Genetic diversity within a declining natural population of Ferocactus histrix (DC) Lindsay

Ferocactus histrix is a barrel cactus that is widespread in Mexico. A population located in Llanos de Ojuelos, a semiarid zone representative of many disturbed regions in north‐central Mexico, was studied. Over a period of 10 years (1997 to 2007), the average number of individuals decreased from 21.95 to 3.53 plants per 300 m². A change in population size structure was also registered over this period of time. In 2008, a plot selected on the basis of plant abundance was established within the population and a genetic analysis was conducted with ISTR and ISSR markers. This analysis revealed low levels of genetic diversity (expected heterozygosity (H_E) = 0.073, Shannon index (I) = 0.113 and H_E = 0.178, I = 0.271, respectively) compared with those of most studied cacti species. The genetic diversity between the different life stages was also evaluated, and a gradual decrease in levels of genetic variation was observed from adults to juveniles and seedlings (H_E = 0.130, I = 0.192 to H_E = 0.103, I = 0.157). These differences, however, were not significant. Loci fixation and a decrease in the frequency of rare alleles were observed in seedling and juvenile classes. The decline in genetic variation may be associated with recent bottlenecks experienced by the population of F. histrix. If the sizes of local populations of F. histrix continue to decrease, genetic variation will be gradually lost, and the risk of extinction will increase.     

Changes in membrane lipids and carotenoids during light acclimation in a marine cyanobacterium Synechococcus sp.

Time course of carotenoid and membrane lipid variation during high light (HL) acclimation (about 85 meu mol m-2 s-1), after transfer from low light (LL) (5-10 meu mol m-2 s-1), was determined in a marine Synechococcus strain. Highperformance liquid chromatography (HPLC) coupled to diode array detector (DAD) or electrospray ionization mass spectrometry (ESI-MS) was used for compound separation and detection. Myxoxanthophyll rose within a time interval of 8 h to 24 h after the onset of exposure to HL. Beta -carotene content started to decrease after 4 h of the onset of exposure to HL. Zeaxanthin content rose with exposure to HL, but it was only significant after 24 h of exposure. Carotenoid changes are in agreement with a coordinated activity of the enzymes of the myxoxanthophyll biosynthetic pathway, with no rate-limiting intermediate steps. Lipid analysis showed all species with a C18:3/C16:0 composition increased their content, the changes of PG (18:3/16:0) and MGDG(18:3/16:0) being primarily significant. Major lipid changes were also found to occur within 24 h. These changes might suggest reduction and reorganization of the thylakoid membrane structure. Hypotheses are also drawn on the role played by lipid molecule shape and their possible effect in membrane fluidity and protein accommodation.     

Cytotoxicity of quinone drugs on highly proliferative human leukemia T cells: reactive oxygen species generation and inactive shortened SOD1 isoform implications

Drugs containing the quinone group were tested on hyperproliferative leukemia T cells (HLTC: Jhp and Jws) and parental Jurkat cells. Doxorubicin, menadione and adaphostin produced different effects on these cell lines. Rapid doxorubicin-induced cell death in Jurkat cells was mediated by caspase activation. Doxorubicin-induced cell death of HLTCs was delayed due to the absence of caspase-3 and -8 expression. Delayed HLTC cell death was mediated and triggered by the generation of reactive oxygen species (ROS). Other drugs containing quinone groups, such as menadione and adaphostin, were also tested on HLTC and both were toxic by a caspase-independent mechanism. The toxicity of these drugs correlated with the generation of the superoxide anion, which increased and was more effective in HLTCs than in parental Jurkat cells. Accordingly, SOD1 activity was much lower in HLTCs than in Jurkat cells. This lower SOD1 activity in HLTCs was associated not only with the absence of the wild-type (16 kDa) SOD1 monomer but also with the presence of a shortened (14 kDa) SOD1 monomer isoform. Moreover, the cytotoxicity of drugs containing the quinone group was prevented by incubation with manganese(III) tetrakis (4-benzoic acid) porphyrin (MnTBAP), a cell-permeable superoxide dismutase mimetic and a potent inhibitor of oxidation. These findings could explain the sensitivity of HLTCs to drugs containing the quinone group using a mechanism dependent on oxidative stress. These observations can also be useful to target hyperproliferative leukemias that are resistant to the classical caspase-dependent apoptotic pathway.     

Phylogenetic community structure during succession: Evidence from three Neotropical forest sites

The phylogenetic structure of communities can reveal forces shaping community assembly, but the vast majority of work on phylogenetic community structure has been conducted in mature ecosystems. Here, we present an analysis of the phylogenetic structure of three Neotropical rain forest communities undergoing succession. In each site, the net relatedness of the community is initially high and consistently declines during succession. This pattern is evident both when comparing plots of different age classes and when comparing stem size classes within each plot: the oldest plots and the youngest stem cohorts, representing the most advanced stages of succession, have the lowest relatedness. Our results suggest that succession leaves a distinct signature in the phylogenetic structure of communities, which may reflect an increasing role of biotic interactions in community assembly during succession. We discuss theoretical explanations for the decline in community phylogenetic relatedness during succession, and suggest directions for future study.     

