Levels Of Chromatin Condensation Research Articles

Changes in chromatin structure associated with germination of maize and their relation with desiccation tolerance

ABSTRACTMorphological and physicochemical measurements of chromatin condensation were made on germinating maize (Zea mays L.) radicles to determine whether the loss of genetic activities that occurs during the loss of desiccation tolerance is linked to irreversible changes in chromatin condensation. Chromatin samples were compared at different stages of germination (0, 24 and 72 h after imbibition), before (control) and after 24 h of desiccation. Morphological changes in chromatin structure and condensation were characterized by a qualitative and quantitative electron microscope study of chromatin which was allowed to spread in 0.2 mol m−3 EDTA and then laid on coated microscope grids. The experiments showed similar levels of chromatin condensation in quiescent embryos and 24‐h‐old radicles (desiccation‐tolerant material). After 72 h of imbibition, when radicle emergence and desiccation intolerance had ceased, the chromatin underwent a major decondensation towards various lower order folded structures. Regardless of the desiccation tolerance stage, an in vivo drying treatment of 24‐ and 72‐h‐old radicles before chromatin extraction did not induce significant changes in the extent of condensation compared to their respective controls. Similar conclusions were drawn from measurements of several spectroscopy properties (absorbance ratios: A260/A240, A260/A400; thermal denaturation, and linear electric dichroism) of chromatin fragments that were obtained after nuclease digestion and then dissolved in 0‐2 mol m−3 EDTA. In quiescent and 24‐h‐old material, chromatin fragments were poorly soluble but highly stable during thermal denaturation. Chromatin fragments were 3‐5‐fold more soluble and less thermally stable in 72‐h‐old material than in 24‐h‐old material. In vivo desiccation had no significant effects on these properties compared to the respective controls. Collectively these data suggest that desiccation did not induce irreversible changes in the condensation properties of chromatin. The likelihood that the decondensation process occurring during germination is linked to the loss of desiccation tolerance is discussed.

Computer-assisted morphonuclear characterization of radiotherapy-induced effects in MXT mouse mammary adenocarcinomas surviving earlier radiotherapy

To present the effects of different radiotherapeutic treatments on the morphonuclear characteristics and growth of the MXT mouse mammary adenocarcinoma. We collected MXT tumor cells by means of fine-needle aspirations during various radiotherapeutic treatments and analyzed the morphological aspects of the cell nuclei by means of the digital cell image analysis of Feulgen-stained nuclei. In addition, we studied the morphonuclear aspects of cells from MXT tumors that had been radioresistant cell enriched. These radioresistant cell-enriched tumors involved MXT tumors that had survived one or two previous radiotherapies. The radiotherapy-induced effects on the morphonuclear characteristics were monitored by means of both monovariate (one-way variance) and multivariate (principal components and step-wise linear discriminant) analyses. The monovariate analyses showed that radiotherapy significantly influenced the values of the parameters relating to nuclear size (nuclear area--NA), the frequency of small dense chromatin clumps (short run length emphasis--SRL) in the nuclei, and the overall chromatin condensation level (local mean--LM). The global effect corresponded to a decrease in the overall chromatin condensation level in the radioresistant cell-enriched MXT tumors. This decrease occurred concomitantly with an increase in the frequency of the small dense chromatin clumps in the nuclei and a decrease in the nuclear area. The multivariate analyses showed that it was possible to quantitate the proportion of "radiosensitive-like" and "radioresistant-like" cell nuclei in the various MXT tumor types under study. The development of certain morphonuclear parameters, that is, the NA, the SRL, and the LM, could be proposed to predict the response of human tumors to radiotherapy as, indeed, could the quantitation of the proportion of radioresistant cells.

Computer-assisted chromatin texture characterization of Feulgen-stained nuclei in a series of 331 transitional bladder cell carcinomas.

