Nucleolus organizer regions and nucleoli

Measurement of protein concentration in bacteria and small organelles under a light transmission microscope

Protein concentration (PC) is an essential characteristic of cells and organelles; it determines the extent of macromolecular crowding effects and serves as a sensitive indicator of cellular health. A simple and direct way to quantify PC is provided by brightfield-based transport-of-intensity equation (TIE) imaging combined with volume measurements. However, since TIE is based on geometric optics, its applicability to micrometer-sized particles is not clear. Here, we show that TIE can be used on particles with sizes comparable to the wavelength. At the same time, we introduce a new ImageJ plugin that allows TIE image processing without resorting to advanced mathematical programs. To convert TIE data to PC, knowledge of particle volumes is essential. The volumes of bacteria or other isolated particles can be measured by displacement of an external absorbing dye ("transmission-through-dye" or TTD microscopy), and for spherical intracellular particles, volumes can be estimated from their diameters. We illustrate the use of TIE on Escherichia coli, mammalian nucleoli, and nucleolar fibrillar centers. The method is easy to use and achieves high spatial resolution.

Delete and survive: strategies of programmed genetic material elimination in eukaryotes

Genome stability is a crucial feature of eukaryotic organisms because its alteration drastically affects the normal development and survival of cells and the organism as a whole. Nevertheless, some organisms can selectively eliminate part of their genomes from certain cell types during specific stages of ontogenesis. This review aims to describe the phenomenon of programmed DNA elimination, which includes chromatin diminution (together with programmed genome rearrangement or DNA rearrangements), B and sex chromosome elimination, paternal genome elimination, parasitically induced genome elimination, and genome elimination in animal and plant hybrids. During programmed DNA elimination, individual chromosomal fragments, whole chromosomes, and even entire parental genomes can be selectively removed. Programmed DNA elimination occurs independently in different organisms, ranging from ciliate protozoa to mammals. Depending on the sequences destined for exclusion, programmed DNA elimination may serve as a radical mechanism of dosage compensation and inactivation of unnecessary or dangerous genetic entities. In hybrids, genome elimination results from competition between parental genomes. Despite the different consequences of DNA elimination, all genetic material destined for elimination must be first recognised, epigenetically marked, separated, and then removed and degraded.

The Nuclear 35S rDNA World in Plant Systematics and Evolution: A Primer of Cautions and Common Misconceptions in Cytogenetic Studies

The ubiquitous presence of rRNA genes in nuclear, plastid, and mitochondrial genomes has provided an opportunity to use genomic markers to infer patterns of molecular and organismic evolution as well as to assess systematic issues throughout the tree of life. The number, size, location, and activity of the 35S rDNA cistrons in plant karyotypes have been used as conventional cytogenetic landmarks. Their scrutiny has been useful to infer patterns of chromosomal evolution and the data have been used as a proxy for assessing species discrimination, population differentiation and evolutionary relationships. The correct interpretation of rDNA markers in plant taxonomy and evolution is not free of drawbacks given the complexities derived from the lability of the genetic architecture, the diverse patterns of molecular change, and the fate and evolutionary dynamics of the rDNA units in hybrids and polyploid species. In addition, the terminology used by independent authors is somewhat vague, which often complicates comparisons. To date, no efforts have been reported addressing the potential problems and limitations involved in generating, utilizing, and interpreting the data from the 35S rDNA in cytogenetics. This review discusses the main technical and conceptual limitations of these rDNA markers obtained by cytological and karyological experimental work, in order to clarify biological and evolutionary inferences postulated in a systematic and phylogenetic context. Also, we provide clarification for some ambiguity and misconceptions in terminology usually found in published work that may help to improve the usage of the 35S ribosomal world in plant evolution.

AgNOR as an effective diagnostic tool for determining the proliferative nature of different types of odontogenic cysts

OBJECTIVE

To determine the proliferative nature of different types of odontogenic cysts using silver-stained nucleolar organizer region (AgNOR) staining.

MATERIALS AND METHODS

Forty histopathological sections of each of odontogenic keratocyst, dentigerous, and radicular growth were taken into study. Two sections were produced using the paraffin block of separate cases, one was stained with hematoxylin and eosin and another segment was stained with silver nitrate method.

RESULTS

AgNOR staining shows black dots and other parts of nuclei show yellow-brown dots.

CONCLUSION

AgNOR, which stain for NOR-related proteins, corresponds to cell multiplication. Their amount regarding the number of AgNORs per cyst can be a good marker of the proliferative action of the cell in aggressive cystic lesion having malignant potential.

Evaluation of the efficacy of AgNOR as a proliferative marker in oral leukoplakia: A morphometric analysis

Background:

Silver stainable nucleolar organizer regions (AgNORs) are replicatory markers which may have a place in objectively characterizing dysplasia.

