quiescent cell microtubule bundle

cellstructuremech:quiescent_cell_microtubule_bundle · Cytoskeleton · Other · Proposed

A stable antiparallel cytoplasmic microtubule bundle assembled during nutrient-exhaustion-induced quiescence in fission yeast, characterized in Schizosaccharomyces pombe. It contains closely packed microtubules, is usually associated with the spindle pole body, and is distinct from the nuclear microtubule array of quiescent budding yeast. [DOI:10.1083/jcb.201502025]

Image (not hosted — OTHER): PMC4494004/fig1

Multipanel figure: fluorescent Atb2 bundles during nutrient exhaustion (A-C), longitudinal and transverse freeze-substitution TEM (D-E), spacing analysis (F), and serial-tomography models (G). Fluorescence bars: 2 micrometers; TEM bars: 200 nm. OTHER · Schizosaccharomyces pombe (NCBITaxon:4896) · D. Laporte, F. Courtout, B. Pinson, J. Dompierre, B. Salin, L. Brocard and I. Sagot (2015), Figure 1, DOI:10.1083/jcb.201502025. CC BY-NC-SA 3.0. Linked without modification. · OTHER · source: PMC PMC4494004/fig1 · DOI:10.1083/jcb.201502025

Synonyms: Q-MT bundle; quiescent cell MT bundle

Part of: GO:0015630 — microtubule cytoskeleton (no local record); GO:0005737 — cytoplasm (no local record)

Has part: cytoplasmic microtubule (GO:0005881)

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

Components

Component	Type	Part of / acts on	Grounding	Genes	Essential	Role
Alpha tubulin	Protein	part of	`InterPro:IPR002452`	atb2	UNKNOWN	Alpha subunit of the bundle microtubules; Atb2 is the fluorescent scaffold reporter. `DOI:10.1083/jcb.201502025` Figures 1-2 identify the stable bundle with GFP-Atb2, TEM and tomography. `InterPro:IPR002452` Complete native InterPro matches verified on 2026-10-05; integrated type=family and scope checked, not inferred from a domain.
Beta tubulin	Protein	part of	`InterPro:IPR002453`		UNKNOWN	Partner tubulin class in the microtubules resolved by TEM; no particular beta-tubulin isoform is assigned from these images. `DOI:10.1083/jcb.201502025` Figure 1D-G resolves microtubules, whose alpha/beta polymer composition is independently defined by GO:0005874. `InterPro:IPR002453` Complete native InterPro matches verified on 2026-10-05; integrated type=family and scope checked, not inferred from a domain. `GO:0005874` Native definition specifies alpha/beta tubulin subunits in microtubules; this supports a polymer-class assertion, not an unobserved Nda3 localization assay.
Mto1-like microtubule nucleation adaptor	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	mto1	ESSENTIAL	Retained bundle-associated nucleation adaptor; required for the bona fide stable bundle in the tested S. pombe conditions. `DOI:10.1083/jcb.201502025` MAP-localization Results report Mto1 on Q-MT bundles. Figure 7E-F shows that five-day mto1 deletion cultures form a long thin cold-sensitive structure, not a bona fide Q-MT bundle. Essentiality refers to that stable architecture, not all tubulin polymerization.
Mto2-like microtubule nucleation adaptor	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	mto2	UNKNOWN	Resident nucleation adaptor redistributed from the nuclear envelope to bundle-associated puncta; proposed nucleation activity is not a directly demonstrated assembly sequence. `DOI:10.1083/jcb.201502025` Figure 4A-B and line scans show Mto2 on the bundle and near constituent microtubule extremities; Figure 5 Results report retained puncta during elongation.
Microtubule-associated protein, MAP65/Ase1/PRC1	Protein	part of	`InterPro:IPR007145`	ase1	DISPENSABLE	Resident microtubule crosslinker; Ase1 contributes to bundle thickness but is not required for a bundle to form in the tested deletion. `DOI:10.1083/jcb.201502025` Figure 4C-F: Ase1 localizes along the bundle; ase1 deletion leaves a thinner bundle. Its established bundling activity supports the crosslinker interpretation, not a measured fixed stoichiometry. `InterPro:IPR007145` Complete native InterPro matches verified on 2026-10-05; integrated type=family and scope checked, not inferred from a domain.
CLASP-like microtubule-associated protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	peg1, cls1	UNKNOWN	Resident microtubule-associated protein enriched in the dense bundle region; a specific stabilization mechanism remains unresolved. `DOI:10.1083/jcb.201502025` Figure 4C and MAP-localization Results place Cls1/Peg1 in the denser bundle region; no bundle-formation necessity is inferred.
Alp7-like microtubule-associated protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	alp7	DISPENSABLE	Resident microtubule-associated protein affecting bundle dimensions; deletion does not abolish bundle formation. `DOI:10.1083/jcb.201502025` Figure 4C-F: Alp7 localizes to the bundle, and alp7 deletion leaves longer bundles with altered fluorescence intensity.
XMAP215	Protein	part of	`InterPro:IPR045110`	alp14, dis1	UNKNOWN	Resident TOG-domain microtubule regulators. Alp14 is required for elongation after refeeding; individual alp14 and dis1 deletions still permit quiescent bundles. `DOI:10.1083/jcb.201502025` Figure 4C-F localizes Alp14 and Dis1 and shows bundles in each single deletion. Figure 7C-D establishes an Alp14 requirement for exit-associated elongation, not bundle formation. No double-deletion or whole-family assembly requirement is asserted. `InterPro:IPR045110` Complete native InterPro matches verified on 2026-10-05; integrated type=family and scope checked, not inferred from a domain.
Klp2-like kinesin-14 motor	Protein	acts on	Reviewed label only (reviewed name; no accession asserted)	klp2	DISPENSABLE	Motor associated with the assembled bundle at faint puncta; a specific quiescent motor-driven sliding activity is not established. `DOI:10.1083/jcb.201502025` Figure 4C detects Klp2 at a few bundle-associated puncta; inspected Figure 4D-F includes klp2 deletion cells that retain bundles.
Tea1-like polarity landmark protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	tea1	UNKNOWN	Bundle-associated polarity landmark/cargo in quiescence, subsequently redistributed to cell tips on refeeding. `DOI:10.1083/jcb.201502025` Figure 6A and Results place Tea1 on Q-MT bundles instead of cell tips; Figure 7A follows tip relocalization after refeeding. Localization does not establish Tea1 as a bundle scaffold or prove a bundle assembly requirement.

