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At least 19 recordsLinked to original sources
PubMed1987

Nucleolus, nucleolar chromosomes, and nucleolus-associated chromatin from early diplotene to dictyotene in the human oocyte.

The shape, relationships, relative DNA content, and nucleolar activity of the short arm of acrocentric bivalents were studied in human oocytes from early diplotene to dictyotene. At the beginning of diplotene, the short arms of the previously paired chromosomes were again separated and displayed the same morphological features as in mitotic prophase chromosomes. They were connected only with the nucleolus. In situ hybridization and silver staining showed that the nucleolar organizer regions (NORs) were located in the peripheral region of the nucleolus. Tritiated-uridine incorporation was active. At birth, the relationships of the acrocentric short arms showed increasing complexity. The chromosomes ended in nucleolus-associated chromatin blocks of irregular shape, containing large quantities of DNA as demonstrated by intense binding of 3H-actinomycin D. The number of chromosomes converging on these chromatin blocks exceeded the number of acrocentrics, suggesting that heterochromatic regions of other chromosomes were associated with the short arm of acrocentrics. In the electron microscope, the NORs were represented by fibrillar centers located on the periphery of the nucleolus and consistently connected with the blocks of dense chromatin. These relationships remained unchanged in the primordial oocyte in the adult ovary. Persistence of 3H-uridine uptake showed that the oocyte was not at a "resting" stage. The possible cytogenetic consequences of these observations are discussed.

Cell Nucleolus↗
PubMed1988

Changes in nucleus, nucleolus and cell size accompanying somatic embryogenesis of Theobroma cacao L. II. Relation between basic protein content and size of nucleus, nucleolus and cell.

Embryo formation from callus of Theobroma cacao L. was associated with the changes in relationship between nuclear, nucleolar and cell sizes and the content of basic proteins (FG-FCF-stained). Together with the increase in nuclear size of callus and proembryo cells the increase in the amount of nuclear basic proteins was found. In the callus cells the increase in nucleolar protein content exceeded that in nucleolus size, which led to the rise in basic protein concentration in the nucleolus. However, in the early stage of embryogenesis the increase in protein content was not so marked as that in callus, which indicated that embryogenesis involved a decrease in concentration of nucleolar basic proteins. Differences between callus and proembryo cells were also observed in the concentration of cytoplasmic proteins. The increase in size of callus cells was the same as the increasing amount of cytoplasmic proteins. In proembryos a significant increase in cell size was accompanied by only slight changes in cytoplasmic proteins. The stimulation of embryogenesis by 2,4-D resulted in an increase of nuclear concentration of basic proteins in proembryos. The intensification of embryogenesis involved the decrease of the concentration of nucleolar proteins together with the increase in concentration of basic cytoplasmic proteins.

Cacao↗
PubMed1992

[The 3-dimensional organization of the nucleolus and the nucleolus organizer regions in differentiated cells. II. The reticular, vacuolized and nucleolonemal nucleoli of hepatocytes from the intact mouse liver and of hepatocytes stimulated to proliferation as a result of partial hepatectomy].

By means of stereological and morphological analysis, the dynamics of nucleolar structural changes in stimulated mouse hepatocytes has been studied. Reticulated and vacuolized nucleoli typical for normally functioning hepatocytes were shown to convert into the nucleolonemal nucleoli, first noticed 18 hours following operation. The process of activation of mouse hepatocyte nucleoli involves two steps. At the first step (within 1-18 hours following operation) a progressive growth of nucleoli volume, due to a simultaneous reduction of vacuolar sizes and growth of RNP component occurs. Such changes were observed in both groups of nucleoli being present in the intact mouse liver, because at this particular step a considerable decrease in the number of vacuolized nucleoli took place. Besides, in the stimulated hepatocyte nucleoli the number and total volume of fibrillar centers increase. However, in spite of their considerable changes, the nucleoli preserve the marks characteristic of the reticulated type. The second step of activation, noted 18 hours after stimulation of hepatocytes, includes more fundamental structural reconstructions. As the result, reticulated nucleoli obtain the nucleolonemal structure. At the same time, on the background of a further decrease in the individual volume and an essential growth of the total volume in the fibrillar centres, a spasmodic increase in the mass of the dense fibrillar component, which is associated with the formation of the continuous strand of the nucleolonema. All this is responsible for the complete changes in structural organization of nucleoli commonly seen in mouse hepatocytes. It is suggested that the cause of such a structural reconstruction may be due to the changes in topography of transcriptionally active regions of rDNA.

