Nucleolar Activity Research Articles

An ultrastructural and cytochemical study of the nucleolus-DNA body complex of Amphiporus lactifloreus oocytes.

The components of the nucleolus-DNA body complex of oocytes from the hoplonemertean, Amphiporus lactifloreus, were studied by electron microscopy and cytochemistry. In the early stages of meiotic prophase I, the nucleus of female germ cells was characterized by a large heterochromatic body. From this body a polymorphic nucleolar apparatus, the nucleolus-DNA body complex, subsequently arose. This nucleolar complex was made up of spherical components termed nucleolar spherulae, which contained fibrillar electron-opaque material with cortical 20 nm dense granules, and characteristic ribbon-shaped components termed nucleolar lamellae also with dense granules. The latter components originated from the former by a process of self-peeling of the spherula cortex. A high level of transcriptional activity was located in the nucleolar spherulae which also contributed with the nucleolar lamellae to the formation of many secondary nucleoli and granular bodies. By ultrastructural cytochemistry a number of DNA-containing structures were visualized in nucleolar areas: first, cytochemically well-characterized DNA of partly decondensed chromatin was demonstrated in the thick cortex of spherulae and the inner part of lamellae arising from spherula cortex; second, more dispersed chromatin fibers, related with the cortical component, were revealed in the core of nucleolar spherulae, where ribonucleoproteins were also seen. A thin layer of ribonucleoproteins was also detected in the edge of both spherulae and lamellae of the nucleolar complex. These findings, which show that the nucleolar complex of previtellogenic oocytes of hoplonemerteans is basically dual, are discussed in terms of two synchronous functions: a) the start of the transcription in the nucleolus, b) dispersal of the intranuclear rDNA as a prerequisite to subsequent nucleolar transcription activity.

The B-Chromosome System ofAllium SphaerocephalonL. (Liliaceae): Types, Effects and Origin

SUMMARYTwo types of B-chromosomes (acrocentric and submetacentric) were observed in the population of Allium sphaerocephalon L. (Liliaceae) analyzed in this report. The submetacentric B-chromosome is an iso-B and the acrocentric B displays nucleolar activity. The B-chromosomes of this species caused a significant increase in the between-cells variance of chiasmata. The possible origin of these B-chromosomes is discussed in relation to several detected chromosome rearrangements (reciprocal unequal translocation and centric fission).

The nucleolar organizer (NOR) and fibrillar centers during plant gametogenesis

The ultrastructure and morphometric features of nucleolar fibrillar centers have been studied in three different plant species over a long period of gametogenesis, extending from premeiosis to after the first postmeiotic mitosis, with respect to variations in nucleolar activity which occur throughout this process. Fibrillar centers represent the structural counterpart of the transcriptionally inactive portions of the nucleolar organizing region (NOR); in some gametogenic stages, no discrete fibrillar centers can be observed and, therefore, the structure of the whole NOR has been studied. Two clearly differentiated types of fibrillar center structure are described, with a close relationship to different stages of nucleolar activity. Stages with high activity show “homogeneous” fibrillar centers, whose chromatin is decondensed, and stages with low activity show “heterogeneous” fibrillar centers with both condensed and decondensed chromatin. These two types had previously been characterized cytochemically by us in somatic cells. Medium-active stages show fibrillar centers “intermediate” between the two main types. The morphometric behavior of fibrillar centers is also related to activity. The number of fibrillar centers per nucleolar section increases with the nucleolar activity, while their size decreases. However, the location of fibrillar centers in the nucleolus does not follow any special pattern, except in middle meiotic prophase I, in which the whole NOR occupies a peripheral position. This is due to a special NOR activity at these stages, whose products are stored as “nucleolar dense bodies.” All these data allow us to conclude that fibrillar centers are highly dynamic structures, extremely sensitive to changes in nucleolar activity.