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.

Alpha tubulin

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P04689`	Tubulin alpha-2 chain	atb2	Schizosaccharomyces pombe 972h- (`NCBITaxon:284812`)	REVIEWED
Role and evidence (2 references) Reference-sequence exemplar for the species-level experiment; this accession does not assert that the exact reference stock was imaged. `DOI:10.1083/jcb.201502025` Figures 1-2: GFP-Atb2 labels the bundle. UniProt names this alpha-2 protein tub1 and retains atb2/alp2 aliases. `https://www.uniprot.org/uniprotkb/P04689/entry` Reviewed entry, gene aliases and source taxon verified live on 2026-10-05; localization comes from the primary experiment.

Mto1-like microtubule nucleation adaptor

Accession	Protein	Gene	Organism	Entry
`UniProtKB:O94488`	Gamma tubulin complex adapter mto1	mto1	Schizosaccharomyces pombe 972h- (`NCBITaxon:284812`)	REVIEWED
Role and evidence (2 references) Reference-sequence exemplar for the species-level experiment; this accession does not assert that the exact reference stock was imaged. `DOI:10.1083/jcb.201502025` MAP-localization Results and Figure 7E-F establish localization and the deletion phenotype. The cytoplasmic adapter is O94488/SPCC417.07c, not the homonymous mitochondrial O13670. `https://www.uniprot.org/uniprotkb/O94488/entry` Reviewed entry, gene aliases and source taxon verified live on 2026-10-05; localization comes from the primary experiment.