The chromatin patterns of Feulgen-stained nuclei in a series of six specimens of normal mucosa and 331 transitional bladder carcinomas, including 293 superficial (Ta and T1) and 38 invasive (T2-T4) cases, were quantitatively described by means of eight parameters relating to densitometric, run-length distribution, and co-occurrence matrix features. The results show that the chromatin texture of the superficial lesions was markedly different from that of the invasive tumours, which exhibited a distinctly more dense and heterogeneous chromatin pattern. The data also show that the increasing level of malignancy, as revealed by the increasing clinical stage, was accompanied by an increase in the overall chromatin condensation level. Only some areas of the nucleus actually increased in density; other pale areas appeared concomitantly with these increasingly denser chromatin areas. This chromatin density increase corresponded to a marked increase in the frequency of small dense chromatin clumps; these joined together into very large dense chromatin clumps, which were distributed more and more heterogeneously in the nucleus as the clinical stage of the tumour increased.

In vitro characterization of radiotherapy-induced morphonuclear modifications on chemosensitive as opposed to chemoresistant neoplastic cells

Purpose : We describe by means of digital cell image analysis the influence of X-ray radiation on three in vitro cultured cell lines for which we set up chemosensitive and chemoresistant variants. Methods and Materials : The three cell lines correspond to the MXT mouse mammary and the T24 and J82 neoplastic human bladder cells. The digital cell image analysis was carried out by computing morphometric (nuclear size), densitometric (proportion of cells in the G2 cell cycle phase), and textural features (chromatin pattern characteristics) on Feulgen-stained nuclei. Results : The results show that such digital cell image analyses make it possible to monitor radiotherapy-induced effects on these morphonuclear characteristics accurately. X-ray radiotherapy induces a dose-dependent increase in the proportion of cells in the G2 phase of the cell cycle along with a decrease in the overall chromatin condensation level. These two concomitant phenomena lead to a marked radiotherapy-induced increase in nuclear size. We also obseved that radiotherapy-induced effects at the morphonuclear level are not only highly specific to the cell type analyzed, that is MXT mouse mammary or J82 or T24 human bladder carcinoma cells, but also to the fact that the cells are either chemosensitive or chemoresistant. Conclusion : The digital cell image analyses of Feulgen-stained nuclei is helpful in monitoring the irradiation-induced morphonuclear modifications.

Image analysis of Feulgen-stained NIH/3T3 cells transformed with DNA of 4-nitroquinoline 1-oxide treated human breast epithelial cells.

The nuclear phenotypes of Feulgen-stained NIH/3T3 cells transformed with 4-nitroquinoline 1-oxide (4NQO) treated, human breast epithelial cell (HBEC) DNA were studied by scanning microspectrophotometry and image analysis and compared with data obtained for nontransformed cells and for NIH/3T3 cells under ras oncogene transfecting situations. The Feulgen-DNA content of the individual nuclei (NQ1, NQ2, and NQ3 phenotypes) of the transformed cells was found not to be deeply affected, although presence of chromatin structures resembling double minutes could be verified in part of the metaphases of the transformed cells. On the other hand, the chromatin supraorganization of these cells showed some changes involving increased (NQ2, NQ3) or decreased (NQ1) levels of condensation. The changes in chromatin packing states, however, were of small magnitude compared with those reported for NIH/3T3 cells transfected with a c-H-ras oncogene or an N-ras-containing MCF-7 cell DNA. It was assumed that the transformation of the NIH/3T3 cells is not always necessarily accompanied by high levels of chromatin condensation. The transformation of the NIH/3T3 cells induced by the 4NQO-treated HBEC DNA and particularly the changes in chromatin condensation in these transformed cells could not be attributed merely to a ras activation elicited by the carcinogen. It is suggested that a more complex transforming mechanism is involved, probably owing to the fact that a whole genomic DNA of the 4NQO-treated HBEC has been used for transfection.

Image analysis of Feulgen-stained c-H-ras-transformed NIH/3T3 cells

Feulgen-DNA content, nuclear phenotypes, and levels of chromatin condensation were evaluated by image analysis in NIH/3T3 cells transformed with the c-H-ras oncogene of T24 cells. Three nuclear phenotypes, differing from those of untransformed control cells and defined in terms of patterns of chromatin condensation, were demonstrated microspectrophotometrically for the tumor cells. Polyploidy could only be observed in nuclei with extensive and deeply stained areas covered with condensed chromatin, i.e., only in a small fraction of the tumor cell nuclear population. The increased chromatin condensation that appeared with cell transformation affected the euchromatin zones. The image analysis provided data that, compared with those obtained in other situations involving cell transformation, could be relevant to the understanding of changes in chromatin supraorganization related to tumorigenesis and to tumor cell diagnosis.