Nucleolar changes in human phytohaemagglutinin-stimulated lymphocytes

Leukocyte Nucleolus and Anisakis pegreffii-When Falling Apart Means Falling in Place

The view of the nucleolus as a mere ribosomal factory has been recently expanded, highlighting its essential role in immune and stress-related signalling and orchestrating. It has been shown that the nucleolus structure, formed around nucleolus organiser regions (NORs) and attributed Cajal bodies, is prone to disassembly and reassembly correlated to various physiological and pathological stimuli. To evaluate the effect of parasite stimulus on the structure of the leukocyte nucleolus, we exposed rat peripheral blood mononuclear cells (PBMC) to the crude extract of the nematode A. pegreffii (Anisakidae), and compared the observed changes to the effect of control (RPMI-1640 media), immunosuppressive (MPA) and immunostimulant treatment (bacterial lipopolysaccharide (LPS) and viral analogue polyinosinic:polycytidylic acid (poly I:C)) by confocal microscopy. Poly I:C triggered the most accentuated changes such as nucleolar fragmentation and structural unravelling, LPS induced nucleolus thickening reminiscent of cell activation, while MPA induced disassembly of dense fibrillar and granular components. A. pegreffii crude extract triggered nucleolar segregation, expectedly more enhanced in treatment with a higher dose. This is the first evidence that leukocyte nucleoli already undergo structural changes 12 h post-parasitic stimuli, although these are likely to subside after successful cell activation.

Spatial organization of transcription by RNA polymerase III

RNA polymerase III (pol III) transcribes many essential, small, noncoding RNAs, including the 5S rRNAs and tRNAs. While most pol III-transcribed genes are found scattered throughout the linear chromosome maps or in multiple linear clusters, there is increasing evidence that many of these genes prefer to be spatially clustered, often at or near the nucleolus. This association could create an environment that fosters the coregulation of transcription by pol III with transcription of the large ribosomal RNA repeats by RNA polymerase I (pol I) within the nucleolus. Given the high number of pol III-transcribed genes in all eukaryotic genomes, the spatial organization of these genes is likely to affect a large portion of the other genes in a genome. In this Survey and Summary we analyze the reports regarding the spatial organization of pol III genes and address the potential influence of this organization on transcriptional regulation.

Repositioning of human interphase chromosomes by nucleolar dynamics in the reverse transformation of HT1080 fibrosarcoma cells

An experimental system which should be valuable for studying the role of spatial positioning of the nuclear genome in human cell function has been developed. Reverse transformation of the malignant HT1080 fibrosarcoma cell line upon treatment with 8-chloro-cAMP results in growth inhibition, cytoskeletal reorganization, changes in nuclear shape and chromatin accessibility, and formation of prominent nucleoli. Fluorescent in situ hybridization was used to study DNA positioning during nuclear remodeling. Morphometric analysis of the hybridization sites for both repetitive sequences and "painting probes" for whole chromosomes indicated dispersal of acrocentric chromosomes in untreated cells and a highly organized central location of these ribosome gene-containing chromosomes in association with one or a few large nucleoli in nondividing treated cells. The results suggest that there was a directed movement of interphase chromosomes during a response which normalized a malignant cell line. These large-scale repositionings may serve two functions in restoring a normal transcriptional setup to the nucleus. First, ribosome genes are placed in the nucleolus, their transcriptional suborganelle. Second, nucleolar anchorings together with additional perinucleolar centromeric associations orient the domain shapes of entire chromosomes, installing gene-rich chromosomal regions into pockets of (accessible) DNAse I-sensitive chromatin populated by spliceosomes.

Number of nucleoli and coiled bodies and distribution of fibrillar centres in differentiating Purkinje neurons of chick and rat cerebellum

We used differentiating chick and rat Purkinje cells to investigate in homologous neurons the influence of the number of nucleolar organizer regions (two in the chick and six in the rat) on the behaviour of the nucleolus and coiled bodies. We employed specific silver-staining methods on smear preparations and on semithin and ultrathin sections. In chick Purkinje cells the number of nucleolar silver-staining granules increased from 15.7 +/- 3 (mean +/- SD) at embryonic day 13 to 23.8 +/- 3 at post-hatching day 7. These nucleolar granules were unevenly distributed between the two nucleoli of binucleolated cells. Electron-microscopic cytochemistry showed that nucleolar granules are equivalent to the fibrillar centres with their associated shell of dense fibrillar component. A reduction in the number of nucleoli was found during the differentiation of both chick and rat Purkinje cells, although in mature cells the average number of nucleoli per cell was higher in the chick (1.60) than in the rat (1.07). The number of coiled bodies decreased from 1.33 in newborn rats to 0.47 at postnatal day 90 in the rat. Coiled bodies were not observed in homologous chick Purkinje cells. The dynamic behaviour of nucleoli and coiled bodies during neuronal differentiation and the relationship of these two nuclear organelles with the number of nucleolar organizer regions is discussed.

