Correlations between sex rate estimates and fitness across predominantly parthenogenetic flatworm populations

One explanation for the success of sexual reproduction is that sex increases the efficacy of natural selection. Recombination and segregation lead to fitness variance among offspring which then offers a wider target for natural selection. Consequently, adaptation to changing environments is accelerated and population mean fitness will increase. We investigated whether low levels of sex are associated with increased fitness variance and mean in parthenogenetic biotypes of the planarian flatworm Schmidtea polychroa. Parthenogenetic S. polychroa are triploid and reproduce clonally with occasional sexual reproduction. By-products and measures of occasional sex are the local presence of tetraploids and elevated levels of genotypic diversity. We correlated the proportion of tetraploids and genotypic diversity with fitness attributes of six genetically differentiated locations within one meta-population. Results indicate strong, positive correlations with variance and with mean offspring number produced during a 5-week period. The ecological and evolutionary implications for the maintenance of parthenogenetic S. polychroa are discussed.     

Heat Shock Protein-Mediated Resistance to High Hydrostatic Pressure in Escherichia coli

A random library of Escherichia coli MG1655 genomic fragments fused to a promoterless green fluorescent protein (GFP) gene was constructed and screened by differential fluorescence induction for promoters that are induced after exposure to a sublethal high hydrostatic pressure stress. This screening yielded three promoters of genes belonging to the heat shock regulon (dnaK, lon, clpPX), suggesting a role for heat shock proteins in protection against, and/or repair of, damage caused by high pressure. Several further observations provide additional support for this hypothesis: (i) the expression of rpoH, encoding the heat shock-specific sigma factor σ³², was also induced by high pressure; (ii) heat shock rendered E. coli significantly more resistant to subsequent high-pressure inactivation, and this heat shock-induced pressure resistance followed the same time course as the induction of heat shock genes; (iii) basal expression levels of GFP from heat shock promoters, and expression of several heat shock proteins as determined by two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins extracted from pulse-labeled cells, was increased in three previously isolated pressure-resistant mutants of E. coli compared to wild-type levels.     

Zinc supplementation increases bone alkaline phosphatase in healthy men.

Zinc takes part in the metabolism of bone as a constituent of the matrix and as an activator of several metallo-enzymes. Animal in vitro and in vivo studies strongly suggest that zinc supplementation could stimulate bone formation and inhibit bone resorption but data in humans remain rare. The biological effects of 50 mg zinc given orally as gluconate in 20 healthy male volunteers were investigated in a 12 weeks double-blind placebo-controlled randomized trial. To investigate bone turnover, total alkaline phosphatases activity (ALP), bone specific alkaline phosphatase activity (BAPE) and BAP mass (BAP-M) concentration were measured as parameters of bone formation while urine calcium and C-terminal collagen peptide were determined as parameters of bone resorption. Samples were obtained in fasting subjects at baseline and after 6 and 12 weeks. In zinc treated subjects, a significant increase was observed at least after 12 weeks in total ALP (p < 0.01), BAP-M (p < 0.05) and BAP-E (p < 0.02). These parameters did not significantly change in the placebo group. Urine zinc/creatinine ratio significantly increased after 6 (p < 0.03) and 12 weeks (p < 0.04) in the zinc-treated group and was significantly different from the placebo group (p < 0.002). There was no significant effect of zinc supplementation on parameters of bone resorption. In conclusion, zinc supplementation at supraphysiological doses increased parameters of bone formation in healthy men while parameters of bone resorption remained unchanged.     

Identification of a novel glyoxylate reductase supports phylogeny-based enzymatic substrate specificity prediction

Phylogenetic analysis of the superfamily of D-2-hydroxyacid dehydrogenases identified the previously unrecognized cluster of glyoxylate/hydroxypyruvate reductases (GHPR). Based on the genome sequence of Rhizobium etli, the nodulating endosymbiont of the common bean plant, we predicted a putative 3-phosphoglycerate dehydrogenase to exhibit GHPR activity instead. The protein was overexpressed and purified. The enzyme is homodimeric under native conditions and is indeed capable of reducing both glyoxylate and hydroxypyruvate. Other substrates are phenylpyruvate and ketobutyrate. The highest activity was observed with glyoxylate and phenylpyruvate, both having approximately the same kcat/Km ratio. This kind of substrate specificity has not been reported previously for a GHPR. The optimal pH for the reduction of phenylpyruvate to phenyllactate is pH 7. These data lend support to the idea of predicting enzymatic substrate specificity based on phylogenetic clustering.     

The uroprotection of mesna on cyclophosphamide cystitis in rats. Its consequences on behaviour and brain activities.

