polar ring of apical complex

GO:0020031 · Cytoskeleton · Other · Proposed

An electron dense ring at the most anterior position of the apical complex, from which the conoid fibers originate; formed during an invasive life cycle stage of an apicomplexan parasite. [GO:0020031]

Synonyms: anterior polar ring of apical complex; upper polar ring of apical complex

Part of: apical complex (GO:0020007)

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

Taxonomic distribution

• NCBITaxon:5811 Toxoplasma gondii — COMMON: The anterior conoid-fiber-origin ring is represented in the Toxoplasma tachyzoite apical complex; modern preconoidal rings are distinguished from the fixed SPMT-origin APR. [DOI:10.1371/journal.ppat.0020013]

Canonical examples

• NCBITaxon:5811 Toxoplasma gondii — Model in which distal preconoidal rings, conoid fibers and the separate SPMT-origin polar ring are distinguished. [DOI:10.1371/journal.ppat.0020013]

Functions

• anterior conoid-fiber origin — The anterior ring marks the distal origin of the conoid fibers, rather than the origin of subpellicular microtubules.
  • GO:0020031 The GO definition specifies the anterior ring from which conoid fibers originate.
  • DOI:10.1371/journal.ppat.0020013 The Introduction places conoid-fiber origins at the distal preconoidal rings, separate from the SPMT-origin polar ring.

Mechanism graphs

Anterior ring and conoid-fiber topology (ASSEMBLY)

The anterior conoid-fiber-origin ring belongs to the apical complex. This historical GO identity is not the fixed multilayer APR of modern protein-localization studies.

Discussions

• CURATION_TODO (OPEN): Resolve exact source-neutral groundings for Toxoplasma APR2-to-APR7 and RNG1 protein families. The first polar-ring record keeps Toxoplasma APR protein cohorts label-only because no exact cross-source protein-family CURIEs were curated for APR2-to-APR7 or RNG1.
• INTERPRETATION (RESOLVED): Keep modern APR composition and gatekeeper evidence separate from GO:0020031. The former component list and graph assigned the fixed multilayer APR to the historical anterior conoid-fiber-origin ring. Tran 2010 places RNG1 below the extruded conoid at the SPMT-origin APR; Ren 2024 places APR2-to-APR7 across fixed APR layers. Koreny 2021 also distinguishes canopy rings from APR1/2. These names and layer numbers cannot be equated directly with the two GO ring identifiers.

Evidence

• DOI:10.1002/cm.20469 Tran et al. 2010, RNG1 is a late marker of the apical polar ring in Toxoplasma gondii, Cytoskeleton.
• DOI:10.1073/pnas.2416602121 Ren et al. 2024, Architecture of the Toxoplasma gondii apical polar ring and its role in gliding motility and invasion, Proceedings of the National Academy of Sciences.
• DOI:10.1371/journal.pbio.3001081 Koreny et al. 2021, Molecular characterization of the conoid complex in Toxoplasma reveals its conservation in all apicomplexans, including Plasmodium species, PLOS Biology.
• GO:0020031 Retained anterior conoid-fiber-origin identity, distinct from the whole modern APR.
• DOI:10.1083/jcb.200112086 Hu, Roos and Murray 2002 distinguish historical anterior and posterior polar rings around the conoid.
• DOI:10.1371/journal.ppat.0020013 Hu et al. 2006 distinguish distal preconoidal rings from the SPMT-origin polar ring.

Curation history

• 2026-09-10T05:56:29Z claude · CREATED_RECORD — Scaffolded by scripts/new_record.py
• 2026-09-10T05:58:05Z claude · EXPANDED_RECORD — Added GO apical-complex parthood, GO and APR synonyms, APR2-to-APR7 and RNG1 protein components, rare eukaryotic and variable Apicomplexa taxonomic scope, Toxoplasma gondii as a canonical example, F-actin flux and motility/invasion functions, an APR2/F-actin function graph, and an APR protein grounding TODO.
• 2026-09-10T06:07:19Z claude · FIXED_EVIDENCE_SCOPE — Replaced GO-only taxonomic-distribution references with Koreny et al. 2021, narrowed the Toxoplasma gondii canonical-example note to Ren et al. 2024 APR architecture and APR2 perturbation evidence, and changed APR2 structural essentiality from CONDITIONAL to UNKNOWN.
• 2026-10-11T19:53:35Z codex · ADDRESS_SAVED_REVIEW — Addressed #2248, #2249: Retained the exact anterior GO identity and replaced the wrongly assigned whole-APR biology with source-supported anterior-ring topology. Broader APR protein/function research remains explicitly separate in a discussion, without forcing all APR layers onto the basal GO ring. Retained APR2 context now distinguishes the middle layer in the resolved three-layer model from broader upper-APR wording. It does not claim APR2 is indispensable for whole-ring assembly.

Source: data/structures/cytoskeleton/polar_ring_of_apical_complex.yaml