The nucleolus

Nucleoli are the sites of biosynthesis of the ribosomal precursors. They contain may copies of the genes for the main rRNAs (18S- and 28 S-rRNA) in the form of tandemly arranged repeats at the chromosomal nucleolar organizer regions (NORs). They also contain the small rRNA (5S-rRNA) that is synthesized outside the nucleolus, specific nucleolar proteins, among them the factors and enzymes necessary for transcription and transcript processing, and the precursor units of the ribosomes. In man as in may vertebrate species, three main components of nucleoli, besides chromatin, can be detected: fibrillar centres (FC), dense fibrillar component (DCF), and granular component (GC). Within a nucleolus the FCs are in many cases situated in its central region. The DFc forms a network of strands surrounding the FCs, but may sometimes reach for out towards the periphery of the nucleolus. The GC is usually situated in the peripheral regions of the nucleolus. In cells with a low level of ribosomal biosynthesis the nucleoli are small, usually with a single FC and little surrounding DFC and GC ("ring-shaped nucleolus"). In active cells the DFC forms a large network enclosing several, sometimes up to hundreds of FCs, and the GC covers a large area in the periphery ("compact nucleoli"). In cells at the onset of a new stimulation, the DFC is very prominent whereas the FCs are few and small, and the GC is also not very extensive ("reticulate nucleoli"). In some special cell types that are very active other arrangements of the structural components are found. In Sertoli cells, for instance, only one nucleolus is found, or occasionally two, each with a single large FC and a distinct area of GC, both areas being engulfed by DFC intermingled with some peripheral GC. Immunocytological and in situ hybridization studies to localize the rRNA genes within the nucleolus have so far led to divergent results. Both fibrillar components, the FCs and the DFC, have been claimed as the most probable candidates. Transcription of rDNA and the subsequent early steps of ribosome biosynthesis are localized in the DFC, whereas later steps (mature rRNA, preribosomes) are localized in the GC. The FCs may also serve as sites for the preparation of the rDNA for transcription, and as a store for certain nucleolar proteins. During mitosis, parts of the nucleolar proteins remain at the NORs. A direct contact between the nucleolus and the nuclear envelope is frequently observed but is not dependent on nucleolar activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Nucleolar silver staining patterns and HLA-DR antigen expression in bronchial epithelial cells in chronic bronchitis

Bronchial epithelial cells obtained by brush biopsy during fiberoptic bronchoscopy performed in 12 patients with chronic bronchitis and 12 healthy control subjects, were investigated for HLA-DR antigen expression and nucleolar silver staining patterns. In all patients with chronic bronchitis the number of bronchial epithelial cells positive to HLA-DR antigen was highly increased (> 90%), whereas in the controls only a few epithelial cells (< 10%) showed a weak HLA-DR antigen expression. Patients with chronic bronchitis showed an increased lymphocytic reaction compared to the control subjects. Both in the patients with chronic bronchitis and in the healthy controls the number of nucleoli was the same. The number of silver stained dots per nucleus was significantly higher in patients with chronic bronchitis than in the control subjects (7.70 +/- 0.87 as against 5.11 +/- 0.52; p < 0.0001). The intensity of the lymphocytic reaction correlated with the HLA-DR antigen expression and the increase in silver staining (Spearman's r = 0.543; p < 0.01). This indicates the influence of inflammation on the activation of epithelial cells derived from the respiratory tract.