We studied the uroprotective effect of mesna, at doses of 40-300 mg/kg/i.p., in single or fractioned injections, on the development of cyclophosphamide (CP, 100 mg/kg/i.p.) cystitis in rats. The study concerns the histological, behavioural and nervous aspects of the disease. The specific effects of mesna, when injected alone, have also been considered. The mesna itself does not have specific deleterious effects, except at a dose of 300 mg/kg which provokes a moderate vesical inflammation although without consequence on the animal's behaviour. Mesna offers good protection against CP cystitis for only certain posologies. The uroprotective effects of mesna reach maxima at doses of 40-100 mg/kg and for fractioned injections given over the entire time frame of the urinary toxic release. The uroprotective effects of other posologies are only partial. The nervous activities were studied through the expression of Fos protein. The repetitive intraperitoneal injection of mesna induced a spinal activity and a preferential contralateral activity of the trigemino/reticular areas of the brainstem spinal cord junction--an effect which was reduced in the presence of CP. The prevention of cystitis by mesna was accompanied only by a reduction in spinal Fos activity, the supraspinal activities remaining high and in strict relationship with the vagal afferent activity. In conclusion, the uroprotective effect of mesna, which requires appropriate posologies, has led to the confirmation of the spinal actions of the CP cystitis, probably via the pelvic nerve, but did not allow a clear distinction between the consequences of the systemic (vagal) and local (spinal, pelvic) actions of CP at supraspinal level.     

Analysis of Cellular Mutants Resistant to Theiler’s Virus Infection: Differential Infection of L929 Cells by Persistent and Neurovirulent Strains

Theiler's murine encephalomyelitis virus (TMEV) is a natural pathogen of the mouse and belongs to the Picornaviridae family. TMEV strains are divided into two subgroups on the basis of their pathogenicity. The first group contains two neurovirulent strains, FA and GDVII, which cause a rapid fatal encephalitis. The second group includes persistent strains, like DA and BeAn, which produce a biphasic neurological disease in susceptible mice. Persistence of these viruses in the white matter of the spinal cord leads to chronic inflammatory demyelination. L929 cells, which are susceptible to TMEV infection, were subjected to physicochemical mutagenesis. Cellular clones that became resistant to TMEV infection were selected by viral infection. Three such mutants resistant to strain GDVII were characterized to determine the step of the virus cycle that was inhibited. The mutation present in one of these mutant cell lines inhibited, by more than 1,000-fold, the entry of strain GDVII but hardly decreased infection by strain DA. In the two other cellular mutants, replication of the viral genome was slowed down. Interestingly, one of these mutant cell lines resisted infection by both the persistent and neurovirulent strains while the second cell line resisted infection by strain GDVII but remained susceptible to the persistent virus. These results show that although they have 95% identity at the amino acid sequence level, neurovirulent and persistent viruses use partly distinct pathways for both entry into cells and genome replication.     

Role of Porins in Sensitivity of Escherichia coli to Antibacterial Activity of the Lactoperoxidase Enzyme System

Lactoperoxidase is an enzyme that contributes to the antimicrobial defense in secretory fluids and that has attracted interest as a potential biopreservative for foods and other perishable products. Its antimicrobial activity is based on the formation of hypothiocyanate (OSCN⁻) from thiocyanate (SCN⁻), using H₂O₂ as an oxidant. To gain insight into the antibacterial mode of action of the lactoperoxidase enzyme system, we generated random transposon insertion mutations in Escherichia coli MG1655 and screened the resultant mutants for an altered tolerance of bacteriostatic concentrations of this enzyme system. Out of the ca. 5,000 mutants screened, 4 showed significantly increased tolerance, and 2 of these had an insertion, one in the waaQ gene and one in the waaO gene, whose products are involved in the synthesis of the core oligosaccharide moiety of lipopolysaccharides. Besides producing truncated lipopolysaccharides and displaying hypersensitivity to novobiocin and sodium dodecyl sulfate (SDS), these mutants were also shown by urea-SDS-polyacrylamide gel electrophoresis analysis to have reduced amounts of porins in their outer membranes. Moreover, they showed a reduced degradation of p-nitrophenyl phosphate and an increased resistance to ampicillin, two indications of a decrease in outer membrane permeability for small hydrophilic solutes. Additionally, ompC and ompF knockout mutants displayed levels of tolerance to the lactoperoxidase system similar to those displayed by the waa mutants. These results suggest that mutations which reduce the porin-mediated outer membrane permeability for small hydrophilic molecules lead to increased tolerance to the lactoperoxidase enzyme system because of a reduced uptake of OSCN⁻.