polaroplast

GO:0160201 · Membrane organelle · Membrane bounded organelle · Proposed

A membrane-bounded organelle found in a microsporidian spore that swells with water and exerts pressure to rupture the polar cap and evert the polar tube. [GO:0160201]

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

Components

Component	Type	Part of / acts on	Grounding	Role
polaroplast membranes	Lipid	part of	Reviewed label only (reviewed name; no accession asserted)	Membrane sheets and tubules that form the polaroplast system in the anterior region of microsporidian spores. `DOI:10.1007/978-3-030-93306-7_8` Han et al. 2022 reviewed the polaroplast as packed lamellar and tubular membrane arrays associated with the microsporidian invasion apparatus. `DOI:10.1128/mbio.02749-23` Lv et al. 2024 tracked Nosema bombycis polaroplast membranes during germination and sporoplasm membrane formation.
anterior lamellar polaroplast	Lipid	part of	Reviewed label only (reviewed name; no accession asserted)	Densely packed lamellar membranes in the anterior sector of the polaroplast. `DOI:10.1007/978-3-030-93306-7_8` Han et al. 2022 reviewed the lamellar polaroplast as a tightly packed anterior membrane array in the spore.
posterior tubular polaroplast	Lipid	part of	Reviewed label only (reviewed name; no accession asserted)	More vesicular and tubular membranes in the posterior polaroplast sector, adjacent to the polar filament straight region. `DOI:10.1007/978-3-030-93306-7_8` Han et al. 2022 reviewed flattened tubules and posterior polaroplast membranes as part of the microsporidian spore invasion apparatus.

Taxonomic distribution

NCBITaxon:6029 Microsporidia — COMMON: The polaroplast is a microsporidian spore organelle and is reviewed as part of the conserved invasion apparatus. [DOI:10.1007/978-3-030-93306-7_8]

Canonical examples

NCBITaxon:27978 Nosema bombycis — Silkworm-infecting microsporidian in which polaroplast membranes were tracked through the polar tube and into the nascent sporoplasm membrane. [DOI:10.1128/mbio.02749-23]

Functions

polar tube firing support — During microsporidian spore germination, the polaroplast expands and participates in the membrane movements coupled to polar tube discharge.
- DOI:10.1007/978-3-030-93306-7_8 Han et al. 2022 reviewed the polaroplast as an anterior membrane organelle associated with polar tube discharge.
- DOI:10.1186/s13071-023-05908-9 Chen et al. 2023 reviewed the microsporidian polar tube invasion apparatus and its relationship to other spore structures.
sporoplasm membrane formation — Polaroplast-derived membrane material travels through the fired polar tube and contributes to the sporoplasm plasma membrane.
- DOI:10.1128/mbio.02749-23 Lv et al. 2024 followed polaroplast membrane transport through the polar tube and transformation into the sporoplasm membrane in Nosema bombycis.

Mechanism graphs

Polaroplast-derived membranes contribute to the expelled sporoplasm (FUNCTION)

Packed polaroplast membranes are stored in the microsporidian spore and, during germination, polaroplast-derived membranes travel through the everted polar tube and are incorporated into the sporoplasm membrane.

Subject	Predicate	Object	Evidence
polaroplast membranes	are packed in	polaroplast	`DOI:10.1007/978-3-030-93306-7_8` Han et al. 2022 reviewed the polaroplast membrane arrays found in dormant microsporidian spores.
polaroplast membranes	translocate through	polar tube	`DOI:10.1128/mbio.02749-23` Lv et al. 2024 visualized polaroplast membrane transport through fired Nosema bombycis polar tubes.
polaroplast membranes	contribute to	sporoplasm membrane	`DOI:10.1128/mbio.02749-23` Lv et al. 2024 linked transported polaroplast-derived membranes to formation of the sporoplasm membrane.

Discussions

CURATION_TODO (OPEN): Resolve exact protein and lipid identities for the polaroplast membrane transport machinery. The current record captures the membrane organelle and its transport behavior, but does not assign exact groundings to lineage-specific transporters, sporoplasm surface proteins or lipid species that may participate in polaroplast remodeling.

Evidence

GO:0160201 Gene Ontology cellular-component term for polaroplast.
DOI:10.1007/978-3-030-93306-7_8 Han, Takvorian and Weiss 2022, The Function and Structure of the Microsporidia Polar Tube, Experientia Supplementum.
DOI:10.1186/s13071-023-05908-9 Chen et al. 2023, The microsporidian polar tube: origin, structure, composition, function, and application, Parasites & Vectors.
DOI:10.1128/mbio.02749-23 Lv et al. 2024, Microsporidia dressing up: the spore polaroplast transport through the polar tube and transformation into the sporoplasm membrane, mBio.

Curation history

2026-09-10T11:31:25Z claude · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-10T11:32:26Z claude · EXPANDED_RECORD — Added polaroplast membrane and lamellar/tubular subregion components, Microsporidia and Nosema bombycis taxonomic scope, polar tube firing and sporoplasm membrane functions, polaroplast evidence, a membrane-transport graph, and a protein/lipid grounding TODO.
2026-09-10T11:42:51Z claude · ADDRESS_REVIEW — Addressed PR #356 review issues #357 and #358 by marking the aggregate polaroplast membrane component as reviewed-label-only and softening the final graph edge to a polaroplast-derived membrane contribution claim.

Source: data/structures/membrane_organelle/polaroplast.yaml