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Biomedical subjects

G Goessens

Publications and source records attributed to G Goessens.

At least 37 records · Page 2Linked to original sources
PubMed1988

Ultrastructural cytochemistry of the nucleolus in rat oocytes at the end of the folliculogenesis.

Various ultrastructural changes occur during follicular growth in the rat oocyte nucleolus. The nucleolus, which has a reticulated fibrillogranular structure at the primordial and primary follicle stages, becomes entirely compact and is made up of a conspicuous and homogeneous mass at the antral follicle stage. In order to define the nature and the functions of this homogeneous mass, cytochemical methods allowing detection of nucleic acids, proteins and lipids were performed at the light microscopic and ultrastructural levels. The results obtained suggest that this nucleolar mass is probably composed of acid proteins which are not silver stained. This proteinaceous mass could be a special kind of nucleolar secretion providing material for meiotic resumption in the oocyte. Cytochemical researches now in progress should supply new information concerning the exact nature and the role of the nucleolar compact mass, which is the essential nucleolar component at the antral follicle stage and which really plays a role in the nucleolus in the first stages of embryogenesis.

Animals↗
PubMed1988

Comparative study of the condensation of chicken erythrocyte and calf thymus chromatins by di- and multivalent cations.

The condensation of chicken erythrocyte (CE) and calf thymus (CT) chromatins upon addition of di- and multivalent cations has been studied using turbidity, precipitation and electric dichroism measurements. For all the cations investigated (Mg2+, Tb3+, Co(NH3)6(3+), spermidine Spd2+ and spermine Sp4+) condensation of CE chromatin occurred before the onset of aggregation, while aggregation of CT chromatin started before condensation with all cations except Mg2+ and Tb3+. Precipitation of CE chromatin required lower di- and multivalent cations concentrations than CT chromatin. The electric dichroism data for both chromatins, at low ionic strength in the absence of di- or multivalent cations, indicated that the nucleoprotein molecules were not totally decondensed but that a "precondensed" state was already present. A positive electric dichroism was observed for the most condensed chromatin fibers, in agreement with the "cross-linker" models. Tb3+ led to less compact condensed particles as judged from the electric dichroism observations, but electron microscopy revealed that "30 nm fibers" were formed. Very little aggregation was produced by Tb3+. On the contrary, spermine produced very large networks of condensed molecules, but large spheroidal particles were also observed. The condensation of CE chromatin happened without changes of solution conductivity upon cation salt addition, regardless of the condensing cation, indicating a cooperative uptake of the ions during this process.

Animals↗
PubMed1988

Localization of DNA within Ehrlich tumour cell nucleoli by immunoelectron microscopy.

The distribution of DNA in Ehrlich tumour cell nucleoli was investigated by means of an immunocytochemical approach involving a monoclonal antibody directed against double- and single-stranded DNA. Immunolabelling was performed either before or after the embedding process. The postembedding labelling method allows better ultrastructural preservation than the preembedding labelling method. In particular, the various nucleolar components are well preserved and identifiable. In the nucleolus, labelling is particularly concentrated over the perinucleolar chromatin and over its intranucleolar invaginations, which penetrate the nucleolar body and often terminate at the fibrillar centres. In addition, aggregates of gold particles are found in the fibrillar centres, preferentially towards the peripheral regions. By contrast, the dense fibrillar component is completely devoid of labelling. The results seem to indicate that DNA containing the rDNA genes is located in the fibrillar centres, with a preference for the peripheral regions. This finding suggests that transcription of the rDNA genes should occur within the confines of the fibrillar centre, probably close to the boundary region of the surrounding dense fibrillar component. The results are discussed in the light of present knowledge of the functional organization of the nucleolus.

Animals↗
PubMed1988

Immunoelectron microscopic study of nucleolar DNA during mitosis in Ehrlich tumor cells.

In order to investigate the DNA localization within Ehrlich tumor cell nucleoli during mitosis, two recent immunocytochemical methods using either an anti-DNA or an anti-bromodeoxyuridine (BrdU) monoclonal antibody have been applied. In both cases, the immunogold labeling has been performed on ultrathin sections of cells embedded either in Lowicryl K4M or in Epon, respectively. Identical results are observed with both immunocytochemical approaches. In the interphase nucleolus, besides the labeling of the perinucleolar chromatin shell and of its intranucleolar invaginations which penetrate into the nucleolar body and often terminate at the fibrillar centers, a few gold particles are also preferentially found towards the peripheral region of the fibrillar centers. In contrast, the dense fibrillar component and the granular component are never labeled. During mitosis, the fibrillar centers persist at the chromosomal nucleolus organizing regions (NOR's) and can be selectively stained by the silver method. However, these metaphase fibrillar centers are no longer decorated by the DNA- or BrdU antibodies. These results indicate that until the end of prophase, rRNA genes are present inside the fibrillar center material, disappear during metaphase and reappear in reconstituting nucleoli during telophase. Thus, fibrillar centers appear to represent structures sui generis, which are populated by rRNA genes only when the nucleolus is functionally active. In segregated nucleoli after actinomycin D treatment, the DNA labeling is exclusively restricted to the perinucleolar chromatin blocks. These findings also suggest that the DNA content of the fibrillar center material varies according to the rRNA transcription level of the cells. The results are discussed in the light of the present knowledge of the functional organization of the nucleolus.