Nucleolar morphology and rDNA in situ hybridisation in monocytes

The aim of this study was to correlate morphological changes of nucleoli of non-proliferating monocytes to their functional activity, since nucleolar morphology is currently considered as a diagnostic marker for cell proliferation. Monocytes from healthy donors were fractionated by current counterflow centrifugation and kept in culture for 6 days. Cells were stimulated by the addition of 200 units/ml interferon gamma (IFN gamma). Under this stimulus the monocytes show no proliferation but a strongly augmented expression of type I Fc IgG receptor, human leucocyte antigen DR, human leucocyte antigen DP and human leucocyte antigen DQ. Morphological changes after stimulation included the appearance of multinucleated cells, typical signs of the activation of rRNA synthesis indicated by an increase in nucleolar size, and changes in nucleolar structure such as the appearance of reticulate and compact nucleoli. The number of nucleolus organiser regions (NORs) visualised by in situ hybridisation was compared with the position and number of nucleoli visualised by silver staining in interphase cells. In comparison with control cultures, activated monocytes show a distinct increase in the number of those NORs that take part in the formation of nucleoli. Our results show that, in non-proliferating activated monocytes, the morphology of nucleoli and the increase of NOR activity are similar to those in proliferating cells. NOR activation is therefore an indicator for cellular activity, but is not necessarily correlated with proliferation.

Centromere autoantigens are associated with the nucleolus

Because of their importance as target antigens in scleroderma and since all other major autoantigens in scleroderma can be localized to the interphase nucleolus, we were interested in a further investigation of the potential relationship between interphase centromeres and the nucleolus. Using human anticentromere autoantibodies (ACA) from patients with the CREST form of scleroderma as probes in indirect immunofluorescence microscopy, we observed nonrandom interphase "clumping" of centromeres in a distribution suggestive of nucleoli. By double-label immunofluorescence comparing the localization of centromeres to nucleolar proteins Ki-67, fibrillarin, or protein B23 (nucleophosmin), interphase centromeres appeared to be localized around and within nucleoli. A number of different ACA sera were tested on HEp-2, HeLa, PtK2, Indian muntjac, 3T3, and NRK cells, all with identical results indicating colocalization between centromeres and nucleoli. Immunoelectron microscopy revealed that interphase centromeres were distributed free in the nucleoplasm, in contact with the nuclear envelope, in contact with and on the periphery of nucleoli, and totally embedded within the confines of the nucleolus itself. Interestingly, actinomycin D treatment dissociated centromeres from localization within the segregated nucleolus. To determine if interphase centromeres were integral components of nucleoli, nucleoli were isolated according to classical methods. By double-label immunofluorescence, immunoelectron microscopy, and Western blotting, it was demonstrated that centromere autoantigens copurified with isolated nucleoli. These studies offer proof that some interphase centromeres can be associated with, and may even be considered part of, the interphase nucleolus. Furthermore, all of the major autoantigens in scleroderma can now be localized to the nucleolus.

Nucleolar silver staining patterns of lymphocytes in sarcoidosis

Bronchoalveolar lavage lymphocytes from 15 patients with pulmonary sarcoidosis and 8 healthy controls were investigated for nucleolar silver staining patterns and lymphocyte subpopulations. Patients with sarcoidosis had increased numbers of silver stained dots versus controls (2.20 +/- 0.24 versus 1.78 +/- 0.07; p less than 0.001). The number of silver stained dots showed the strongest positive correlation to helper cells (OKT 4+) (r = 0.781; p less than 0.0001). These results may be interpreted as further evidence of lymphocytic activation, especially of helper cells (OKT 4+) in pulmonary sarcoidosis.

Correlation of morphological patterns of nucleoli in alveolar macrophages with HLA-DR antigen expression in sarcoidosis

BACKGROUND

Alveolar macrophages from patients with sarcoidosis express increased quantities of HLA-DR during activation. Because silver staining has been described as a sensitive indicator of cellular activity a study was performed to examine whether it relates to HLA-DR antigen expression.

METHODS

The relation between silver staining patterns of nucleoli and HLA-DR antigen expression was examined in alveolar macrophages collected by bronchoalveolar lavage from 11 patients with pulmonary sarcoidosis and 11 control subjects.

RESULTS

The mean (SD) number of silver stained protein dots associated with the nucleolar organiser regions (AgNORs) was significantly higher in alveolar macrophages from patients with sarcoidosis (7.5 (1.5)) than in those from control subjects (5.6 (0.6)). The number of silver stained dots in alveolar macrophages correlated significantly with the intensity and the density of HLA-DR antigen expression in the patients with sarcoidosis.

