PubMed Health⌕ Search

Biomedical subjects

J Erenpreisa

Publications and source records attributed to J Erenpreisa.

At least 19 recordsLinked to original sources
PubMed2006

Sperm chromatin structure and male fertility: biological and clinical aspects.

Sperm chromatin/DNA integrity is essential for the accurate transmission of paternal genetic information, and normal sperm chromatin structure is important for sperm fertilizing ability. The routine examination of semen, which includes sperm concentration, motility and morphology, does not identify defects in sperm chromatin structure. The origin of sperm DNA damage and a variety of methods for its assessment are described. Evaluation of sperm DNA damage appears to be a useful tool for assessing male fertility potential both in vivo and in vitro. The possible impact of sperm DNA defects on the offspring is also discussed.

Abortion, Spontaneous↗
PubMed1999

Aberrations of cell cycle and cell death in normal development of the chick embryo growth plate.

The epiphyses of femurs from 7.5-15 day chicken embryos were studied by electron microscopy. Several forms of aberrant cell cycles were present: (1) in the perichondrium, polyploid metaphases, segmentating large (giant) cells, and mitotic catastrophe (midway between mitosis and apoptosis) were observed; (2) in the resting zone, premature chromosome condensation was found; (3) in the proliferative zone, approximately 5% of divisions were aberrant, representing most often mitosis restitution from metaphase and more seldom from the anaphase; (4) in all layers, 'dark chondrocytes' representing a premortal form of hypersecretory cells undergoing often a-mitotic nuclear segmentation were present. Many of the aberrations of cell cycle were combined with cell death. These deviations omitting or adapting the cell cycle check-points represent evidently the normal epigenetic mechanisms of development and repair. At the same time, by origin and appearances they seem very close to the loss of the growth control displayed by malignant tumours. This connection is briefly analysed in view of some current concepts of carcinogenesis.

Animals↗
PubMed1998

Aberrant death in dark chondrocytes of the avian growth plate.

Growth plate chondrocytes of embryonic chick femurs were examined by electron microscopy, cytophotometry and autoradiography. Apart from the well-described 'light' chondrocyte, a different 'dark' type of chondrocyte was present, comprising 10 - 35% of the cell population. They were found at all stages of chondrocyte differentiation and in all ages of the femurs studied. Well developed rough endoplasmatic reticulum and Golgi complex, many secretory vesicles, energetically active mitochondria and a lot of glycogen, indicating high activity of the cytoplasm, were combined with low RNA synthesis, gentle margination and scattered compaction of the chromatin. DNA cytometry revealed that most of dark cells were diploid, but 15 - 30% were tetraploid, with the absence of an S-phase. Substantial loss of DNA was found in about 10% of dark chondrocytes. The TUNEL reaction demonstrated a limited number of DNA strand breaks. Advanced dark cells possessed the nuclear features of both apoptosis and necrosis. Besides chromomeric-chromonemic compaction, a chromatin arrangement similar to that of prometaphase and metaphase, as well as amitotic nuclear segregation, all of them degenerative, were found. Our interpretation is that the dark chondrocytes undergo an aberrant type of cell death which may be combined with aberrant cell cycle. Cell death of dark chondrocytes is preceded by a pre-mortal burst of secretion.

Animals↗
PubMed1997

Apoptotic cell nuclei favour aggregation and fluorescence quenching of DNA dyes.

Apoptotic cell nuclei are known to stain hyperchromatically with absorption dyes and dimly with many DNA fluorochromes. We hypothesised that both optical phenomena have the same cause--the ability of apoptotic chromatin to aggregate cationic dyes. This hypothesis was tested using prednisolone-primed rat thymus, which is known to contain apoptotic cells. The apoptotic cells were classified as early and late, based on their morphology, in thin and semithin sections and in thymus imprints on slides. Direct reaction for DNA strand breaks (TUNEL) indicated the presence of breaks in both categories of cells, with more intense labelling in late apoptosis. The chromatin ultrastructure of early apoptotic cells initially retained the supranucleosomal order of packaging which characterises control cells, whereas the dense chromatin of late apoptotic cells possessed the degraded structure. Absorption spectra of the toluidine blue-stained early apoptotic cell chromatin revealed a metachromatic shift, indicating a change of DNA conformation and polymerisation of the dye. When the staining was performed by acridine orange (preceded by a short acid treatment), a paradoxical several-fold increase of fluorescence intensity at a several-fold dilution of the dye was found. The simultaneous reduction of the ratio of red to green components of fluorescence confirmed that the concentration-dependent fluorescence quenching was due to aggregation of the dye. The results suggest that the enhanced affinity of the chromatin of early apoptotic cells for cationic dyes is associated with conformational relaxation rather than degradation of DNA. In late apoptotic cells, the very dense packaging of degraded DNA promotes further aggregation of dyes. The results suggest alternative methods for detection and discrimination of early and late apoptotic cells.

Acridine Orange↗
PubMed1996

Epigenetic selection as a possible component of transdifferentiation. Further study of the commitment of hypertrophic chondrocytes to become osteocytes.