Animals↗
PubMed1987

Behaviour of nucleolus during mitosis. A comparative ultrastructural study of various cancerous cell lines using the Ag-NOR staining procedure.

The aim of the present work was to study the distribution and the behaviour of the silver-staining nucleolar organizer region (Ag-NOR) proteins at the ultrastructural level during interphase and mitosis in five human and murine cancerous cell lines each characterized by a typical nucleolar morphology. During interphase the Ag-NOR proteins are restricted to the fibrillar centres (F.C.) and/or to the dense fibrillar component (D.F.C.). During prophase the silver-staining components come into close contact with some chromosomes and are arranged with a typical polarity: chromosome, F.C. and D.F.C. Then F.C. and D.F.C. together form roundish silver-stained structures and integrate in part within indentations at the periphery of the metaphase chromosomes. During anaphase and telophase large and small spherical silver-staining structures may be seen. They correspond respectively to the metaphase NORs and to numerous structures which appear de novo within ribonucleoprotein (RNP) material localized between the chromosomes. During late telophase the number of the small silver-staining structures decreases whereas the size of the larger ones increases. Then the interphase nucleoli recover their typical shape. These results suggest that when rRNA synthesis is impaired during mitosis the inactive NORs assume a structure and a localization which are not typical of the cell line. In contrast the F.C. and D.F.C. are probably two aspects of the NORs whose typical distribution, relative to the other nucleolar components, gives the interphasic nucleolus its characteristic morphology.

Anaphase↗
PubMed1987

Evolution of the rat oocyte nucleolus during follicular growth.

The ultrastructural evolution of the nucleolus was followed during follicular growth by means of a silver staining procedure. The oocyte nucleolus in the primordial and primary follicles consists of strands of dense fibrillar silver-stained component and aggregates of granules which are devoid of silver grains. Small fibrillar centres are also recognized and appear to have less silver stainability. At the secondary follicle stage, a new nucleolar component appears in the reticulated oocyte nucleolus. This component is devoid of silver grains. During follicle growth, at the antral follicle stage, this new component seems to fuse and the nucleolus becomes constituted of a compact homogeneous mass which exhibits a vacuole at the end of the oocyte maturation. The results obtained suggest that this nucleolar mass is essentially made of proteins and particularly of acidic proteins.

Animals↗
PubMed1986

Ultrastructural study of the relationships between the various nucleolar components in Ehrlich tumour and HEp-2 cell nucleoli after acetylation.

In the present study, we analysed the relationships between various nucleolar components in Ehrlich tumour and HEp-2 cells, using acetylation. Under these conditions, we found contacts between the condensed intranucleolar chromatin and the fibrillar centre, illustrating the continuity between the DNA present inside the fibrillar centre and that of condensed associated chromatin. We also found that although the dense fibrillar component is usually situated at the periphery of the fibrillar centre, it is sometimes found inside the centre. On the other hand, the layer of dense fibrils bordering the fibrillar centre is interrupted by nucleolar interstices. In addition, in HEp-2 cell nucleoli with a reticulated appearance, the numerous small fibrillar centres are bound together by strands of dense fibrillar component. These observations are discussed in terms of relationships between nucleolar ultrastructure and function(s).

Acetylation↗
PubMed1986

[Nucleolar vacuoles observed in rat oocytes].

Recently Merveille and al (1984) using light microscope have observed intranucleolar cavities in rat ovocytes from large antral follicles. They have showed that the frequency of these vacuoles increases when follicular growth is stimulated by gonadotropins. In this paper, the ultrastructure of the nucleolar cavities has been studied. Two types of cavities are visible in these nucleoli: 1. nucleolar "interstices" present at the periphery of the nucleoli in remnants of the granular component and of the dense fibrillar components; 2. nucleolar "vacuoles" which are located in the homogeneous substance forming the greatest part of the nucleolus. The nucleolar vacuoli generally are clear-cut and spherical. The density of their content is similar to the nucleoplasm but they don't communicate to the nucleoplasm. By means of cytochemical to detect Ag-NOR proteins (Ploton and al [1983]) and basic proteins (Sheridan and Barnett [1984]), dense fibrillar component of the nucleolus but no basic proteins may be seen in the wall of the cavity. Moreover no evidence of relation between the presence of the vacuoles and the process of follicular atresia has been found.

Animals↗
PubMed1985

Heart structure and ventricular ultrastructure of hemoglobin- and myoglobin-free icefish Channichthys rhinoceratus.