Differentiating characteristics of myocardial nuclei in cardiomyopathy

Myocardial tissue obtained by endomyocardial biopsy was semiquantitatively evaluated for nuclear and nucleolar characteristics in six groups of patients: patients with normal cardiac function (group 1), doxorubicin-induced cardiomyopathy (group 2), idiopathic cardiomyopathy (group 3), alcoholic cardiomyopathy (group 4), post-viral cardiomyopathy (group 5), and chronic valvular heart disease (group 6). From each patient, ten nuclei containing nucleoli were examined and rated on the basis of the following characteristics: chromatin clumping, number of fibrillar centers per nucleolus, nucleolonemal structure, size of nucleolus, number of nucleoli per nucleus, and stage of nucleolar change. Mean values for the nuclear characteristics in each group were compared with normal values using the unpaired t test. In the doxorubicin treated group there were significantly increased chromatin clumping, decreased fibrillar centers, decreased nucleolonemal structure, and increased numbers of contracted nucleoli (indicating later stage). These changes may be linked to lowered nuclear and nucleolar activity. In the idiopathic and post-viral groups, characteristics were consistent with increased nuclear and nucleolar activity. There were no significant changes from normal in the nucleolar features of either the alcoholic or valvular groups. Further comparisons between groups using one-way analysis of variance and multivariate statistical analysis support the conclusion that there are significant differences in the nuclear and nucleolar characteristics of these groups.

Nucleolar activity during rat hepatocarcinogenesis : A. Deleener 1, M. Kirschvolders 1, H. Barbason 2, J. de Gerlache 3 and M. Lans 31Vrije Universiteit Brussel, Brussels, Belgium; 2Universiteit de Liège, Liège, Belgium; 3Universiteit Catholoque de Louvain, Brussels, Belgium

Nucleolar activity during rat hepatocarcinogenesis : A. Deleener 1, M. Kirschvolders 1, H. Barbason 2, J. de Gerlache 3 and M. Lans 31Vrije Universiteit Brussel, Brussels, Belgium; 2Universiteit de Liège, Liège, Belgium; 3Universiteit Catholoque de Louvain, Brussels, Belgium

Effect of Nucleosides on Nucleologenesis and Nucleolar Activity in Onion Root Meristems

Brief treatments of the roots of Allium cepa L. bulbs with either 5×10-5 or 5×10-4 M adenosine stimulate nucleologenesis and accelerate chromatin decondensation in post-mitotic nuclei of meristem cells. However, at one order of magnitude higher (5×10-3 M adenosine), both nucleologenesis and chromatin decondensation are depressed. Neither of these two processes is altered when roots are treated with other ribonucleosides (guanosine, cytidine, uridine, at 5×10-4 M). In addition to the cytological effects, the stimulatory doses of adenosine produce an important enhancement of the «in vivo» 3H-uridine incorporation into total RNA in the meristems. Determinations of 3H-UTP incorporation in meristems made permeable, under conditions which preferentially measure endogenous RNA polymerase I activity, reveal a slight increase in the number of nascent rRNA chains in such adenosine-pretreated roots.

Suppression of ribosomal gene expression in oocytes and nurse cells of a polychaete as a result of polyamine synthesis inhibition

The role of the polyamines in ribosomal gene expression was evaluated in the polychaete Ophryotrocha labronica by analyzing the effects of polyamine synthesis inhibition on RNA synthesis during oogenesis, a period characterized by intense nucleolar activity. At various stages of oogenesis adult polychaete females were blocked in their polyamine synthesis by the addition of 10 mM dl-α-difluoromethylornithine (DFMO) to the sea water in which they were cultivated. To monitor RNA synthesis during DFMO treatment the animals were pulse-labeled with [5- 3H]uridine and processed for autoradiography. Light and electron microscope autoradiographs demonstrate that DFMO treatment suppresses incorporation of label into nucleolar RNA (rRNA) both in the oocytes and their associated nurse cells. The ultrastructural appearance of both cell types reveals interference with nucleolar and ribosomal activity; the endoplasmic reticulum is deprived of ribosomes, and the production of protein granules (vitellogenesis) is reduced. The high specificity of DFMO for polyamine synthesis and the fact that the effects of DFMO were counteracted by addition of a low concentration (10 μM) of putrescine shows that the observed interference with ribosomal gene expression is indeed due to polyamine deficiency.

An ultrastructural study of oogenesis in a marine triclad

The ultrastructural features of oocyte differentiation were studied in the marine triclad Cercyra hastata. Oocytes at several stages of maturation, each surrounded by follicle cell projections, are present within each of the two ovaries. A pre-vitellogenic and a vitellogenic stage have been detected in the oogenesis of C. hastata. The pre-vitellogenic stage is mainly characterized by an increase in the nuclear and nucleolar volume and activity, and the appearance and development of cortical granule precursors which are elaborated by the Golgi complex. In early phases of the vitellogenic stage, intense delamination and blebbing of the nuclear envelope occurs which probably contributes to an increase in number of cytoplasmic membranes and to transfer of nuclear material to the cytoplasm. The rough endoplasmic reticulum is extensively developed and often assumes a ‘whorl’ array. Several areas of yolk precursor formation appear in the whorls. Numerous 2–5 μm protein yolk globules are subsequently formed which appear surrounded by a double membrane (cisternae of the smooth endoplasmic reticulum) and become randomly distributed throughout the cytoplasm of mature oocytes. The peripheral ooplasm is occupied by a monolayer of electron-dense cortical granules. Finally, the evolutionary significance of the autosynthetic mechanism of yolk production is discussed.

