Nucleolar structure

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.

mRNA transport in yeast: time to reinvestigate the functions of the nucleolus

Nucleocytoplasmic transport of mRNA is vital to gene expression and may prove to be key to its regulation. Genetic approaches in Saccharomyces cerevisiae have led to the identification of conditional mutants defective in mRNA transport. Mutations in approximately two dozen genes result in accumulation of transcripts, trapped at various sites in the nucleus, as detected by in situ hybridization. Phenotypic and molecular analyses of many of these mRNA transport mutants suggest that, in yeast, the function of the nucleus is not limited to the biogenesis of pre-ribosomes but may also be important for transport of poly(A)+ RNA. A similar function of the animal cell nucleolus is suggested by several observations.

Proliferation and maturation indices in nephrogenic rests and Wilms tumor; the emergence of heterogeneity from dormant nodular renal blastema

Independent nephrogenic rests (NRs) accompany many Wilms tumors (WTs), exhibit a range of qualities suggesting dormancy, maturation, regression, and hyperplasia, and may carry the WT-1 mutation. We assessed nucleolar organizer regions, proliferating cell nuclear antigen (PCNA) activity, cytoplasmic filament expression, and nuclear morphology in 79 nephrogenic rests accompanying 20 WTs. We found a direct relationship between the size of a blastematous NR and the AgNOR number per nucleus and a close correlation with PCNA activity. The blastema of most NRs > 1 cm in diameter was indistinguishable from blastema of most WTs. The smallest NR usually had a low number of silver-reactive nucleolar organizing regions (AgNORs), low PCNA activity, and absent cytoplasmic filaments, all characteristics of a nascent dormant state in which both proliferation rate and protein synthetic activity are low. Intermediate filament expression was variable in blastema of larger NRs; cytoplasmic filaments correlated with emergence of epithelial maturation and absence of filaments with accumulation of immature cells; mature epithelial structures in NRs had low AgNOR number and PCNA activity representing a terminal dormant state. The majority of blastemal cells in most WTs and in one-third of large hyperplastic NRs lack cytoplasmic filaments. This, plus the occasional finding in large NRs of features more typical of WTs such as prevalence of apoptosis, patches of frank necrosis, multinodular architecture, and expanses of monomorphic, poorly vascularized blastema with low PCNA activity, suggest that it may be possible to distinguish NRs that are progressing toward WT from those that are merely hyperplastic. This study refines the concepts of dormancy and hyperplasia as expressed in NRs and provides a general framework for probing the relationship of molecular events to progression of a small proportion of NRs to WT. Criteria used herein to define dormancy and hyperplasia may be useful in assessing lesions other than typical WT, such as unusually large or extensive NRs or uncommon differentiated WTs where the potential for aggressive behavior may be lower than in usual WTs.

Abnormal integrity of the nucleolus associated with cell cycle arrest owing to the temperature-sensitive ubiquitin-activating enzyme E1

A mouse cell mutant, ts85, containing the temperature-sensitive ubiquitin-activating enzyme was arrested in G2 phase at the non-permissive temperature. In the arrested cells, azure C, a nucleolus-specific stain, revealed a U-shaped or ring-shaped arrangement of nucleolar lobes with an unstained region in the center. Silver staining of the nucleolar organizer region (NOR) and fluorescence in situ hybridization (FISH) with rDNA both gave signals in azure C-positive regions. Electron microscopic examination revealed a cloud of unidentified electron-dense particles (diameter approximately 70 nm) in the azure C-negative center space. When the arrested cells were released into M-phase, we observed the association of NOR-bearing chromosomes with a pulverization-like abnormality. FISH with rDNA and NOR silver staining demonstrated that the pulverization-like abnormality was restricted to NORs. The frequent occurrence of persistent nucleolar material in prophase and prometaphase of the stressed cells after release indicated a delayed dissociation of the nucleolus that brought about the abnormal chromosomes in M-phase. ts85 cells transfected with the mouse E1 cDNA recovered growth at the non-permissive temperature and no longer showed abnormal nucleolar morphology. It seems that the ubiquitin system plays a role in the dissolution of the nucleolus, possibly involving the NOR-bearing chromosomes.

Three-dimensional co-location of RNA polymerase I and DNA during interphase and mitosis by confocal microscopy

The relative three-dimensional co-location of RNA polymerase I (RPI) and DNA was studied using confocal laser scanning microscopy during interphase and all the steps of mitosis in human cancerous cells. For each step of the cell cycle, immunolabeled RPI molecules and DNA specifically stained with chromomycin A3 were simultaneously imaged at high resolution through numerous optical sections. Then, all the data obtained were used to generate transverse sections, anaglyphs and volumic representations, which are all prerequisite approaches to a representative study of the three-dimensional organization of the nucleolus and the mitotic chromosomes. Our results indicated that in the interphasic nuclei, in which DNA is organized as a regular 3-D network, RPI was present within numerous irregular spheres arranged as several twisted necklaces. During metaphase, RPI labeling was segregated into pairs of spheres and typical crescent-shaped structures; both were centrally located within the set of chromosomes. During anaphase and telophase, a typical central and symmetric arrangement of labeled structures was systematically seen among the decondensing chromosomes, arranged as a regular cylinder and as a hollow half-sphere, respectively. This typical 3-D organization of structures containing RPI relative to DNA is another strong example of the non-random organization of the genome during interphase and mitosis.

Ultrastructural localization of rDNA and rRNA by in situ hybridization in the nucleolus of human spermatids

The ultrastructural localization of rDNA and rRNA within the nucleolus of human spermatids was investigated by in situ hybridization at steps 1 and 2. Two different digoxigenin-labeled human probes from the rRNA transcription unit were used. Identification of hybrids was performed with immunogold techniques. Comparative observations in the Sertoli cell nucleolus as controls revealed that rDNA was predominantly visualized in the threads of the dense fibrillar component, while rRNA was detected over both the fibrillar component and the granular component. Within the nucleolus of round spermatids in the same sections of seminiferous tubules, rDNA labeling was localized over the spherical or stranded dense fibrillar components. rRNA labeling was found not only over these components but also in the adjacent nucleoplasm rich in ribonucleoprotein particles. These results are consistent with the view that the round spermatid nucleolus is transcriptionally active.

