Spirostomum myoneme fishnet

cellstructuremech:spirostomum_myoneme_fishnet · Cytoskeleton · Other · Proposed

A mesh-like cortical myoneme characterized in Spirostomum, containing intersecting centrin/spasmin-rich fibrillar bundles and giant Sfi1-like scaffold proteins. The extended network shortens during calcium-triggered cell contraction and is distinct from adjacent microtubule bundles and from an isolated scaffold-centrin protein complex. [DOI:10.1126/sciadv.add6550]

Image (not hosted — CC_BY_NC_4_0): PMC9946354.1 F5

Spirostomum minus myoneme mesh in Figure 5B/C. B compares centrin signal (red) with anti-GSBP2 signal (green) using merged optical layers. C compares anti-GSBP1 (red) with anti-GSBP2 (green) in a single optical layer and includes Western insets. Anti-GSBP2 recognizes both GSBP proteins. Panel A is a predicted partial protein complex, not a native mesh reconstruction. FLUORESCENCE · Spirostomum minus (NCBITaxon:402029) · Jing Zhang, Weiwei Qin, Che Hu, Siyu Gu, Xiaocui Chai, Mingkun Yang, Fang Zhou, Xueyan Wang, Kai Chen, Guanxiong Yan, Guangying Wang, Chuanqi Jiang, Alan Warren, Jie Xiong and Wei Miao; Copyright 2023 The Authors, exclusive licensee American Association for the Advancement of Science; CC BY-NC 4.0; Figure 5 of Giant proteins in a giant cell, Science Advances, doi:10.1126/sciadv.add6550, via PubMed Central. Link only; no repository copy or adaptation. · CC_BY_NC_4_0 · source: PMC PMC9946354.1 F5 · DOI:10.1126/sciadv.add6550

Synonyms: Spirostomum mesh-like contractile fibrillar system; myoneme

Part of: GO:0030863 — cortical cytoskeleton (no local record)

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
Myonemal centrin-family proteins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Calcium-binding centrin/spasmin constituents of the contractile bundles, exemplified by Spasmin 1 and 2 in S. minus. Localization and proteomics do not establish an exhaustive paralogue inventory or individual assembly requirements. `DOI:10.1126/sciadv.add6550` Results on spasmin identification combine whole-cell MS with centrin, GSBP1 and GSBP2 immunoprecipitation-MS. Figure 5 uses anti-centrin staining, not antibodies distinguishing Spasmin 1 from Spasmin 2. `DOI:10.1073/pnas.2601408123` Published abstract reports centrin localization by immunofluorescence and immunogold electron microscopy in S. ambiguum. Full journal methods were not accessible; no exact paralogue or quantitative result is imported.
Giant Sfi1-like myoneme scaffold proteins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Repeat-rich centrin/spasmin-binding scaffold class, exemplified by GSBP1 and GSBP2 in S. minus. Evidence supports mesh membership, but limited RNAi phenotypes do not establish each paralogue's universal assembly requirement. `DOI:10.1126/sciadv.add6550` Sequence, transcript, MS, immunoprecipitation, Western and localization Results support GSBP1/GSBP2. Anti-GSBP1 is specific in the reported Western, whereas anti-GSBP2 recognizes both proteins; its fluorescence is not an isoform-specific GSBP2 map. GSBP2 is abundant in GSBP1 immunoprecipitates. `DOI:10.1073/pnas.2601408123` Published abstract reports Sfi1-homolog localization and calcium-dependent compaction/self-association of a reconstituted centrin-Sfi1 repeat complex. That assay is not reconstitution of the complete native fishnet.

Canonical examples

NCBITaxon:402029 Spirostomum minus — Clonal culture isolated from East Lake, Wuhan, and maintained at 22 degrees C. Species identification used live morphology, protargol staining and SSU rDNA comparison. Figure 5 and proteomic/RNAi experiments concern this culture; no strain taxon or genus-wide prevalence is inferred. [DOI:10.1126/sciadv.add6550]
NCBITaxon:37688 Spirostomum ambiguum — Published title and abstract identify the experimentally imaged myoneme fishnet and its centrin/Sfi1 constituents. The associated 2024 preprint main text was read separately; inaccessible final methods are not used to assign a strain, exact native stoichiometry or numerical phenotype to this species. [DOI:10.1073/pnas.2601408123]

