Dynamics of a novel centromeric histone variant CenH3 reveals the evolutionary ancestral timing of centromere biogenesis

The centromeric histone H3 variant (CenH3) serves to target the kinetochore to the centromeres and thus ensures correct chromosome segregation during mitosis and meiosis. The Dictyostelium H3-like variant H3v1 was identified as the CenH3 ortholog. Dictyostelium CenH3 has an extended N-terminal domain with no similarity to any other known proteins and a histone fold domain at its C-terminus. Within the histone fold, α-helix 2 (α2) and an extended loop 1 (L1) have been shown to be required for targeting CenH3 to centromeres. Compared to other known and putative CenH3 histones, Dictyostelium CenH3 has a shorter L1, suggesting that the extension is not an obligatory feature. Through ChIP analysis and fluorescence microscopy of live and fixed cells, we provide here the first survey of centromere structure in amoebozoa. The six telocentric centromeres were found to mostly consist of all the DIRS-1 elements and to associate with H3K9me3. During interphase, the centromeres remain attached to the centrosome forming a single CenH3-containing cluster. Loading of Dictyostelium CenH3 onto centromeres occurs at the G2/prophase transition, in contrast to the anaphase/telophase loading of CenH3 observed in metazoans. This suggests that loading during G2/prophase is the ancestral eukaryotic mechanism and that anaphase/telophase loading of CenH3 has evolved more recently after the amoebozoa diverged from the animal linage.     

Integrative Pathway-Based Approach for Genome-Wide Association Studies: Identification of New Pathways for Rheumatoid Arthritis and Type 1 Diabetes

Genome-wide association studies (GWAS) led to the identification of numerous novel loci for a number of complex diseases. Pathway-based approaches using genotypic data provide tangible leads which cannot be identified by single marker approaches as implemented in GWAS. The available pathway analysis approaches mainly differ in the employed databases and in the applied statistics for determining the significance of the associated disease markers.So far, pathway-based approaches using GWAS data failed to consider the overlapping of genes among different pathways or the influence of protein–interactions. We performed a multistage integrative pathway (MIP) analysis on three common diseases - Crohn''s disease (CD), rheumatoid arthritis (RA) and type 1 diabetes (T1D) - incorporating genotypic, pathway, protein- and domain-interaction data to identify novel associations between these diseases and pathways. Additionally, we assessed the sensitivity of our method by studying the influence of the most significant SNPs on the pathway analysis by removing those and comparing the corresponding pathway analysis results. Apart from confirming many previously published associations between pathways and RA, CD and T1D, our MIP approach was able to identify three new associations between disease phenotypes and pathways. This includes a relation between the influenza-A pathway and RA, as well as a relation between T1D and the phagosome and toxoplasmosis pathways. These results provide new leads to understand the molecular underpinnings of these diseases.The developed software herein used is available at http://www.cogsys.cs.uni-tuebingen.de/software/GWASPathwayIdentifier/index.htm.     

Molecular mechanisms of drug resistance in natural Leishmania populations vary with genetic background

The evolution of drug-resistance in pathogens is a major global health threat. Elucidating the molecular basis of pathogen drug-resistance has been the focus of many studies but rarely is it known whether a drug-resistance mechanism identified is universal for the studied pathogen; it has seldom been clarified whether drug-resistance mechanisms vary with the pathogen's genotype. Nevertheless this is of critical importance in gaining an understanding of the complexity of this global threat and in underpinning epidemiological surveillance of pathogen drug resistance in the field. This study aimed to assess the molecular and phenotypic heterogeneity that emerges in natural parasite populations under drug treatment pressure. We studied lines of the protozoan parasite Leishmania (L.) donovani with differential susceptibility to antimonial drugs; the lines being derived from clinical isolates belonging to two distinct genetic populations that circulate in the leishmaniasis endemic region of Nepal. Parasite pathways known to be affected by antimonial drugs were characterised on five experimental levels in the lines of the two populations. Characterisation of DNA sequence, gene expression, protein expression and thiol levels revealed a number of molecular features that mark antimonial-resistant parasites in only one of the two populations studied. A final series of in vitro stress phenotyping experiments confirmed this heterogeneity amongst drug-resistant parasites from the two populations. These data provide evidence that the molecular changes associated with antimonial-resistance in natural Leishmania populations depend on the genetic background of the Leishmania population, which has resulted in a divergent set of resistance markers in the Leishmania populations. This heterogeneity of parasite adaptations provides severe challenges for the control of drug resistance in the field and the design of molecular surveillance tools for widespread applicability.     

Time-dependent inhibition of platelet cyclo-oxygenase by indomethacin is slowly reversible

Indomethacin has been charterized as a time-dependent, irreversible inhibitor of cyclo-oxygenase, yet its effects on human platelets have been found to be reversible . To understand this apparent contradiction, we have investigated the kinetics of recovery of platelet thromboxane production after a single dose of indomethacin. The inhibition of platelet thromboxane production was greater than would be expected from the levels of indomethacin found in the plasma suggesting that the time-dependent inhibition occurs . Yet recovery of platelet thromboxane production was faster than expected for the irreversible inhibitor, with 50% of control values being regained within 24 hours after ingestion of the drug. When platelets were isolated and resuspended in homologous drug-free plasma, slow recovery of thromboxane production was seen to occur with 50% of control activity regained in 100 minutes. This recovery was much slower than that seen from a competitive inhibitor of cyclo-oxygenase, ibuprofen. Ibuprofen-treated platelets recovered nearly completely immediately on being resuspended in drug-free plasma. When microsomes were isolated from platelets, then treated with indomethacin, no time-dependent recovery of activity was seen. The recovery of cyclo-oxygenase after indomethacin inhibition appears to be limited to the unperturbed enzyme in this natural milieu.     