Prognostic relevance of pretreatment proliferative rapidity of marrow blast cells in childhood acute lymphoblastic leukaemia

Cell proliferation rate is a well-established prognostic factor in cancer, but it has not been considered to identify the risk group of childhood acute lymphoblastic leukaemia (ALL) at presentation. We carried out a study to demonstrate the prognostic importance of the rapidity of cell proliferation in patients with ALL. To measure the rapidity of cell proliferation we used the parameter relative to the area of silver-stained nucleolar organiser regions (AgNORs) as evaluated by morphometric analysis on smeared marrow blast cells. The mean AgNOR area of leukaemic marrow cells was measured in 119 children. By using a cut-off value of 3 microns2, we identified a group of 91 children with low proliferating blast activity (mean AgNOR value 2.11 microns2) and a group of 28 children with high proliferating activity (mean AgNOR value 3.29 microns2). The group of patients with a mean AgNOR value > 3 microns2 was characterised by a higher number of deaths, more frequent relapse and shorter time interval to relapse than the group of patients with mean AgNOR value < 3 microns2 (P < 0.01). Multivariate analysis performed to include T-cell immunophenotype, FAB morphology, leucocyte count and presence of mediastinal mass showed that the mean AgNOR value was the only independent predictor of unfavourable event-free survival probability (P > 0.01). Our results indicate that the rapidity of marrow blast cell proliferation is an important prognostic parameter in childhood ALL and should be routinely introduced in the group risk definition.

Nucleologenesis: U3 snRNA-containing prenucleolar bodies move to sites of active pre-rRNA transcription after mitosis

We have investigated the distribution of U3 snRNA and rRNA in HeLa cells and normal rat kidney cells during interphase and mitosis. U3 snRNA, known to be involved in pre-rRNA processing, was detected in nucleoli and coiled bodies during interphase, whereas rRNA was distributed in the nucleoli and throughout the cytoplasm. By comparison, ribosomal protein S6 was detected in nucleoli, coiled bodies, and in the cytoplasm. During nucleologenesis, pre-rRNA was observed in newly forming nucleoli during late telophase but not in prenucleolar bodies (PNBs), whereas U3 snRNA was detected in forming nucleoli and PNBs. Similar findings to those reported here for the localization of U3 snRNA have been reported previously for the U3 small nuclear ribonucleoprotein fibrillarin. These results suggest that components involved in pre-rRNA processing localize to discrete PNBs at the end of mitosis. The nucleolus is formed at specific telophase domains (nucleolar organizing regions) and the PNBs, containing factors essential for pre-rRNA processing, are recruited to these sites of rRNA transcription and processing.

Nucleolar organizer regions in bladder cancer: application to urinary cytology

OBJECTIVES

We investigated the relationship between the numbers of nucleolar organizer regions (NORs) in nonmalignant reactive cells and those in transitional cell carcinomas using urinary exfoliated cell specimens. Another aim of this study was to determine whether higher numbers of NORs are correlated with tumors with higher pathologic grade.

METHODS

Nucleolar organizer regions, which are important for regulating protein synthesis, were counted by means of a silver staining technique in urinary exfoliated cells from 34 patients with transitional cell carcinoma (TCC) and in 30 patients with other urologic diseases (controls).

RESULTS

The number of argyrophilic proteins of the nucleolar organizer region (Ag-NORs) per cell (mean +/- SD) was 2.9 +/- 0.5 in the control group and 5.5 +/- 1.9 in patients with TCC, which was significantly higher than that in the controls (p < 0.001). It was 4.0 +/- 1.0 in patients with grade 1 TCC, 5.4 +/- 2.0 in those with grade 2 TCC, and 6.5 +/- 1.2 in those with grade 3 TCC. Although no statistically significant difference was observed between the groups, the patients with grade 2 TCCs with higher numbers of Ag-NORs showed a tendency to have more diffuse and/or invasive lesions.

CONCLUSIONS

This method is simple and quick, and can identify low-grade malignancy. It could be used as a tool for further grading of grade 2 TCCs and for determining prognosis.

Morphological and functional changes accompanying the acquisition of meiotic competence in ovarian goat oocyte

In order to determine at which follicular size goat oocytes were capable of resuming and completing meiosis, we evaluated their ability to mature in vitro and measured their maturation promoting factor (MPF) activity by histone H1 kinase assay. The results indicated that goat oocyte meiotic competence developed progressively in follicles ranging from 0.5 to 3 mm; the oocytes acquired the ability to resume meiosis in follicles of 0.5-0.8 mm, to reach metaphase I (MI) in follicles of 1-1.8 mm, and to reach metaphase II (MII) in follicles larger than 3 mm. The presence of MPF activity was first observed in oocytes arrested at early prometaphase I and reached a maximum level in oocytes blocked in metaphase I (MI). In the second part of this study, RNA synthesis and nucleolar changes were analyzed during the growth period. The acquisition of meiotic competence was accompanied by nucleolar compaction and a dramatic decrease in RNA synthesis. Changes in protein patterns were also analyzed, but only slight differences were observed among oocytes from the different classes.

Multiplication of 28S rDNA and NOR activity in chromosome evolution among ants of the Myrmecia pilosula species complex

Chromosomal localization of rDNA in samples of five taxa of the Mymecia pilosula species complex (Hymenoptera: Formicidae: Myrmeciinae) with 2n = 3 (M. croslandi), 8 (M. imaii), 10 (M. banksi), 18 (M. haskinsorum), and 27 (M. pilosula) was carried out by fluorescence in situ hybridization (FISH) using cloned M. croslandi rDNA (pMc.r2) including the coding region for 28S rRNA. Results show that (1) the 28S rDNA in the genome of these ants is repetitive and is localized in pericentromeric C-bands, (2) the number of chromosomes carrying rDNA is two in M. croslandi, M. imaii and M. banksi, six in M. haskinsorum and ten in M. pilosula, and (3) only one or two clusters of rRNA genes generate nucleoli in each species. We suggest that the rDNA in the ancestral stock of the M. pilosula complex was localized originally in a pericentromeric C-band, and multiplied by chance with time during saltatory increases in C-banding following episodes of centric fission. Most rDNA multiplied on various chromosomes seems to be inactivated and eliminated from the genome, together with C-bands, by AM-inversion or centric fusion, with the remnant rDNAs dispersed in the genome by centric fission and AM-inversion.

