THE IMMUNOLOCALIZATION OF SMALL NUCLEAR RIBONUCLEOPROTEIN-PARTICLES IN TESTICULAR CELLS DURING THE CYCLE OF THE SEMINIFEROUS EPITHELIUM OF THE ADULT-RAT

The objective of this study was to determine the cellular and subcellu lar distribution of small nuclear ribonucleoprotein particles (snRNPs) in the adult rat testis in relation to the different cell types at th e various stages of the cycle of the seminiferous epithelium. The dist ribution of snRNPs in the nucleus and cytoplasm of germ cells was quan titated in an attempt to correlate RNA processing with morphological a nd functional changes occurring during the development of these cells. Light-microscopic immunoperoxidase staining of rat testes with polycl onal anti-Sm and monoclonal anti-Y12 antibodies localized spliceosome snRNPs in the nuclei and cytoplasm of germ cells up to step 10 spermat ids. Nuclear staining was intense in Sertoli cells, spermatogonia, spe rmatocytes, and in the early steps of round spermatid development. Alt hough comparatively weaker, cytoplasmic staining for snRNPs was strong est in mid and late pachytene spermatocytes and early round spermatids . Quantitative electron-microscopic immunogold labeling of Lowicryl em bedded testicular sections confirmed the light-microscopic observation s but additionally showed that the snRNP content peaked in the cytopla sm of mid-pachytene spermatocytes and in the nuclei of late pachytene spermatocytes. The immunogold label tended to aggregate into distinct loci over the nuclear chromatin. The chromatoid body of spermatids and spermatocytes and the finely granular material in the interstices of mitochondrial aggregates of spermatocytes were found to be additional sites of snRNP localization and were intensely labeled. This colocaliz ation suggests that these dense cytoplasmic structures may be function ally related. Anti-U1 snRNP antibodies applied to frozen sections show ed the same LM localization pattern as spliceosome snRNPs. Anti-U3 snR NP antibodies applied to frozen sections stained nucleoli of germ cell s where pre-rRNA is spliced.