Chromocentre integrity and epigenetic marks

The epigenetic modification of histones dictates the formation of euchromatin and heterochromatin domains. We studied the effects of a deficiency of histone methyltransferase, SUV39h, and trichostatin A-dependent hyperacetylation on the structural stability of centromeric clusters, called chromocentres. We did not observe the expected disintegration of chromocentres, but both SUV39h deficiency and hyperacetylation in SUV39h+/+ cells induced the re-positioning of chromocentres closer to the nuclear periphery. Conversely, TSA treatment of SUV39h?/? cells re-established normal nuclear radial positioning of chromocentres. This structural re-arrangement was likely caused by several epigenetic events at centromeric heterochromatin. In particular, reciprocal exchanges between H3K9me1, H3K9me2, H3K9me3, DNA methylation, and HP1 protein levels influenced chromocentre nuclear composition. For example, H3K9me1 likely substituted for the function of H3K9me3 in chromocentre nuclear arrangement and compaction. Our results illustrate the important and interchangeable roles of epigenetic marks for chromocentre integrity. Therefore, we propose a model for epigenetic regulation of nuclear stability of centromeric heterochromatin in the mouse genome.     

Stepping transfer messenger RNA through the ribosome

tmRNA (transfer messenger RNA) is a unique molecule used by all bacteria to rescue stalled ribosomes and to mark unfinished peptides with a specific degradation signal. tmRNA is recruited by arrested ribosomes in which it facilitates the translational switch from cellular mRNA to the mRNA part of tmRNA. Small protein B (SmpB) is a key partner for the trans-translation activity of tmRNA both in vivo and in vitro. It was shown that SmpB acts at the initiation step of the trans-translation process by facilitating tmRNA aminoacylation and binding to the ribosome. Little is known about the subsequent steps of trans-translation. Here we demonstrated the first example of an investigation of tmRNA.ribosome complexes at different stages of trans-translation. Our results show that the structural element at the position of tmRNA pseudoknot 3 remains intact during the translation of the mRNA module of tmRNA and that it is localized on the surface of the ribosome. At least one SmpB molecule remains bound to a ribosome.tmRNA complex isolated from the cell when translation is blocked at different positions within the mRNA part of tmRNA.     

The use of water lettuce (Pistia stratiotes L.) for rhizofiltration of a highly polluted solution by cadmium and lead

The effectiveness of heavy metal uptake from contaminated nutrient solution by four aquatic macrophytes (Pistia stratiotes L., Salvinia auriculata AubL, Salvinia minima Baker, and Azolla filiculoides Lam) was estimated in this study. The influence of cadmium (3.5 mg L(-1) and 10.5 mg L(-1)) and lead (25 mg L(-1) and 125 mg L(-1)) on the stress symptoms was observed through the determination of chlorophyll content and transpiration rate over 14 days of the experiment. The results of the present study showed extreme reductions in Cd and Pb concentrations in solution during the first 4 days. The accumulation of Pb in plant tissues was the highest during the first 4 days and was more than 10 times higher in the roots (42,862 mg kg(-1)) than in the leaves (3867 mg kg(-1)). The accumulation of Cd slowly increased and was the highest at the end of the experiment. Concentrations in roots (3923 mg kg(-1)) were roughly 6 times higher than in the leaves (624 mg kg(-1)). Results showed significant decrease in the transpiration rate at Pb treatment and a significant increase at Cd treatment during 48 hours of exposition.     

Physiological and anatomical responses of wheat to induced dehydration and rehydration

Hydroponically grown wheat seedlings of two prominent Bulgarian cultivars (Katya and Prelom) were subjected to 48 h osmotic stress with PEG 8000 and were then rehydrated. The degree of stress was evaluated by monitoring relative water content, lipid peroxidation level, and accumulation of free proline and hydrogen peroxide in the leaves. Anatomy and ultrastructure of leaf tissue were observed under light microscopy. After imposition of stress, drought tolerant cultivar Katya displayed higher free proline content and significantly lower malondialdehyde and peroxide concentration in leaves than in the leaves of susceptible cultivar Prelom. After 24 h of rehydration Katya showed better ability to restore leaf water status and an apparent tendency towards recovery, whereas Prelom sustained higher levels of hydrogen peroxide, lipid peroxidation products and free proline and markedly low relative water content. Here, we have uncovered some of the characteristics displayed by cultivar Katya that enable it to survive and recover from severe osmotic stress. Interestingly, there was congruence between our results and the high level of cultivar Katya drought tolerance observed in the field.     

Conformational changes and their role in non-radiative energy dissipation in photosystem II reaction centres.