The structural and ultrastructural characteristics of the heart of Channichthys rhinoceratus, an antarctic teleost devoid of respiratory pigments, are described and compared with those obtained from the red-blooded related species Notothenia rossii. The heart of the icefish is characterized by a spongy myocardium supplied with a highly developed arterial coronary system. This vasculature includes a subepicardial system and an extensive intratrabecular capillary network. Arterial hilar network and Thebesian vessels may also be present. The bulbus arteriosus shows unusually large spheroid structures located in the middle layer of the wall. Both white- and red-blooded species display comparable myocardial cell morphology and organelle distribution. However, the mitochondrial cristae of the former are more densely packed and the sarcolemma possesses numerous caveolae. A large proportion of non-contractile cells is also found in the icefish ventricular wall.

Adaptation, Physiological↗
PubMed1985

Effects of osmotic shocks on the ultrastructure of different tissues and cell types.

This study deals with the effects of hyper- and hypo-osmotic media on the ultrastructure of four different types of cells and tissues: rat pheochromocytoma cells of line PC12, mouse Ehrlich ascites tumor cells, rat kidney cortex and intestine. Application of hyper-osmotic conditions induces in the nuclear compartment of the tested cell types a condensation of chromatin, a ruffling of the nuclear envelope with loosening of condensed chromatin from the lamina, and an apparent loss of nucleolar fibrillar component which disappears in a background of diffuse granular material. In hypo-osmotic media, there is a marked decondensation of chromatin and a fragmentation of the granular material of the nucleolus. As far as the cytoplasmic compartment is concerned, the electron density of the cytosol is markedly increasing when going from hypo- to hyper-osmotic conditions and there is no vacuolization in hypo-osmotic media. In kidney cortex slices, application of hypo-osmotic shocks further results in a marked reduction of the extracellular space delimited by the infoldings of the tubular cells plasma membranes. These modifications are discussed in relation to the volume regulation process and the changes in ion concentration that occur in cells submitted to anisosmotic media.

Animals↗
PubMed1985

Effects of 2-mercapto-1-(beta-4-pyridethyl)-benzimidazole (MPB) on Ehrlich cell nucleoli: stereological analysis.

The effects of MPB, a strong inhibitor of RNA synthesis, have been analysed at the ultrastructural level by means of stereological methods. After treatment, an increase in the nucleolar volume is observed. This enlargement is due to vacuolization of the nucleoli. However, the relative volumes of the nucleolar components are modified in various directions: the volume of the granular component decreases whereas the fibrillar centres increase in size. These results are discussed in terms of relations between morphology and function of the nucleolus.

Animals↗
PubMed1985

Re-evaluation of the site of transcription in Ehrlich tumour cell nucleoli.

Recent electron microscopic immunolocalization studies (Scheer and Rose, 1984) indicated that RNA polymerase I is located in, and probably confined to, the fibrillar centres of the nucleoli. This conclusion appears to be in contradiction to previous autoradiographic studies reporting that transcription of rRNA genes takes place in the dense fibrillar component. Despite the fact that rRNA transcription occurs in the dense fibrillar component of Ehrlich tumour cell nucleoli, we show in the present paper that dense fibrillar component containing rapidly labelled RNA can be visualized not only around but also inside the fibrillar centres.

Animals↗
PubMed1984

Nuclear bodies in mouse lymphoid cells stimulated by lipopolysaccharide.

C57 BL/6J mouse spleen lymphocytes have been stimulated by a polyclonal mitogene, the lipopolysaccharide of E. coli (LPS). Depending on the LPS concentration, two pathways of B lymphocyte differentiation can be obtained. At low dose, the population is mainly composed of blast cells (85%) and at a high dose, the latter transforms into plasma cells (80%). Four types of nuclear bodies have been distinguished and quantitatively studied at several stages of cell differentiation. Only the simple nuclear bodies type A, which could be related to the nuclear matrix, show quantitative modifications in small lymphocytes. Connections between granular nuclear bodies (type D) and nucleolar material have been observed. Some granular nuclear bodies exhibit a morphological zone similar to the nucleolar fibrillar centre as well as fibrillar and granular components. Autoradiographic studies indicate that the granular nuclear bodies contain RNA synthesized elsewhere in the nucleus and that this RNA subsequently migrates to the cytoplasm. Furthermore connections between granular nuclear bodies and chromatin have also been observed.

Animals↗
PubMed1981

[Study of human synovial cells in culture].

Normal human synovial cells are cultivated in vitro; they actively multiply and fibroblast-like cells with structural characteristics of intermediate synoviocytes are obtained. In view of analyzing some functional aspects of this cell line, their endocytotic capacities have been studied. They also have been cultivated in a medium deprived of serum; a new cell type develops ("dendritic cells"). The latter are analyzed (cell division, endocytosis). As a comparison, human pulmonary fibroblasts (W I 38 line) and mouse macrophages are cultivated and studied under the same experimental conditions.

Culture Techniques↗