Materials and Methods:

A study of various morphometric parameters related to AgNORs was performed in basal and parabasal layers of normal human oral epithelium, nondysplastic leukoplakia, and dysplastic leukoplakia employing photomicrographs of silver stained paraffin embedded sections using image analysis, to assess the usefulness of these parameters in distinguishing dysplastic leukoplakia from nondysplastic oral leukoplakia.

Results:

Out of various mean AgNOR related parameters, AgNOR count, area, perimeter, and proportion were found to be higher in dysplastic leukoplakia as compared to nondysplastic leukoplakia. On statistical analysis, AgNOR count showed statistically significant differentiation between dysplastic and nondysplastic leukoplakia. While other parameters can distinguish normal oral epithelium from dysplastic and nondysplastic leukoplakia.

Conclusion:

To conclude, the AgNOR count is the most appropriate marker to differentiate between dysplastic and nondysplastic leukoplakia.

C6orf89 encodes three distinct HDAC enhancers that function in the nucleolus, the golgi and the midbody

We report here that C6orf89, which encodes a protein that interacts with bombesin receptor subtype-3 and accelerates cell cycle progression and wound repair in human bronchial epithelial cells (Liu et al., 2011, PLoS ONE 6: e23072), encodes one soluble and two type II membrane proteins that function as histone deacetylases (HDAC) enhancers. Soluble 34/64sp is selectively targeted to the nucleolus and is retained in nucleolar organiser regions (NORs) in mitotic cells. Nucleolar 34/64sp is integrated into the ribosomal gene transcription machinery, colocalises and coimmunoprecipitates with the Pol I transcription factor UBF, and undergoes a dramatic relocalisation to the nucleolus upon the arrest of rDNA transcription, protein synthesis and PI3K/mTORC2 signalling. Membrane 42/116mp localises to the Golgi and the midbody, and its controlled ectopic expression provokes the disruption of the Golgi cisternae and hinders the separation of daughter cells and the completion of mitosis. The latter effect is also produced by the microinjection of an affinity-purified amfion antibody. The identification of C60rf89 as a gene that encodes three distinct proteins with the capacity to enhance the activity of histone deacetylases (HDACs) in the nucleolus, the Golgi and the midbody provides new information regarding the components of the acetylome and their capacity to interact with different functional groups in the cell.

DNA replication initiation patterns and spatial dynamics of the human ribosomal RNA gene loci

Typically, only a fraction of the ≥600 ribosomal RNA (rRNA) gene copies in human cells are transcriptionally active. Expressed rRNA genes coalesce in specialized nuclear compartments – the nucleoli – and are believed to replicate during the first half of S phase. Paradoxically, attempts to visualize replicating rDNA during early S phase have failed. Here, I show that, in human (HeLa) cells, early-replicating rDNA is detectable at the nucleolar periphery and, more rarely, even outside nucleoli. Early-replicated rDNA relocates to the nucleolar interior and reassociates with the transcription factor UBF, implying that it predominantly represents expressed rDNA units. Contrary to the established model for active gene loci, replication initiates randomly throughout the early-replicating rDNA. By contrast, mostly silent rDNA copies replicate inside the nucleoli during mid and late S phase. At this stage, replication origins are fired preferentially within the non-transcribed intergenic spacers (NTSs), and ongoing rDNA transcription is required to maintain this specific initiation pattern. I propose that the unexpected spatial dynamics of the early-replicating rDNA repeats serve to ensure streamlined efficient replication of the most heavily transcribed genomic loci while simultaneously reducing the risk of chromosome breaks and rDNA hyper-recombination.

Heterochromatin and rDNA 5S and 45S sites as reliable cytogenetic markers for castor bean (Ricinus communis, Euphorbiaceae)

The increasing need for renewable energy resources has led to higher demands for biofuel, a scenario where the castor bean (Ricinus communis L.) seed oil represents a promising source of raw material. Despite that, information regarding the genome organization of R. communis is still scarce, impairing the application of modern biotechnological and breeding procedures. The present work brings the first evaluation of the mitotic chromosomes of this species, including 10 potentially interesting accessions for cultivation in semi-arid environments aiming at the biofuel production. The approach included standard staining, fluorochrome staining (CMA/DAPI), fluorescent in situ hybridization (FISH) with rDNA 5S and 45S, as well as silver impregnation. All accessions were diploid with 2n=2x=20, displaying mainly metacentric chromosomes, with CMA-positive bands (GC-rich) in all pairs of the complement. After silver impregnation, one to 14 nucleoli were observed, while the FISH with rDNA 45S revealed two large sites and a variety of minor dots, and the DNAr 5S hybridized in a single pair. The observed features were discussed and compared with literature data regarding pachytene bivalents.