Abnormalities in vascular arachidonic acid metabolism in the infant of the diabetic mother.

The infant of the diabetic mother has an increased incidence of thromboses in utero and in the neonatal period. In the adult with diabetes a decrease in prostacyclin formation has been suggested as a cause for the atherothrombotic tendency. We therefore evaluated arachidonic acid metabolism in infants of diabetic mothers. Endogenous radioimmunoassayable 6-keto prostaglandin F1 alpha (PGF1 alpha) was normal in umbilical vessels obtained from the infants of diabetic mothers whose glucose homoeostasis was maintained when compared with control values. Nevertheless, a significant inhibition of vascular production of 6-keto PGF1 alpha was observed in infants born to mothers with raised HbA1C concentrations. A decrease in the concentration of plasma 6-keto PGF1 alpha was also seen in the infants of diabetic mothers when compared with control neonates. The correlation observed between plasma 6-keto PGF1 alpha concentrations and endogenous vascular prostacyclin formation in the infants of diabetic mothers indicates that the in vitro deficiency of prostacyclin formation reflects a concomitant in vivo abnormality.     

A model of stem cell population dynamics: in silico analysis and in vivo validation

The proper renewal and maintenance of tissues by stem cell populations is simultaneously influenced by anatomical constraints, cell proliferation dynamics and cell fate specification. However, their relative influence is difficult to examine in vivo. To address this difficulty we built, as a test case, a cell-centered state-based computational model of key behaviors that govern germline development in C. elegans, and used it to drive simulations of cell population dynamics under a variety of perturbations. Our analysis provided unexpected possible explanations for laboratory observations, including certain 'all-or-none' phenotypes and complex differentiation patterns. The simulations also offered insights into niche-association dynamics and the interplay between cell cycle and cell fate. Subsequent experiments validated several predictions generated by the simulations. Notably, we found that early cell cycle defects influence later maintenance of the progenitor cell population. This general modeling approach is potentially applicable to other stem cell systems.     

The comparative pharmacokinetics of ceftriaxone in the blood and bronchial secretion in patients with different durations in the course of chronic bronchitis

The study on ceftriaxone penetration into bronchial secretion showed that in patients with a short-term history of chronic bronchitis (no more than 3 years) ceftriaxone used in a dose of 1 g once a day intramuscularly was detectable in the bronchial secretion within 10 hours after the administration, its concentrations being 0.67-2.41 micrograms/ml in 3 hours, 15.87 micrograms/ml in 4.5 hours, 4.58 micrograms/ml in 6.5 hours and 2.29 micrograms/ml in 10 hours. In patients with a long-term history of chronic bronchitis (mean 10 to 20 years) the presence of ceftriaxone in the bronchial secretion was detectable in a concentration of 0.51-3.75 micrograms/ml only in 2 hours after its administration. Beginning from the 5th hour after the administration its detection failed. This is indicative of lower ceftriaxone penetration into the bronchial secretion of such patients. The duration of chronic bronchitis did not influence ceftriaxone pharmacokinetics in blood. The contents of the antibiotic in serum and bronchial secretion were determined by HPLC (the resolving power of 0.5 micrograms/ml).     

The mitogenic effect of 15- and 12-hydroxyeicosatetraenoic acid on endothelial cells may be mediated via diacylglycerol kinase inhibition

15-Hydroxyeicosatetraenoic acid (15-HETE), a major lipoxygenase metabolite of arachidonic acid in fetal bovine aortic endothelial cells, was a mitogen for these cells, stimulating both cell proliferation and DNA synthesis in the presence of serum and serum-deprived cells. In [14C]arachidonic acid-labeled confluent endothelial cell monolayers, 15-HETE (30 microM) caused an elevation of [14C]diacylglycerol (DAG) with a concomitant decrease in cellular [14C]phosphatidylinositol (PI) in both unstimulated and stimulated cells. 1-Oleoyl-2-acetylglycerol, a synthetic DAG analog, stimulated endothelial cell DNA synthesis in a concentration-dependent manner. In [3H]inositol-labeled cells, 15-HETE also caused a decrease in cellular PI content under both basal and stimulated conditions. 15-HETE, however, had no effect on either isolated phospholipase C activity or phosphoinositide turnover in lithium chloride-treated cells. In intact cells, 15-HETE (30 microM) inhibited the synthesis of [3H]PI from [3H]inositol (80% inhibition, p less than 0.001). In human red cell membranes, the production of phosphatidic acid from endogenous DAG was inhibited by 15-HETE in a concentration-dependent manner with an IC50 of 41 microM. Although 12-HETE had effects similar to those of 15-HETE, the parent compound arachidonic acid did not affect DNA synthesis or DAG kinase activity. Our study thus demonstrates that the mitogenic activity of 15- and 12-HETE on endothelial cells may be mediated via DAG kinase inhibition with the concomitant accumulation of cellular DAG.