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A Stahl

Publications and source records attributed to A Stahl.

At least 37 records · Page 2Linked to original sources
PubMed1996

Localization of ribosomal genes in human spermatogonia by fluorescent in situ hybridization and confocal microscopy.

The distribution of ribosomal RNA genes in nucleoli is still a matter of controversy. We have investigated the nucleolus of human type A spermatogonia, which displays a single, large fibrillar center. Silver-staining was used to localize the fibrillar center by light microscopy. Fluorescent in situ hybridization was performed on the same cell, using a 5.8-kb probe specific for a transcribed region of the ribosomal genes. The fluorescent area exactly corresponded to the silver-stained area. The three-dimensional distribution of rDNA was studied in horizontal and orthogonal sections using a confocal laser scanning microscope. The presence of the fluorescent signal throughout the whole silver-stained structure demonstrated that the fibrillar center, and at least a part of the dense fibrillar component, contained most of the rDNA.

Cell Nucleolus↗
PubMed1996

The distribution of Ag-NORs proteins and ribosomal RNA genes in human spermatogonia: an original procedure associating silver-staining, fish and confocal microscopy.

It is generally accepted that Ag-NORs proteins are associated with nucleolar components engaged in rRNA synthesis. Since conflicting results have been reported concerning the intranucleolar sites of active ribosomal genes, the relationships between the silver-stained areas and the distribution of rDNA were analyzed in human spermatogonia using confocal microscopy of fluorescent in situ hybridized preparations previously stained with silver. The fluorescent signal strictly corresponded to the silver-stained area, identified at the ultrastructural level as the fibrillar center and the surrounding dense fibrillar component. A quantitative evaluation of nucleolar activity solely based on silver-staining may be misleading, taking into account that only Ag-positive proteins located in the dense fibrillar component can be associated with transcriptional activity, while those stored in the fibrillar center are associated with non-transcribed rRNA genes.

DNA, Ribosomal↗
PubMed1995

The urokinase-type plasminogen activator receptor, a GPI-linked protein, is localized in caveolae.

The urokinase plasminogen activator receptor (uPAR), a glycosylphosphatidylinositol-linked glycoprotein, plays a central role in the regulation of pericellular proteolysis and participates in events leading to cell activation. Here, we demonstrate that uPAR, on a human melanoma cell line, is localized in caveolae, flask-shaped microinvaginations of the plasma membrane found in a variety of cell types. Indirect immunofluorescence with anti-uPAR antibodies on the melanoma cells showed a punctated staining pattern that accumulated to stretches along sides of cell-cell contact and membrane ruffles. uPAR colocalized with caveolin, a characteristic protein in the coat of caveolae, as demonstrated by double staining with specific antibodies. Further, uPAR could be directly localized in caveolae by in vivo immunoelectron microscopy. Both uPAR and its ligand, uPA, were present in caveolae enriched low density Triton X-100 insoluble complexes, as shown by immunoblotting. From such complexes, caveolin could be coprecipitated with uPAR-specific antibodies suggesting a close spatial association between uPAR and caveolin that might have implications for the signal transduction mediated by uPAR. Further, functional studies indicated that the localization of uPAR and its ligand in caveolae enhances pericellular plasminogen activation, since treatment of the cells with drugs that interfere with the structural integrity of caveolae, such as nystatin, markedly reduced cell surface plasmin generation. Thus, caveolae promote efficient cell surface plasminogen activation by clustering uPAR, uPA, and possibly other protease receptors in one membrane compartment.

Caveolin 1↗
PubMed1995

[Respective value of glycated hemoglobin and fructosamine assays in the care of diabetes mellitus].

The monitoring of metabolic balance in diabetes mellitus involves the assay of cumulative markers of protein glycation. Glycated hemoglobin, particularly the major component HbA1c, and fructosamine, which reflects glycated plasma protein levels, are the most commonly used parameters. Nevertheless, their utilization is still under discussion with respect to methodologies used, as well as to their respective interest in clinical diabetology. This review shows current opinion concerning the analytical and physiopathological use of these biological indicators.

Chromatography, Ion Exchange↗
PubMed1994

Binding of urokinase to its receptor promotes migration and invasion of human melanoma cells in vitro.

Previously, we reported that urokinase-type plasminogen activator (uPA) plays a pivotal role in extracellular matrix dissolution by malignant melanoma cells. Here, we demonstrate that a highly metastatic melanoma cell line (M24met) that secretes uPA expresses high levels of the uPA receptor (uPAR), 2.4 x 10(6) binding sites/cell with a KD of 5.67 x 10(-10) M. The receptor was identified as a 55,000-60,000 kDa cell surface protein. Although M24met cells secrete uPA, they are unable to efficiently utilize this enzyme for invasion, unless it is bound to its receptor. This contention is based on the finding that an antibody against uPAR (monoclonal antibody 3936) inhibited invasion of M24met cells through a reconstituted basement membrane (Matrigel) up to 33%, while a reduction of uPA catalytic activity by its plasminogen activator inhibitor-2 resulted in 46% inhibition of invasion. Furthermore, uPAR is involved in signal transduction events in M24met cells, since both uPA and its amino-terminal fragment stimulated the migration of melanoma cells toward Matrigel, resulting in maximal increases of 32 and 72%, respectively. Our results indicate that both uPA and uPAR are involved in melanoma metastasis and that uPAR contributes to at least two important steps in this process, matrix dissolution and migration.