Predictors of postoperative distant recurrences in esophageal carcinoma

Pathologic factors and the number of nucleolar organizer region proteins (AgNORs) were evaluated as predictors of postoperative recurrence in distant organs in 92 patients with curatively resected esophageal carcinoma. The rate of distant recurrence was significantly higher in patients with venous invasion (53%; 19 of 36) than in those without invasion (21%; 12 of 56) (p < 0.01) and was also higher in patients with an AgNOR score greater than or equal to 4 (49%; 19 of 39) than in those with an AgNOR score less than 4 (23%; 12 of 53) (p < 0.02). The rate of recurrence was significantly higher in patients with both venous invasion and AgNOR score greater than or equal to 4 (67%; 16 of 24) than in the other patients. These findings indicate that the combination of venous invasion and a high AgNOR score predicts distant postoperative recurrences in patients with curatively resected esophageal carcinoma.

Unusual chromosome structure of fission yeast DNA in mouse cells

Chromosomes from the fission yeast Schizosaccharomyces pombe have been introduced into mouse cells by protoplast fusion. In most cell lines the yeast DNA integrates into a single site within a mouse chromosome and results in striking chromosome morphology at metaphase. Both light and electron microscopy show that the yeast chromosome region is narrower than the flanking mouse DNA. Regions of the yeast insert stain less intensely with propidium iodide than surrounding DNA and bear a morphological resemblance to fragile sites. We investigate the composition of the yeast transgenomes and the modification and chromatin structure of this yeast DNA in mouse cells. We suggest that the underlying basis for the structure we see lies above the level of DNA modification and nucleosome assembly, and may reflect the attachment of the yeast DNA to the rodent cell nucleoskeleton. The yeast integrant replicates late in S phase at a time when G bands of the mouse chromosomes are being replicated, and participates in sister chromatid exchanges at a high frequency. We discuss the implications of these studies to the understanding of how chromatin folding relates to metaphase chromosome morphology and how large stretches of foreign DNA behave when introduced into mammalian cells.

Immunocytochemical characterization of human NOR-90 (upstream binding factor) and associated antigens reactive with autoimmune sera. Two MR forms of NOR-90/hUBF autoantigens

The 90-kDa nucleolus organizer region autoantigen (NOR-90) was previously shown to be identical to the human upstream binding factor (hUBF) and composed of two Mr forms. In this study, thirteen human anti-NOR-90/hUBF autoimmune sera were used to further characterize NOR-90/hUBF and its associated autoantigens. Nucleolar and nucleoplasmic staining of interphase cells and NOR staining in mitosis were observed with all sera by immunofluorescence. All sera showed equal reactivity with both high and low Mr forms in Western blotting and immunoprecipitation, suggesting that the cellular content and distribution for both Mr forms were approximately equal. Using extracts of [35S]methionine- and [32P]orthophosphate-labeled cells, phosphorylated and nonphosphorylated NOR-90/hUBF were identified for both Mr forms and these two populations were recognized by human autoantibodies. In immunoprecipitation analyses, the nonphosphorylated population was readily extracted while the phosphorylated population was tightly bound. Clinical data were available for 8 patients in whom anti-NOR-90/hUBF autoantibodies were present. They had diverse diagnoses including SLE, rheumatoid arthritis and malignancies. Although only one patient was diagnosed as scleroderma, Raynaud's phenomenon was observed in 4 of the 8 patients. Interestingly, one NOR-90/hUBF serum was shown to contain additional antibodies to RNA polymerases I and II.

Cytochemical features common to nucleoli and cytoplasmic nucleoloids of Olea europaea meiocytes: detection of rRNA by in situ hybridization

We used light and electron microscopic techniques to study the composition of cytoplasmic nucleoloids during meiotic division in Olea europaea. Nucleoloids were found in two clearly distinguishable morphological varieties: one similar in morphology to the nucleolus, and composed mainly of dense fibrillar component, and another surrounded by many ribosome-like particles. Cytochemical and immunocytochemical techniques showed similar reactivities in nucleoloids and the nucleolus: both are ribonucleoproteic in nature, and possess argyrophillic, argentaffinic and highly phosphorylated proteins. Immunohistochemical techniques failed to detect DNA in either structure. In situ hybridization to a 18 S rRNA probe demonstrated the presence of ribosomal transcripts in both the nucleolus and nucleoloids. These similarities in morphology and composition may reflect similar functionalities.

Nucleolar organizer regions in small nodular lesions representing early stages of human hepatocarcinogenesis

BACKGROUND

It is believed that in the early stages of hepatocarcinogenesis, some adenomatous hyperplasias (AH) progress to early hepatocellular carcinoma (eHCC), and that many eHCC develop into overt hepatocellular carcinoma (HCC) through nodule-in-nodule formation. However, the proliferative activity of these small nodular lesions has not been fully investigated.

METHODS

Cell proliferative activity was assessed by counting nucleolar organizer region-associated proteins (Ag-NOR) in paraffin sections of 12 AH nodules, 25 eHCC nodules, and 8 nodule-in-nodule lesions. In nodule-in-nodule lesions, an area of well-differentiated HCC corresponding to eHCC and a discrete inner nodule area composed of obvious HCC were examined.

RESULTS

Mean Ag-NOR numbers of extranodular parenchyma, AH, and eHCC were 1.35, 1.35, and 1.75 (P < 0.01), respectively. With regard to the relative Ag-NOR number compared with that of parenchyma, there was no overlap between AH and eHCC with a border of 1.1-fold except in one specimen. In nodule-in-nodule lesions, the mean Ag-NOR number (2.53) in the inner nodular area was much higher (P < 0.01) than that of the area of eHCC (mean, 1.88).

CONCLUSIONS

A stepwise increment of Ag-NOR number was demonstrated in accordance with the multistep of the AH to eHCC to nodule-in-nodule lesion sequence of hepatocarcinogenesis. Thus, it was proposed that the Ag-NOR count may be a practical and objective parameter for assessing the malignant potential of hepatocellular neoplasms histopathologically.

Cytochemistry and immunocytochemistry of nucleolar chromatin in plants

This review attempts to document the most relevant data currently available on the in situ localization of nucleolar chromatin on plant cells. The data provided by the most powerful and recent in situ techniques, such as DNA specific ultrastructural staining, immunogold labelling, in situ molecular cytochemistry, in situ hybridization or confocal microscopy, are summarized and discussed in the light of the potential and limitations of each individual methodology. The presence of DNA in both fibrillar centres and regions of the dense fibrillar component is extensively documented. Data on the nucleolar distribution of other important macromolecules involved in ribosomal transcription are also shown and referred to with regard to the location of DNA. The comparison with the available data on the animal cell nucleolus points towards models of similar functional organization in both plant and animal nucleoli.