Variation in size of Ag-NORs and fluorescent rDNA in situ hybridization signals in six breeds of domestic pig

Variation of the size of silver-stained nucleolar organizer regions (NORs) of chromosomes 10 and 8 was studied in pigs of six breeds (Sus scrofa L.). The silver deposits were quantified by image analysis and the results were normalized for each Ag-NOR chromosome. In general, normalized values for chromosomes 10 were higher than those for chromosomes 8, suggesting that the NOR activity of chromosomes 10 is dominant as compared to that of chromosomes 8. However, high values for chromosomes 8 were found in the Meishan breed and in some Piétrain pigs, indicating a high transcriptional activity of the rRNA genes on these chromosomes. In some pigs, the relative quantities of rDNA in chromosomes 10 and 8 were investigated by fluorescent in situ hybridization and the results were compared with those of the silver staining procedure. It is concluded that Ag-NOR sizes on chromosomes 10 are relatively well correlated to the number of rRNA genes, whereas the absence or the small size of Ag-NORs on chromosomes 8, often observed in pigs, is the result of low NOR activity rather than of absence of rDNA.

The nucleolar functional asynchrony--imbalance--in the granulopoietic proliferating compartment of patients suffering from chronic myeloid leukemia

Nucleoli were studied in all stages of the granulopoietic proliferating compartment in the bone marrow of patients suffering from chronic myeloid leukemia to provide an information on the incidence of the nucleolar functional asynchrony (imbalance) in these cells. The nucleolar functional asynchrony is morphologically expressed by the presence of "active" large nucleoli with a relatively uniform distribution of ribonucleic acid (RNA) and "resting" ring shaped nucleoli with RNA only in their peripheral part in one and the same cell. This phenomenon was noted in a small but constant percentage of myeloblasts and decreased in myelocytes regardless of the phase of the disease and therapy. In addition, the nucleolar functional asynchrony was also noted in all stages of the granulopoietic proliferating compartment of control not-leukemic persons.

Change in size, number and morphology of the nucleoli in human hearts as a result of hyperfunction

In the present study we examined light-microscopically the nuclei of 16 hearts (7 normal hearts, 7 hearts with hypertrophy and 2 hearts with atrophy) for the size, number and morphology of their nucleoli. The size of the nucleoli, defined as the total area of all nucleoli per nucleus, was an early and sensitive indication of a beginning hypertrophy of the myocardium. It increased in parallel to the total heart weight and to the total area of the nucleus of the cell, but initially the size of the nucleoli changed earlier than the other parameters. We found an increase of the ratio in the total area of the nucleoli per nucleus to the total area of the nucleus at the beginning of clinical hyperfunction. This ratio normalised during chronic hyperfunction. The number of the nucleoli also increased during hyperfunction, but it did not exceed the number of nucleolus organiser regions (NOR) given by the number of chromosomes. Nevertheless, we found numbers of nucleoli higher than 10 because, the number of NORs increases during polyploidization. Regarding the morphology of the nucleoli in hearts with hypertrophy, we found a predomination of the nucleoli with a highly branched nucleolonemal structure as an indication of an increased RNA synthesis.

Polytene chromosomes in mammalian cells

This article deals with the structural and functional organization of polytene chromosomes in mammals. Based on cytophotometric, autoradiographic, and electron microscopic data, the authors put forward a concept of nonclassic polytene chromosomes, with special reference to polytene chromosomes in the mammalian placenta. In cells with nonclassic polytene chromosomes, two phases of the polytene nucleus cycle are described, such as the endointerphase (S phase) and endoprophase (G phase). The authors generalize that the main feature of nonclassic polytene chromosomes is that forces binding the sister chromatids are much weaker than in the Diptera classic polytene chromosomes. This concept is confirmed by comparative studies of human, mink, and fox polytene chromosomes. The final step of the trophoblast giant cell differentiation is characterized by a transition from polyteny to polyploidy, with subsequent fragmentation of the highly polyploid nucleus into fragments of low ploidy. Similarities and dissimilarities of pathways of formation and rearrangement of nonclassic polytene chromosomes in mammals, insects, plants, and protozoans are compared. The authors discuss the significance of polyteny as one of the intrinsic conditions for performance of the fixed genetic program of trophoblast giant cell development, a program that provides for the possibility of a long coexistence between maternal and fetal allogenic organisms during pregnancy.

