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W Engel

Publications and source records attributed to W Engel.

At least 199 records · Page 11Linked to original sources
PubMed1983

Silver staining of nucleolus organizer regions during human spermatogenesis.

The sizes and staining intensities of the nucleolus organizer regions (NORs) in human spermatogenesis were studied qualitatively and quantitatively with the silver (Ag)-staining technique. The Ag-stainability of the NORs is a measure of the transcriptional activity of the ribosomal RNA genes. Ag-stained NORs are present during the whole period of meiotic prophase up to pachytene and totally absent in the two meiotic metaphases. In the early spermatids the Ag-stainability of the NORs reappears and persists up to the beginning of the elongation phase of the nuclei. This pattern of NOR-activity during spermatogenesis is common for all vertebrates. However, in human spermatogenesis the absolute sizes of the NORs in the pre- and postmeiotic stages as well as the interphase arrangement of the postmeiotically reactivated NORs show characteristic properties not found in any other species. The cytochemistry of the argentophilic material, the significance of the synthesis of ribosomal RNA in spermatogenesis, and the characteristic arrangement of the Ag-stained NORs in the spermatids are discussed.

Animals↗
PubMed1983

Hidden breaks in ribosomal RNA of phylogenetically tetraploid fish and their possible role in the diploidization process.

Hidden breaks occur in the ribosomal RNA of tetraploid Cyprinid fish such that the large ribosomal RNA (28 S) yields upon denaturation two RNA fragments of 8.7 X 10(5) and 5.0 X 10(5) daltons, whereas the small rRNA (18 S) yields fragments of 3.2 X 10(5) to 5.0 X 10(4) daltons. In tetraploid Cyprinids hidden breaks occur only in the rRNA of somatic tissue and not in oocytes and sperm cells. Hidden breaks can be detected only slightly in diploid Cyprinid species. Ribosomes purified from somatic tissue of tetraploid Cyprinids show a reduced efficiency in protein synthesis in vitro. The ribosomal proteins from diploid and tetraploid Cyprinid fish show considerable electrophoretic differences. This is discussed in light of a possible functional role of hidden breaks in rRNA in the process of diploidization of gene expression in tetraploid Cyprinid species.

Animals↗
PubMed1983

Proacrosin and the differentiation of the spermatozoa.

Using the indirect immunofluorescence staining technique, the occurrence and localization of proacrosin, the zymogen form of acrosin, was studied during spermatogenesis in the bull, ram, boar and rabbit. Proacrosin staining was demonstrable for the first time in the early haploid spermatid and increased with the differentiation of the spermatid to spermatozoon. The spermatozoon is covered by a cap-like structure of uniform fluorescence corresponding to the acrosomal compartment of the male gamete. No fluorescence could be found in diploid spermatogenic cells, i.e., in spermatogonia and spermatocytes. An identical developmental pattern of proacrosin was observed with the indirect immunoperoxidase staining technique. However, with this staining technique a distinct distribution of proacrosin staining was observed in the acrosome of epididymal and ejaculated spermatozoa of the bull, ram, boar, rabbit and man. Proacrosin seems to be distributed in the acrosome in granules rather than in the homogeneous form, as was indicated by the results of indirect immunofluorescence staining.

Acrosin↗
PubMed1983

Proacrosin/acrosin activity during spermiohistogenesis of the bull.

Acrosin and its zymogen form, proacrosin, were extracted from early and late spermatids, from ejaculated and epididymal spermatozoa (caput, corpus, and cauda) of the bull. Activity of proacrosin/acrosin and the time course of proacrosin activation were studied. It turned out that proacrosin/acrosin activity is first demonstrable in haploid spermatids, increases during spermiohistogenesis in the testis, and remains nearly constant in epididymal and ejaculated spermatozoa.

Acrosin↗
PubMed1983

Acrosin in the spermiohistogenesis of mammals.