Nucleolar fibrillar centres in plant meristematic cells: ultrastructure, cytochemistry and autoradiography.

In plant cells nucleolar fibrillar centres (FCs) undergo ultrastructural changes, depending on the nucleolar activity. We have found two types of FC structure in nucleoli with either high or low activity, to which we have given the conventional names of homogeneous and heterogeneous, respectively. The first type is characterized by the presence of fibres that we describe structurally and cytochemically as decondensed chromatin; the second type, in addition to these fibres, contains a variable number of dense cores made up of condensed chromatin. Moreover, RNA does not appear to be present in FCs, while proteins are a major component. Autoradiography after tritiated uridine incorporation shows that FCs are not the site of transcription, but that this takes place in the fibrillar component; the same result is obtained using the lead acetate fixation technique for detecting orthophosphate ions. This fact leads us to think that FCs are not the whole interphasic counterpart of the mitotic nucleolar organizing region (NOR), as stated by other authors, but only the portion of the NOR that is temporarily inactive in transcription; the transcriptionally active part of the NOR is in the fibrillar component, bound to its earliest product of transcription. Thus, FCs and the fibrillar component constitute a functional unit.

Nucleolar organizer structure and activity in a nucleolus without fibrillar centres: the nucleolus in an established Drosophila cell line.

Classical electron-microscopic techniques (enzymic digestion, EDTA regressive staining) allied with autoradiographic studies after [3H]uridine incorporation or after RNA synthesis initiated by an exogeneous RNA polymerase in the presence of tritiated GTP, enabled us to describe the fine structure and activity of the nucleolus in an established Drosophila cell line. This nucleolus is composed of a large central multilobed core containing proteins, RNA molecules and a DNA-containing component. This core is surrounded by and connected to large clumps of dense fibrillar nucleolus-associated chromatin, which are intermingled with fibrillogranular ramifications extending from the core towards the nuclear envelope. These ramifications are covered by granules of ribosomal ribonucleoprotein. As shown by EDTA regressive staining the nucleolar core contains a ribonucleoprotein network, which unravels and ramifies within a fibrous matrix. RNA synthesis takes place at the level of this network in the internal part of the core. The molecules synthesized are associated with proteins and are exported out of the core in the form of granules. Although it is composed of the same constituents as other nucleoli, the nucleolus of Drosophila cells seems to be less organized, in that it never displays fibrillar centres, which have been referred to as the nucleolar counterparts of the nucleolus-organizers in a wide variety of organisms.

Stimulation of in vitro RNA Synthesis by Pretreating Plants with Auxins is Due to Auxin-Induced Ethylene Production

Summary Nucleoli isolated from mung bean ( Phaseolus aureus ROXB.) hypocotyls were much more active in carrying out in vitro RNA synthesis when prepared from seedlings previously sprayed with solutions of IAA or 2,4-D. No difference was found between the molecular weight of the RNA synthesised by nucleoli from control plants and those sprayed with auxins. The response to auxins developed a few hours after spraying and in vitro nucleolar activity continued to increase for at least 18 h. A large increase in ethylene evolution by auxin-sprayed plants was detected before the stimulation of nucleolar RNA synthesis. A similar stimulation of nucleolar RNA synthesis was found after plants were sprayed with a solution of the ethylene-generating compound ethephon and increased RNA synthesis was observed after exposing plants to ethylene alone. It is suggested that the increase in nucleolar RNA synthesis brought about by spraying plants with auxin is caused by auxin-induced ethylene production. It is further suggested that the enhanced activity is due to an increase in the number of RNA polymerase I molecules bound to the rRNA genes in the nucleoli.

The study of X-rays and TCDD effects on satellite associations may suggest a simple model for application in environmental mutagenesis.