Ultrastructural rRNA localization in plant cell nucleoli. RNA/RNA in situ hybridization, autoradiography and cytochemistry

The distribution of ribosomal transcripts in the plant nucleolus has been studied by non-isotopic in situ hybridization in ultrathin Lowicryl K4M sections and by high-resolution autoradiography after labelling with tritiated uridine. In parallel, cytochemical techniques were applied to localize RNA on different plant nucleolar components of Allium cepa L. root meristematic cells and Capsicum annuum L. pollen grains. For RNA/RNA in situ hybridization, several biotinylated single-stranded ribosomal RNA probes were used for mapping different fragments of the 18 S and the 25 S rRNA gene transcribed regions. Ribosomal RNAs (from pre-rRNAs to mature 18 and 25 S RNAs) were found in the nucleolus, in the dense fibrillar (DFC) and granular components (GC). Hybridization signal was found at the periphery of some fibrillar centres (FCs) with probes recognizing both 18 and 25 S rRNA sequences. A quantitative study was performed to analyze the significance of this labelling. Incorporation of tritiated uridine into roots was carried out and, later, after a long time-exposure, autoradiography revealed the presence of newly synthesized RNA mainly in the DFC and at the periphery of the FCs. The presence of RNA in these areas was also confirmed by the cytochemical techniques used in this study. Taken together, these data favour the hypothesis that transcription can begin at the periphery of the FCs, although we cannot exclude the possibility that the DFC plays a role in this process.

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)

Ultrastructural evidence of sexual dimorphism in supraoptic neurons: a morphometric study

We have recently shown that in spite of the absence of receptors for gonadal steroids in the supraoptic nucleus (SON) of the rat hypothalamus, the volume of the nucleus and the size of its neurons are larger in males than in females, and that these differences between male and female rats are correlated with body weight and dependent on the vasopressinergic neurons. As supraoptic neurons and their organelles enlarge when they are engaged in active peptidergic secretion we have carried out a morphometric ultrastructural analysis to determine if cell structures involved in the synthesis and storage of neurosecretory material also display weight-dependent sex dimorphism. Groups of six male and six female rats aged 30, 60 and 180 days were used. Nucleoli, rough endoplasmic reticulum and neurosecretory granules were analysed and we estimated their volume or surface densities and the total volume of nucleoli and rough endoplasmic reticulum, and total surface area of rough endoplasmic reticulum. We found that, with the exception of neurosecretory granules, the densities of the organelles did not differ among the groups studied, but total values were higher in males. These differences were found to be weight-dependent. Since the organelles studied are regarded as reliable indicators of the neurosecretory activity of supraoptic neurons, our data fully support the view that the weight-dependent sexual dimorphism observed in this nucleus reflects greater synthetic activity of its vasopressinergic neurons associated with the need to maintain water balance in larger bodies.

Nucleolus-like morphology produced during the in vitro reassociation of nucleolar components

Nucleoli, the sites of rRNA synthesis, rRNA processing, and the assembly of ribosomes, are dynamic organelles that, in most cells, disperse and reform during mitosis. The mechanisms that regulate nucleolar formation are unknown as is the relationship between nucleolar morphology and the pathway of ribosome biogenesis. In this report we describe the in vitro formation of nucleolus-like particles (NLPs) from soluble extracts of nucleoli. NLPs, which reached sizes comparable to nucleoli (1-3 microns), were found to contain 40% of the nucleolar DNA, RNA, and protein. The ultrastructure of NLPs resembled that of a number of in vivo structures including compact nucleoli, prenucleolar bodies, and pseudonucleoli. The particles were composed of two morphologically distinct regions. The core resembled the dense fibrillar component (DFC) of nucleoli while the cortex resembled the granular component (GC) of nucleoli. The cortex of NLPs contained numerous 15-20 nm osmophilic granules that resembled the preribosomes found in the GC of nucleoli. The distribution of nucleolar proteins in NLPs also resembled that in nucleoli. BN46/51, a component of the GC of nucleoli, was restricted to the GC-like cortex of NLPs. A mAb that bound to the DFC of nucleoli, bound only to the DFC-like core of NLPs while a second mAb that bound to both the DFC and GC of nucleoli, bound to both the core and cortex of NLPs. Thus solubilized components of nucleoli can reassociate in vitro to produce particles that resemble nucleoli in their size, ultrastructure, and protein distribution.

Identification and characterization of a sphere organelle protein

Sphere organelles are nuclear structures in amphibian oocytes that are easily visible by light microscopy. These structures are up to 10 microns in diameter and have been described morphologically for decades, yet their function remains obscure. The present study defines a protein component of the sphere organelle, named SPH-1, which is recognized by a mAb raised against purified Xenopus laevis oocyte nucleoplasm. SPH-1 is an 80-kD protein which is localized specifically to spheres and is undetectable elsewhere on lampbrush chromosomes or in nucleoli. We show using confocal microscopy that SPH-1 is localized to the cortex of sphere organelles. Furthermore, we have isolated a cDNA that can encode SPH-1. When epitope-tagged forms of SPH-1 are expressed in X. laevis oocytes the protein specifically localizes to spheres, demonstrating that the cloned cDNA encodes the sphere antigen. Comparison of the predicted amino acid sequence with sequence databases shows SPH-1 is related to p80-coilin, a protein associated with coiled bodies; coiled bodies are nuclear structures found in plant and animal cells. The sphere-specific mAb stains X. laevis tissue culture cells in a punctate nuclear pattern, showing that spheres or sphere antigens are present in somatic cells as well as germ cells and suggesting a general and essential function for spheres in all nuclei.

Structure, function and assembly of the nucleolus

Most events of ribosome biogenesis--such as transcription of the ribosomal RNA (rRNA) genes, processing of their primary transcripts into mature rRNAs and assembly with ribosomal and nonribosomal proteins to form the preribosomes--are confined to a special nuclear compartment, the nucleolus. Immunogold labelling and in situ hybridization at the ultrastructural level are providing novel insights into structure-function relationships of the nucleolus, and in vitro systems are beginning to shed light on the molecular mechanisms involved in the reforming of nucleoli after mitosis.