Animals↗
PubMed1992

[The 3-dimensional organization of the nucleolus and the nucleolus organizer regions in differentiated cells. III. Changes in the nature of the distribution of argentophilic proteins in the nucleoli of mouse hepatocytes with stimulation of the hepatocytes to proliferation].

The stereological and morphological analysis of Ag-positive zones revealed the principal difference in quantity and distribution of Ag-NOR proteins in reticulated and nucleolonemal nucleoli of mouse hepatocytes. It is shown that reticulated nucleoli of resting hepatocytes are characterized with the presence of discrete rounded Ag-positive zones, whose quantitative parameters correspond to the fibrillar centers and dense fibrillar component taken together. The analysis of the three-dimensional structure of Ag-positive zones of nucleolonemal nucleoli has revealed considerable changes in quantity and distribution of Ag-NOR proteins due to proliferative stimuli. 22 hours following operation, a continuous, strongly winding strand of nucleolonema is revealed in the nuclei. Taking into account that Ag-NOR proteins are associated with the transcriptionally active regions of rDNA it may be suggested that this structural conversion was due to decondensation and activation of inactive regions of r-chromatin. A considerable growth of Ag-positive zone volume during the conversion of reticulated nucleoli into the nucleolonemal type may be explained by the increase in Ag-NOR protein contents.

Animals↗
PubMed1988

[3-dimensional organization of the nucleolus and the nucleolus-organizing regions in differentiated cells. I. Ring-shaped nucleoli in the endotheliocytes, smooth-muscle cells and fibroblasts in the mouse].

The method of ultra-thin serial sections was used to study the three-dimensional structure and to perform the quantitative analysis of ring-shaped nucleoli of kidney and liver endotheliocytes, smooth muscle cells of kidney arterioles and fibroblasts of mice. Spatial models of ring-shaped nucleoli with one fibrillar centre are given. For the quantitative analysis the following parameters were measured: the number and volumes of nucleoli, fibrillar centers, RNP-containing structures, the vacuolar system and the RNP-index (the latter is a ratio of RNP-part and fibrillar center volumes). Nucleoli of the same type of cells, occasionally in the same nucleus, were found to differ sharply in their fibrillar center shape. Differences in the mean volume values of nucleoli, fibrillar centers and the RNP-part between some cell populations are sufficiently well pronounced. Within the same population ring-shaped nucleoli have, as a rule, specific volume values of nucleoli, RNP and fibrillar centers. The comparison of quantitative data obtained on different cell types showed that the mean RNP-index values were the most stable parameter. The structural relation between fibrillar centers, intra- and perinucleolar chromatin and lacunar region is shown. The structural organization of intranucleolar chromatin and rRNA in the nucleolar body and in fibrillar centers is discussed.

Animals↗
PubMed1988

Changes in nucleus, nucleolus and cell size accompanying somatic embryogenesis of Theobroma cacao L. I. Relationship between DNA and total protein content and size of nucleus, nucleolus and cell.

There was a linear relation between an increase in DNA content and size of nuclei, nucleoli and cells in callus and proembryos (Theobroma cacao L.). In callus the increase of DNA content was accompanied by proportional increase in nuclear size whereas in proembryos the increase in nuclear size did not match the increasing amount of DNA. The stimulation of embryogenesis by 10(-2) mg/l 2,4-D was associated with increase in nuclear and nucleolar size and with decrease in cell sizes. Inhibition of embryogenesis by 1.0 mg/l 2,4-D+10% coconut water did not change nuclear size, but increased cell size in relation to the control. The process of embryo formation was accompanied by changes in relationship between nuclear, nucleolar and cell size and the total (DNFB-stained) proteins content. In callus as well as in proembryo the increase in total protein content in nucleus was not equivalent to the increasing sizes of nuclei which leads to the decrease in nuclear protein concentration. Similar situation was observed for nucleoli. Differences were found in the concentration of cytoplasmic proteins between the callus and proembryo cells. The stimulation of embryogenesis by low concentration of 2,4-D resulted in decrease in concentration of total proteins in nuclei and nucleoli and the increase in cytoplasm.