Satellite associations were used as parameters to test nucleolar organizer activity. Assuming that toxic and/or mutagenic agents may affect the ribosomal genes, satellite associations in human lymphocytes were analysed following exposure to X-rays and compared with the satellite association pattern of subjects exposed to TCDD. A significant decrease in the satellite association frequency in D group chromosomes was found both in irradiated lymphocytes and in subjects exposed to Dioxin. The findings seem to be in accordance with the hypothesis based on random damage of functional nucleolar organizing regions.

Influence of 3-methylcholanthrene on liver nucleolar and nucleoplasmic activities of protein kinases and RNA polymerases

The experiments were designed to investigate some details of the action of 3-methylcholanthrene (3-MC) on the regulation of transcription. After a single intraperitoneal dose of 3-MC a significant increase in the activities of both nucleolar and nucleoplasmic protein kinases in hepatic cells of young rats was found. The maximal stimulation took place 24 hr after the administration of 3-MC and the extent of activation was much greater in the nucleolar fraction. There is a significant elevation of the activities of both functional forms, free and template-engaged, of RNA polymerase A 24 hr after a single injection of 3-MC. Free and engaged forms of extranucleolar RNA polymerase B show a different behaviour: after 24 hr of 3-MC administration the engaged form is markedly enhanced while the activity of the free enzyme shows a significant decrease. The more moderate increase in total RNA polymerase B activity is obviously preceded by a transfer of the enzyme from ‘free’ to ‘engaged’ form. Since the enhancement of protein kinase activities was accompanied by the stimulation of nuclear RNA polymerases we suggest that both kinds of enzymes are involved in an epigenetic mechanism of the inducing action of 3-MC on cytochrome P 1-450.

Preferential occurrence of wheat-rye meiotic pairing between chromosomes of homoeologous group 1

Wheat-rye homoeologous pairing in both ABRR and (0-7)A(0-7)BRR plants takes place preferentially between homoeologous chromosomes of group 1. This suggests either a much greater affinity between wheat and rye chromosomes for this group or more efficient pairing initiation because of common nucleolar organizer activities. 1A-1R associations were more frequent than 1B-1R associations though in both cases pairing was restricted mostly to the long arms. From the variation in these particular chromosome arms the three following factors might hinder the wheat-rye pairing: regular homologous pairing of rye chromosomes, presence of prominent telomeric C-bands in rye chromosomes or occurrence of wheat-wheat homoeologous pairing.

Variability of the nucleolar organizer activity in human lymphocytes via Ag-staining

Chromosomes with Ag staining that varies from one metaphase to the other can be distinguished from those with an Ag-staining that is the same in all metaphases. The intercellular variation of an Ag-NOR can be attributed to many different factors. Whatever the importance of technical factors, they do not seem to account for the large variations in Ag-staining which were observed for each ac. This suggests the existence of a natural intercellular variability of the NOR's activity. The variation of the Ag-stainability of a given NOR, the diversity of Ag-stainings observed on the ten ac of one individual and the differences that exist between individuals raise the question of the existence of a compensation of activity between nucleolar organizers. The study, for each individual, of the mean sum of staining per metaphase reveals that this value is not absolutely constant from one individual to another; in the carriers of Robertsonian fusions it is smaller than in chromosomally normal individuals. The analysis of the transmission shows that inactive NORs remain inactive and that active NORs present a variation in the activity from one generation to the next.

Ultrastructural visualization of nucleolar organizer activity during early germination of Zea mays L

The ultrastructural localization of [ 3H]uridine-labeled RNA synthesized in the nuclei of maize embryo root cells during early germination is studied using high resolution autoradiography combined with a differential staining for nucleoproteins. It is demonstrated that transcription takes place in the nucleolar organizer region (NOR) which, in this material, is clearly visible during the first 8 h of germination. The molecules of pre-rRNA synthesized during this starting period of germination are probably unprocessed. They could be involved in the formation of the perichromatin-type granules which we observe in close proximity to or rarely within the NOR. After 72 h of germination, the NOR and the granules are no longer detected and the nucleolus is almost uniformely labeled after [ 3H]uridine incorporation. Nucleoplasmic radioactivity is often associated with small clumps of fibrillar material resembling perichromatin fibrils, regardless of the period of germination. This observation suggests the occurrence of perichromatin fibrils in nuclei of higher plant cells, where these structures have not been identified so far.

Nucleolar activity in lectin-stimulated peripheral blood lymphocytes of several species of domestic animals.