Epoxysuccinyl peptide-derived cathepsin B inhibitors: modulating membrane permeability by conjugation with the C-terminal heptapeptide segment of penetratin

Besides its physiological role in lysosomal protein breakdown, extralysosomal cathepsin B has recently been implicated in apoptotic cell death. Highly specific irreversible cathepsin B inhibitors that are readily cell-permeant should be useful tools to elucidate the effects of cathepsin B in the cytosol. We have covalently functionalised the poorly cell-permeant epoxysuccinyl-based cathepsin B inhibitor [R-Gly-Gly-Leu-(2S,3S)-tEps-Leu-Pro-OH; R=OMe] with the C-terminal heptapeptide segment of penetratin (R=epsilonAhx-Arg-Arg-Nle-Lys-Trp-Lys-Lys-NH2). The high inhibitory potency and selectivity for cathepsin B versus cathepsin L of the parent compound was not affected by the conjugation with the penetratin heptapeptide. The conjugate was shown to efficiently penetrate into MCF-7 cells as an active inhibitor, thereby circumventing an intracellular activation step that is required by other inhibitors, such as the prodrug-like epoxysuccinyl peptides E64d and CA074Me.     

Targeted inactivation of the mecB gene, encoding cystathionine-gamma-lyase, shows that the reverse transsulfuration pathway is required for high-level cephalosporin biosynthesis in Acremonium chrysogenum C10 but not for methionine induction of the cephalosporin genes

Targeted gene disruption efficiency in Acremonium chrysogenum was increased 10-fold by applying the double-marker enrichment technique to this filamentous fungus. Disruption of the mecB gene by the double-marker technique was achieved in 5% of the transformants screened. Mutants T6 and T24, obtained by gene replacement, showed an inactive mecB gene by Southern blot analysis and no cystathionine-gamma-lyase activity. These mutants exhibited lower cephalosporin production than that of the control strain, A. chrysogenum C10, in MDFA medium supplemented with methionine. However, there was no difference in cephalosporin production between parental strain A. chrysogenum C10 and the mutants T6 and T24 in Shen's defined fermentation medium (MDFA) without methionine. These results indicate that the supply of cysteine through the transsulfuration pathway is required for high-level cephalosporin biosynthesis but not for low-level production of this antibiotic in methionine-unsupplemented medium. Therefore, cysteine for cephalosporin biosynthesis in A. chrysogenum derives from the autotrophic (SH(2)) and the reverse transsulfuration pathways. Levels of methionine induction of the cephalosporin biosynthesis gene pcbC were identical in the parental strain and the mecB mutants, indicating that the induction effect is not mediated by cystathionine-gamma-lyase.     

Effects of elemental composition on the incorporation of dietary nitrogen and carbon isotopic signatures in an omnivorous songbird

The use of stable isotopes to infer diet requires quantifying the relationship between diet and tissues and, in particular, knowing of how quickly isotopes turnover in different tissues and how isotopic concentrations of different food components change (discriminate) when incorporated into consumer tissues. We used feeding trials with wild-caught yellow-rumped warblers (Dendroica coronata) to determine delta15N and delta13C turnover rates for blood, delta15N and delta13C diet-tissue discrimination factors, and diet-tissue relationships for blood and feathers. After 3 weeks on a common diet, 36 warblers were assigned to one of four diets differing in the relative proportion of fruit and insects. Plasma half-life estimates ranged from 0.4 to 0.7 days for delta13C and from 0.5 to 1.7 days for delta15N . Half-life did not differ among diets. Whole blood half-life for delta13C ranged from 3.9 to 6.1 days. Yellow-rumped warbler tissues were enriched relative to diet by 1.7-3.6% for nitrogen isotopes and by -1.2 to 4.3% for carbon isotopes, depending on tissue and diet. Consistent with previous studies, feathers were the most enriched and whole blood and plasma were the least enriched or, in the case of carbon, slightly depleted relative to diet. In general, tissues were more enriched relative to diet for birds on diets with high percentages of insects. For all tissues, carbon and nitrogen isotope discrimination factors increased with carbon and nitrogen concentrations of diets. The isotopic signature of plasma increased linearly with the sum of the isotopic signature of the diet and the discrimination factor. Because the isotopic signature of tissues depends on both elemental concentration and isotopic signature of the diet, attempts to reconstruct diet from stable isotope signatures require use of mixing models that incorporate elemental concentration.