Accumulation of reduced pheophytin in photosystem II under illumination at low redox potential is known to be accompanied by a pronounced decrease of a chlorophyll fluorescence yield. Simultaneous measurement of this fluorescence quenching and absorbance changes in photosystem II reaction centres, in the presence of dithionite, showed each event to have a different temperature dependence. While fluorescence quenching was suppressed more than 20 times when measured at 77 K, pheophytin accumulation decreased only 5 times. At 77 K, the fluorescence was quenched considerably, but only in those reaction centres where reduced pheophytin had been accumulated at room temperature before sample freezing. This showed that the accumulation of reduced pheophytin above 240 K was accompanied by an additional, most probably conformational, change in the reaction centre that substantially enhanced non-radiative dissipation of excitation energy.     

Adrenomedullin is a novel marker of tumor progression in neuroendocrine carcinomas.

Adrenomedullin is a multi-functional polypeptide hormone. Its involvement in angiogenesis and vasodilator action support the hypothesis that adrenomedullin may be a secretory product of neuroendocrine tumors and contribute to tumor progression. Plasma levels of adrenomedullin were measured by radioimmunoassay in 46 patients with neuroendocrine carcinomas of the gastroenteropancreatic and bronchial system. Tissue expression of adrenomedullin was studied using monoclonal antibodies on pretreated paraffin embedded tissues in a group of 31 patients. Adrenomedullin plasma levels were significantly elevated in patients compared to healthy age-matched controls (p < 0.001). The highest plasma levels were found in patients with neuroendocrine carcinomas of bronchial, midgut and unknown origin. Patients with progressive disease had higher plasma levels than patients with stable disease (p < 0.001). Of the examined tumor samples, 55 % showed cytoplasmic staining for adrenomedullin > 5 % of the total tumor area. Plasma levels and tissue expression of adrenomedullin did not correlate with functional activity of the tumors or presence of the carcinoid syndrome, but did with tumor progression (p < 0.001 and p < 0.014). In conclusion, plasma and tissue expression of the angiogenic peptide adrenomedullin are predictive of tumor progression in patients with neuroendocrine carcinomas. Adrenomedullin might represent a useful prognostic marker in patients with neuroendocrine carcinomas.     

Computer literacy enhancement in the Teaching Hospital Olomouc. Part I: project management techniques. Short communication

Information explosion and globalization make great demands on keeping pace with the new trends in the healthcare sector. The contemporary level of computer and information literacy among most health care professionals in the Teaching Hospital Olomouc (Czech Republic) is not satisfactory for efficient exploitation of modern information technology in diagnostics, therapy and nursing. The present contribution describes the application of two basic problem solving techniques (brainstorming, SWOT analysis) to develop a project aimed at information literacy enhancement.     

Induction and decline of HPRT mutants and deletions following a low dose radiation exposure at Chernobyl

This study was conducted to evaluate the ability of mutation in the hypoxanthine-phosphoribosyltransferase gene (HPRT) to detect radiation-induced mutation in lymphocytes of Russian Chernobyl Clean-up workers, particularly as a function of time after exposure. It is part of a multi-endpoint study comparing HPRT mutation with chromosome translocation and glycophorin A mutation [Radiat. Res. 148 (1997) 463], and extends an earlier report on HPRT [Mutat. Res. 431 (1999) 233] by including data from all 9 years of our study (versus the first 6 years) and analysis of deletion size. Blood samples were collected from 1991 to 1999. HPRT mutant frequency (MF) as determined by the cloning assay was elevated 16% in Clean-up workers (N=300, the entire group minus one outlier) compared to Russian Controls (N=124) when adjusted for age and smoking status (P=0.028). Since exposures occurred over a short relative to the long sampling period, the year of sampling corresponded roughly to the length of time since exposure (correlation coefficient=0.94). When date of blood sample was considered, Control MF was not time dependent. Clean-up worker MF was estimated to be 47% higher than Control MF in 1991 (P=0.004) and to decline 4.4% per year thereafter (P=0.03). A total of 1123 Control mutants and 2799 Clean-up worker mutants were analyzed for deletion type and size by PCR assay for retention of HPRT exons and flanking markers on the X chromosome. There was little difference between the overall deletion spectra of Clean-up workers and Controls. However, there was a decline in the average size of deletions of Clean-up workers as time after exposure at Chernobyl increased from 6 to 13 years (P< or =0.05). The results illustrate the sensitivity of HPRT somatic mutation as a biomarker for populations with low dose radiation exposure, and the dependence of this sensitivity on time elapsed since radiation exposure.