Ultrastructural characteristics of primordial germ cells in the quail embryo

An avian species, the quail has become a desirable animal model in experimental embryology and reproductive biology. To understand the ultrastructural characteristics of primordial germ cells (PGC) of this species, we studied PGC in the Japanese quail (Coturnix coturnix japonica) embryo at various developmental stages from their appearance in the germinal crescent through migration to settlement in the gonadal ridges by means of electron microscopy. The results were compared with those of another well-known avian species, the chick. Several ultrastructural characteristics of quail PGC not described previously in chick PGC were observed as follows: 1) No glycogen particles were detected in the cytoplasm at any stage examined. 2) Electron-dense and membrane-bounded granules were found in the PGC cytoplasm during the sexually indifferent gonadal stages. 3) Quail PGC were characterized by a prominent nucleolus associated with condensed chromatin (heterochromatin), and the developmental changes of the nucleus were noted; the nucleolus initially appeared as a compact mass at the germinal crescent stage and became dispersed at later stages during the colonization of the gonadal ridges. These findings suggest several physiological and functional differences in the cell cycle between these two avian species. This is the first report describing detailed ultrastructural characteristics of PGC in the quail embryo.

Alterations in nuclear matrix ultrastructure of G1 mammalian cells following heat shock: resinless section electron microscopy, biochemical, and immunofluorescence studies

Heat shock is known to inhibit vital nuclear functions associated with DNA and RNA metabolism. It has been proposed that the reported heat-induced excess protein accumulation in the nuclear matrix (NM) fraction may alter NM sites crucial for DNA and RNA processing. To test this hypothesis, we examined the fine structure of the NM in synchronous populations of G1 Chinese hamster ovary cells before and after heating by using the technique of resinless section electron microscopy. Heat did induce morphological alterations in the NM. The NM of control cells contained a honeycomb-like arrangement of fibers after chromatin removal. Following heat shock, NMs appeared as more highly anastomosing networks of polymorphic fibers and an overall increase in electron density was observed. Residual nucleoli from heated NMs underwent alterations in distributions of electron density both internally and at their peripheries. The increase in electron density observed in heated NMs was accompanied by an increase in protein mass and a relatively smaller increase in RNA mass as indicated by parallel sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) and isotopic labeling (protein/DNA and RNA) studies. Some excess protein accumulation could also be directly localized onto NM fibers by use of antibodies to heterogeneous ribonucleoprotein complex antigens. It is concluded that alterations of NM fine structure can reflect the heat-stressed state of the cell, may account for the heat-induced inhibition of nucleic acid metabolism, and may be useful as an indicator of physiological or pathological stress in general.

Multi-chromosomal location of ribosomal RNA genes and heterochromatin association in brown trout

The ribosomal rRNA genes have been mapped by fluorescent in situ hybridization (FISH) to brown trout chromosomes. One major NOR chromosome pair and 8 novel minor NOR chromosome pairs have been found. Both major and minor NORs were closely related to polymorphic heterochromatin, as revealed by FISH and C-banding. These results are discussed with respect to NOR expression, the relationship between rDNA and heterochromatin, and evolutionary aspects.

Ultrastructural distribution of DNA and RNA within the nucleolus of human Sertoli cells as seen by molecular immunocytochemistry

The precise distribution of DNA and RNA within the human Sertoli cell nucleolus has been investigated, at the ultrastructural level, by cytochemical and molecular immunocytochemical techniques. In Sertoli cells, the nucleolar components show a typical spatial distribution. The fibrillar centres are not surrounded by a layer of dense fibrillar component, but come in contact only with strands of dense fibrillar component. These fibrillar parts of strands are the extensions of granular strands connected to a large granular mass. These strands delimit numerous nucleolar interstices in which chromatin fibres are clearly obvious. Using the in situ terminal deoxynucleotidyl transferase/immunogold procedure for detecting DNA, we find evident label exclusively over the chromatin fibres enclosed in the nucleolar interstices and over the fibrillar centres, and no significant label over the dense fibrillar component and granular component of the nucleolus. Furthermore, using the polyadenylate nucleotidyl transferase/immunogold procedure for detecting RNA, we show that label is deposited not only over the granular component and dense fibrillar component, as expected, but also quite obviously over the fibrillar centres. No label is seen over the interstices containing chromatin.

Different patterns of rDNA distribution in Pisum sativum nucleoli correlate with different levels of nucleolar activity

We have used in situ hybridization with probes to rDNA, labelled either with digoxygenin or directly with fluorescein, to determine the arrangement of these genes within the nucleoli of Pisum sativum L. root cells. Confocal laser scanning microscopy was used to image the three-dimensional structures revealed, but we have also compared this technique with deconvolution of conventional (wide-field) fluorescence images measured with a cooled CCD camera, and have shown that the results are remarkably similar. When the deconvolution technique was applied to the confocal data it gave clearer images than could be achieved by confocal microscopy alone. We have analysed the distribution of rDNA in the different cell types observable in root tips: the quiescent centre; active meristematic cells; and relatively differentiated root cap, epidermal and cortical cells. In addition to four perinucleolar knobs of condensed, inactive rDNA genes, corresponding to the four nucleolar organizers in P. sativum, which were the most brightly labelled structures, several characteristic patterns of intranucleolar labelling were apparent, including bright foci, large central chromatin masses, and fine, decondensed interconnecting fibres. The larger and more active the nucleolus, the smaller the proportion of condensed perinucleolar rDNA. In some large and active meristematic nucleoli, all the internal rDNA is decondensed, showing that transcription cannot be restricted to the bright foci, and is most likely to occur on the decondensed fibres.

Localization of ribosomal DNA in Rhagoletis pomonella (Diptera: Tephritidae) by in situ hybridization

The ribosomal DNA (rDNA) of Rhagoletis pomonella was localized within both salivary gland polytene chromosomes and somatic cell mitotic chromosomes by in situ hybridization using the heterospecific Drosophila melanogaster rDNA clone, Dm238. In situ hybridization analysis of polytene nuclei showed that R. pomonella rDNA is located in the nucleolus and adjacent granular network of chromosome 1. The site of origin of rDNA is within this isomorphic granular network. The preservation of nucleolar ultrastructure in some polytene chromosome preparations allowed light microscope localization of R. pomonella rDNA to the apparent periphery of fibrillar centres within fibrillar complexes. In somatic cell nuclei, DM238 hybridized to the nucleolus organizing region (NOR) located on chromosome 1 at the site of the secondary constriction. The frequency distribution of heteromorphisms for rDNA content, differential appearance of secondary constrictions, non-pairing of the NOR and differences in homologue lengths suggests that the structural differentiation of this region in chromosome 1 is sex linked. This the first published description of the salivary gland polytene chromosomes from R. pomonella, and we include a tentative karyotype description, polytene chromosome maps and comments on their suitability for banding and molecular analysis.