Combined light and fluorescent microscopical imaging of nucleolar organizer regions and cellular rRNA as detected by fluorescent in situ hybridization

A method for combined light and fluorescent microscopic imaging of nucleolar organizer regions and cellular rRNA is described. Nucleolar organizer regions were detected by silver staining (Ag-NOR), and rRNA was detected by fluorescent in situ hybridization (FISH). MG-63 human fibrosarcoma cells were silver stained prior to in situ hybridization. To quantitate Ag-NOR within individual cells, brightfield images were digitized, and the total Ag-NOR area/nucleus was determined. Fluorescent images were digitized, and the total cellular fluorescence was calculated after correction for nonuniformity of illumination. By using this method, it was shown that the Ag-NOR procedure did not significantly affect the fluorescence intensity related to FISH. Furthermore, the hybridization procedure did not interfere with quantitation of Ag-NOR. With this method, both Ag-NOR and rRNA product can be quantitated within the same cell. Because the relationship of rRNA content to cell proliferation is well established, correlation to quantitative Ag-NOR parameters within individual cells will contribute to the better definition of the relationship of quantitative Ag-NOR indices with cellular proliferation.

Nuclear phospholipids during the adaptation of human EUE cells to hypertonic stress

The phospholipid component of interphase nuclei was analysed in EUE cells (an established cell line from embryonic human epithelium) grown in an isotonic culture medium and during the adaptation process to a hypertonic medium, using a highly specific ultracytochemical procedure, viz. labelling with the phospholipase A2 gold-complex. Within the nucleus, the phospholipids were localized in domains involved in different steps of the synthesis and processing of the RNA. These localizations did not vary at the two key steps of the adaptation process to hypertonic medium: short-term treatment (6 h) representing critical shock condition, and long-term growth (5 days) representing the adapted cells under survival conditions. On the contrary, deep changes of the labelling intensity of phospholipids at these sites occurred at the different times of hypertonic treatment and followed the same course as those observed in the ultramorphological patterns of transcription: the chromatin condensation, as evaluated by image analysis, the permanent nucleolar components, the interchromatin and the perichromatin granules. These data endorse the hypothesis that nuclear phospholipids could be involved in different steps of the transcriptional activity. They are indicative of the deep changes occurring in the EUE cells submitted to hypertonic stress.

Assessment of Yqh translocations

Two initially presumed Yqh translocations, one to Xp and another to 21p, were assessed by conventional banding procedures, 5-azacytidine treatment, electron microscopy, and fluorescence in situ hybridisation. While the Yqh nature of the heterochromatic block from Xp was confirmed, this was not the case with the 21ph+ variant. In conclusion, conventional banding techniques are insufficient to diagnose Y;G translocations.

Somatic pairing of centromeres and short arms of chromosome 15 in the hematopoietic and lymphoid system

Normal human bone marrow and peripheral blood leukocytes as well as malignant cells from a variety of leukemias and lymphomas, demonstrate somatic pairing of centromeres and p arms of chromosome 15 during interphase. This phenomenon, effected by sequences on the p arm and requiring the intranuclear transport of spatial domains for at least one of the homologs, was not seen in amniotic fluid cells, uterine cervical tissue or in tissue fibroblasts. These studies contribute to the recent evidence of somatic pairing of homologous chromosomes in man and provide support for mobile chromosomal domains in interphase. It appears that sequences on the p arm of chromosome 15, possibly the nucleolar organizing genes, are uniquely important in the maturation of benign and malignant cells of hemato-lymphopoietic origin.

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)

The effect of different fixatives and length of fixation time on subsequent AgNOR staining for frozen and paraffin-embedded tissue sections

The AgNOR technique has been used extensively in studies investigating the possibility that the numbers and appearances of the intranuclear structures stained are markers of malignancy. The method has the advantage of being applicable to many different types of histological material, including paraffin-embedded tissue. However, it has been suggested that the visualization of AgNORs is dependent on the type and time of fixation employed. This study set out to measure this effect with the following commonly-used fixatives: acetone, absolute ethanol, methanol, Carnoy's fluid, Bouin's fluid, 4% glutaraldehyde, 10% neutral buffered formalin and 10% formol-saline. Both frozen sections and blocks of fresh tonsil were fixed for varying times, the blocks of tissue then being processed routinely. With the frozen sections AgNORs were easier to discern than in sections of paraffin-embedded tissue, and more intranucleolar AgNORs were visible when alcoholic fixatives were used than with aldehyde fixation. The effects of different fixatives on AgNOR appearance in paraffin sections is, however, more complex. Despite the variation caused by different fixatives, AgNORs could be demonstrated adequately with all the fixatives studied. It is concluded that fixation is not a limitation to the study of AgNORs provided that the time and type of fixative is controlled.