Mto2-like microtubule nucleation adaptor

Accession	Protein	Gene	Organism	Entry
`UniProtKB:Q9USP7`	Gamma tubulin complex adapter mto2	mto2	Schizosaccharomyces pombe 972h- (`NCBITaxon:284812`)	REVIEWED
Role and evidence (2 references) Reference-sequence exemplar for the species-level experiment; this accession does not assert that the exact reference stock was imaged. `DOI:10.1083/jcb.201502025` Figure 4A-B: Mto2-GFP redistributes onto RFP-Atb2-positive bundles. `https://www.uniprot.org/uniprotkb/Q9USP7/entry` Reviewed entry, gene aliases and source taxon verified live on 2026-10-05; localization comes from the primary experiment.

Microtubule-associated protein, MAP65/Ase1/PRC1

Accession	Protein	Gene	Organism	Entry
`UniProtKB:Q9HDY1`	Anaphase spindle elongation protein 1	ase1	Schizosaccharomyces pombe 972h- (`NCBITaxon:284812`)	REVIEWED
Role and evidence (2 references) Reference-sequence exemplar for the species-level experiment; this accession does not assert that the exact reference stock was imaged. `DOI:10.1083/jcb.201502025` Figure 4C: GFP-tagged protein colocalizes with RFP-Atb2 in five-day cultures. Figure 4D-F shows retained bundles after ase1 deletion. `https://www.uniprot.org/uniprotkb/Q9HDY1/entry` Reviewed entry, gene aliases and source taxon verified live on 2026-10-05; localization comes from the primary experiment.

CLASP-like microtubule-associated protein

Accession	Protein	Gene	Organism	Entry
`UniProtKB:O42874`	Protein peg1	peg1	Schizosaccharomyces pombe 972h- (`NCBITaxon:284812`)	REVIEWED
Role and evidence (2 references) Reference-sequence exemplar for the species-level experiment; this accession does not assert that the exact reference stock was imaged. `DOI:10.1083/jcb.201502025` Figure 4C: GFP-tagged protein colocalizes with RFP-Atb2 in five-day cultures. The paper calls this protein Cls1/Peg1. `https://www.uniprot.org/uniprotkb/O42874/entry` Reviewed entry, gene aliases and source taxon verified live on 2026-10-05; localization comes from the primary experiment.

Alp7-like microtubule-associated protein

Accession	Protein	Gene	Organism	Entry
`UniProtKB:Q9URY2`	Microtubule protein alp7	alp7	Schizosaccharomyces pombe 972h- (`NCBITaxon:284812`)	REVIEWED
Role and evidence (2 references) Reference-sequence exemplar for the species-level experiment; this accession does not assert that the exact reference stock was imaged. `DOI:10.1083/jcb.201502025` Figure 4C: GFP-tagged protein colocalizes with RFP-Atb2 in five-day cultures. Figure 4D-F documents bundles in alp7 deletion cells. `https://www.uniprot.org/uniprotkb/Q9URY2/entry` Reviewed entry, gene aliases and source taxon verified live on 2026-10-05; localization comes from the primary experiment.

XMAP215

Accession	Protein	Gene	Organism	Entry
`UniProtKB:O94534`	Spindle pole body component alp14	alp14	Schizosaccharomyces pombe 972h- (`NCBITaxon:284812`)	REVIEWED
Role and evidence (2 references) Reference-sequence exemplar for the species-level experiment; this accession does not assert that the exact reference stock was imaged. `DOI:10.1083/jcb.201502025` Figure 4C: GFP-tagged protein colocalizes with RFP-Atb2 in five-day cultures. Figures 5B and 7C-D link Alp14 to elongating tips and the exit defect. `https://www.uniprot.org/uniprotkb/O94534/entry` Reviewed entry, gene aliases and source taxon verified live on 2026-10-05; localization comes from the primary experiment.
`UniProtKB:Q09933`	Phosphoprotein p93	dis1	Schizosaccharomyces pombe 972h- (`NCBITaxon:284812`)	REVIEWED
Role and evidence (2 references) Reference-sequence exemplar for the species-level experiment; this accession does not assert that the exact reference stock was imaged. `DOI:10.1083/jcb.201502025` Figure 4C: GFP-tagged protein colocalizes with RFP-Atb2 in five-day cultures. Figure 4D-F shows longer bundles in dis1 deletion cells. `https://www.uniprot.org/uniprotkb/Q09933/entry` Reviewed entry, gene aliases and source taxon verified live on 2026-10-05; localization comes from the primary experiment.

