Fourteen laboratories participated in a national slide exchange study to investigate whether borderline nuclear changes (BNC) constitute a reliable reporting category. Slides were submitted by participating laboratories, having achieved a 100% intralaboratory consensus at the primary screener, checker, and medical levels. Sets of seven slides were examined in laboratories for 1 week, and exchanges were undertaken over a 6-month period. Each laboratory was requested to submit three consensus opinions on each slide at the primary screener, checker, and medical levels. Response patterns for submitted slides achieving a reporting category consensus at the 50 and 80% consensus levels indicated that negative, BNC, and mild dyskaryosis are distinct and comparable categories. Similarly, the two subcategories of BNC with or without human papillomavirus (HPV) are nearly as distinct as the overall BNC category. The percentage of submitted slides achieving consensus at consensus levels between 50 and 80% produced variable findings with regard to the practical success of the main reporting categories. The negative category was reasonably successful, whereas mild dyskaryosis was consistently poor. Borderline nuclear changes were successful at the 50% consensus level but showed a rapid decline by the 65% consensus level. The reason(s) for this remains speculative but indicates a possible potential of BNC to work successfully with additional training and education. Reporting practices were not consistent among the laboratories and differences were identified between medical and nonmedical staff. A high use of the BNC category was noted in slides that failed to achieve consensus. A national study assessing all grades of abnormalities would appear essential. 相似文献
The fundamental problems that face us in the development of suitable assay systems for the detection of potentially aneugenic (aneuploidy-inducing) chemicals include: (a) the diversity of cellular targets and mechanisms where perturbations of structure and function may give rise to changes in chromosome number, and (b) the phylogenetic differences that exist between species in their mechanism and kinetics of cell division and their metabolic profiles. A diverse range of assay systems have been developed, which have been shown to have potential for use in the detection of either changes in chromosome number or of perturbations of the events which may be causal in the induction of aneuploidy.
Chromosome number changes may be detected cytologically by karyotypic analysis, or by the use of specialised strains in which aneuploid progeny may be observed due to phenotypic differences with aneuploid parental cells or whole organisms. Techniques for the detection of cellular target modifications range from in vitro studies of tubulin polymerisation to observations of the behaviour of various cellular organelles and their fidelity of action during the division cycle.
The diversity of mechanisms which may give rise to aneuploidy and the qualitative relevance of events observed in experimental organisms compared to man make it unlikely that the detection and risk assessment of the aneugenic activity of chemicals will be possible using a single assay system. Optimal screening and assessment procedures will thus be dependent upon the selection of an appropriate battery of predictive tests for the measurement of the potentially damaging effects of aneuploidy induction. 相似文献
Seedlings of barley were grown either in continuous darkness or under a diurnal 12 h light/12 h dark cycle and the effects on NADPH-protochlorophyllide oxidoreductase were followed at two different levels. Firstly, the relative content of the mRNA encoding the NADPH-protochlorophyllide oxidoreductase was measured by dot-blot hybridization. Secondly, changes in the enzyme polypeptide were monitored either by the method of immunoblotting or by immunogold labelling of ultrathin sections of Lowicryl-embedded leaf tissue. Our results demonstrate that drastic diurnal changes in the level of mRNA sequences and the enzyme protein are unlikely to occur in plants which have been grown under natural light/dark conditions. In the dark, protein and mRNA accumulation occurs at an early developmental stage. These results are difficult to reconcile with the suggestion that the massive accumulation of mRNA and enzyme protein in dark-grown seedlings is primarily the consequence of an artificially extended darkperiod. In addition to the plastid-specific NADPH-protochlorophyllide oxidoreductase a closely related polypeptide has been detected outside the plastid in the surrounding cytoplasm (Dehseh et al. 1986b, Planta 169, 172–183). During the diurnal light/dark treatment of seedlings the concentrations of the two protein populations did not show any variation indicative of an exchange between the two protein populations across the plastid envelope.Abbreviation poly(A)+RNA
polyadenylated RNA 相似文献
Shells of Bosminidae and Chydoridae are quantitatively preserved in lake sediments. The chronological deposition of these
remains provides the means for longterm observation of these Cladocera, both in terms of species and communities.
Chydorid analysis, as based on subfossil assemblages, is an analysis of community and provides direct observation of community
dynamics over extended periods of time. It has proved to be a valuable method to obtain information on the influence of environmental
factors and time on community characteristics.
Morphological variation inBosmina (Eubosmina) has been followed for some thousand years. This is of special interest for the evaluation of taxonomic rank (species, forms)
if closely related taxa have co-existed.
Bosmina successions, as well as shifts in the chydorid fauna, are related to environmental change. Thus, cladoceran analysis of lake
sediments provides information on the developmental history of lakes and allows observation of the effects of longterm environmental
changes, such as climatic changes and eutrophication. 相似文献
A model is presented which explains the biological role of the leader peptide in protein export. Along the lines of this model, the conformational changes of a protein with environment serves as a general mechanism for translocation. The leader peptide in the cytoplasm takes a hairpin like conformation which reverts to an extended helix upon integration into the membrane. The essential features of this model are in accord with recent results of protein export. 相似文献
Twelve male Sprague-Dawley rats (21 days old) were randomly assigned into two experimental groups: sea level control (CONT) and hypobaric hypoxia (HYPO). The HYPO rats were kept in an hypobaric chamber maintaining a simulated altitude of 4000 m (61.1 kPa). After 10 weeks of treatment, the rat hindlimb muscles [soleus (SOL) and extensor digitorum longus (EDL)] were subjected to histochemical and electro-mechanical analyses. Results indicated that compared to CONT the HYPO SOL muscle had a significantly greater relative distribution of fast-twitch-oxidative-glycolytic (FOG) fibres (28.9% SEM 2.0 vs 18.3% SEM 1.8, P less than 0.01) with a significant decrease in slow twitch oxidative fibre distribution (69.5% SEM 2.4 vs 82.9% SEM 3.1, P less than 0.01). Compared to CONT the HYPO EDL muscle also manifested a significant increase in FOG fibre distribution (51.6% SEM 0.8 vs 46.6% SEM 1.1, P less than 0.01), but this was accompanied by a significant decrease in fast twitch glucolytic fibres (44.3% SEM 0.9 vs 49.2% SEM 1.7, P less than 0.05). These histochemical fibre type transformations accompanied significant and expected changes in the electro-mechanical parameters tested in situ, e.g. maximal twitch force, maximal rate of force development, contraction time, half relaxation time, force: frequency curve, and fatigability. It was concluded that chronic hypobaric hypoxia could have a potent influence upon the phenotype expression of muscle fibres. 相似文献
Circumnutation of Phaseolus vulgaris L. cv. Blanc de Juillet twining shoots was examined at the cellular level. Cell growth was monitored inside the free-moving part of the shoot as a function of time and position with respect to the terminal bud. Complete elongation of epidermal cells required >7 days. A 60% increase in length of the cells in the bending zone was observed. Scanning and transmission electron microscopy studies showed the elasticity of cell walls, the extent of plasmodesmata and endoplasmic reticulum of epidermal cells. The osmotic potential in epidermal cells of the bending zone displayed significant differences only between the concave and convex sides. The pattern of cell growth in twining shoots is discussed. Circumnutation could be seen as a consequence of periodic turgor changes inducing periodic growth. 相似文献