SummaryNucleolar activities in lectin‐stimulated peripheral blood lymphocytes of cattle, sheep, horse, pig, dog, rabbit and chicken were determined. A good correspondence between the species‐specific number of NOR chromosomes per diploid genome and the numbers of separated silver stained clusters in interphase nuclei of lectinstimulated PBL was established.ZusammenfassungNukleolare Aktivitäten in Lektin‐stimulierten peripheren Blutlymphozyten bei verschiedenen HaustierartenDie nukleolaren Aktivitäten Lektin‐stimulierter, peripherer Blutlymphozyten von Rind, Schaf, Pferd, Schwein, Hund, Kaninchen und Huhn wurden bestimmt.Eine gute Übereinstimmung zwischen den artspezifischen Anzahlen der NOR Chromosomen im diploiden Chromosomensatz und den Anzahlen separierter, silbergefärbter NOR Areale in Interphasenkernen Lektin‐stimulierter peripherer Blutlymphozyten wurde festgestellt.RésuméActivités nucléolaires des lymphocytes du sang périphérique stimulés à la lectine chez différents animaux domestiquesOn a déterminé les activités nucléolaires de lymphocytes du sang périphérique stimulés à la lectine chez le bovin, le mouton, le cheval, le porc, le chien, le lapin et la poule.Une bonne concordance a été établie entre les nombres spécifiques des chromosomes NOR en composition chromosomale diploïde et les nombres des surfaces NOR séparées, colorées à l'argent dans des noyaux d'interphases des lymphocytes du sang périphérique stimulés à la lectine.ResumenActividades nucleolares en los linfocitos hemáticos periféricos estimulados con lectina en diversos animales domésticosSe valoraron las actividades nucleolares de los linfocitos hemáticos periféricos estimulados con lectina de vacunos, oveja, caballo, cerdo, perro, conejo y gallina.Se comprobó una concordancia buena entre las cifras específicas de especie de los cromosomas NOR en el juego diploide de cromosomas y las cifras de areales NOR separados con impregnación argéntica en los núcleos interfaseales de los linfocitos hemáticos periféricos estimulados con lectina.

Effect of 3-methylcholanthrene administration on hepatic ribonucleic acid polymerase activities

The effect of the in vivo administration of 3-methylcholanthrene upon rat hepatic RNA polymerase activities was investigated. Aggregrate RNA polymerase activity assayed in liver nuclei was stimulated by 33% over control. Characterization of the individual RNA polymerase activities by virtue of their differential sensitivity to α-amanitin revealed that RNA polymerase I activity was maximally increased by 70% at approx. 16 h post-administration of the polycyclic hydrocarbon; RNA polymerase II activity was stimulated by 33%. The kinetics of RNA polymerases I and II stimulation differed in that the nucleolar enzyme's activity increased earlier and peaked later. RNA polymerase III activity was not significantly different from control. Phenobarbital, another inducer of the mixed function oxidases, had essentially no effect on the activity of hepatic RNA polymerases. Solubilization of the RNA polymerases followed by separation on diethylaminoethyl (DEAE)-Sephadex allowed for a comparison of the treated and control enzymatic activities using a common exogenous template. While no qualitative difference was evident, RNA polymerases I and II isolated from 3-methylcholanthrene-treated rats again were more active than control, indicating an effect of the polycyclic hydrocarbon at the level of the enzyme.

Genetic determination of nucleolar organizer activity in human chromosomes

Axosomatic contacts of pyramidal neurons and those of neurones of celiac ganglia in rats are characterized by diverse types of relationships and by many-component complexes. The metric parameters of axosomatic contacts of pyramidal neurons do not change with age but the proportion of active contacts increases. With age, the celiac ganglia show an increase in the diameter of contact axons and in the number of deeply invaginated contacts. Meanwhile the proportion of active contacts diminishes. These changes within the system of axosomatic contacts appear to develop in response to subsidence of neurons and their contacts with age and thus have a compensatory-adaptive significance.

Variation in nucleolar organizer activity in lymphocytes of females with adenocarcinoma.

With the use of Ag staining and conventional light microscopy, a difference is visualized in the frequency of nucleolar organizer regions between PHA-stimulated lymphocytes from normal females and females with various types of adenocarcinoma. This difference in NOR activity is more pronounced in G chromosome than D chromosomes. It is feasible that rDNA gene activity in PHA-stimulated lymphocytes is augmented in patients with adenocarcinoma due to the presence of plasma mediators arising from cellular malignancies. The NOR regions located on G chromosomes are considered to be more sensitive to these mediators than those on D chromosomes.