Using the indirect immunofluorescence staining technique, the developmental pattern of acrosin during spermatogenesis of boar, ram, rabbit, mouse, rat, and Russian hamster (Phodopus sungorus) was studied. Specific antibodies against purified boar acrosin raised in rabbits cross-reacted with the acrosin of all species investigated thus suggesting that the antigenic determinants of the acrosin molecule cross-reacting with anti-boar acrosin antiserum have been highly conserved in mammalian evolution. During spermatogenesis acrosin was first demonstrable in haploid spermatids and increased in the course of the differentiation of the spermatids to spermatozoa. During the entire period of spermatid differentiation acrosin appeared in juxtaposition to the nucleus. In boar and ram the results obtained with the indirect immunofluorescence staining procedure were confirmed with the indirect immunoperoxidase staining method.

Acrosin↗
PubMed1983

The Z-chromosome is involved in the regulation of H-W (H-Y) antigen gene expression in Xenopus.

H-W (H-Y) antigen was investigated in diploid, triploid, and tetraploid Xenopus hybrids. These hybrids differ from each other with respect to their sex chromosome constitution-they all have a single W chromosome but one to three Z chromosomes. The H-W antigen concentration is reduced with increasing numbers of Z chromosomes. In the diploid and triploid hybrids the single W chromosome is able to guarantee ovary development, but among the tetraploids both male and female animals occur. However, both sexes have identical H-W antigen titers in the somatic tissues. It can be concluded that in these tetraploid hybrids with a ZZZW sex chromosome complement, the amount of H-W antigen is too low to sustain ovary development in all cases. Our results clearly indicate that in Xenopus a Z-coded gene is involved in the regulation of H-W antigen gene expression. In man and mouse there is evidence that such a regulatory gene is located on the X chromosome. Because of the concordance of man, mouse, and Xenopus we hypothesize that not only was the H-Y (H-W) antigen gene conserved during evolution but also the genes engaged in its regulation.

Animals↗
PubMed1983

A direct demonstration of somatically paired heterochromatin of human chromosomes.

Human lymphocyte cultures were treated with different concentrations of 5-azacytidine for various lengths of time. This cytosine analog induces very distinct undercondensation in the heterochromatin of chromosomes 1, 9, 15, 16, and Y if applied in low doses during the last hours of culture. These regions are further distinguished by their intense distamycin A/DAPI-staining and highly methylated DNA. In interphase nuclei, these heterochromatic regions are frequently somatically paired. These somatic pairings are preserved up to the metaphase stage in the 5-azacytidine-treated cultures and are thus susceptible to direct analysis. The specific effect of 5-azacytidine on the heterochromatin of these chromosomes, its conserving effect on somatic pairing, and some of the consequences of the somatic pairing on the development of human chromosome aberrations are discussed.

Adult↗
PubMed1982

Evolutionary conservation of a common pattern of activity of nucleolus organizers during spermatogenesis in vertebrates.

The patterns of activity of the nucleolus organizer regions (NORs) in the spermatogeneses of ten species of all non-mammalian classes of vertebrates and one species of the cephalochordates were investigated with the silver (Ag)-staining technique. The Ag-stainability of the NORs is a measure of the transcriptional activity of the ribosomal RNA genes. In all species, there is a very similar pattern of NOR-activity in the various stages of spermatogenesis. The qualitative analysis of the Ag-stainability of the NORs was in very good agreement with the results obtained for mammals: Ag-stained NORs are detectable during the entire meiotic prophase up to the pachytene stage, completely absent in the meiotic metaphases I and II, and again demonstrable in early spermatid nuclei. The results confirm the occurrence of postmeiotic reactivation of the RNA genes. The preferential inhibition of rRNA synthesis by low doses of actinomycin D induced a rapid decline of the Ag-stainability of the postmeiotically reactivated NORs. The significance of the evolutionary conservation of the postmeiotic NOR-reactivation is discussed.

Animals↗
PubMed1982

Depth of information in photoelectron microscopy.

The depth of information is defined as the distance below the surface of a specimen from which information is contributed at a specific resolution. A simplified model of photoemission is used to explore the relationship between electron escape depths and depth of information in photoelectron microscopy (PEM or photoemission electron microscopy). The depth of information is equal to the escape depth when the escape depth is small relative to the instrument resolution. When the escape depth is large compared to the instrument resolution or when information is carried for example by reflected light, the image consists of well resolved surface detail at the instrument resolution and dimmer, more diffuse, images of detail below the surface. Thus the same sample can exhibit different depths of information depending on the image details of interest. Other mechanisms of transmitting information to the surface, for example induced topography, are discussed, and experimental examples are given.