Nucleolar organizer regions in malignant salivary gland tumors

Proliferative activity of carcinomas arising from salivary glands was analyzed by enumeration of argyrophilic nucleolar organizer regions (AgNORs). The mean numbers of AgNORs in the various tumors were as follows: mucoepidermoid carcinoma, 2.20; acinic cell carcinoma, 2.51; adenoid cystic carcinoma (ACC), 2.57; carcinoma in pleomorphic adenoma, 1.00 (benign component) and 3.99 (cancer-bearing area); salivary duct carcinoma, 4.49; polymorphous low-grade adenocarcinoma, 3.37; sebaceous carcinoma, 2.57; oncocytic carcinoma, 4.63; adenocarcinoma, 4.53. Cells of most tumors showed heterogeneous activity within the same tumor. In mucoepidermoid carcinoma, the mucous cells had suppressed activity in comparison with the epidermoid cells and intermediate cells. In ACC, the activity of the tumor cells increased according to growth pattern in the order tubular, glandular and solid. In carcinoma in pleomorphic adenoma, vigorous proliferative activity was observed in the malignant component, whereas less active cells were seen in the myxoid or chondroid matrix. AgNOR staining was useful for distinguishing benign from malignant regions in carcinoma in pleomorphic adenoma. Our results suggest that mucoepidermoid carcinoma, acinic cell carcinoma and ACC, except for that with a solid growth pattern, may be considered as low-grade malignancies, whereas solid-type ACC, the cancer component in carcinoma in pleomorphic adenoma and some of the other carcinomas have high-grade malignant behavior.

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.

Proliferative activity in normal salivary gland and pleomorphic adenoma. A study by argyrophilic nucleolar organizer region (AgNOR) staining

Proliferative activity of the structural components of normal salivary glands (27 cases) and characteristic histological areas in salivary pleomorphic adenoma (51 cases) was examined by visualization of argyrophilic nucleolar organizer regions (AgNORs). In the normal salivary gland, there were clusters of cells, each with two or three AgNOR dots, within the intercalated ducts. The mean number of AgNORs in this portion was 1.80, which was significantly higher than in the other epithelial parts. This indicates vigorous proliferative activity of the intercalated ducts, and thus the ducts may play an important role as reserve cells in neoplastic transformation. In pleomorphic adenoma, solid nests had a high AgNOR count (1.61), showing a significant difference from the tumor cells scattered in the "stroma". Thus the decrease in proliferative ability might occur concurrently with formation of the extracellular matrix.

Argyrophylic nucleolar organiser regions (AgNOR's) as a prognostic indicator in breast carcinoma

Silver staining nucleolar organiser regions (AgNOR's) were determined in archival histological specimens of breast carcinoma. Representative samples from forty-eight female patients were counted manually for AgNOR's--median 3.85 (range 1.1-10.2 AgNOR's per cell). Taking the median value of 3.85 as a cutoff, the patients were divided into two groups: A = Those with AgNOR counts > 3.85; B = Patients with AgNOR counts < or = 3.85. The 5 year survival was 21% in group A and 85% in group B (p < 0.001). There was no significant correlation between AgNOR's and tumour size, lymph node status, tumour grade, menopausal status and oestrogen receptors. We conclude that nucleolar organiser regions may be useful as a prognostic indicator in breast carcinoma especially in patients in whom other prognostic information is unavailable.

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.

Age-related influence of piracetam on mitotic index and number of silver-stained nucleolus organizer regions

Mitotic indices and the number of silver-positive nucleolus organizer regions (AgNORs) were scored in phytohemagglutinin-stimulated cultures of peripheral lymphocytes from two age groups of females (mean = 23.1 and 84.0 yr, respectively) under the influence of Piracetam (2-oxo-pyrrolidine-1-acetamid; Nootropil, Reg. No. 17051) and in simultaneously set up control cultures without Piracetam addition. Piracetam concentrations of 10, 14 and 16 mg/ml culture medium produced a highly significant, decreasing effect on both parameters tested, without an age-related difference. Lower Piracetam concentrations (2 and 4 mg/ml culture medium) showed a depressant effect on some of the cultures only; but, on average, there was a rather equal, significant, dose-dependent, linear decrease of the mitotic indices of both age groups, whereas the suppressive effect on the number of AgNORs was significant in cultures from the young females only.

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.

