The Cajal body (CB) is a conserved non-membrane nuclear structure where several steps of small nuclear RNP particle (snRNP) biogenesis take place. It has been proposed that CB formation follows a liquid-liquid phase separation model, but this hypothesis has never been rigorously tested. Here, we applied live-cell imaging to show that the key CB assembly factor coilin is mobile within the CB, and we revealed a diffusion barrier that limits the coilin exchange between CBs and the nucleoplasm. We generated single aa mutations and demonstrated that RNA-dependent coilin oligomerization and coilin interaction with snRNP are essential for CB formation and maintenance. We applied these data to formulate a mathematical model that links the movement of coilin within the nucleoplasm, CB, and across the boundary with its oligomerization and snRNP binding. Our results illustrate CB as a structure dynamically responding to snRNP assembly and recycling.

• MeSH
• Coiled Bodies * metabolism   genetics   MeSH
• HeLa Cells MeSH
• Nuclear Proteins * metabolism   genetics   MeSH
• Humans MeSH
• Protein Multimerization MeSH
• Mutation MeSH
• Ribonucleoproteins, Small Nuclear * metabolism   genetics   MeSH
• Spliceosomes * metabolism   genetics   MeSH
• Protein Binding MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Nuclear Proteins * MeSH
• p80-coilin MeSH Browser
• Ribonucleoproteins, Small Nuclear * MeSH

The nucleus of higher eukaryotes contains a number of structures that concentrate specific biomolecules and play distinct roles in nuclear metabolism. In recent years, the molecular mechanisms controlling their formation have been intensively studied. In this brief review, I focus on coilin and Cajal bodies. Coilin is a key scaffolding protein of Cajal bodies that is evolutionarily conserved in metazoans. Cajal bodies are thought to be one of the archetypal nuclear structures involved in the metabolism of several short non-coding nuclear RNAs. Yet surprisingly little is known about the structure and function of coilin, and a comprehensive model to explain the origin of Cajal bodies is also lacking. Here, I summarize recent results on Cajal bodies and coilin and discuss them in the context of the last three decades of research in this field.

• Keywords
• Cajal bodies, coilin, snRNA, snRNP, snoRNA, telomerase RNA,
• MeSH
• Cell Nucleus * MeSH
• Coiled Bodies * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH