sphere organelle

GO:0071601 · Ribonucleoprotein · Other · Proposed

A nuclear body that is found in the germinal vesicles of amphibian oocytes, and consist of three major parts: a remarkably spherical body about 5-10 pm in diameter, smaller spherical or nearly spherical granules on the surface, and inclusions of various sizes that strongly resemble the surface granules. The parts of the sphere organelle have distinct compositions, including splicing snRNAs and proteins. [GO:0071601]

Part of: nuclear lumen (GO:0031981)

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
coilin/SPH-1	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Coilin-related SPH-1 protein concentrated in the cortex of Xenopus laevis sphere organelles. `DOI:10.1083/jcb.122.4.767` Tuma, Stolk and Roth 1993 localized SPH-1 specifically to the cortex of Xenopus laevis sphere organelles and found that cloned SPH-1 encodes a p80-coilin-related protein.
U7 snRNA	Rna	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Small nuclear RNA concentrated in amphibian oocyte sphere organelles and able to induce coiled-body-like structures when increased in Xenopus oocyte nuclei. `DOI:10.1007/s004120050385` Tuma and Roth 1999 described amphibian oocyte sphere organelles as coiled bodies containing high concentrations of U7 snRNA and showed that increasing nuclear U7 snRNA induced coiled-body-like structures in Xenopus oocytes.

Taxonomic distribution

NCBITaxon:8355 Xenopus laevis — VARIABLE: Sphere organelles were characterized in Xenopus laevis oocyte germinal vesicles as large nuclear bodies marked by cortex-localized SPH-1. [DOI:10.1083/jcb.122.4.767]

Canonical examples

NCBITaxon:8355 Xenopus laevis — Xenopus laevis oocytes were used to clone SPH-1 and localize SPH-1 to the sphere-organelle cortex. [DOI:10.1083/jcb.122.4.767]

Mechanism graphs

SPH-1 and U7 snRNA mark sphere organelles (ASSEMBLY)

Xenopus laevis sphere organelles contain cortex-localized coilin-related SPH-1 protein and U7 snRNA, and increased U7 snRNA can induce coiled-body-like structures in oocyte nuclei.

Subject	Predicate	Object	Evidence
coilin/SPH-1	localizes to	sphere organelle	`DOI:10.1083/jcb.122.4.767` Tuma, Stolk and Roth 1993 localized SPH-1 specifically to sphere organelles and placed it at the sphere cortex.
U7 snRNA	induces	coiled body-like structure	`DOI:10.1007/s004120050385` Tuma and Roth 1999 showed that injecting U7 snRNA or functional U7 snRNA genes induced coiled-body-like structures in vivo.

Discussions

CURATION_TODO (OPEN): Resolve the full RNA/protein composition and Cajal-body homology boundary for amphibian oocyte sphere organelles. This first GO:0071601 record captures SPH-1/coilin and U7 snRNA while leaving other splicing snRNAs, sphere surface granule proteins, amphibian species breadth and the exact sphere-organelle/Cajal-body homology model to a later pass.

Evidence

GO:0071601 Gene Ontology cellular-component term for sphere organelle.
GO:0016604 Gene Ontology cellular-component parent term for nuclear body.
GO:0031981 Gene Ontology cellular-component term for the nuclear lumen; sphere organelles are amphibian-oocyte germinal-vesicle nuclear bodies.
DOI:10.1002/dvg.1020160107 Gall, Tsvetkov, Wu and Murphy 1995 reviewed the sphere organelle/coiled body as a nuclear component related to coiled bodies, prenucleolar bodies and insect Binnenkorper.
DOI:10.1083/jcb.122.4.767 Tuma, Stolk and Roth 1993, Identification and characterization of a sphere organelle protein, Journal of Cell Biology.
DOI:10.1091/mbc.5.10.1119 Wu, Murphy and Gall 1994 targeted human p80-coilin to sphere organelles in Xenopus oocyte germinal vesicles.
DOI:10.1007/s004120050385 Tuma and Roth 1999, Induction of coiled body-like structures in Xenopus oocytes by U7 snRNA, Chromosoma.

Curation history

2026-09-28T06:33:59Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-28T06:35:07Z codex · EXPANDED_RECORD — Added nuclear-body parentage, nuclear-lumen parthood, SPH-1/coilin and U7 snRNA components, Xenopus laevis scope, GO/DOI evidence, a nonmechanistic SPH-1/U7 sphere-organelle assembly graph and a sphere/Cajal-body boundary TODO.
2026-09-28T06:35:52Z codex · TIGHTENED_EVIDENCE — Narrowed the Xenopus laevis canonical-example note to the SPH-1 cloning and sphere-cortex localization claim supported by its Tuma, Stolk and Roth 1993 reference.

Source: data/structures/ribonucleoprotein/sphere_organelle.yaml