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R Czaker

Publications and source records attributed to R Czaker.

At least 19 recordsLinked to original sources
PubMed2002

Virus-like particles in an antarctic Aggregata sp.: I. Sporogonial stages.

An unknown Aggregata sp. was found in the renal organ of an antarctic Benthoctopus sp., when it was inspected for the presence of dicyemid mesozoans. Merozoites invaded the renal epithelium, whereas sporogonial stages resided in the submucosal connective tissue. Interestingly, individuals of all developmental stages were found to be infected with hitherto unknown virus-like particles. These virus-like particles, spherical in shape, nonenveloped and measuring approximately 30 nm in diameter, could be observed in the nuclei as well as within the cytoplasm. Greater amounts of virus-like particles tended to be arranged in paracrystalline arrays. Although the infection was extensive, it obviously had no pathogenic effect on the parasites themselves. On the basis of the host specificity, size, morphology and histochemical analysis, which suggested the putative viral genome as RNA, a relationship with Totoviridae is assumed.

Animals↗
PubMed2001

Newly identified 'wanderer' cells in the dicyemid mesozoan Kantharella antarctica: a new mode of reproduction?

In the nematogen of the dicyemid mesozoan Kantharella antarctica two types of germinal cells are present which differ in size and composition of their organelles: the voluminous type A germinal cells, with high amounts of glycogen, small vesicles and a cortically arranged cytoskeleton, which differentiate into migratory 'wanderer' cells and the small type B germinal cells, with polarly arranged bundles of microtubules, which develop asexually into vermiform embryos. Type A germinal cell, however, becomes polarized during its differentiation, whereby the nucleus and all remaining organelles concentrate at one pole and the cytoskeleton organizes into a pseudopod at the other. Now called 'wanderer' cell, it leaves the nematogen by opening the junctions along the contact zones of neighbouring cells using this intercellular space like an excretory duct. This polarized migratory cell exhibits conspicuous morphological features that are similar to mature sperm of nematodes, whereby the characteristics of the cytoskeleton resemble that of amoeboid Protozoa.

Animals↗
PubMed2000

Extracellular matrix (ECM) components in a very primitive multicellular animal, the dicyemid mesozoan Kantharella antarctica.

One of the most vital synapomorphic properties of metazoans is the presence of an extracellular matrix (ECM), i.e., a complex of proteoglycans, adhesive glycoproteins, and collagens. The genetically controlled ECM mediates between the respective receptors morphogenesis and cell differentiation and is central to gastrulation, i.e., the process which generates the embryonic germ layers, upon which all metazoan body structures are based. However, the primitive metazoans include a phylum, viz. the Dicyemida, which lacks any kind of typical metazoan ECM structures including a basement membrane, and hence does not develop through gastrulation. Since the ECM components fibronectin, laminin, and type IV collagen, all of which are essential constituents of each basement membrane, have been proved to be evolutionary ancient molecules from the lowest metazoans up to vertebrates, antibodies against the respective vertebrate ECM components were employed by electron microscopy to look for these molecules also in the dicyemid mesozoan Kantharella antarctica. As a result, all three protein families showed an immunolabel which was localized intracellularly and intimately associated with the cell membranes as well as with the submembranously arranged delicate filamentous network. The immunolabel was most intense in the fibronectin-like protein, followed by the type IV collagen-like protein and weakest in the laminin-like protein. From an evolutionary point of view, this kind of distribution of ECM components, primarily found in intracellular regions, seems to reflect a very primitive situation of the structures of the respective ECM molecules having not yet reached their definitive position outside the cell, thus generating the complete biological function of typical ECM. Moreover, these results confirm the long-standing presumption that the dicyemid mesozoan body structure might be the missing link between the Protozoa and Metazoa.

Animals↗
PubMed1994

Ultrastructural study of an unusual crystalloid in the Sertoli cells of the bull.

An unusual type of crystalloid was found in the cytoplasm of bull Sertoli cells. Located in the immediate vicinity of the nucleus, this crystalloid is a non-membrane bound ovoid-shaped structure with maximum dimensions of 10 microns in length and 3 microns in width. It consists of closely packed parallel arrays of zigzag coursing 13 nm filaments and is closely associated with a number of cell organelles like mitochondria, smooth endoplasmic reticulum, lysosomes and the juxtanuclear network of vimentin filaments. This specific aspect is discussed in relation to a possible role in the transport of steroidogenic metabolites and/or other secretory products.

Animals↗
PubMed1987

Relative position of constitutive heterochromatin and of nucleolar structures during mouse spermiogenesis.

In this study, the selective fluorochrome staining of constitutive heterochromatin and a specific ultrastructural silver-staining of nucleolar material (i.e., the nucleolus organizing regions) were undertaken to be used as indicators for the chromosomal arrangement during mouse spermiogenesis. Since in mice all somatic chromosomes are telocentric and the constitutive heterochromatin and nucleolar organizing regions are closely associated to the centromeres, this combination of techniques provided for the first time ultrastructural evidence 1) for the dispersion of the constitutive heterochromatic chromocentre and a centrifugal migration to the postacrosomal portion of the nuclear envelope where constitutive heterochromatin seems to mediate the assembling of microtubules in the so-called manchette. As elongation continues, the constitutive heterochromatin migrates back into central position and forms the "focous of earlier condensing chromatin", which initiates further chromatin condensation. 2) The fate of the nucleolus during spermiogenesis could also be further clarified: The nucleolus is first associated with the chromocentre, but starts to disintegrate during elongation phase. However, argyrophilic remnants are still visible in the centre of the nucleus, pointing to an ongoing transcriptional activity. When they final disappear, they leave behind "nuclear vacuoles" in the dense chromatin mass of the mature sperm nucleus.