Klp2-like kinesin-14 motor

Accession	Protein	Gene	Organism	Entry
`UniProtKB:Q9US03`	Kinesin-like protein 2	klp2	Schizosaccharomyces pombe 972h- (`NCBITaxon:284812`)	REVIEWED
Role and evidence (2 references) Reference-sequence exemplar for the species-level experiment; this accession does not assert that the exact reference stock was imaged. `DOI:10.1083/jcb.201502025` Figure 4C: GFP-tagged protein colocalizes with RFP-Atb2 in five-day cultures. Figure 4D-F includes klp2 deletion bundles. `https://www.uniprot.org/uniprotkb/Q9US03/entry` Reviewed entry, gene aliases and source taxon verified live on 2026-10-05; localization comes from the primary experiment.

Tea1-like polarity landmark protein

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P87061`	Tip elongation aberrant protein 1	tea1	Schizosaccharomyces pombe 972h- (`NCBITaxon:284812`)	REVIEWED
Role and evidence (2 references) Reference-sequence exemplar for the species-level experiment; this accession does not assert that the exact reference stock was imaged. `DOI:10.1083/jcb.201502025` Figures 6A and 7A: Tea1-GFP redistribution onto the quiescent bundle and back to cell tips. `https://www.uniprot.org/uniprotkb/P87061/entry` Reviewed entry, gene aliases and source taxon verified live on 2026-10-05; localization comes from the primary experiment.

Canonical examples

NCBITaxon:4896 Schizosaccharomyces pombe — Species examined by GFP-Atb2 microscopy, freeze-substitution TEM and serial electron tomography after nutrient exhaustion. ENA confirms the species identifier; no all-fungi prevalence or exact stock identity is asserted. [DOI:10.1083/jcb.201502025]

Functions

Polarity reestablishment after quiescence — Elongation of the pre-existing bundle and restoration of microtubule dynamics support timely return of polarity factors and actin organization to cell tips in refed S. pombe.
- DOI:10.1083/jcb.201502025 Figures 5 and 7: refeeding, MBC treatment, alp14 deletion and cold-treated mto1 deletion distinguish regrowth and polarity defects. The interventions also affect new microtubules, so they do not isolate an exclusive bundle-only pathway.

Mechanism graphs

Microtubule recovery supports polarity reestablishment (FUNCTION)

S. pombe quiescence exit; a physiological mechanism, not a resolved glucose-sensing pathway. Recovery includes elongation of the old bundle and new interphase microtubules, which the perturbations do not selectively separate.

Subject	Predicate	Object	Evidence
Glucose refeeding	stimulates	Q-MT elongation and recovery of microtubule dynamics	`DOI:10.1083/jcb.201502025` Figure 5A and quiescence-exit Results: glucose-only refeeding and cycloheximide experiments. Translation-independent microtubule remodeling does not mean cell growth is translation independent.
Q-MT elongation and recovery of microtubule dynamics	supports	Cell-tip polarity reestablishment	`DOI:10.1083/jcb.201502025` Figure 7A-F: MBC, alp14 deletion and cold-treated mto1 deletion impair or delay repolarization and alter subsequent cell shape. These perturbations affect microtubules beyond the pre-existing bundle; no unique sufficiency or exclusive pathway is asserted.

