Nuclear bodies (NBs): a newly "rediscovered" organelle.

Nuclear bodies (NBs) were first described in detail some 30 years ago, by conventional electron microscopy, as prominent interchromatin structures found primarily in the nuclei of malignant or hyperstimulated animal cells. Subsequent studies have shown that NBs are ubiquitous organelles, but they are numerically and morphologically quite varied. With the recent discovery of human autoantibodies against several key nuclear antigens present in some NBs, these structures are once again the subject of much attention. At least one class of NBs, coiled bodies, has been shown to be nucleolus-derived and to contain not only nucleolus-associated antigens, but also many of the snRNP components involved in pre-mRNA splicing. These data suggest that coiled bodies, and perhaps other NBs as well, are multifunctional and may be involved in the processing or transport of both pre-mRNA and pre-rRNA. Further evidence is provided showing that NBs constitute distinct nuclear domains whose functional significance is just now emerging.