Animals↗
PubMed1985

Distinct argyrophilic cytoplasmic organelles revealed during mouse spermiogenesis. A fine structural and cytochemical study.

An electron microscopic Ag-staining method was used to study the argyrophilia of specific cytoplasmic organelles that appear during mouse spermiogenesis. The microtubuli of the centrioles are surrounded by a thin layer of argyrophilic material that also surrounds the microtubuli of their derivatives, e.g., the centriolar adjunct, the axoneme, and some structures of the connecting piece. As the mantle, i.e., the junctional complex between Sertoli cell and spermatid, develops, the involved regions of its plasma membranes are covered with silver precipitates. The apical portion of the nuclear ring as well as that of the perforatorium show clear argyrophilia. Besides these structures, a number of ring-shaped and spheroidal bodies at various sites in the cell also are decorated with silver precipitates. Most of these argyrophilic structures show a positive reaction with the EDTA method, too, suggesting that they contain ribonucleoprotein and might be of nucleolar origin. Since, furthermore, most of these structures are known to contain distinct cytoskeletal proteins, it is assumed that the staining reaction might be caused by proteins that are associated with the genuine cytoskeletal proteins.

Animals↗
PubMed1985

Morphogenesis and cytochemistry of the postacrosomal dense lamina during mouse spermiogenesis.

During the elongation phase of spermiogenesis in the mouse, a layer of electron-dense material appears just below the posterior portion of the acrosomal zonule. Subsequently this material accumulates on the outer side of the nuclear envelope immediately subjacent to the caudal tip of the acrosomal zonule--the anlage of the future postnuclear band--as well as on the inner side of the plasma membrane vis-à-vis to this region--the anlage of the future postacrosomal dense lamina (PADL). Corresponding to further development the postacrosomal region of the nucleus becomes directly enveloped by the plasma membrane, and the PADL, situated on its inner side, grows adequately. The postnuclear band, however, staying the same size as in the preceding elongation phase, gets shifted to the caudal end of the PADL, where it closes the perinuclear space. Since the anlagen and the mature PADL and postnuclear band show the same cytochemical reactions as the dense basal plaque of the acrosomal zonule and the thin layer on the nuclear envelope vis-à-vis to it, a relationship between these structures can be assumed. Furthermore, the demonstration of ribonucleoproteins in all these structures is discussed in connection with a possible nucleolar genesis.

Acrosome↗
PubMed1984

Observations on the dynamics of argyrophilic nucleolar material in the nuclei of mice spermatids.

Applying a new silver staining technique it could be shown that in very early spermatids strong argyrophilia in nucleoli is confined to their granular and fibrillar components; fibrillar centers are devoid of silver. During subsequent developmental stages remnants of these nucleolar components are present in the form of intensively silver stained clusters of coiled fibers. As chromatin condensation proceeds, these fibrous structures decrease in size and density and are finally completely absent. The nucleus of the mature sperm contains only the space in which they formerly existed, now silver negative, as the so-called 'nuclear vacuole'.

Animals↗
PubMed1980

Detection of nucleolus organizer regions (NOR) in the chromosomes of the domestic pig (Sus scrofa domestica L.).

In the domestic pig (Sus scrofa domestica L.) nucleolar organizer regions (NOR) were detected by a combined silver-Giemsa method (Ag-G). The main sites of NORs are the secondary constrictions of chromosomes 8 and 10. Sometimes an additional NOR was observed near the centromere of 1 homologue of chromosome 11. Association of NORs were seen only between chromosomes 10 and at a very low frequency.

Animals↗
PubMed1977

A photometric method for quantifying the polymorphisms in human acrocentric chromosomes.

Photometric measurements on photomicrographs of quinacrine mustard--stained metaphase chromosomes, processed by a reverse developing procedure provide quantitative data on the polymorphisms of human acrocentric chromosomes. The method described is intended for population studies. The method is easily reproducible, allowing comparisons of data obtained by different laboratories.

Chromosomes↗
PubMed1976

Increased sister chromatid exchange events in the human late replicating X.

Human female blood cultures were labeled with BrdU for detecting sister chromatid exchanges (SCEs) by the Hoechst 33258 fluorescence technique. Late labeling with 3H-thymidine and autoradiography allowed the identification of the late replicating X. The mean number of SCEs in the cells was 13. The isopycnotic X showed an exchange frequency according to its relative length in the karyotype; in the late replicating X a doubled number of SCE events was observed.

Chromatids↗
PubMedDate not supplied

Nucleolus organizer regions in the chromosomes of the llama.

Silver nitrate (Ag-AS) staining was applied to chromosome preparations from the llama (Lama glama). The NORs were detected on the secondary constrictions of the short arms or the stalks of five small acrocentric chromosome pairs.

Animals↗