CONCLUSIONS

Silver staining may be a sensitive tool for the investigation of the biological cell activity of alveolar macrophages in sarcoidosis.

Quantitative determination of rDNA transcription units in vertebrate cells

The adenosine analogue 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) unravels the compact nucleoli to necklace-like structures when applied to living cells. The nucleolar beads contain RNA polymerase I (RPI) and argyrophilic proteins, both properties considered to be characteristic of ribosomal gene activity. Each granule is supposed to represent a single transcription unit consisting of an actively transcribing gene and its RPI complex. Indirect immunofluorescence with anti-RPI antibodies was used to determine the number of transcription units in DRB-treated cells of some representative mammals, marsupials, birds, and amphibians. We estimate that 45 to 145 rRNA genes are transcriptionally active in vertebrate fibroblasts, depending on the species. Nucleolar transcriptional activity does not correlate with the total number of rRNA genes. During in vitro aging of fibroblasts, the number of transcription units appears to remain unchanged. Different cell types of one same organism show varying numbers of transcription units, reflecting their differential metabolic activity. A particular situation exists in phytohemagglutinin-stimulated lymphocytes. In the course of nucleolar activation, the number of transcription units is increased considerably, implying that formerly inactive rRNA genes are recruited for transcription. The opposite phenomenon is observed during spermatogenesis. With the diploid spermatocytes developing into haploid spermatids, the transcriptionally active rRNA genes decrease in number until rRNA synthesis is completely blocked.

Different nucleolar antigen expression in resting and proliferating human lymphocytes as studied by fluorescence microscopy and flow cytometry

The aim of this study was to investigate the use of a nucleolar antigen to discriminate between proliferating and resting cells. Antinucleolar antibodies (Si87) were obtained from a scleroderma patient. The specificity of immunostaining was verified and morphological changes in nucleoli were monitored using a fluorescence microscope. Fluorescence of propidium iodide-stained DNA and nucleolar immunofluorescence were measured by flow cytometry. Following phytohaemagglutinin stimulation the number of nucleoli of normal human peripheral blood lymphocytes increased about 3-fold, accompanied by enlargement of nucleolar size. Simultaneously a mean increase in total immunofluorescence per cell by a factor of three was detected. The method developed and applied here allows a discrimination between resting and proliferating human lymphocytes on the basis of their nucleolar antigen content.

Fibrillar center distribution in nucleoli of PHA-stimulated human lymphocytes

We have utilized acidic toluidine blue staining for RNA and immunofluorescence staining for RNA polymerase 1 to visualize the distribution of fibrillar centers (FCs) in nucleoli of PHA-stimulated human lymphocytes. At 0 h, there is a single large fibrillar center in each nucleolus which splits into smaller and more numerous FCs until the number of FCs reaches five, the number of nucleolus organizers in normal haploid human cells. With time, each FC then "unwinds" to form linear arrays of smaller FCs until the maximum number of FCs approaches the ribosomal gene copy number of 200 at 48 h in culture. It is hypothesized that in the most active state, each nucleolar FC visualized by RNA polymerase 1 staining actually represents a single transcription unit and the distance between adjacent FCs is occupied by the nontranscribed spacer region. We conclude that the number of fibrillar centers per nucleolus can be used as a direct quantitative measure of nucleolar transcriptional activity.

Ribosomal DNA is located and transcribed in the dense fibrillar component of human Sertoli cell nucleoli

The distribution of rDNA and the uptake of tritiated uridine was investigated in nucleoli of human Sertoli cells. The nucleolar components in these cells are spatially arranged in a highly ordered and invariable way and can be recognized in both light and electron microscopy. The pattern of distribution of rDNA and the pattern of uridine uptake in these nucleoli correspond to the distribution of the dense fibrillar component but cannot be correlated to the shape and size of the fibrillar centers in these cells. It therefore can be concluded that the dense fibrillar component, and not the fibrillar centers, is the site of rDNA location and transcription in nucleoli of human Sertoli cells.