Nucleoli, nucleolar chromosomes and ribosomal genes in the human spermatocyte

The formation and development of nucleoli and their connections with the nucleolar chromosomes were studied in human spermatocytes using electron microscopy, silver staining of nucleolus organizer regions (NORs), high resolution autoradiography and in situ hybridization in order to localize rRNA genes and their transcription in the different stages of meiotic prophase I. At leptotene, new nucleoli were formed, consisting of a fibrillar centre surrounded by a cap of dense fibrillar component. Following [3H]uridine uptake, label was found only over the dense fibrillar component. In situ hybridization revealed rDNA mainly in the dense fibrillar component and in the chromatin. During zygotene, nucleoli increased in size. The fibrillar centre was connected with the secondary constriction region of the nucleolar bivalent and was partially surrounded by dense fibrillar component. This shell of dense fibrillar component merged into a fibrillo-granular mesh that extended away from the fibrillar centre. Autoradiography following [3H]uridine uptake again showed the label overlaying the dense fibrillar component and the proximal part of the fibrillo-granular strands. With in situ hybridization in both the light and electron microscope, signal was mainly found in the dense fibrillar component. A small quantity of label was observed in the peripheral region of the fibrillar centre and in the adjacent chromatin. From early to late pachytene segregation of nucleolar components occurred, with a reduction in the dense fibrillar component that formed a narrow rim around the fibrillar centre with small extensions along the granular component. [3H]uridine incorporation progressively decreased. In situ hybridization showed signal located mainly in the dense fibrillar component and in the chromatin corresponding to the condensed short arm of the nucleolar bivalent. Our results indicate that the majority of rDNA is located and transcribed in the dense fibrillar component; only a small amount is present in the peripheral part of the fibrillar centre and may be transcribed there. Moreover, from leptotene to zygotene, rDNA unravels from the nucleolar chromosome into the nucleolar dense fibrillar component. From zygotene to late pachytene a progressive return to the condensed acrocentric short arm is observed.

The endocrine pancreas of glucagon- and somatostatin-immunized rabbits. II. Electron microscopy

An active or passive immunization against hormones and the subsequent neutralization of hormones by circulating antibodies is a valuable tool for the identification of hormonal action. To recognize presumed local (autocrine, paracrine) effects exerted by pancreatic hormones, the endocrine pancreas of rabbits was investigated electron-microscopically after long-term immunization against glucagon or somatostatin. Glucagon immunization resulted in hyperplasia and hypertrophy of glucagon- (A-) cells and in their increased metabolic activities: They showed prominent nucleoli, increased amounts of endoplasmic reticulum, Golgi areas, and mitochondria. These changes were paralleled by alterations in secretion granules (increased size, decreased hormonal content), increased numbers of lysosomes (crinophagic bodies), and an increment of the filamentous system. Basically, these findings point to an autocrine regulation of A-cells. Following somatostatin immunization, somatostatin- (D-) cells were hyperplastic but unchanged in their metabolic state. Instead, insulin-(B-) cells and A-cells exhibited equivalents of increased cellular activities (parameters, see above). This stimulation most probably is caused by cancelled paracrine (inhibitory) effects of somatostatin. The changes observed after both immunizations were differently expressed in morphologically heterogeneous islet types (size, angioarchitecture, cellular composition, microtopology of the various cell types). It is concluded, therefore, that the regulation of islets is not uniform. Autocrine and paracrine effects exerted by islet hormones are of different significance in individual islets, or they interfere differently with other regulatory signals.

Nucleolar organizer regions in various human brain tumors

Nucleolar organizer regions (NOR's) are loops of deoxyribonucleic acid (DNA) which transcribe to ribosomal ribonucleic acid (RNA) by RNA polymerase I. They possess vital significance in the ultimate synthesis of cellular proteins. A silver colloid staining technique for demonstration of NOR-associated proteins (Ag-NOR's) was applied to paraffin-embedded sections from 128 varied brain tumors and to chromosomal preparations from cultured brain-tumor cells. There was a statistically significant difference in the mean number of Ag-NOR's per nucleus between low-grade tumors (1.98/nucleus) and high-grade tumors (2.95/nucleus). It is suggested that the mean number of Ag-NOR's may represent the proliferative potential of brain tumors. Furthermore, high-grade tumors usually showed relatively large Ag-NOR's in a scattered distribution. In chromosomal preparations, the cultured cells displayed five to 12 Ag-NOR's on acrocentric chromosomes. Five of eight cell lines examined demonstrated ectopic Ag-NOR's. This simple staining technique can be easily applied to routinely processed paraffin-embedded sections and will become a useful tool for quick estimation of the proliferative potential of human brain tumors.

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.

