The nuclei of epithelial cells of the uterine cervix of normal women and of patients with various degrees of dysplasia, carcinoma in situ, and invasive carcinoma were studied by means of electron microscopy. Nuclear ribonucleoprotein components and chromatin were contrasted using preferential methods for RNA and DNA. Changes in the distribution of the extranucleolar ribonucleoprotein-containing structures were found, ranging from low-grade dysplastic lesions to invasive carcinoma. Compared with normal epithelial cells, dysplastic and neoplastic cells possess more nuclear bodies, as well as deep invaginations of the nuclear envelope and lobulations. Morphometric parameters estimated were nuclear volume, numerical density of perichromatin granules (PCG), and fraction of nuclear volume occupied by compact chromatin. The pattern of values of these parameters in the cell layers of normal cervical epithelium was disrupted in all the lesions. These data suggest that the processes studied induce early alterations in transcription and processing and/or exportation of mRNA to the cytoplasm. Two populations of cells were found in invasive carcinomas, one with large nuclei, sparse compact chromatin, and few PCG, and the other with small nuclei, abundant compact chromatin, and numerous PCG. Their morphologic features indicate that the former population is composed of relatively undifferentiated cells, while the letter is made up of well-differentiated cells which could be neoplastic or entrapped normal cells.

In order to study if there are differences between cells of the same tissue with one and two nucleoli, nuclear and nucleolar volume, density of tritiated uridine incorporation, amount of DNA per nucleus and intensity of cytoplasmic basophilia were measured in mononucleolated and binucleolated rat epithelial endometrial cells, in onion root meristematic cells and in chick embryo matrix cells of the central nervous system, neuroblasts and neurons. No significant differences in nuclear volume, density of tritiated uridine incorporation and amount of DNA per nucleus were found between cells of the same type with diverse numbers of nucleoli. Binucleolated endometrial cells, matrix cells, and root meristematic cells have biphasic distributions of nucleolar volumes. One peak of this distribution roughly coincides with the nucleolar volume of mononucleolated cells, the other peak corresponds almost to double the volume. As the density of uridine incorporation is the same irrespective of the nucleolar number and volume, the cells with larger nucleolar volumes have higher pre-rRNA synthesis. These cells also have higher amounts of ribosomes in the cytoplasm, as revealed by the photometric study of basophilia. It is concluded that in this population of cells the ribosomal production is regulated to a higher steady equilibrium than in the general population. This difference is not due to polyploidism or to the increased DNA content of G2 phase cells. Binucleolated neuroblasts and neurons have nucleolar volumes similar to those of mononucleolated ones.

The localization and abundance of the estrogen receptor activation factor (E-RAF) and a small nuclear ribonucleoprotein (snRNP) complex containing three proteins, p32, p55 and p60, which interact with the nuclear estrogen receptor II (nER II), have been studied in rat endometrial epithelial cells by means of immunofluorescence and high resolution quantitative immunocytochemistry. In the cytoplasm E-RAF is associated with the rough endoplasmic reticulum. In the nucleus it is mainly localized at the interchromatin space, and surrounding the clumps of compact or semi-condensed chromatin. Quantitative analyses show that the abundance of E-RAF in the nucleus increases after ovariectomy and decreases 3 minutes after estradiol administration. These results are in agreement with the currently available biochemical data. Double immunolocalizations demonstrate that p32, p55, p60 co-localize with other splicing-related protein. High resolution immunolocalization shows that p32, p55, p60 are associated with perichromatin fibrils (co-transcriptional splicing) and with clusters of interchromatin granules (storage of splicing-related molecules). The nuclear abundance of the snRNP complex decreases with ovariectomy, increases within 3 minutes after estradiol administration and remains higher than that in ovariectomized animals for 27 minutes. These results strongly support the previous data on the role of nER-II in the regulation of mRNA transcription and its export from the nucleus to the cytoplasm.

Genetic variability in sexually reproducing organisms results from an exchange of genetic material between homologous chromosomes. The genetic exchange mechanism is dependent on the synaptonemal complex (SC), a protein structure localized between the homologous chromosomes. Current structural models of the SC are based on electron microscopy, super resolution, and expansion microscopy studies using chemical fixatives and sample dehydration of gonads, which are methodologies known to produce structural artifacts. We have developed a novel electron microscopy sample-preparation approach where pachytene cells are isolated from mouse testis by FACS, followed by cryo-fixation and cryo-substitution to achieve visualization of a close-to-native structure of the SC. We found that the central region of the SC was wider than previously recognized, and the transverse filaments more densely packed in the central region. Furthermore, we identified a structure nucleating the central element of the SC.

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