Interphasic nucleolar organizer region distribution as a diagnostic parameter to differentiate benign from malignant epithelial tumors of human intestine

The distribution of the interphasic nucleolar organizer regions (NORs) has been investigated in five hyperplastic polyps, five adenomatous polyps and fifteen colonic adenocarcinomas. The study was performed using electron microscopy and paraffin-embedded sections stained for Ag-NOR proteins. Malignant tumor cells were characterized by a large number of NORs which were small in size and showed a scattered distribution. Nuclei of both types of polyp had only a small number of large-sized NORs in a clustered distribution. In two adenomatous polyps, cells were also observed with an NOR distribution pattern intermediate between that of frankly benign and malignant lesions.

Development of the nucleolus in early goat embryos

In vivo nucleologenesis was studied in goat embryos from the pronuclear stage to the blastocyst stage by light and electron microscopy. Ultrastructural changes of the nucleoli were characterized by the following progression: homogeneous electron-dense fibrillar primary nucleoli in the pronucleus; small, dense fibrillar masses dispersed in clusters of chromatin at the two-cell stage; ring-shaped nucleoli made up of a fibrillar center surrounded by a layer of dense fibrillar components at the four-cell stage; reticulated nucleoli composed of a three-dimensional network of fibrillar components surrounded by small amounts of granular components at the eight-cell stage; fully developed compact-type nucleoli consisting of several fibrillar centers each surrounded by a layer of fibrillar components and abundant granular components in morulae and blastocysts. Moreover, it was concluded that activation of rRNA transcription, as evidenced by specific silver nitrate staining of the nucleolus organizer regions of metaphase chromosomes, occurs at the two- to four-cell stage and that the morphological changes accompanied a substantial increase in nucleolar transcriptional activity up to the blastocyst stage. This study provides evidence that a structure-function relationship exists during nucleologenesis in goat embryos.

Spatial redistribution of ribosomal chromatin in the fibrillar centres of human circulating lymphocytes after stimulation of transcription

We have studied the distributional changes of the completely extended ribosomal chromatin present in the fibrillar centres of resting human lymphocytes after phytohemagglutinin (PHA) treatment. In thin sections of resting lymphocytes selectively stained for DNA, the extended non-nucleosomal chromatin was located in a solitary, large agglomerate which corresponds to the solitary, large fibrillar centre observed in uranium-lead-stained sections. At 20 h after PHA stimulation the ribosomal chromatin agglomerate appeared to be fragmented into smaller agglomerates which correspond to numerous fibrillar centres surrounded by a thick rim of dense fibrillar component. The mean area of ribosomal chromatin agglomerates from resting lymphocytes was found to be 0.772 mu 2 + 0.125 SD, whereas in stimulated lymphocytes it was found to be 0.184 mu 2 + 0.052 SD. At 20 h after PHA treatment ribosomal RNA (rRNA) synthesis was 8-fold greater than the control value, whereas DNA synthesis had not started. These results indicate that ribosomal chromatin of resting lymphocyte fibrillar centres contains transcribable sequences, temporally not expressed.

Structural changes in nucleoli during inhibition of protein- and RNA-biosynthesis

A variety of cells (unstimulated human lymphocytes, phytohemagglutinin-stimulated human lymphocytes, diploid human fibroblasts, human melanoma cells, and Hela cells) were subjected in vitro to inhibition of protein biosynthesis by puromycin. Hela cells were also treated with actinomycin D to inhibit RNA-synthesis. Under puromycin treatment, the fibrillar centers of the nucleoli were smaller in all actively dividing cell types, whereas in small inactive lymphocytes from peripheral blood the inhibition of protein synthesis had no noticeable effect. Nucleoli with nucleolonema changed into compact nucleoli under puromycin treatment. When RNA-synthesis was inhibited, the fibrillar centers remained at an approximately constant volume. These findings indicate that proteins localized in the fibrillar centers are involved in, and are used up during, rDNA-transcription and/or further steps of ribosome biogenesis. The changes in nucleolar architecture after the inhibition of protein synthesis suggest that transcriptional processes become concentrated near sites where proteins have been stored, i.e. the fibrillar centers.

Ultrastructural organization of nucleoli in benign naevi and malignant melanomas

We have studied the ultrastructural organization of nucleoli in benign naevi and malignant melanomas. In benign naevus cells the nucleoli displayed a compact ribonucleoprotein distribution, with one or two large fibrillar centres. In malignant melanoma cells the nucleoli were large with an irregular, nucleolonema-like ribonucleoprotein distribution and they exhibited numerous, small fibrillar centres. Statistical evaluation of the size of fibrillar centres indicated a mean value of 0.482 micron 2 +/- 0.136 SD for naevi and 0.221 micron 2 +/- 0.128 SD for malignant melanomas. These features, together with the more dispersed chromatin pattern of malignant melanoma nuclei compared with those of benign naevus cells, are proposed as diagnostic parameters which differentiate benign naevi from malignant melanomas at the ultrastructural level.