Chromosome topology in mammalian interphase nuclei

Since 1968, when Comings published the pioneering paper on "the rationale for an ordered arrangement of chromatin in the interphase nucleus," technical methods have progressed tremendously and improved our understanding of interphase organization. The existence of highly ordered organizational patterns of the cell nucleus appears to be beyond any doubt and it is difficult to escape the conclusion that interphase chromosome topology is important for the complex regulation of the many varied and interrelated nuclear processes. However, it is worth emphasizing that a universally valid principle of chromosome arrangement does not exist and, therefore, any generalization of interphase patterns can be misleading. The factors of order according to which the chromosomes are arranged inside the nucleus are manifold: (1) Individual chromosomes remain in spatially separated domains throughout interphase, preventing an intermingling of the decondensed euchromatin. (2) Chromosome regions that contain constitutive heterochromatin associate into larger chromocenters. (3) In most cell types direct associations between interphase domains of homologous chromosomes are not observed. In others homologous heterochromatic regions tend to be paired preferentially. (4) Interphase chromosomes do not float freely in the nucleoplasm; they are associated to varying degrees with the nuclear membrane and other components of the nuclear scaffold. The number of attachment sites for each chromosome to the nuclear membrane is relatively low. (5) The positions of centromeres (and pericentromeric heterochromatin) are nonrandom and characteristic of each cell type. Specific centromere movements occur during the cell cycle, during differentiation, and under certain pathophysiological conditions. (6) The telomeric chromosome ends are particularly prone to associate in certain somatic cell types and in meiotic prophase cells. (7) The arrangement of repetitive DNA families appears to determine a structural framework of the interphase nucleus. Different cell types of one organism can exhibit marked differences in their repetitive DNA framework, whereas cells that are in an identical differentiated state or an identical phase of the cell cycle often show comparable interphase patterns even in evolutionarily distant species. (8) The various steps of ribosome biogenesis take place in a precise fashion within a separate nuclear domain, the nucleolus. The topologically well-defined nucleolar substructures are required for rDNA transcription and pre-rRNA processing. (9) A compartmentalization of transcriptional and processing events is also evident in the rest of the nucleus. However, it is not yet known if the in situ sites of transcription and RNA processing for a particular (nonribosomal) gene or gene family are actually adjacent. (10) DNA replication is precisely spatiotemporally regulated within the nucleus. The replication domains are immobilized on the nuclear matrix.(ABSTRACT TRUNCATED AT 400 WORDS)

AgNOR staining in benign hyperplasia and carcinoma of the prostate

We have modified existing techniques for silver staining of nucleolar organizer regions of intact interphase cells by hypotonic swelling and by formic acid treatment to reduce background staining. This allowed the microscopic identification and counting of individual AgNORs in the nucleoli. The method was used on nine adenomatous prostatic samples (including one of normal prostate tissue outside a localized tumor) and on seven prostatic adenocarcinomas. In general, the adenomatous samples displayed fewer AgNORs (mean 13 dots/cell) than did the carcinomas (mean 24 dots/cell). Although no cells with very high AgNOR counts were found in specimens from nonmalignant tumors, two of the adenomatous prostates did have AgNOR profiles that to a large extent overlapped with those of carcinomas. A highly differentiated carcinoma (of which only very small amounts were present in the sample) had low AgNOR counts. The three moderately differentiated carcinomas had more silver-positive material than the nonmalignant prostates but less than the three poorly differentiated carcinomas. The latter tumors also had a substantial proportion of cells with greater than 60 AgNOR counts, something that was never seen in carcinomas with higher differentiation. The data indicate that analysis of silver staining-positive material in intact interphase cells may help distinguish between benign and malignant prostatic tumors and between highly malignant and low malignant carcinomas.

Morphometry of nucleoli as an indicator for grade of malignancy of bladder tumors

To establish a new indicator for the classification of human urinary bladder cancers, the nucleoli of normal epithelial and neoplastic cells were analyzed, using morphometric techniques. By electron microscopy, the nucleolar profiles of cells from grade 2 and 3 transitional cell carcinomas were often small and irregular. Morphometry showed that the nucleolar volumes, nucleolar/nuclear volume ratios, volume densities of various nucleolar components, and the numbers of fibrillar centers (FCs) altered significantly with an increase in tumor grade. In particular, an increase in FC numbers in the nuclei of higher grade tumors was associated with a decrease in individual volume. The number of FCs in intact urothelial cells obtained from patients with bladder tumors is significantly larger than in the normal urothelial cells. This may be related to the multicentric origin of bladder cancers. These results suggest that morphometric analysis of nucleoli is useful in evaluating the degree of differentiation and invasive capacity of human bladder tumor cells. In particular, the number and individual volume of FCs may be an indicator of tumor malignancy.

Silver staining of nucleolar organizer region associated proteins using polyethylene glycol as the protective colloidal developer

A simple modification to the silver staining technique for the demonstration of nucleolar organizer region associated proteins is described. Polyethylene glycol 20,000 is used instead of gelatin as the colloidal developer. This modified technique remains a one stage procedure that is quick and easy to perform. It results in reduced precipitate and less non-specific staining with specimens in which it had been previously difficult to demonstrate these intranuclear silver staining structures.