Cacao↗
PubMed1990

[The Sertoli cell nucleolus in domestic and wild animals].

Sertoli cells produce special microenvironment for developing germ cells; therefore it is assumed that they play primary role in the onset and control of spermatogenesis. In this connection we extended our previous study on the ultrastructure of Sertoli cells in different domestic and wild animals with special regard to nucleolus. Sertoli cells of domestic and wild ruminants possess the typical vesicular nucleolus except for fallow deer, in this species no vesicular nucleolus occurs in Sertoli cells even during the rut. In roe.buck, another wild ruminant with seasonal spermatogenesis, cyclic changes were found in the nucleolus of Sertoli cells. If no spermatogenesis is present, the Sertoli cells have a reticular nucleolus. Membranous vesicles appear in the nucleolus of Sertoli cells of roe-buck at the onset of spermatogenesis 1-2 months before rut. In domestic ruminants with continuous spermatogenesis the vesicular nucleolus in Sertoli cells is present permanently. During postnatal development of bull and ram the vesicular nucleolus appears in Sertoli cells just before the onset of spermatogenesis. In experimental cryptorchidism of bulls a vesicular nucleolus is found in the Sertoli cells. Our observations and experiments support a hypothesis that Sertoli cells have primary role at the onset and the maintenance of spermatogenesis.

Animals↗
PubMed1989

Elimination of the nucleolus from the nucleus of a living cell by centrifugation (a literature review).

The following effects involving the nucleolus take place during centrifugation of living cells at centrifugal forces of several thousand g to several hundred thousand g: settling of the nucleolus in centrifugal direction on the nuclear envelope; pulling the latter as a long stalk with the nucleolus at its end (or alternatively an easy perforation of the nuclear envelope by the nucleolus); release of the nucleolus into the cytoplasm or its expulsion out of the cell; occasional stratification of the nucleolus in the nucleus; fusion of many nucleoli together under centrifugal pressure. The asymmetric topography of the nuclear envelope is considered to be one of the causes of its different resistance to the penetration of the nucleolus. Elimination of the nucleolus from cancer cell nuclei to test the nucleolar contribution to cell malignancy is suggested as one conceivable application of the centrifugal technique of cell enucleolation.

Animals↗
PubMed1991

Segregation of the nucleolus during mitosis in budding and fission yeast.

The segregation of the nucleolus during mitosis was examined in Saccharomyces cerevisiae and Schizosaccharomyces pombe by indirect immunofluorescence using antibodies directed to highly conserved anti-nucleolus antigens. In mitotic S. pombe cells, the nucleolus appears to trail the bulk of the DNA. In wild-type cells of S. cerevisiae, the nucleolus segregates alongside the bulk of the genomic DNA. Based on its distance from the centromere, we would expect the rDNA in both organisms to segregate behind the majority of the genomic DNA, if telomeric regions trail centromeric regions as in other eukaryotes. We therefore suggest that in S. cerevisiae the nucleolus is attached to other parts of the nucleus which enable it to segregate along with the bulk of the DNA. The segregation of the nucleolus in topoisomerase mutants and nuclear division mutants of S. cerevisiae was also investigated. In cdc14 mutants which arrest at late anaphase, the vast majority of the DNA is separated, but the nucleolar antigens remain extended between the mother and daughter cells. Thus, the CDC14 gene of S. cerevisiae appears to be important for the separation of the nucleolus at mitosis.

Autoimmunity↗
PubMed1976

Chromosomal constitution of nucleolus-associated chromatin in man.

Use of specific stains permits analysis of the frequency of nucleolus-associated heterochromatin in chromosomes 1 and 9 from human fibroblasts. In 81 per cent of interphase nuclei the heterochromatic segment of both No. 1 chromosomes is associated with the nucleolus, while in 19 per cent only one heterochromatic segment shows such an association with the other occupying a random position in the nucleoplasm. The nucleolar association of chromosome 9 heterochromatin is less constant: in 42.3 per cent of the nuclei both segments are associated with the nucleolus, in 39 per cent of the nuclei only one heterochromatic segment presents such an association, and in 18.7 per cent neither of the two heterochromatic segments is in nucleolar association. In 6 per cent of the cells, one or two chromosome 9 heterochromatic segments are in contact with the nuclear membrane. In situ hybridization using tritium-labeled 28S and 18S RNA shows that in the interphase nucleus the acrocentric short arms, carriers of ribosomal cistrons, are associated with the nucleolus. These observations demonstrate the complexity of the nucleolus-associated chromatin which, in addition to segments of chromosomes 1, 9, 13, 14, 15, 21, 22, may include the Y chromosome. They also confirm that the nucleolus constitutes one of the orientation points determining the relative localization of chromosomes in the interphase nucleus.