Ultrastructural distribution of DNA within the nucleolus of various animal cell lines or tissues revealed by terminal deoxynucleotidyl transferase

We have used the highly sensitive in situ terminal deoxynucleotidyl transferase method, applied to ultrathin sections, to investigate the location of DNA within nucleoli of various animal cells. In all the nucleoli studied, intense labelling is revealed over the peri- and intranucleolar condensed chromatin. Gold particles are also consistently found over the fibrillar centres, especially at their periphery, namely in the border area between the fibrillar centres and the dense fibrillar component, whereas the dense fibrillar component itself seems to be free of label in nucleoli in which these two compartments can be distinguished. We conclude that, in transcriptionally active nucleoli of this type, DNA is a characteristic constituent of the fibrillar centres, distinguishing them functionally from the dense fibrillar component. Some nucleoli exhibit neither fibrillar centres nor a dense fibrillar component, but have a single, albeit heterogeneous accumulation of fibrillar material; gold particles are consistently seen over some parts of this fibrillar compartment. This suggests that certain parts of the fibrillar material are functionally similar to the fibrillar centres of those nucleoli that possess them.

New data concerning the functional organization of the mammalian cell nucleolus: detection of RNA and rRNA by in situ molecular immunocytochemistry

We have investigated the fine spatial distribution of RNA and rRNA within the Ehrlich tumor cell nucleolus by in situ hybridization with a biotin-labeled probe and by two new strategies, the polyadenylate nucleotidyl transferase-immunogold technique and immuno-labeling with anti-RNA antibodies. Besides the presence, as expected, of RNA and rRNA in the granular component and the dense fibrillar component, we show, for the first time, significant label over all the fibrillar centers of the nucleoli. When RNA and DNA were detected simultaneously on the same sections, only the fibrillar centers were positive for both. These results throw light on the controversial subject of the precise location of transcribing rRNA genes within the nucleolus. The fibrillar centers, and not the dense fibrillar component, should thus be the site of rRNA synthesis.

Interphasic nucleolar organizer regions expression and cell kinetics evaluation during gastric carcinogenesis induced by nitrosoguanidine in the rat

An increased number of interphasic nucleolar organizer regions containing ribosomal cistrons associated with argyrophilic proteins (AgNORs) has been described in human malignant tumor cells. In this study variations in AgNOR numbers have been compared with changes of cell kinetics, evaluated by the mitotic count (MC) and bromodeoxyuridine labeling index (BrdU LI), during gastric carcinogenesis induced with N-methyl-N'-nitro-N-nitrosoguanidine (NG) in rats. Significant differences (2 P < 0.005) in AgNOR mean numbers, evaluated in the antral isthmic cells, in MC mean values and BrdU LI, evaluated in the whole antral cellular population, were found when comparing areas of acute gastritis, atrophy and hyperplasia in NG-treated rats with the normal mucosa in controls. No differences were observed in MC and BrdU LI between normal antrum and carcinoma cells which showed an AgNORs mean number lower than in the isthmic cells of controls (2 P < 0.005). Moreover, significant correlations were found comparing changes in AgNOR numbers with MC (r = 0.89, P < 0.001) and BrdU LI (r = 0.66, P < 0.001) in different lesions. These data show that evaluation of AgNOR numbers does not allow the identification of malignant cells in NG-induced gastric carcinoma. However AgNOR quantification seems to be a reliable index of cell kinetics and related well with the cellular dividing fraction.

Localization by high resolution in situ hybridization of the ribosomal minichromosomes during the nucleolar cycle of Physarum polycephalum

We have used biotinylated rDNA probes to localize by in situ hybridization the extrachromosomal genes for ribosomal RNA in the slime mold Physarum polycephalum. We established conditions that allow for highly specific hybridization at the ultrastructural level and determined that the 60-kb palindromic rDNA molecules are confined to the nucleolus in interphase. Our study definitively locates these extrachromosomal genes in mitosis in the form of thin DNA fibers contained within nucleolar remnants. We further show that these rDNA minichromosomes do not condense and that they segregate as entities independent of the condensed chromosomal DNA. In telophase, these minichromosomes migrate from the poles toward the equatorial region of the nucleus in a direction opposite that of the chromosomes. Our results illustrate the discontinuous nature of the nucleolar organizing region in Physarum.

Relationship between interphase AgNOR distribution and nucleolar size in cancer cells

We have studied the relationship between interphase nucleolar organizer region (NOR) distribution and nucleolar size in cancer cells at light-microscopical level. Thirteen cases of formalin-fixed bladder cancer and fifteen cases of methacarn-fixed tumours of different origin were used. Nucleoli of the former cases were stained by Phloxine B and of the latter by Toluidine Blue. Selective visualization of interphase NORs was obtained by carrying out the one-step silver staining reaction for AgNOR proteins (Ploton et al., 1986). The area occupied by Phloxine B- or Toluidine Blue-stained nucleoli and interphase silver-stained NORs was measured by means of an automated image analyser. Both in bladder cancers and in the other tumour lesions nucleolar and interphase AgNOR areas were linearly related (r = 0.95 and r = 0.96, respectively, P < 0.001). The close relationship between the area of nucleoli and that of silver-stained nucleolar structures was maintained even if the silver-staining procedure was prolonged beyond the optimal time length for selective interphase NOR staining. In the latter case, however, single interphase AgNORs were no longer visible within the nucleolar body which was, in fact, homogeneously stained. These data indicate that evaluation of the interphase AgNOR area has the same relevance, in tumour pathology, as whole nucleolar size measurement.

Characterization and immunolocalization of RNA polymerase I transcription factor UBF with anti-NOR serum in protozoa, higher plant and vertebrate cells

We have used anti-NOR serum from a patient with rheumatoid arthritis, to study its reactivity on different phylogenetically separated species such as protozoa, higher plants, birds and mammals. The biochemical characteristics of the antigens detected after applying mono- and two-dimensional electrophoresis and electrophoretic transfers confirm that they correspond to the rRNA polymerase I transcription factor UBF. We have demonstrated the different molecular sizes, depending on the cell complexity, but the same neutral isoelectric points in whole cell extracts of the different species. We have also demonstrated an immunolocalization of this transcription factor to the fibrillar component in all the species studied. These results suggest a high conservation of UBF throughout evolution and the possibility of using this anti-NOR serum as a tool for the study of the structure, nucleolar organization and functional roles of the different nucleolar components.