Intratubular germ cell neoplasia of the testis: identification by placental alkaline phosphatase immunostaining and argyrophilic nucleolar organizer region quantification

We assessed the value of placental alkaline phosphatase (PLAP) immunostaining and argyrophilic nucleolar organizer region (AgNOR) quantification as techniques for the identification of intratubular germ cell neoplasia (ITGCN), and compared them with hematoxylin-eosin and periodic acid-Schiff staining. We examined 46 malignant testicular germ cell tumors for the presence of ITGCN; 43 had sufficient tubules available for assessment. We also examined 16 cryptorchid testes, 16 testicular biopsies from 10 subfertile men, and 12 normal adult intrascrotal testes. In tubules adjacent to invasive tumors, hematoxylin-eosin staining identified 30 cases (70%) of ITGCN, while PLAP and AgNOR staining identified 36 cases (84%). All the seminomas (18) and 22 of 28 nonseminomatous germ cell tumors were PLAP-positive and had high AgNOR counts. Intratubular germ cell neoplasia was not identified in the other groups examined; germ cells in these groups were PLAP-negative and had low AgNOR counts. Cells of ITGCN showed cytoplasmic block positivity with periodic acid-Schiff staining but this was not a consistent finding. We conclude that ITGCN is present adjacent to most invasive germ cell tumors, and is reliably identified by hematoxylin-eosin staining when fully developed. Periodic acid-Schiff staining was not helpful as normal spermatogonia were also positive. Staining with PLAP and AgNOR were useful diagnostic adjuncts, but results with PLAP were easier to interpret.

Sequential changes in the nucleoli of human spermatogonia with special reference to rDNA location and transcription

The nucleoli of human spermatogonia were studied using electron microscopy, silver staining, radioautography and in situ hybridization. In all types of A spermatogonia, nucleoli were consistently located at the periphery of the nucleus and contained a single fibrillar center associated with the nuclear envelope. In B spermatogonia, nucleoli were centrally located in the nuclei and showed several fibrillar centers or were found to disintegrate. Nucleolar morphology was found to be a good, though not an unequivocal indicator of spermatogonial type. The observed changes in nucleolar morphology reflect the differentiation of spermatogonia: the nucleolar disintegration seen in B spermatogonia corresponds to a pre-leptotene cessation of rDNA transcription. In radioautographs following 3H-uridine uptake, the label was consistently found over the dense fibrillar component, except in the B spermatogonia with disintegrating nucleoli, where no uptake could be detected. In situ hybridization demonstrated that the distribution of rDNA did not correspond to the site of the fibrillar center but to the dense fibrillar component. Compared with radioautographs, this finding clearly established that transcribed units of rDNA were located in the dense fibrillar component. Silver staining was strongly positive in fibrillar centers and in the dense fibrillar component. In Ap spermatogonia the silver deposit was often localized at the edge of the fibrillar threads. The relationships between silver-stained proteins and transcribed and nontranscribed portions of ribosomal genes are reevaluated.

The volumes and morphology of human chromosomes in mitotic reconstructions

Ten unpretreated normal human male fibroblast cells in mitosis were completely reconstructed from micrographs of between 82 and 119 consecutive serial sections. All 46 chromosomes and their centromeres could be reconstructed in every cell. Measurements of chromosome volumes and centromere indices are presented. The data enabled allocation of all chromosomes to their groups (A to G), and chromosomes 1, 2, 3, 6, 9, 16, 17, 18 and Y were individually identified. Comparisons with published karyotypes showed that volume measurements correlated well with measurements of DNA content and chromosome length. Centromere indices also showed good correlation, but the acrocentric chromosomes were more unequally armed than found by length measurement. Secondary constrictions at the nucleolar organising region were visible on about a third of the acrocentric chromosomes. One chromosome of the C group, number 9, had a diffuse subcentromeric region (DSR) on the long arm, at the position of the constitutive heterochromatin and (in meiotic cells) the paramere.

Are AgNORs useful in distinguishing follicular hyperplasia from follicular lymphoma?

Argyrophilic nucleolar organiser regions (AgNORs) in 28 follicular lymphomas and 30 lymph nodes showing reactive follicular hyperplasia were studied to see if they were helpful in distinguishing follicular lymphoma from follicular hyperplasia in paraffin wax tissue sections. Mean nuclear counts were greater in follicular hyperplasia (3.71 v 3.11). This difference was significant but counts overlapped so much that they were of no practical value in distinguishing between both conditions. Higher counts may reflect greater proliferative activity in follicular hyperplasia.

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.