Stentor myoneme system

cellstructuremech:stentor_myoneme_system · Cytoskeleton · Other · Proposed

The cortical system of longitudinal contractile filament bundles, historically termed M bands, characterized in Stentor coeruleus. Its prominent posterior myonemes are distinct from the adjacent microtubular Km fibers; this record does not denote every centrin-containing cortical assembly. [DOI:10.1126/science.177.4047.447]

Image (not hosted — CC_BY_NC_SA_4_0): PMC2108994.1 Figure 16

Figure 16: longitudinal section of a contracted Stentor coeruleus myoneme, with a transverse-section inset. The source scale bar is 0.1 micrometer. This is fixed-cell ultrastructure, not a molecular reconstruction. TEM · Stentor coeruleus (NCBITaxon:5963) · B. Huang and D. R. Pitelka, Figure 16, The contractile process in the ciliate, Stentor coeruleus. I. The role of microtubules and filaments, Journal of Cell Biology 57 (1973), doi:10.1083/jcb.57.3.704, via PubMed Central; CC BY-NC-SA 4.0. Link only; no repository copy or adaptation. · CC_BY_NC_SA_4_0 · source: PMC PMC2108994.1 Figure 16 · DOI:10.1083/jcb.57.3.704

Synonyms: Stentor M-band system; myonemes

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	Centrin-related calcium-binding constituents of the myonemes; the antibody evidence does not resolve the complete native paralogue inventory. `DOI:10.1111/j.1550-7408.2005.00048x` Publisher abstract: three antibody preparations label myonemes, not the adjacent Km fibers in alpha-tubulin double-labeling experiments. Immunoblots identify a calcium-binding, caltractin-related protein. Full article methods were inaccessible.
Myonemal Sfi1-family scaffold proteins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Repeat-rich scaffold proteins localized to posterior myonemes and lateral connections; knockdown supports a role in regional centrin organization, not a defined minimal assembly stoichiometry. `https://escholarship.org/content/qt48v7x2m3/qt48v7x2m3_noSplash_81e16ae35ca9c5219383afd7085febfb.pdf` Yan dissertation, Chapter 2, pp. 26-32: Sfi1-1 (SteCoe_17904), Sfi1-2 (SteCoe_25973) and Sfi1-3 (SteCoe_10021) localize to myonemes and posterior lateral bands, but not the anterior centrin mesh. Antibody blots contain nonspecific bands; peptide-block and RNAi immunofluorescence controls are reported. This is the dissertation conclusion; the later final-paper manuscript resolves additional cortical layers as described below. `DOI:10.1016/j.cub.2026.06.062` Final-paper author manuscript PMC13637444.1, Sfi1 Results and Figure 3 legend: outer lateral Sfi1 bands are distinct from the anterior centrin mesh, but deeper anterior layers show Sfi1/centrin mesh colocalization. In the posterior outer cortex, centrin surrounds rather than colocalizes with the lateral bands. This depth-resolved account qualifies the dissertation conclusion; it does not equate every centrin-positive structure with posterior myonemes. Peptide-block and immunofluorescence controls are reported, with nonspecific Western bands and Sfi1-2/Sfi1-3 RNAi cross-depletion as specificity limits.

Canonical examples

NCBITaxon:5963 Stentor coeruleus — Experimental organism for the ultrastructural comparison of myonemes and Km fibers. The species identifier was verified at ENA; no genus-wide prevalence is asserted. [DOI:10.1083/jcb.57.3.704]

Functions

Rapid cell-body contraction — The myoneme system contributes to shortening of the cell body in response to stimulation.
- DOI:10.1126/science.177.4047.447 Primary high-speed cinematography follows M bands straightening before regional body shortening. Mechanical and electrical stimulation differ in the spatial progression of contraction; the signal is not directly identified.
- DOI:10.1016/j.cub.2026.06.062 Final-paper author manuscript PMC13637444.1, contractile-machinery Results and STAR Methods: Sfi1-1 and Sfi1-2 RNAi conditions impair stimulus-evoked contraction; responses depend on the stimulus and isoform-targeting condition. Sfi1-2/Sfi1-3 cross-depletion prevents an isoform-exclusive interpretation. No exact kinetics or native force-generation mechanism is asserted here.

