Nuclear bodies in mouse splenic lymphocytes: II - Cytochemistry and autoradiography during stimulation by concanavalin A.

Nuclear bodies (NB) are poorly understood nucleoplasmic structures frequently observed in many animal cell types. Murine lymphocytes mitogenically stimulated with concanavalin A contain 5 types of NB. In order to examine the origin and function of the NB we have carried out cell fractionation and have performed cytochemistry, immunocytochemistry and autoradiography at the electron microscope level. Regressive staining for RNP showed that simple NB (types I and II) and the shells of complex NB (types III, IVa and V) consist of a non-chromatinic fibrillar material which is most likely proteinaceous. Projections of this material from the NB surface appear to link the NB to nucleoplasmic fibrogranular elements. The fibrillar, filamentous and granular components of the cores of complex NB were largely RNP and in some instances closely resembled fibrogranular areas in the nucleoplasm. Chromatin masses were seen occasionally in the cores. All NB types remained unstained after nucleolus-specific silver nitrate staining, and were also not stained by a centromere-specific antibody. Autoradiography was performed along long-term labelling with 3H-uridine, 3H-thymidine or 3H-leucine. The NB were not labelled by any of the precursors, indicating that macromolecular synthesis does not play a major role in NB evolution in these cells. By fractionation, we showed that NB co-isolated with the nuclear matrix, and were linked to the fibrogranular nuclear matrix component by projections from the surface of the NB. A possible role of NB in RNA processing is discussed.