Discussions

CURATION_TODO (RESOLVED): Keep the cytoplasmic fission-yeast bundle distinct from generic static bundles and budding-yeast nuclear arrays. GO:0099070 is broader and explicitly marks Q-MT names as narrow synonyms. GO:1905720 is also broader. Hidden- and ignored-inclusive searches and parsed corpus identities found no existing Q-MT record. The 2015 Discussion distinguishes antiparallel cytoplasmic Q-MT from the parallel nuclear S. cerevisiae array; the 2024 eLife study concerns the latter. OTHER denotes the whole multi-filament array, not a single FILAMENT.
CURATION_TODO (RESOLVED): Do not turn frequent spindle-pole-body attachment into universal parthood. Figure 1C and Discussion include unattached bundles. The array is part of the cytoplasm and microtubule cytoskeleton, not modeled as a constitutive subpart of the spindle pole body.
CURATION_TODO (OPEN): Find exact whole-protein families for six label-only component classes. Live complete InterPro lookups were checked for Mto1 O94488, Mto2 Q9USP7, Cls1/Peg1 O42874, Alp7 Q9URY2, Klp2 Q9US03 and Tea1 P87061. Missing exact family grounding remains explicit; domains, repeats and the generic kinesin family are not substituted. Revisit when an authority supplies an exact family.
CURATION_TODO (RESOLVED): Separate bundle residents from perturbation-only factors and neighboring actin bodies. Mal3 and Tip1 were not detected in quiescent cells; Klp5/Klp6 deletion changes bundle dimensions but does not itself show residence in the read experiments. Actin-body proteins Fim1, Acp2 and App1, plus cell-pole markers/exocyst subunits, are not imported as Q-MT residents. No gamma-tubulin complex is added solely from the proposed Mto1/Mto2 assembly model.
KNOWLEDGE_GAP (OPEN): Resolve the molecular basis of quiescent bundle stabilization. Mto1 deletion supports a requirement for the bona fide stable architecture, while proposed Mto1/Mto2-dependent nucleation and microtubule pile-up in Figure 8 remain models. The paper does not identify a quiescence-specific capper or establish a GTP-depletion mechanism. FRAP, drug and cold resistance bound stability to the measured assays rather than proving zero turnover indefinitely.
CURATION_TODO (RESOLVED): Separate efficient polarity recovery from longevity or immediate tubulin-store release. Refeeding stimulates growth from bundle ends while early bundle intensity persists, supporting use of free cytoplasmic tubulin. MBC and alp14 deletion affect both old-bundle elongation and new interphase bundles; cold-treated mto1 deletion removes cytoplasmic microtubules more broadly. These interventions support microtubule-dependent repolarization, not an exclusive Q-MT-only pathway or demonstrated survival/protein-protection function.
CURATION_TODO (RESOLVED): Retain measurement context without inventing a universal size or stoichiometry. Figure 1B microtubule numbers are estimated from calibrated GFP-Atb2 intensity, as specified in fluorescence microscopy Methods, not directly counted in every bundle. Bundle lengths, occupancy and polymer number vary with culture age and mutant. TEM/tomography establish architecture; no fixed physical-property value is imposed.
CURATION_TODO (RESOLVED): Avoid family-wide prevalence and unverified strain or dataset claims. Only S. pombe is a canonical example. Protein accessions are reference-sequence exemplars, not a claim that reference strain 972h- was the imaged stock; supplementary strain Table S1 was not inspected. The adopted iModulonDB inventory lists 28 datasets and no S. pombe dataset. No broad fungal distribution, TraitMech link, exact Complex Portal composition or structural dataset is inferred.

Evidence

DOI:10.1083/jcb.201502025 Laporte et al. (2015), PMID 26124291. Native PMC4494004.1 Results, Discussion and Methods read; Figures 1 and 4 visually inspected. Primary fluorescence, perturbation and ultrastructural evidence.
GO:0099070 Native non-obsolete static microtubule bundle entry has Q-MT names as NARROW synonyms: broader parent, not identity.
GO:1905720 Native cytoplasmic microtubule bundle term is a broader is-a parent.
GO:0015630 — microtubule cytoskeleton Native microtubule cytoskeleton term denotes the encompassing framework.
GO:0005737 — cytoplasm Native cytoplasm term supports the compartment relation; the nucleus is excluded.
GO:0005881 Native cytoplasmic microtubule term describes constituent polymers, not the whole bundle.

Curation history

2026-10-05T15:41:08Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-05T15:43:21Z codex · EXPANDED_RECORD — Added ten component classes and ten verified protein examples, bounded function and graph, inspected link-only imaging, and explicit identity, grounding and experimental limitations.
2026-10-05T15:43:57Z codex · REFINED_PROVENANCE — Added direct GO, comparative literature, InterPro, taxonomy and dataset-inventory provenance to boundary discussions.
2026-10-11T21:55:48Z codex · ADDRESS_SAVED_REVIEW — Addressed #2259: exposed preserved discussion explanations and graph scope in supported display fields.

Source: data/structures/cytoskeleton/quiescent_cell_microtubule_bundle.yaml