Thermal performance curves of Paramecium caudatum: a model selection approach

The ongoing climate change has motivated numerous studies investigating the temperature response of various organisms, especially that of ectotherms. To correctly describe the thermal performance of these organisms, functions are needed which sufficiently fit to the complete optimum curve. Surprisingly, model-comparisons for the temperature-dependence of population growth rates of an important ectothermic group, the protozoa, are still missing. In this study, temperature reaction norms of natural isolates of the freshwater protist Paramecium caudatum were investigated, considering nearly the entire temperature range. These reaction norms were used to estimate thermal performance curves by applying a set of commonly used model functions. An information theory approach was used to compare models and to identify the best ones for describing these data. Our results indicate that the models which can describe negative growth at the high- and low-temperature branch of an optimum curve are preferable. This is a prerequisite for accurately calculating the critical upper and lower thermal limits. While we detected a temperature optimum of around 29 °C for all investigated clonal strains, the critical thermal limits were considerably different between individual clones. Here, the tropical clone showed the narrowest thermal tolerance, with a shift of its critical thermal limits to higher temperatures.     

Effects of a synthetic PEG-ylated Tie-2 agonist peptide on endotoxemic lung injury and mortality

A synthetic 7-mer, HHHRHSF, was recently identified by screening a phage display library for binding to the Tie-2 receptor. A polyethylene-oxide clustered version of this peptide, termed vasculotide (VT), was reported to activate Tie-2 and promote angiogenesis in a mouse model of diabetic ulcer. We hypothesized that VT administration would defend endothelial barrier function against sepsis-associated mediators of permeability, prevent lung vascular leakage arising in endotoxemia, and improve mortality in endotoxemic mice. In confluent human microvascular endothelial cells, VT prevented endotoxin-induced (lipopolysaccharides, LPS O111:B4) gap formation, loss of monolayer resistance, and translocation of labeled albumin. In 8-wk-old male C57Bl6/J mice given a ～70% lethal dose of endotoxin (15 mg/kg ip), VT prevented lung vascular leakage and reversed the attenuation of lung vascular endothelial cadherin induced by endotoxemia. These protective effects of VT were associated with activation of Tie-2 and its downstream mediator, Akt. Echocardiographic studies showed only a nonsignificant trend toward improved myocardial performance associated with VT. Finally, we evaluated survival in this mouse model. Pretreatment with VT improved survival by 41.4% (n = 15/group, P = 0.02) and post-LPS administration of VT improved survival by 33.3% (n = 15/group, P = 0.051). VT-mediated protection from LPS lethality was lost in Tie-2 heterozygous mice, in agreement with VT's proposed receptor specificity. We conclude that this synthetic Tie-2 agonist, completely unrelated to endogenous Tie-2 ligands, is sufficient to activate the receptor and its downstream pathways in vivo and that the Tie-2 receptor may be an important target for therapeutic evaluation in conditions of pathological vascular leakage.     

DNA methylation variability at growth-related imprints does not contribute to overweight in monozygotic twins discordant for BMI

Defective genomic imprinting is often associated with syndromes that include abnormal growth as a clinical phenotype. However, whether differential methylation at imprinted loci also contributes to nonsyndromic abnormal body weight regulation is yet unknown. In this study, we investigated a potential contribution of aberrant DNA methylation at nine differentially methylated regions (DMRs) to the development of nonsyndromic overweight. Sixteen monozygotic (MZ) twins discordant for BMI (BMI difference ranging from 2.9-9.5 kg/m(2)) were recruited from the East Flanders Prospective Twin Survey. DNA extracted from saliva samples was bisulfite-treated followed by PCR amplification of target regions in DMRs most representative for abnormal growth syndromes: KvDMR1, H19 CTCF4, H19 CTCF6, IGF2 DMR0, IGF2 DMR2, GRB10, MEST, SNRPN, GNAS XL-α-s and GNAS Exon1A. At the DMRs analyzed, methylation-dependent primer extension experiments revealed only small intrapair differences in methylation indexes (MI) between the heavy and lean co-twins. In addition, no significant correlations between intrapair BMI differences and intrapair differences in MI were observed. In conclusion, DNA methylation variability at the nine DMRs analyzed does not seem to contribute to the discordancy in BMI observed in these MZ twins.     

Reduced oxygen supply explains the negative force-frequency relation and the positive inotropic effect of adenosine in buffer-perfused hearts

In isolated rat hearts perfused with HEPES and red blood cell-enriched buffers, we examined changes in left ventricular pressure induced by increases in heart rate or infusion of adenosine to investigate whether the negative force-frequency relation and the positive inotropic effect of adenosine are related to an inadequate oxygen supply provided by crystalloid perfusates. Hearts perfused with HEPES buffer at a constant flow demonstrated a negative force-frequency relation, whereas hearts perfused with red blood cell-enriched buffer exhibited a positive force-frequency relation. In contrast, HEPES buffer-perfused hearts showed a concentration-dependent increase in left ventricular systolic pressure [EC50 = 7.0 +/- 1.2 nM, maximal effect (Emax) = 104 +/- 2 and 84 +/- 2 mmHg at 0.1 microM and baseline, respectively] in response to adenosine, whereas hearts perfused with red blood cell-enriched buffer showed no change in left ventricular pressure. The positive inotropic effect of adenosine correlated with the simultaneous reduction in heart rate (r = 0.67, P < 0.01; EC50 = 3.8 +/- 1.4 nM, baseline 228 +/- 21 beats/min to a minimum of 183 +/- 22 beats/min at 0.1 microM) and was abolished in isolated hearts paced to suppress the adenosine-induced bradycardia. In conclusion, these results indicate that the negative force-frequency relation and the positive inotropic effect of adenosine in the isolated rat heart are related to myocardial hypoxia, rather than functional peculiarities of the rat heart.     

Genotyping of Chromobacterium violaceum isolates by recA PCR-RFLP analysis

Intraspecies variation of Chromobacterium violaceum was examined by comparative sequence - and by restriction fragment length polymorphism analysis of the recombinase A gene (recA-PCR-RFLP). Primers deduced from the known recA gene sequence of the type strain C. violaceum ATCC 12472(T) allowed the specific amplification of a 1040bp recA fragment from each of the 13 C. violaceum strains investigated, whereas other closely related organisms tested negative. HindII-PstI-recA RFLP analysis generated from 13 representative C. violaceum strains enabled us to identify at least three different genospecies. In conclusion, analysis of the recA gene provides a rapid and robust nucleotide sequence-based approach to specifically identify and classify C. violaceum on genospecies level.     

Inferring the effects of demography and selection on Drosophila melanogaster populations from a chromosome-wide scan of DNA variation

Identifying regions of the Drosophila melanogaster genome that have been recent targets of positive Darwinian selection will provide evidence for adaptations that have helped this species to colonize temperate habitats. We have begun a search for such genomic regions by analyzing multiple loci (about 250) dispersed across the X chromosome in a putatively ancestral population from East Africa and a derived European population. For both populations we found evidence for past changes in population size. We estimated that a major bottleneck associated with the colonization of Europe occurred about 3,500-16,000 years ago. We also found that while this bottleneck can account for most of the reduction in variation observed in the European sample, there is a deficit of polymorphism in some genomic regions that cannot be explained by demography alone.