COIL (coilin) is the defining protein component of Cajal bodies (CBs), specialized nuclear organelles involved in small nuclear ribonucleoprotein (snRNP) modification and assembly. As a structural scaffolding protein, coilin localizes to the nucleoplasm and nucleolus, where it organizes the assembly of spliceosomal snRNPs through direct interaction with U1 and U2 snRNA species. The protein's role in nucleoplasmic snRNP biogenesis is essential for pre-mRNA splicing function. Coilin also participates in identical protein binding interactions, suggesting its involvement in higher-order oligomerization within Cajal body architecture. While the provided abstracts do not contain specific information regarding COIL mutations or direct disease associations, the protein's critical function in snRNP assembly indicates that COIL dysfunction would likely impair splicing capacity and cellular viability. The precise mechanisms by which coilin mutations contribute to human disease remain incompletely characterized in the available literature, though defects in Cajal body formation and function have been implicated in various pathological conditions affecting gene expression regulation.