Functions

Calcium-triggered cell contraction — The cortical myoneme network contributes to rapid whole-cell shortening after calcium stimulation. This contractile role does not establish the complete molecular shortening mechanism or the energy source for subsequent re-extension.
- DOI:10.1126/sciadv.add6550 In the RNAi experiments, a minority of type-E distorted cells appeared only in GSBP-targeted conditions and failed to contract during observation in 1 mM calcium. Mesh disruption was imaged in selected GSBP2-RNAi type-E cells. Other abnormal morphologies also occurred in controls and retained contraction.
- DOI:10.1073/pnas.2601408123 Published abstract connects the imaged fishnet with calcium-triggered cell shortening and reports repeat-complex compaction in vitro. No full-native-mesh sufficiency claim, exact kinetics or binding stoichiometry is curated.

Discussions

CURATION_TODO (RESOLVED): Delimit the Spirostomum myoneme fishnet from other centrin assemblies. Shared calcium-binding proteins and a mesh-like appearance do not establish identity or justify equating all myonemes across taxa.
CURATION_TODO (OPEN): Resolve exact component-family groundings and the complete native molecular inventory. Proteomic enrichment, antibody localization and repeat predictions do not determine every member, direct contact or subunit copy number.
CURATION_TODO (RESOLVED): Preserve the RNAi phenotype scope and antibody cross-reactivity. Rare affected cells and cross-reacting antibodies cannot establish uniform depletion, universal assembly requirements or isoform-specific localization.
CURATION_TODO (RESOLVED): Keep neighboring cortical structures and proposed calcium-handling machinery outside the established constituent list. Proximity, model coupling and predicted physiological roles are not evidence of molecular membership in the contractile bundles.
CURATION_TODO (OPEN): Reconcile native contraction and re-extension mechanisms with the final 2026 repeat-complex experiments when full experimental text is available. A successful simulation or partial-complex assay does not by itself resolve native fishnet force generation, sufficient composition or recovery energetics.
CURATION_TODO (RESOLVED): Distinguish the observed network from predicted structures and retain link-only reuse. A mixed figure must not be presented as a native molecular reconstruction, and a noncommercial licence does not permit repository hosting under current policy.

Evidence

DOI:10.1126/sciadv.add6550 Zhang et al. (2023), Giant proteins in a giant cell. Read primary Introduction, spasmin/backbone identification, RNAi, cortical organization and Discussion; culture/species, MS, immunoprecipitation, immunofluorescence, Western and RNAi Methods; Figures 5-9 legends. Figure 5 was visually inspected. Versioned PMC metadata and JATS verify DOI, PMID 36812318, non-retracted status and CC BY-NC 4.0.
DOI:10.1073/pnas.2601408123 Lannan et al. (2026), A centrin-Sfi1 myoneme fishnet powers ultrafast calcium-triggered contraction in the giant ciliate Spirostomum ambiguum. Publisher significance/abstract and PubMed/Europe PMC metadata were read. Publisher full text requires access; PubMed lists PMC13229174 as available on 2026-11-29, later than this curation. Europe PMC provides no full body. Only explicit qualitative abstract-level findings are used.
DOI:10.1101/2024.11.07.622534 Lannan et al. 2024 preprint, PMC11581044 version 2. Read Introduction, all Results, Discussion and Figures 1/3 legends in JATS, but not supplementary Methods. This is not the final 2026 article; numeric estimates and tentative molecular models are not silently promoted to final-version results.
DOI:10.1016/j.cell.2025.09.027 Mikus et al. comparative centrin discussion distinguishes the Paramecium infraciliary lattice from the Spirostomum fishnet. This is contextual comparison, not a new Spirostomum experiment or evidence of equivalence to Lacrymaria meshes.
GO:0005622 Verified non-obsolete intracellular anatomical structure; broad is-a parent for an extended intracellular network rather than a single resolved complex.
GO:0030863 — cortical cytoskeleton Verified non-obsolete cortical cytoskeleton; the fishnet is part of, not equivalent to, the entire cortical framework.

Curation history

2026-10-03T21:57:09Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-03T21:58:42Z codex · EXPANDED_RECORD — Added scoped primary evidence, two component classes, verified species examples, calcium-triggered contraction, molecular and assay limits, and inspected link-only Figure 5 with its noncommercial licence.

Source: data/structures/cytoskeleton/spirostomum_myoneme_fishnet.yaml