The nuclear skeleton and the spatial arrangement of chromosomes in the interphase nucleus of vertebrate somatic cells

The topologic distribution of interphase chromosomes established by using various cytologic methods and data concerning the DNA-nuclear skeleton interactions in isolated nuclear fractions were reviewed and discussed. Comparison of these different data clearly showed that the position of chromosomes observed in situ is in agreement with the results obtained from isolated nuclear fractions, indicating that all DNA molecules are bound to the peripheral nuclear skeleton. Moreover, the in situ position of the rDNA near the nuclear envelope can be correlated with the existence of a nucleolar skeleton connected to the peripheral nuclear skeleton. Taking into account the discrepant results regarding the actual existence of an internal nuclear skeleton, we attempted to analyze how the various nuclear skeletal structures described in the literature can be involved in both the distribution of chromosomes and in their chromatin organization. As many questions are still unanswered, we considered the modes of investigation that seem to be the most promising.

Nucleolar changes during the first steps of experimental hepatocarcinogenesis in rats

Silver stainability of hepatocytes as an expression of nucleolar activity was studied in vivo during rat hepatocarcinogenesis. Male Wistar rats were injected with one dose of diethylnitrosamine (200 mg/kg body weight dissolved in 0.9% NaCl), followed by a selection procedure with a short exposure to 2-acetylaminofluorene in combination with a proliferative stimulus, such as the administration of CCl4. Finally, after 1 week of a normal diet, some of the rats were treated with phenobarbital. After enzymatic isolation, the hepatocytes were silver stained; the estimation of nucleolar activity was determined by a cytomorphologic analysis of the silver-stained nuclei. It was demonstrated that during the first steps of hepatocarcinogenesis, both diethylnitrosamine, as initiator, and phenobarbital, as promotor, induce modifications of the nucleolar morphology in silver-stained hepatocytes.

Intercellular NOR-Ag-variability in man. II. Search for determining factors, clonal analysis

Intercellular, nonartifactual variability of nucleolar organizer region (NOR)-Ag-staining was studied in cultured human peripheral blood lymphocytes, skin and embryonic fibroblasts. No differences in number and character of variable NORs and intensity of their staining were observed between lymphocytes stimulated to proliferate with phytohemagglutinin and pokeweed mitogen, as well as lymphocytes of first- and second division. The number of NOR associations per cell and the number of associated chromosomes per association were also similar. In a given individual these criteria were similar in lymphocytes and fibroblasts. In all nine clones derived from three independent parental fibroblast cultures the intercellular NOR-Ag-variability was similar to that observed in a given parental cell line. A significant decrease in the number of metaphases containing NOR associations was observed in second-division lymphocytes compared with first-division ones, as well as in skin fibroblasts compared with lymphocytes.

Comparison of metaphase and interphase nucleolar activity in Hela-CCL2 cells and PHA-stimulated human lymphocytes

Metaphase and interphase nucleolar activity in cultured Hela-CCL2 cells and PHA-stimulated human lymphocytes have been studied with silver nitrate staining. In metaphase, we examined the relationship between the actual number of active NORs (AgNORs) and total number of NOR-bearing acrocentrics. Interphase silver staining over the nucleus was analyzed cytodensitometrically and morphologically. From all investigations, Hela-CCL2 cells and lymphocytes were shown to have similar levels of nucleolar activity. Our results suggest that there is a form of regulation of nucleolar activity in malignant Hela-CCL2 cells as compared to PHA-stimulated human lymphocytes.

Silver staining, immunofluorescence, and immunoelectron microscopic localization of nucleolar phosphoproteins B23 and C23

Nucleolar organizer region (NOR)-specific silver staining and immunolocalization of nucleolar phosphoproteins B23 and C23 were compared in Novikoff hepatoma ascites cells. Silver staining and protein C23 immunostaining were both localized in the fibrillar shell surrounding the fibrillar center and in the fibrillar center. During mitosis, silver staining and protein C23 were localized at the NORs. Therefore, protein C23 and the silver-staining protein both seem to be associated with rDNA-containing structures (Mirre and Stahl 1981). A comparison of toluidine blue staining specific for RNA and B23 immunostaining demonstrated that protein B23 was associated with RNA-containing regions of the nucleolus and was absent from the fibrillar centers. Localization of these proteins and their functions are discussed in relation to the organization of the nucleolus.