Importance of interphase nucleolar organizer regions in tumor pathology

The importance of the distribution of silver-stained nucleolar organizer regions (Ag-NORs) in interphase nuclei for diagnostic and prognostic purposes in tumor pathology has been reviewed. The available data demonstrated that interphase Ag-NOR evaluation may be of help in distinguishing malignant from hyperplastic or normal cells. On the other hand, there is increasing evidence that a relationship exists between the quantity of interphase Ag-NORs and the prognosis of malignant tumors: the greater the number of interphase Ag-NORs, the worse is the prognosis. This can be explained by the observation that the interphase Ag-NOR quantity is strictly related to the cell proliferation rate. The procedures used for the measurement of the interphase Ag-NOR quantity are also critically discussed.

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.

Evidence for the presence of complex high-molecular mass N-linked oligosaccharides in intranuclear glycoproteins from HeLa cells

Nonhistone proteins were extracted in 0.4 M NaCl from membrane-depleted nuclei of HeLa cells grown in the presence or the absence of [5,6-3H]fucose. Control experiments strongly suggest that most extracted proteins were indeed nuclear components. Several proteins, present in the 0.4 M NaCl nuclear extract, with M(r) ranging from 35,000 to 115,000 were identified on Western blots as fucosylated glycoproteins owing to their binding to the fucose-specific lectin, Ulex europeus agglutinin I. Results of experiments involving mild alkaline treatment and peptide N-glycosidase F digestion showed that the carbohydrate moieties of these fucosylated nuclear glycoproteins were N-linked to the polypeptide backbone. Analysis of the N-glycans revealed the presence of two populations of sialylated oligosaccharides on the basis of their relative molecular masses. The sensitivity of the high-M(r) oligosaccharides to endo-beta-galactosidase and their incorporation of [3H]glucosamine suggest that they could contain repeating N-acetyllactosamine units. [3H]Fucose incorporated into nuclei was confined to the nucleoli, as judged by autoradiography of sections cut through cells grown in the presence of [3H]fucose. Electron microscopy autoradiography showed that the fibrillar centers were never labeled, while silver grains were observed on the dense and the granular components of nucleoli. Taking into account of these data most nuclear fucosylated glycoproteins extracted in 0.4 M NaCl might be nucleolar ribonucleoproteins.

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.

Scattering of the silver-stained proteins of nucleolar organizer regions in Ishikawa cells by actinomycin D

Scattering of the silver-stained proteins of nucleolar organizer regions (Ag-NOR proteins) was produced by actinomycin D in Ishikawa cells. Scattering of Ag-NOR proteins was found only in cells treated with actinomycin D and various other agents had no effect. Scattering was dose-dependent up to 10(-2) micrograms/ml of actinomycin D, but it was not found at higher concentrations that caused marked inhibition of total DNA and RNA synthesis. Actinomycin D (10(-2) micrograms/ml) caused the following changes: (i) nucleolar segregation and (ii) emergence of dense fibrillar bodies in the nucleoplasm. Ag-NOR proteins were observed on the fibrillar centers and surrounding fibrillar components in control nucleoli, on the fibrillar and amorphous zones in segregated nucleoli, and on the dense fibrillar bodies emerging in the nucleoplasm. The scattering of Ag-NOR proteins was due to the argyrophilic nature of the dense fibrillar bodies. Actinomycin D (10(-1) micrograms/ml) also caused similar morphological alterations in the nucleolus and nucleoplasm, but Ag-NOR proteins were observed only on nucleolar remnants.

Characterization and immunolocalization of a nucleolar antigen with anti-NOR serum in HeLa cells

We have used a serum from a patient with rheumatoid arthritis and found it to immunoblot with a 92- to 88-kDa protein doublet with an isoelectric point of around 7.5 after mono- and two-dimensional electrophoresis in whole HeLa cells. By means of immunofluorescence and immunoelectron microscopy we have found it to specifically react with the nucleolar fibrillar component. After quantitative analysis under the electron microscope, we have demonstrated a similar labeling both in the fibrillar centers and the dense fibrillar component, using two different gold-coupled markers. When transcription was inhibited under physiological conditions (mitosis) or after AMD treatment the antigen remained, as shown by immunoblotting and immunolabeling with anti-NOR serum. These biochemical characteristics, which coincide with those of the ribosomal transcription human upstream binding factor, together with the immunolocalization with anti-NOR serum, allow us to discuss the possible role of these antigens in rDNA transcription.

Ultrastructural detection of DNA within the nucleolus by sensitive molecular immunocytochemistry

This paper describes a new technique for locating DNA on semithin or ultrathin sections of aldehyde-fixed and plastic-embedded cells or tissues. Sections were incubated in a medium containing bromodeoxyuridine (BUdR) triphosphate and terminal deoxynucleotidyltransferase. The labeled nucleotides bound at the surface of the sections were subsequently detected with an anti-BUdR antibody and immunoglobulin-gold complex. On semithin sections, labeled nucleotide detection was achieved by an amplification step with silver enhancement. This technique was applied to a wide variety of biological materials allowing a sensitive detection of DNA-containing structures, even where these are present in very low amounts. Examples of high resolution and sensitive detection include the DNA present in mitochondria, chloroplasts, mycoplasmas, and DNA viruses. Special attention focused on the location of DNA inside the nucleolus. In Ehrlich tumor cell nucleoli, DNA was detected in the fibrillar centers and not in the dense fibrillar component. Identical results were found in the nucleoli of other cell types. These results contradict earlier data but conform with other recent immunocytochemical observations concerning the correlation between structure and function in the nucleolus. This method provides a useful tool for investigations requiring highly precise correlations between a molecular function and a given ultrastructural morphology.