Cell Movement↗
PubMed1994

Localization of rDNA transcription sites in nucleoli of human Sertoli cells: an EM quantitative autoradiographic study using 3H-uridine.

The sites of rDNA transcription within human Sertoli cell nucleoli have been localized using EM autoradiography after a 45-min pulse of 3H-uridine and an exposure time of 6 months. Two successive quantitative image analyses, one derived from the 50% probability circle method and the other from the cross-fire method, allowed us to estimate the radioactivity incorporated within each nucleolus compartment. This study demonstrated that rDNA transcription occurred mainly at the border between fibrillar centers and dense fibrillar components and to a lesser extent within the dense fibrillar component. The other Sertoli cell nucleoli compartments did not incorporate 3H-uridine and therefore were not involved in rDNA transcription.

Autoradiography↗
PubMed1994

The genetics of retinoblastoma.

Retinoblastoma is a malignant tumor of the eye that affects about one in 20,000 young children and occurs as hereditary and non-hereditary (sporadic) forms. It results from successive loss or inactivation of the two alleles of the Rb1 gene, located in 13q14. A chromosomal deletion in 13q14 is revealed by cytogenetic investigation in about 5% of affected patients. Molecular studies have confirmed that inactivation of both alleles of the Rb1 gene, even by point mutation, is required for tumorigenesis, leading to the concept of antioncogenes or tumor suppressor genes. The protein (p110RB) produced by the Rb1 gene is involved in cell cycle regulation. Absence or abnormal forms of the protein may result in deregulation of the cell cycle and subsequent cell proliferation. Association of p110RB with viral oncoproteins may be a step in tumorigenesis. Differences in penetrance and expressivity among families, could be explained by balanced insertional translocation and by defects of the Rb1 gene, which codes for a shortened Rb protein with partial oncosuppressor function. Techniques allowing analysis of Rb1 mutations can be successfully used to predict or exclude the development of retinoblastoma in newborn infants.

Chromosomes, Human, Pair 13↗
PubMed1993

Changing attitudes toward the old in Oriental families in Israel.

Old people held a central position in traditional Jewish-Oriental family and society. After immigration to Israel this changed within a very short time, as Israel's Western-style society is not based upon the authority of the elder generation. Often this change was accompanied by the development of negative attitudes toward the aged, appearing in many families as disrespect and even as physical neglect of parents. But in other families the traditional attitudes of honoring the elder generation were retained, although in them too the rise of the nuclear family led to loss of power and importance formerly held by the aged members. The changing attitudes within the family are reflected in discussions by disadvantaged soldiers of Oriental origin in classes for basic training in the Israeli army and by answers of fifth-grade children to questions on their relations with their grandparents.

Aged↗
PubMed1993

[Purification of leucine-endopeptidase from Saccharomyces cerevisiae inner mitochondrial membrane].

Several proteolytic activities have been extracted from isolated yeast mitochondrial inner membranes, in the presence of Tween 20. Absence of matrix and cytoplasmic contamination has been checked. A leucine-endopeptidase has been purified to homogeneity. It has an apparent molecular mass of 66 kDa and a pHi near 8.6. It is a serine-protease, which hydrolyses synthetic polypeptides whose leucine carboxylic group is engaged, as well as various macromolecular proteins; its optimal pH is 7.2.

Chemical Phenomena↗
PubMed1992

Human ribosomal RNA gene repeats are localized in the dense fibrillar component of nucleoli: light and electron microscopic in situ hybridization in human Sertoli cells.

The distribution of the human ribosomal gene repeat within human Sertoli cell nucleoli was investigated with the help of DNA-DNA in situ hybridization at the light and electron microscopic level. Probes from both the transcribed part of the gene repeat and the "non-transcribed" spacer were found to hybridize predominantly to the dense fibrillar component of nucleoli. It therefore can be concluded that the dense fibrillar component of nucleoli is the major site of the intranucleolar location of the ribosomal DNA. This holds true not only for the dense fibrillar component adjacent to fibrillar centers, but also for the dense fibrillar component remote from the fibrillar centers.

Cell Nucleolus↗
PubMed1991

Three dimensional reconstruction of human pachytene spermatocyte nuclei of a 17;21 reciprocal translocation carrier: study of XY-autosome relationships.

A study of XY-autosome relationships at the pachytene stage in an infertile 17-21 reciprocal translocation carrier was undertaken by means of three dimensional reconstruction. Synaptonemal complexes and the sex vesicle were analysed on electron microscopic serial sections and the reconstruction was performed on transparent sheets and on a Samba 2000 (Alcatel TITN) image analysis system. All asynapsed segments were entirely included in the sex vesicle, the chromatin fibre of the autosomes and sex chromosomes being tightly intermingled. In one nucleus, the four arms of the quadrivalent were paired, except around the breakpoints where an interstitial asynapsis was observed. In the other nuclei, a terminal asynapsis involving one or two arms of the quadrivalent was found. In the sex vesicle, autosomal asynapsed segments showed the same morphological characteristics as those of X and Y chromosomes. This observation agrees with the hypothesis of the extension of gene inactivation from sex chromosomes to autosomes.

Cell Nucleus↗
PubMed1991

Nucleoli, nucleolar chromosomes and ribosomal genes in the human spermatocyte.

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

Autoradiography↗