Cell Nucleolus↗
PubMed1992

Centromere autoantigens are associated with the nucleolus.

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

Autoantigens↗
PubMed1988

Origin of nucleolus-like bodies found in the nucleoplasm and cytoplasm of Vicia faba meristematic cells.

Cytohistochemical staining and RNase-gold labelling have been applied to root-tip meristematic cells of Vicia faba to study the origin and biological significance of 2 types of inclusions: one seen in the nucleoplasm and the other in the cytoplasm of early telophase cells. They have been termed "dense bodies" and "cytoplasmic nucleolus-like bodies" (NLB), respectively. Both types of inclusions respond positively to silver staining and ribonucleoprotein (RNP) staining in a similar fashion to nucleolus. Interestingly, the dense bodies label heavily with the RNase-gold complex, as does the nucleolus, while the cytoplasmic NLB have no affinity with the label. In most cases, the dense bodies label more heavily than the nucleolus. Light microscope surveys reveal that the dense bodies sometimes appear to be released from the surface of the nucleolus. On the other hand, prenucleolar material showing the same silver staining and RNP preferential staining characteristics as the dense bodies begin to accumulate on the surface of chromosomes in mid-anaphase. This material does not label with RNase-gold. These data are discussed in terms of the hypothesis that the dense bodies are derived from the nucleolus by direct budding or fragmentation, and the cytoplasmic NLB are composed of prenucleolar material that failed to attach to chromosomes.

Cell Nucleolus↗
PubMed1976

Expression of human and suppression of mouse nucleolus organizer activity in mouse-human somatic cell hybrids.

Most mouse-human somatic cell hybrids show preferential loss of human chromosomes, absence of human 28S ribosomal RNA, and suppression of human nucleolus organizer activity, as visualized by the Ag-AS silver histochemical stain. In contrast, the mouse-human hybrids studied here show preferential loss of mouse chromosomes. The hybrids were made by fusion of HT-1080-6TG human fibrosarcoma cells with BALB/c mouse peritoneal macrophages or strain 129 mouse teratocarcinoma cells. The Ag-AS staining method shows nucleolus organizer activity of chromosomes 13, 14, 15, 21 (rarely), and 22 in the human parent and chromosomes 12, 15, 16 (rarely), and 18 in the BALB/c mouse parent. In the hybrid cells the human nucleolus organizer regions are active, as shown by Ag-AS staining and involvement in "satellite association." The mouse nucleolus organizer regions are not stained by the Ag-AS method even though mouse chromosomes 12, 15, and 18 are present in the BALB/c hybrids and at least one copy of each mouse chromosome is present in the teratocarcinoma-derived hybrids. Thus, in these mouse-human hybrids, unlike those that lose human chromosomes, only human nucleolus organizer activity is expressed, and mouse nucleolus organizer activity is suppressed.

Animals↗
PubMed1985

Morphometric analysis of the nucleolus during the life cycle of human odontoblasts.

Developing first premolars were used as a model system to obtain information on the nucleolar structure of human odontoblasts at several stages of their life cycle. Four stages were defined by their location within the tooth: a) preodontoblasts were located at the growing tip of the root; b) secretory odontoblasts in the apical region; c) transitional odontoblasts in the middle region; and d) aged odontoblasts in the coronal region. Preodontoblasts have a small nucleolus (0.55 micron 2) with few strands of dense fibrillar material radiating from the fibrillar center. Secretory odontoblasts are characterized by a large (1.24 micron 2), irregular, and reticulated nucleolus. The fibrillogranular material, the largest component in all nucleoli, reaches maximal size at this stage (0.88 micron 2). Fibrillar centers occupy about the same area (0.1 micron 2) throughout the odontoblast's life cycle. As the formation of primary dentin is completed, the nucleolus of transitional odontoblasts is reduced in size (0.54 micron 2). Finally, the aged odontoblasts have a small, compact nucleolus (0.39 micron 2), with segregated components. Morphologic analysis and quantification of size and component areas of nucleoli obtained with an image analyzer indicated that secretory odontoblasts had the most active, and aged odontoblasts the least active, nucleolus.