Mechanism graphs

Nonmechanistic summary of Sfi1 knockdown phenotypes (FUNCTION)

Subject	Predicate	Object	Evidence
RNAi against the implicated Sfi1 isoforms	produces	Reduced myoneme cables	`DOI:10.1016/j.cub.2026.06.062` PMC13637444.1 cortical-patterning Results report reduced centrin incorporation in posterior myonemes in Sfi1-1 and Sfi1-2 RNAi conditions, with altered anterior/posterior patterning rather than reduced total centrin fluorescence. Sfi1-2/Sfi1-3 cross-depletion limits isoform attribution. This remains a nonmechanistic intervention summary: cable-pattern changes and contraction impairment are parallel outcomes, not proof that cable loss mediates the defect.
RNAi against the implicated Sfi1 isoforms	produces	Impaired stimulus-evoked contraction	`DOI:10.1016/j.cub.2026.06.062` PMC13637444.1 contractile-machinery Results and STAR Methods report reduced or incomplete contraction in the implicated knockdown conditions. Sfi1-2/Sfi1-3 cross-depletion and stimulus-dependent responses preclude a universal or isoform-exclusive requirement. No exact kinetics, native force-generation mechanism or mediation by cable loss is inferred.

Discussions

CURATION_TODO (RESOLVED): Distinguish the Stentor myoneme system from homonymous and neighboring assemblies. A shared protein or historical name does not establish structural equivalence.
CURATION_TODO (OPEN): Resolve exact myonemal family mappings and native molecular composition. Broad family matches and localization do not establish exact class equivalence, paralogue completeness or copy number.
CURATION_TODO (RESOLVED): Keep other cortical assemblies out of the myoneme constituent list. Adjacency or shared centrin labeling does not establish molecular membership.
CURATION_TODO (OPEN): Resolve native force generation beyond the observed Sfi1 perturbation outcomes. Fixed-state morphology, localization and knockdown do not uniquely determine a molecular motor cycle.
CURATION_TODO (RESOLVED): Use direct historical terminology provenance and expose the graph's evidence limits in the generated page. Same-agent review found that the M-band alias had an indirect source assignment and that the renderer did not display the graph scope fields.
CURATION_TODO (RESOLVED): Reconcile the dissertation and final-paper Sfi1 localization accounts. Cortical depth and source version affect how colocalization can be interpreted.

Evidence

DOI:10.1083/jcb.57.3.704 Huang and Pitelka (1973). Full primary PDF and Figures 16/17 inspected; versioned PMC metadata verifies DOI, PMID 4633444 and non-retracted status. Molecular coiling is an interpretation of fixed-state morphology, not a directly resolved transition.
DOI:10.1126/science.177.4047.447 Newman (1972). Primary PMC author manuscript read, including methods and figure legends; PMID 5043148. Cinematic evidence is not calcium imaging.
DOI:10.1111/j.1550-7408.2005.00048x Maloney et al. (2005), PMID 16014010. Publisher abstract read; full-text/PDF access was not obtained. Localization at membranelle bases is additional centrin distribution, not evidence that those bases are the myoneme system.
DOI:10.1016/j.cub.2026.06.062 Yan et al. (2026), PMID 42476139. At initial curation on 2026-10-04, only the published abstract and metadata were readable through the checked Cell/ScienceDirect routes. The final-paper author manuscript PMC13637444.1 became available on 2026-10-05. Relevant centrin/Sfi1 localization, cortical-patterning and contraction Results, Discussion and STAR Methods were read on 2026-10-12 in official checksum-verified JATS. This is not the dissertation or the publisher typeset PDF; supplementary movies were not inspected and no new numeric values are curated.
https://escholarship.org/content/qt48v7x2m3/qt48v7x2m3_noSplash_81e16ae35ca9c5219383afd7085febfb.pdf Connie Yan, Oral Regeneration in Stentor coeruleus: Cytoskeletal Patterning and Cell Cycle Control. Chapter 2 localization and RNAi results and relevant methods read. This dissertation is a separate source version, not the final journal article.
GO:0005622 Verified intracellular anatomical structure: broad is-a parent.
GO:0030863 — cortical cytoskeleton Verified cortical cytoskeleton: encompassing framework, used as part_of.

Curation history

2026-10-04T00:21:29Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-04T00:22:58Z codex · EXPANDED_RECORD — Added source-bounded centrin/Sfi1 components, verified species example, contraction function, nonmechanistic perturbation graph, identity and evidence limits, and inspected link-only Figure 16.
2026-10-04T00:23:32Z codex · REFINED_GRAPH_WORDING — Use produces for the impaired-contraction outcome state so the predicate does not invert the reported phenotype.
2026-10-04T00:39:25Z codex · ADDRESSED_ADVERSARIAL_REVIEW — Corrected direct M-band definition/synonym provenance and made the nonmechanistic graph scope and mediation limits visible; retained PROPOSED status and linked both review issues.
2026-10-12T04:02:04Z codex · RECONCILED_SOURCE_VERSIONS — Addressed issue 2282: reconcile dissertation Sfi1 localization with the final-paper cortical-depth account; update inspected methods and RNAi specificity limits without changing identity, status or graph topology.

Source: data/structures/cytoskeleton/stentor_myoneme_system.yaml