Transdifferentiation of hypertrophic chondrocytes into osteogenic cells was induced in 14 day chick embryo femurs by cutting through the region of hypertrophic cartilage. The process was studied in organ culture, using electron microscopy, staining for alkaline phosphatase, immunocytochemistry of collagen type I and proliferative cell nuclear antigen, and in situ localization of DNA strand-breaks. In addition, DNA and RNA synthesis were studied by 3[H]-T and 3[H]-U radioautography. Loss of ECM components from the cut edge occurred in culture. During the 12 day period necessary for transdifferentiation we observed phenotypic instability and bi-potentiality, the death of some cells and the gradual promotion of the osteoblastic phenotype in the survivors. Transition from chondrocytic to osteoblastic phenotype progressed stepwise, through variable mosaic intermediates, and involved a few cell cycles including asymmetric (differential) divisions. Proliferating and apoptotic cells were found in close proximity. As judged by the relative proportion of apoptotic cells and composition of the surrounding intralacunar matrix, negative selection of intermediate cell types displaying chondrocytic and altered mosaic phenotypes occurred. When the osteoblastic lineage was finally established, apoptotic cells were no longer present. Our hypothesis is that after disruption of cell-cell or cell-matrix interactions and lack of growth factors certain cells are selected and channelled through proliferation into the new stable phenotype. This process is targeted by the environment through a set of pre-determined steps.

Animals↗
PubMed1996

The phenotypic switch from chondrocytes to bone-forming cells involves asymmetric cell division and apoptosis.

We have investigated the early cellular events that take place during the phenotypic switch from hypertrophic chondrocytes to bone-forming cells in a) chondrocytes located inside intact lacunae after embryonic chick femurs had been cut through the hypertrophic cartilage and cultured for 1-15 days; and b) at the cartilage/marrow interface of femurs after short-term culture. Ultrastructural studies were combined with in situ methods localizing proliferating and apoptotic cells, and 3D-reconstructions of confocal images of the cartilage/marrow edge. The crucial event in the phenotypic switch was an asymmetric cell division which resulted in one daughter cell which underwent apoptosis and another viable daughter cell which subsequently differentiated to an osteogenic cell, i.e to a smaller basophilic cell that was positive for alkaline phosphatase, type I collagen, osteonectin, osteopontin, bone sialoprotein and osteocalcin and that, after 12-15 days in culture, could synthesize a mineralized bone matrix within intact lacunae. The present results suggest a mechanism whereby differentiated cells can change their phenotype. At least one mitotic division seems to be required to fix the commitment to the new phenotype.

Animals↗
PubMed1995

Osteogenic differentiation of hypertrophic chondrocytes involves asymmetric cell divisions and apoptosis.

We have investigated the early cellular events that take place during the change in lineage commitment from hypertrophic chondrocytes to osteoblast-like cells. We have induced this osteogenic differentiation by cutting through the hypertrophic cartilage of embryonic chick femurs and culturing the explants. Immunocytochemical characterization, [3H]thymidine pulse-chase labeling, in situ nick translation or end labeling of DNA breaks were combined with ultrastructural studies to characterize the changing pattern of differentiation. The first responses to the cutting, seen after 2 d, were upregulation of alkaline phosphatase activity, synthesis of type I collagen and single-stranded DNA breaks, probably indicating a metastable state. Associated with the change from chondrogenic to osteogenic commitment was an asymmetric cell division with diverging fates of the two daughter cells, where one daughter cell remained viable and the other one died. The available evidence suggests that the viable daughter cell then divided and generated osteogenic cells, while the other daughter cell died by apoptosis. The results suggest a new concept of how changes in lineage commitment of differentiated cells may occur. The concepts also reconcile previously opposing views of the fate of the hypertrophic chondrocyte.

Alkaline Phosphatase↗
PubMed1994

Differentiation and programmed cell death in Sa-45 tumour treated with bone inducer.

The relationship between differentiation and concerted cell death was studied using ultrastructural, histochemical and immunochemical methods in solid rat fibrosarcoma Sa-45 grown in the presence of demineralized bone matrix. The control tumour consisted mostly of undifferentiated cells with few poorly or moderately differentiated cells. In the presence of the inducer, cells with a more differentiated pattern appeared in the surrounding area. The proliferative activity in the presence of the inducer was 3 to 5 times lower but the apoptotic index was higher than in the controls. However, complete differentiation was induced only in stromal cells, whereas the parenchymal cells showed signs of enhanced but incomplete differentiation. The ultrastructural signs of programmed cell death progressed in them faster than the corresponding features of maturation, thus leaving differentiation incomplete.

Animals↗
PubMed1993

Interphase genome as the active space: chromatin dynamics during chick embryo chondrogenesis.