Immunofluorescence studies on proteins B23 and C23 in nucleoli of human lymphocytes

Nucleoli of normal and leukemic lymphocytes were studied by cytochemical and immunofluorescence methods to provide more information on the nucleolar presence and distribution of proteins B23 and C23. Annular nucleoli of human lymphocytes represent a very convenient subject for such studies, since they consist of one centrally located large fibrillar center surrounded by RNP components. In such nucleoli, protein C23 was present mainly in the central nucleolar region and protein B23 was found mostly in the periphery. The nucleolar area immunostained for protein B23 was usually larger than that stained for protein C23. The distribution of protein C23 appeared to be similar to that of intensely stained nucleolar argyrophilic components. No substantial differences were found between the distribution of proteins B23 and C23 in nucleoli of normal and leukemic lymphocytes. In lymphocytes of patients treated with chemotherapy, the immunofluorescence was diminished for protein B23 and particularly so for protein C23.

Studies on chromatin organization in a nucleolus without fibrillar centres. Presence of a sub-nucleolar structure in KCo cells of Drosophila

In embryonic cell-line derivative KCo of Drosophila melanogaster, the nucleolus, like most nucleoli, contains a small proportion of ribosomal DNA (1-2% of the total nucleolar DNA). The ribosomal DNA is virtually the only active gene set in the nucleolus and is found among long stretches of inactive supercoiled heterochromatic segments. We have demonstrated by use of a Feulgen-like ammine-osmium staining procedure that, depending on the state of growth, more or less fibres of decondensed DNA emanating from the intra-nucleolar chromatin (which is in continuity with the nucleolus-associated chromatin) ramify and unravel within the central nucleolar core to be transcribed. The nucleolus expands or contracts with the variation of activity and could belong to a supramolecular matricial structure such as is shown after extraction of the nuclei. After a long period of exposure to high doses of actinomycin D, the central nucleolar core became an homogeneous fibrous structure that could be interpreted as an aggregate of protein skeletal elements. The mechanism of repression and derepression of the nucleolar chromatin could thus be explained by a mechanism involving in part a sub-nucleolar structure. We propose a schematic organization of the nucleolar chromatin in KCo cells of Drosophila and discuss it in relation with other nucleolar organizations.

Changes in nucleolar structure, number and size in cellular activation and inactivation. Observations in human phytohaemagglutinin-treated lymphocytes

Lymphocytes in human peripheral blood are small, relatively inactive cells. The addition of phytohaemagglutinin (PHA) to cultures of these cells causes a marked increase in cellular and nuclear size, DNA-synthesis and metabolic activity, which reaches a maximum three days after the onset of culturing. The cells then undergo an inactivation process over a period of approximately ten days by which time they have reverted to cells resembling small, inactive lymphocytes. Within the first three days, nucleoli increase in size and number, changing from ring-shaped to nucleolonema-exhibiting to compact nucleoli. In the course of the inactivation process the nucleoli decrease in size and change from compact nucleoli directly into ring-shaped nucleoli. Thus activation and inactivation pathways are different. There is an increase in the number of nucleoli during the inactivation phase up to the seventh day in culture, followed by a slight decrease until day 14. This suggests that nucleoli in metabolically active cells have a tendency to fuse, whereas those in inactive cells tend to fragment.

The number of nucleolar silver-stained granules of active nucleolus organizer regions in mitotic and interphase cells of rat Yoshida and Zajdela ascitic tumors

To provide more information on the number of silver-stained granules (SSGs) of active mitotic nucleolus organizer regions (NORs) as well as interphase nucleoli, rat Yoshida ascitic sarcoma and Zajdela ascitic hepatoma cells were studied by means of standardized one-step and two-step silver-staining procedures. The number of SSGs of mitotic active NORs was relatively constant and corresponded to the number of active NORs of animals bearing the tumors investigated. Some anaphases and telophases were "asymmetric", i.e. chromosomal figures (future nuclei) in one and the same cell contained different number of SSGs (active NORs). The incidence of such asymetric anaphases and telophases was higher in aneuploid (hypoploid) Zajdela hepatoma than in euploid (diploid) Yoshida sarcoma cells. In the interphase, the number of SSGs was low in small or large cells with distinct chromocenters or chromosomes condensation presumably representing postmitotic and premitotic cells. In contrast, the highest number of SSGs was noted in nucleoli of large cells which were usually characterized by a fine chromatin structure.

