IMMUNOCYTOCHEMICAL CHARACTERIZATION OF NUCLEAR RIBONUCLEOPROTEIN FIBRILS IN CELLS OF THE CENTRAL-NERVOUS-SYSTEM OF THE RAT

Nucleoplasmic structural constituents observed in partially decondense d nuclei of the central nervous system of the rat were analyzed by pos tembedding immunoelectron microscopy using antibodies specifically rec ognizing heterogenous nuclear ribonucleoprotein (hnRNP) and small nucl ear ribonucleoprotein (snRNP) complexes and DNA. Fibrogranular RNP str uctures (polyparticles) were found in close proximity to DNA containin g fibrillar areas resulting from partial dispersion of compact chromat in, The polyparticle-type fibrils are labeled by antibodies recognizin g hnRNP core proteins as well as snRNPs (Sm antigen or 70 kDa protein of U1snRNP) or the m(3)G-cap structure of snRNAs, These observations s uggest that such polyparticle-type fibrils correspond to extended peri chromatin fibrils. Partially decondensed perichromatin granules are ra rely labeled by anti-snRNP or snRNA antibodies. When labeling occurs i t is restricted to the periphery of the granules. However, anti-hnRNP antibodies frequently label these granules, Our results favor the idea , previously proposed for Balbiani ring granules, that perichromatin g ranules are formed by the folding of hnRNP containing perichromatin fi brils (polyparticles) in the process of splicing, and that mature peri chromatin granules contain already spliced messenger RNA.