The rearrangement of the chromatin that takes place during cytodifferentiation was studied using TV image analysis in chick limb bud cartilage stained for DNA. The redistribution of the chromatin was compatible with the Rabl orientation: chromatin was extended radially from the centromeric ring to the telomere pole in young chondroblasts, and contracted back in ageing chondrocytes. The direction and gradient of this redistribution correlate with the changes in DNA content within the chromocentres formed by pericentromeric heterochromatin. In turn, intercalary heterochromatin regulates the condensation of the adjacent euchromatin depending upon the position in this radial-polar gradient.

Animals↗
PubMed1993

The chromatin network: image analysis of differentiating chick embryo chondrocytes.

The chromatin network was revealed in DNA stained cell imprints of developing chick embryo chrondrocytes using the recently developed method of TV image processing. The network consists of two classes of alveoles. The large alveoles, which accompany large chromocentres, are concentrated at the centromeric nuclear pole representing the most stable part of the network. The small alveoles, connected with the small chromocentres and located around the chromosome arms and telomeric ends, are dynamic. These smaller alveoles appear in differentiating chondroblasts and disappear in ageing chondrocytes. Ectopic conjunctions involving constitutive and intercalary heterochromatin are responsible for the network formation.

Algorithms↗
PubMed1992

Influence of chromatin condensation on the absorption spectra of nuclei stained with toluidine blue.

To study the influence of chromatin condensation on the absorption spectra of nuclei stained with toluidine blue, DNA staining methods--which favour or prevent dye polymerization--were applied to the imprints of rat tissues that differed greatly in the density of chromatin packing. It is stated that all factors promoting dye polymerization cause a left shift of the spectra while the factors preventing it, a right one. It was found that condensation of the chromatin can raise prerequisites that both enhance and hinder polymerization, and that the final result depends on the staining method, the manner of chromatin folding, and the density of its packing.

Absorption↗
PubMed1991

Accumulation of DNA within chromocentres of terminally differentiating chick embryo chondrocytes.

Automated television (TV) densitometric technique which allows the recognition and recording of chromatin compartments was applied to the study of chromatin rearrangement during chondrogenesis. Genetically active chondroblasts and inactive definite chondrocytes of E7 chick cartilage model, stained on the imprints for DNA, were a subject for the comparative study. Large chromatin granules with constant morphometric parameters, displaying positive staining for C-heterochromatin and identified as chromocentres, were found to accumulate 30% of cellular DNA, doubling its concentration during chondrogenic maturation. A test for the DNA content ethalonization proved this to be due to redistribution of DNA from the euchromatinic compartment.

Animals↗
PubMed1989

Two mechanisms of chromatin compaction.

2 types of chromatin compaction were studied by cytochemical and ultrastructural approach. The 1st type was induced by cultivating transformed cells with dimethylsulfoxide. It caused cell transition into a more differentiated state coupled with the appearance of multiple small chromatin condensates. The 2nd type was induced by nonionic detergent Triton X-100 and/or saline penetration inside the nuclei. It was found to be connected with hypercompaction of chromocenters with their integral areas left unincreased. Both types of chromatin compaction differ in their capacity to induce toluidine blue polymerization on DNA substrate and in stability of DNA towards an early step of acid hydrolysis. The relation of the 2 mechanisms of chromatin compaction to different ways of DNA folding is discussed.

Animals↗
PubMed1983

Effect of triton X-100 on cytochemical and ultrastructural pattern of chromatin.

The action of Triton X-100 on chromatin was observed in normal rat liver, thymus and ascites hepatoma cells. For DNA cytochemistry and thin-section electron microscopy the cells were treated with the permeabilizing 0.05% concentration of Triton 0.5-1% Triton treatment was applied to rat thymus nuclei spread on electron microscopic supports. Triton caused a compactness of chromatin in stained nuclei, in ultrathin sections and nuclear spreads. The most prominent feature of the tritonized higher order fibre is an increased regularity of its structure. In the nuclei stained for DNA with toluidine blue, Triton caused a sharp increase of optical density in the comparable zone of the spectral maximum and a shift to the shorter wave lengths. Cells treated with Triton exhibit an exaggerated anisotropic staining reaction. The cytochemical and cytophysical changes induced by Triton X-100 are explained by a polymerization caused by an increased regularity of the chromatin fibre structure.

Animals↗
PubMed1982

Lysis of cell nuclei on perforated electron microscopic supports.

The technique of gentle nuclear lysis for electron microscopic observation is suggested, which comprises adsorption of isolated nuclei on a positively charged pricked supporting film and sequential short-timed installation of the support with its back onto the filter paper moistened by lysing solution. The advantage of the method is slow, gradient-like, and to some extent regulated treatment allowing to visualize nuclear structures in their integrity.

Animals↗
PubMed1981

Staining of DNA with uranylacetate in hydrolysed ultrathin sections.

Rat liver and hepatoma cells fixed with formaldehyde, embedded into Epon and treated on sections with 5 n HCl and then with aqueous uranylacetate show preferential DNase-sensitive reaction. The reaction is highly dependent upon proper fixation, hydrolysis improves its specificity. The binding of the contrast with DNA is of ionic nature. Because of its simplicity, sufficient contrast and resolution the suggested technique is recommended for ultrastructural studies of DNA-containing substrates.

Animals↗