.200112086 Hu, Roos and Murray 2002, A novel polymer of tubulin forms the conoid of Toxoplasma gondii, Journal of Cell Biology.
DOI:10.1371/journal.ppat.0020013 Hu et al. 2006, Cytoskeletal Components of an Invasion Machine--the Apical Complex of Toxoplasma gondii, PLOS Pathogens.
DOI:10.1002/advs.202206595 Li et al. 2023, Cryo-Electron Tomography of Toxoplasma gondii Indicates That the Conoid Fiber May Be Derived from Microtubules. Results and Figure 2 independently resolve basal-directed ICMT extension.

2026-09-22T13:08:26Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-22T13:09:14Z codex · EXPANDED_RECORD — Added GO microtubule parentage and apical-complex parthood, a reviewed label-only alpha/beta tubulin component, Toxoplasma gondii scope, GO/DOI evidence, a nonmechanistic intraconoid microtubule topology graph, and curation discussions for filament-end factors and the conoid-fiber boundary.
2026-09-22T13:20:34Z codex · ADDRESSED_REVIEW — Addressed PR #1283 review issues #1284 and #1285 by narrowing the end-factor TODO evidence note and moving the Toxoplasma canonical-example note onto direct Hu et al. 2006 evidence.
2026-10-11T19:53:40Z codex · ADDRESS_SAVED_REVIEW — Addressed #2253: Removed the over-specific anterior-ring projection edge and matching prose, retaining the GO definition with explicit ambiguity and primary basal-extension context.