subpellicular microtubule

GO:0020025 · Cytoskeleton · Filament · Proposed

A singlet microtubule that lies underneath the inner membrane pellicle complex and emanates from the basal ring of the conoid. [GO:0020025]

Part of: apical complex (GO:0020007)

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

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 conventional singlet subpellicular microtubules of Toxoplasma. `GO:0005874` Gene Ontology defines microtubules as polymeric tubulin tubes. `DOI:10.1371/journal.ppat.0020013` Hu et al. 2006 described alpha/beta-tubulins in Toxoplasma conventional microtubules, including the subpellicular microtubules.

Taxonomic distribution

NCBITaxon:5811 Toxoplasma gondii — COMMON: Toxoplasma tachyzoites have 22 singlet subpellicular microtubules attached at the polar ring of the apical complex and running beneath the inner membrane complex. [DOI:10.1371/journal.ppat.0020013]

Canonical examples

NCBITaxon:5811 Toxoplasma gondii — Apicomplexan model in which the 32 nm periodicity shared by isolated subpellicular microtubules and the overlying pellicular intramembranous-particle lattice was studied structurally. [DOI:10.1242/jcs.110.1.35]

Functions

pellicle microtubule scaffold — Subpellicular microtubules form a longitudinal cortical microtubule scaffold beneath the inner membrane pellicle complex and alongside the pellicular intramembranous-particle lattice in Toxoplasma.
- DOI:10.1242/jcs.110.1.35 Morrissette, Murray and Roos 1997 resolved a 32 nm periodicity in isolated Toxoplasma subpellicular microtubules and the overlying pellicle particle lattice.
- DOI:10.1371/journal.ppat.0020013 Hu et al. 2006 described the Toxoplasma subpellicular microtubules as cytoskeletal elements closely associated with the cytoplasmic face of the IMC.

Mechanism graphs

Tubulin singlets extend from the polar ring under the Toxoplasma IMC (ASSEMBLY)

Alpha- and beta-tubulins polymerize into the 22 conventional subpellicular microtubules that attach at the polar ring of the Toxoplasma apical complex, run beneath the inner membrane pellicle complex, and align with a periodic intramembranous-particle lattice.

Subject	Predicate	Object	Evidence
alpha- and beta-tubulins	polymerize into	subpellicular microtubule	`GO:0005874` Gene Ontology defines microtubules as polymeric tubulin tubes. `DOI:10.1371/journal.ppat.0020013` Hu et al. 2006 placed the Toxoplasma subpellicular microtubules among the parasite's conventional alpha/beta-tubulin microtubules.
subpellicular microtubule	attaches to	basal ring of apical complex	`DOI:10.1371/journal.ppat.0020013` Hu et al. 2006 localized EGFP-TgDLC at the sites where Toxoplasma subpellicular microtubules attach to the polar ring. `GO:0020032` GO distinguishes the basal SPMT-origin ring from the anterior conoid-fiber-origin ring GO:0020031.
subpellicular microtubule	lies underneath	inner membrane pellicle complex	`GO:0020025` Gene Ontology defines the subpellicular microtubule by its position under the inner membrane pellicle complex. `DOI:10.1371/journal.ppat.0020013` Hu et al. 2006 described the Toxoplasma subpellicular microtubules as closely associated with the IMC cytoplasmic face.
subpellicular microtubule	associates with	pellicular intramembranous-particle lattice	`DOI:10.1242/jcs.110.1.35` Morrissette, Murray and Roos 1997 found the same 32 nm repeat in isolated subpellicular microtubules and in the pellicular intramembranous-particle rows thought to overlie them.

Discussions

CURATION_TODO (OPEN): Resolve exact component boundaries and source-neutral groundings for subpellicular microtubule end proteins, plus-end factors, and IMC particle-lattice linkers. Morrissette, Murray and Roos resolved an intramembranous-particle lattice aligned with Toxoplasma subpellicular microtubules, and Hu et al. localized proteins such as TgDLC, TgMORN1 and TgCentrin2 near subpellicular microtubule ends or daughter scaffolds. This record leaves those factors out until exact conserved constituent, linker, marker or assembly-factor boundaries are curated.
INTERPRETATION (RESOLVED): Keep GO:0020025 scoped to apicomplexan subpellicular microtubules rather than kinetoplastid cortical microtubule arrays that share the same plain-English name. The phrase subpellicular microtubule is also used in Trypanosoma literature, but GO:0020025 is taxon-constrained to Apicomplexa and defined by apicomplexan IMC and conoid topology. This record therefore curates only the apicomplexan structure.
INTERPRETATION (RESOLVED): Use the exact basal SPMT-origin ring in the attachment graph. The former graph grounded the generic polar-ring name to GO:0020031, whose definition denotes the anterior conoid-fiber-origin ring. GO:0020025 and GO:0020032 identify the basal SPMT-origin topology, in agreement with the primary anatomical distinction.

Evidence

GO:0020025 Gene Ontology cellular-component term for the apicomplexan subpellicular microtubule.
GO:0005874 Gene Ontology places subpellicular microtubules under the microtubule class.
GO:0020007 Gene Ontology models subpellicular microtubules as part of the apicomplexan apical complex.
DOI:10.1242/jcs.110.1.35 Morrissette, Murray and Roos 1997, Subpellicular microtubules associate with an intramembranous particle lattice in the protozoan parasite Toxoplasma gondii, Journal of Cell Science.
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:10.1155/2014/893272 Sheriff, Lim and He 2014 tracked YFP-alpha-tubulin incorporation into Trypanosoma brucei subpellicular microtubules; the article is cited here only to distinguish kinetoplastid cortical arrays from GO:0020025.
GO:0020032 Exact basal-ring identity for the SPMT-origin attachment site; not a synonym for the entire modern multilayer APR.

Curation history

2026-09-22T11:58:42Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-22T12:00:13Z codex · EXPANDED_RECORD — Added GO microtubule parentage and apical-complex parthood, a reviewed label-only alpha/beta tubulin component, Toxoplasma gondii scope, DOI/GO evidence, a nonmechanistic cortical topology graph, and curation discussions for accessory components and the Apicomplexa-specific GO boundary.
2026-09-22T12:11:53Z codex · REVIEW_FIXES — Addressed PR #1277 review issues #1278 and #1279 by narrowing the Toxoplasma canonical-example note to the Morrissette et al. 1997 lattice evidence and adding direct Sheriff et al. 2014 evidence for excluded Trypanosoma subpellicular microtubule usage.
2026-10-11T19:53:42Z codex · ADDRESS_SAVED_REVIEW — Addressed #2254: Retargeted the SPMT attachment node and edge coherently to GO:0020032, preserving the lattice, molecular constituents and Trypanosoma boundary.

Source: data/structures/cytoskeleton/subpellicular_microtubule.yaml