The morphological relationship in electron microscopy between NOR-silver proteins and intranucleolar chromatin

The relative distribution of NOR proteins and chromatin fibers in the nucleoli was visualized in human cell line. The chromatin was revealed by a Feulgen-like procedure using osmium-ammine as DNA tracer. This selective staining was combined with NOR-silver staining. We provide morphological evidence for constant overlapping of the silver deposit sites with dispersed intranucleolar chromatin fibers. Silver stained proteins were sometimes observed in contact with the chromatin fibers, suggesting that at least some of the Ag-NOR proteins might be closely connected with the dispersed nucleolar DNA.

The influence of the cell cycle on structure and number of nucleoli in cultured human lymphocytes

The nucleoli of lymphocytes undergo a typical sequence of structural changes after stimulation by phytohaemagglutinin. These changes are independent of the cell cycle. Neither the inhibition of DNA-synthesis (by adenosine and methotrexate), nor the elimination of postmitotic interphase nuclei (by a colchicine block of mitoses), nor the release from such blocks has a noticeable effect on nucleolar structure or on the sequence of nucleolar changes. The number of nucleoli per cell is clearly influenced by the cell cycle. Mitosis leads to a marked increase in the number of nucleoli, whereas in all stages of interphase a decrease occurs.

The silver-staining technique--a tool for characterizing lymphocyte populations in mammalian peripheral blood

Nucleolus organizer regions (NORs) of the peripheral blood lymphocytes (PBL) of 9 mammalian species were analyzed by means of a silver-staining procedure. Species-specific NOR patterns were demonstrated. The number of NOR chromosomes was positively correlated with the nucleolar coefficient, and negatively correlated with the relative frequencies of uninucleolar cells in PBL interphase.

Silver staining of the neuronal nucleus in electron microscopy: nucleolar organization in supraoptic nuclei of the rat hypothalamus

The present paper describes a simple, efficient method for silver impregnation of supraoptic nuclei of the rat hypothalamus using a modification of the ammoniacal silver technique of Cajal (1903). This procedure, involving a silver-developer sequence in tissue blocks prior to plastic embedding, permits the simultaneous study of Ag-impregnated supraoptic neurons at both light and electron microscopic levels. Visualization of secretory magnocellular neurons impregnated by this technique using the electron microscope reveals a good preservation of nuclear structures. A selective accumulation of silver grains was observed over heterochromatin clumps and nucleoli, which allows the identification of the nucleolar fibrillar centers and also the dense fibrillar component as the main areas involved in the silver reaction. The meaning of such a silver-distribution pattern is discussed in the light of recent ultrastructural and biochemical data.

Further studies on the cytochemistry of the standardized silver staining of interphase nucleoli in smear preparations of Yoshida ascitic sarcoma cells in rats

Silver staining procedure for the selective demonstration of nucleolar silver stained granules (SSG) and for the simultaneous demonstration of SSG and nucleolar silver stained matrix (SSM) were studied in smears of rat Yoshida sarcoma cells. The successful results of these procedures depend mainly on the quality of silver nitrate and formaldehyde. However, both chemicals can be easily standardized and stabilized disregarding their origin and batch. In standardized procedures (one-step procedure for the selective demonstration of SSG and two-steps procedure for the simultaneous demonstration of SSG and SSM) the silver is apparently bound to acidic groups of proteins of SSG and SSM. The proteins of SSG and SSM seem to be different but both belong to the group of acidic non-histone proteins. According to the results of digestion experiments a possibility also exists that the acidic proteins of SSG may be associated with DNA. The identification of SSG visualized by described standardized procedures was determined not only by cytochemical extraction tests but also by biological experiments. The latter demonstrated that the number of SSG in Yoshida sarcoma cells decreases after treatment of experimental animals with actinomycin D and therefore depends on the state of the nucleolar RNA synthesis.