polar tube anchoring disc

GO:0160202 · Spore · Other · Proposed

A structural component of the microsporidian spore's invasion apparatus that is located at the anterior end of the spore and serves to attach the polar tube to the inside of the spore wall. [GO:0160202]

Synonyms: polar tube anchoring disk

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
EnP1	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	EnP1		UNKNOWN	Spore wall protein that is abundant in the polar sac/anchoring disk region of Encephalitozoon spores and supports host-cell adherence. `DOI:10.1128/EC.00113-07` Southern et al. 2007 localized EnP1 in Encephalitozoon spores to the endospore, exospore, and polar sac/anchoring disk region by transmission immunoelectron microscopy and tested EnP1-dependent host-cell adherence in vitro.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

EnP1

Accession	Protein	Gene	Organism	Entry
`UniProtKB:Q8SWL3`	Spore wall and anchoring disk complex protein EnP1	EnP1	Encephalitozoon cuniculi GB-M1 (`NCBITaxon:284813`)	REVIEWED
Role and evidence (1 reference) Reviewed UniProtKB entry for Encephalitozoon cuniculi EnP1, whose experimental localization evidence includes the anchoring disk complex. `DOI:10.1128/EC.00113-07` Southern et al. 2007 experimentally localized EnP1 in the Encephalitozoon spore wall and polar sac/anchoring disk region.

Taxonomic distribution

NCBITaxon:6029 Microsporidia — COMMON: The anchoring disc is modeled as part of the microsporidian spore-stage polar-tube invasion apparatus; this row is scoped to the infectious spore stage rather than every vegetative cell. [DOI:10.1016/j.ijpara.2005.04.003]

Canonical examples

NCBITaxon:6035 Encephalitozoon cuniculi — Mammal-infecting microsporidian in which the EnP1 spore wall protein was localized to the polar sac/anchoring disk region of the spore. [DOI:10.1128/EC.00113-07]

Functions

polar tube attachment — The anchoring disc attaches the intracellular polar tube to the inside of the anterior spore wall, positioning the tube for apical release during germination.
- GO:0160202 GO:0160202 defines the polar tube anchoring disc as the anterior invasion-apparatus component that attaches the polar tube to the inside of the spore wall.
- DOI:10.1016/j.ijpara.2005.04.003 Xu and Weiss 2005 reviewed polar-tube attachment and discharge as part of microsporidian spore invasion.

Mechanism graphs

Anchoring disc tethers the polar tube at the spore apex (FUNCTION)

The anchoring disc sits at the anterior spore end, holds the polar tube against the inside of the spore wall, and marks the region from which the everting polar tube exits during germination.

Subject	Predicate	Object	Evidence
polar tube anchoring disc	resides at	anterior spore end	`GO:0160202` GO:0160202 defines the structure by its anterior spore location.
polar tube anchoring disc	attaches	polar tube	`GO:0160202` GO:0160202 defines the anchoring disc by its role in attaching the polar tube to the inside of the spore wall. `DOI:10.1016/j.ijpara.2005.04.003` Xu and Weiss 2005 reviewed the anchoring structure as part of the microsporidian polar-tube invasion apparatus.
polar tube	exits from	anterior spore end	`DOI:10.1128/EC.00113-07` Southern et al. 2007 described the polar sac/anchoring disk region as the area from which the everting polar tube is released.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral component groundings for the polar tube anchoring disc. EnP1 is experimentally localized to the polar sac/anchoring disk region, but the full molecular composition of the anchoring disc and polar sac remains incompletely resolved in this record.

Evidence

GO:0160202 Gene Ontology cellular-component term for the polar tube anchoring disc.
DOI:10.1016/j.ijpara.2005.04.003 Xu and Weiss 2005, The microsporidian polar tube: a highly specialised invasion organelle, International Journal for Parasitology.
DOI:10.1111/j.1462-5822.2009.01362.x Williams 2009, Unique physiology of host-parasite interactions in microsporidia infections, Cellular Microbiology.
DOI:10.1128/EC.00113-07 Southern et al. 2007, EnP1, a Microsporidian Spore Wall Protein That Enables Spores To Adhere to and Infect Host Cells In Vitro, Eukaryotic Cell.

Curation history

2026-09-13T11:28:55Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-13T11:29:33Z codex · EXPANDED_RECORD — Added polar-tube anchoring-disk synonymy, a conservative EnP1 component with a reviewed UniProtKB example, Microsporidia and Encephalitozoon scope, polar-tube attachment function, DOI/GO evidence, a nonmechanistic anchoring graph, and a component grounding TODO.

Source: data/structures/spore/polar_tube_anchoring_disc.yaml