Electrons↗
PubMed1982

Patterns of cyclic AMP phosphodiesterases in the rat pineal gland: sex differences in diurnal rhythmicity.

Rat pineal cyclic AMP (cAMP) phosphodiesterases (PDEs) were studied during male development and in adult females by means of gel electrophoresis, kinetic analysis, and diurnal activity measurements. In both male and female rats, two molecular forms of PDE coexisted. In neonatal-infantile males (birth to day 20 of age) a third isozyme was detected. The kinetic properties of PDEs were essentially similar in infantile and adult male rats with respect to the Kms; however, a minimal Vmax was observed at 10.00 a.m. in adults, but not in neonatal animals. PDE activity in male rats was maximal between 2.00 a.m. and 4.00 a.m., and also at 4.00 p.m., and was minimal at 10.00 a.m. This pattern appeared to develop during the infantile period of life. The pattern of activity observed in adult female rats was similar to that of adult males, except that it lacked a pronounced afternoon peak. The diurnal PDE activity profile of castrated male adult rats was similar to female adults and testosterone substitution in male castrated rats resulted in a pattern which resembled that of adult male controls. In addition to the above measurements, testosterone serum levels have been determined during all of these experiments.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1981

Serological evidence for H-Y antigen in XO-female mice.

H-Y antigen was examined in XX-, XY-, and XO- mice using spleen, kidney, and liver cells of the animals for the absorption of the anti-H-Y antiserum produced in the rat. The cells of the XY- and XO-mice were found to be H-Y antigen-positive while the cells of the XX-mice were negative. As in Turner syndrome patients with 45,X, in the XO-female mice the H-Y antigen titre was reduced as compared to normal XY-male mice; intermediate values between those of normal male and female mice were obtained. These results clearly indicate that as in man, in the mouse the structural gene for H-Y antigen is not Y-linked but is located on an autosome. Furthermore, the concept of the regulation of the H-Y antigen gene expression in the human (Wolf et al. 1980a, b) by an X-linked repressor gene, escaping X-inactivation in the XX-female and an Y-linked inducer gene also seems to hold true in the mouse.

Animals↗
PubMed1981

The capacity of ovarian cells of the postnatal rat to reorganize into histiotypic structures.

Cell-reorganization experiments in vitro were performed with dissociated rat ovaries at different ages of postnatal development, namely newborn, 8-10, 15-22, and 90-day-old. Ovarian cells consistently aggregated into follicularlike structures. Follicular organization ion vitro is comparable to the ovarian histology of the respective age. The histogenic properties conserved by ovarian cells are considered to be related with the morphogenetic processes steadily occurring in the ovary.

Animals↗
PubMed1981

Cyclic AMP phosphodiesterase in Leydig cell preparations of the rat testis.

Enzymatic digestion of the interstitial tissue of early juvenile and adult rat testes resulted in an enrichment of the Leydig cell population. The cells of the intertubular preparation from adult testes were separated by centrifugal elutriation, according to differences in sedimentation velocity, a counter-flow centrifugation technique leading to 70% Leydig cell purity. Using this approach, it was possible to demonstrate that Leydig cells from adult testes contain only low affinity isoenzymes of cyclic AMP phosphodiesterase (PDE; E.C.: 3.1.4.17), an intracellular regulator of cAMP. Starch gel electrophoresis showed that the isozyme of cAMP PDe of Leydig cells is masked in crude testis homogenates due to the relatively low level of these cells in the total population. In Leydig cells, there are two different electrophoretic forms expressed which resemble two of eleven different molecular forms of cAMP PDE demonstrated for comparison in 21 different organs of the adult rat. An interstitial cell preparation from early juvenile testes, with a Leydig cell content of up to 20%, was also investigated electrophoretically with regard to molecular forms of cAMP PDE, the properties of which were characterized by kinetics analysis of cAMP hydrolysis. The results presented are discussed in relation to the onset of testosterone synthesis in Leydig cells of prepubertal rats leading to the initiation of male puberty.

3',5'-Cyclic-AMP Phosphodiesterases↗