Coiled bodies are a special type of small round nuclear body, composed of coiled fibers and granules, especially prominent in the nucleoplasm of highly active cells (Brasch and Ochs (1992) Exp. Cell Res. 202, 211-223). Although no specific function has been assigned to coiled bodies, they contain spliceosome snRNAs and
proteins, as well as the nucleolar U3
RNA-associated
protein fibrillarin. In the present study, we have used
antibodies to the coiled body-specific
protein p80-coilin, together with double-label immunofluorescence, confocal microscopy and immunoelectron microscopy, to examine the distribution of coiled bodies in a number of different
breast cancer cell lines. By immunofluorescence, all cell lines had prominent coiled bodies in the nucleoplasm and several cell lines appeared to have coiled bodies within the nucleolus itself. Double-label immunofluorescence and confocal
laser scanning microscopy confirmed the nucleolar localization of coiled bodies. Besides containing
p80-coilin, nucleoplasmic and nucleolar coiled bodies contained
fibrillarin and Sm
proteins. By conventional and immunoelectron microscopy, nucleolar coiled bodies appeared as discrete structures within the nucleolus in a number of different morphotypes, distinct from the normal nucleolar domains of granular component, dense fibrillar component, and fibrillar centers. While the significance of finding coiled bodies in the nucleolus of certain
breast cancer cell lines is at present unknown, this represents the first report of coiled bodies and Sm staining in the nucleolus of mammalian cells.