Bicuspid↗
PubMed1989

Higher order structure is present in the yeast nucleus: autoantibody probes demonstrate that the nucleolus lies opposite the spindle pole body.

A panel of sera from 892 autoimmune patients was screened by indirect immunofluorescence on mammalian cells. Seventy-three sera were identified that recognize the nucleolus. Three of these sera appear to stain the nucleolus in yeast, suggesting that they recognize highly conserved antigens. These three sera also immunoprecipitate mammalian U3 snRNA-containing particles, which reside in the nucleolus and have been implicated in rRNA processing. Double immunofluorescence experiments with anti-nucleolus and anti-tubulin antibodies revealed a novel form of non-random nuclear organization in yeast. The spindle pole body and the nucleolus-both of which are associated with the nuclear envelope-preferentially localize at opposite ends of the nucleus. Organization of these and other components into specific regions of the nucleus may be important for optimizing their proper function.

Autoantibodies↗
PubMed1977

The nucleolus and meiosis during microsporogenesis in Endymion non-scriptus (L.).

Stages of meiosis from the bluebell Endymion non-scriptus (L.) were studied by electron microscopy. The segregated components of the nucleolus at meiotic prophase underwent fragmentation and dissolution at pachytene-diplotene. Nucleoli were absent during both meiotic divisions and reformed on the nucleolus organizer into a fibrillar mass from scattered fibrillar components at the dyad and tetrad stages. Ti is argued that the fibrillar region shows continuity through nuclear division though undergoing structural transformations in the process. Nucleolar reformation occurs on condensed nucleolus organizers. Processing of the ribosomal precursors and the resumption of RNA synthesis is discussed in relation to the dispersal of the nucleolus organizer into the fibrillar region of the reformed nucleolus.

Cell Nucleolus↗
PubMed1985

Chronobiological studies on the nucleolus.

Chronobiological studies on the nucleolus were performed, using stereological analysis at the electron microscopic level, on different cell types in permanent interphasic state, in rats submitted to various lighting regimen. During the dark span (12L/12D): (1) in sympathetic neurons of superior cervical ganglion circadian changes in nucleolar organization were characterized by an increase in volumes of the nucleolus and each of its components, namely, fibrillar centres, dense fibrillar, granular and vacuolar components; (2) concerning the fibrillar centres, regarded as the interphasic counterpart of nucleolar organizing regions (NORs), the most striking fact, only observed in sympathetic neurons, is the occurrence of a single large-type fibrillar centre, accompanied by small-type fibrillar centres which are present throughout the 24-hr period; (3) the overall increase in volume of fibrillar centres was shown to correspond to a marked drop in the number (up to 4 fold) of small-type fibrillar centres, the unit volume of which (0.01 mum3) remaining unchanged over the 24-hr period and to an increase in size of a large-type fibrillar centre, the volume of which is 100 fold greater than the latter and (4) cytochemical studies showed that the Ag-NOR proteins exhibit a marked increase in amount, suggesting a circadian rhythmicity of these nucleolar proteins. These results, discussed in the light of our current understanding of the nucleolus, briefly summarized in this paper, suggest that the circadian rhythm of the nucleolus and of its components is correlated with circadian rhythms in both transcriptional activity and processing of preribosomes. Analogies between sympathetic neurons and the two other cell types studied, namely, chromaffin cells of adrenal medulla and vagal sensory neurons of nodose ganglion, led to the conclusion that rhythmicity is a fundamental characteristic of the nuclear structure devoted to ribosome biogenesis. Attention is focused on the superior cervical ganglion in which amplitude of nucleolar rhythms are greater and in which fibrillar centres exhibit a particular pattern. These results are discussed with regard to the role played by this sympathetic paravertebral ganglion which is known to regulate circadian rhythmic activities of the rat pineal gland. The persistence of these nucleolar rhythms in continuous lighting, as demonstrated in sympathetic superior cervical ganglion neurons, provide evidence that they are endogenously generated. The intrinsic factors underlying these rhythms in morpho-functional organization of the nucleolus are yet unknown.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenal Medulla↗