Cell cycle-dependent migration of the DNA-binding protein Ku80 into nucleoli

The DNA-binding protein Ku (p70/p80) was originally discovered through the use of human autoimmune sera. In attempts to search out nucleolar proteins in relation to nucleolar dynamic changes, we developed monoclonal antibodies against nuclear proteins. One antibody, termed LL1, received particular attention since asynchronous cells exhibited tremendous differences in their nucleolar fluorescence intensities after immunostaining. The LL1 protein was proven to be the Ku subunit p80 (Ku80) by cDNA cloning and sequencing. Possible correlations between the heterogeneous distribution of Ku80 in nucleoli and the cell cycle were examined. HeLa cells were synchronized at M phase by arrest with nocodazole, or at the G1/S boundary by sequential treatments with thymidine and aphidicolin. These cells were then released by culturing in fresh medium to allow the cell cycle to progress synchronously. Immunofluorescent detection of Ku80 revealed that nucleoli of the cells at the G1/S boundary had very small amounts of Ku80, which was mainly present in the nucleoplasm. Ku80 was gradually accumulated in nucleoli during S phase and reached the maximum at late S or G2 phase. Immunoblotting experiments showed that cell extracts prepared from different phases of the cell cycle had virtually identical amounts of Ku80. These results suggest that Ku80 migrates from nucleoplasm to nucleoli in a cell cycle-dependent manner.

NuMA: an unusually long coiled-coil related protein in the mammalian nucleus

A bank of 892 autoimmune sera was screened by indirect immunofluorescence on mammalian cells. Six sera were identified that recognize an antigen(s) with a cell cycle-dependent localization pattern. In interphase cells, the antibodies stained the nucleus and in mitotic cells the spindle apparatus was recognized. Immunological criteria indicate that the antigen recognized by at least one of these sera corresponds to a previously identified protein called the nuclear mitotic apparatus protein (NuMA). A cDNA which partially encodes NuMA was cloned from a lambda gt11 human placental cDNA expression library, and overlapping cDNA clones that encode the entire gene were isolated. DNA sequence analysis of the clones has identified a long open reading frame capable of encoding a protein of 238 kD. Analysis of the predicted protein sequence suggests that NuMA contains an unusually large central alpha-helical domain of 1,485 amino acids flanked by nonhelical terminal domains. The central domain is similar to coiled-coil regions in structural proteins such as myosin heavy chains, cytokeratins, and nuclear lamins which are capable of forming filaments. Double immunofluorescence experiments performed with anti-NuMA and antilamin antibodies indicate that NuMA dissociates from condensing chromosomes during early prophase, before the complete disintegration of the nuclear lamina. As mitosis progresses, NuMA reassociates with telophase chromosomes very early during nuclear reformation, before substantial accumulation of lamins on chromosomal surfaces is evident. These results indicate that the NuMA proteins may be a structural component of the nucleus and may be involved in the early steps of nuclear reformation during telophase.

TEM cytochemical study of the localization of phospholipids in interphase chromatin in rat hepatocytes

The electron microscopy cytochemical detection of phospholipids in well-defined areas in the interphase nuclei of hepatocytes has been obtained by the acid haematein test, modified for electron microscopy and by the phospholipase A2-colloidal gold method. The specificity of both methods were controlled by enzymatic digestion with phospholipase. The main intra-nuclear localization of phospholipids is at the border between the condensed and dispersed chromatin, where non-ribosomal RNA is also revealed by RNase-gold labelling. Phospholipids are detected, too, over the clusters of interchromatin granules and in the fibrillar component of the nucleolus.

Identification and localization of a nucleolin homologue in onion nucleoli

A protein homologous to nucleolin, a major nucleolar protein with multifunctional features involved in pre-rRNA synthesis and early processing, has been identified and localized in situ in onion root meristematic cells by different techniques, which have included the use of an antibody raised against hamster nucleolin. The protein was identified on Western blots of nucleolar proteins as a 64-kDa band, by means of the anti-nucleolin antibody, bismuth staining, and the silver staining-nucleolar organizer (Ag-NOR) method. The experiments also suggested that nucleolin could be a target of these two cytochemical stainings. Although the 64-kDa band corresponds to a major nucleolar protein, it is a minor one among total nuclear proteins. The same techniques were used in situ at the ultrastructural level, and the immunogold detection of the nucleolin homologue was quantitatively evaluated. The protein accumulates in the transition area from nucleolar fibrillar centers to the dense fibrillar component, which is considered to be the structural result of ribosomal gene transcription. Out of this transition area, the dense fibrillar component may be divided into two regions, proximal and distal with respect to fibrillar centers, which show, respectively, the significant and unsignificant presence of nucleolin; we interpret this fact as the expression of the topological arrangement of pre-rRNA processing. Fibrillar centers themselves showed a weak but significant labeling with the anti-nucleolin antibody. However, bismuth staining was absent from the interior of fibrillar centers, indicating that the nucleolin in them is not phosphorylated. Ag-NOR staining uniformly covered fibrillar centers and the dense fibrillar component (at least in its proximal region), but it did not stain condensed chromatin inclusions in heterogeneous fibrillar centers, showing that the binding of nucleolin to chromatin is associated with its decondensation. This work provides additional evidence of the high phylogenetic conservation of molecular motifs which take part in ribosome biogenesis.

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.

Effects of dimethyl sulfone (DMSO2) on early gametogenesis in Caenorhabditis elegans: ultrastructural aberrations and loss of synaptonemal complexes from pachytene nuclei

The free-living nematode Caenorhabditis elegans has been used extensively for studies in developmental and reproductive genetics. Recently, toxicologic studies have been initiated using specific sex chromosome mutations. In the present study, high incidence of male (him) mutants, him-5 and him-8, were treated with dimethyl sulfone (DMSO2), the primary metabolite of dimethyl sulfoxide (DMSO). In addition to differential effects on X-chromosome nondisjunction, loss of viability and fertility were observed. Much lower concentrations of DMSO2 were required to elicit the same aberrational effects characteristic of DMSO (1); thus, the toxicity of the former was significantly more potent. The observed decrease in life span was associated with senescent morphology of meiotic prophase nuclei, such that nuclei from young and old specimens could not be differentiated. Aging in oocytes at pachytene is characterized by nucleo-cytoplasmic aberrations, increased density of the nucleoplasm and cytoplasm, and decrease in numbers of mitochondria. Increasing concentrations of DMSO2 resulted in a corresponding decrease in fertility and increased production of abnormal gametes. At DMSO2 concentrations higher than 1.0%, synaptonemal complexes (SC) were absent from pachytene nuclei; thus, effective pairing and segregation of homologous chromosomes was prohibited. Since the SC is essential for regulating pairing and subsequent separation of bivalents, the lack of an SC explains the loss of fertility, due to the production of unbalanced gametes, observed in DMSO2-treated specimens.