Condensation of supercoiled DNA induced by MnCl2.

Multivalent cations condense DNA in vitro, but it had been thought that a valence of at least + 3 was required in aqueous solution. We have found that Mn2+ can produce toroidal condensates of supercoiled plasmid DNA, but not of linearized plasmid. Mg2+ does not cause condensation, and neither MgCl2 nor NaCl can negate the effect of MnCl2, indicating that the condensation mechanism with Mn is not primarily electrostatic. Supercoiled MnDNA is more extensively digested than the linear form by S1 nuclease. Supercoiling appears to cooperate with Mn2+ in stabilizing helix distortions and also provides a "pressure" that enhances lateral association.     

Multispecies coexistence of trees in tropical forests: spatial signals of topographic niche differentiation increase with environmental heterogeneity

Neutral and niche theories give contrasting explanations for the maintenance of tropical tree species diversity. Both have some empirical support, but methods to disentangle their effects have not yet been developed. We applied a statistical measure of spatial structure to data from 14 large tropical forest plots to test a prediction of niche theory that is incompatible with neutral theory: that species in heterogeneous environments should separate out in space according to their niche preferences. We chose plots across a range of topographic heterogeneity, and tested whether pairwise spatial associations among species were more variable in more heterogeneous sites. We found strong support for this prediction, based on a strong positive relationship between variance in the spatial structure of species pairs and topographic heterogeneity across sites. We interpret this pattern as evidence of pervasive niche differentiation, which increases in importance with increasing environmental heterogeneity.     

Warsaw Breakage Syndrome, a Cohesinopathy Associated with Mutations in the XPD Helicase Family Member DDX11/ChlR1

The iron-sulfur-containing DNA helicases XPD, FANCJ, DDX11, and RTEL represent a small subclass of superfamily 2 helicases. XPD and FANCJ have been connected to the genetic instability syndromes xeroderma pigmentosum and Fanconi anemia. Here, we report a human individual with biallelic mutations in DDX11. Defective DDX11 is associated with a unique cellular phenotype in which features of Fanconi anemia (drug-induced chromosomal breakage) and Roberts syndrome (sister chromatid cohesion defects) coexist. The DDX11-deficient patient represents another cohesinopathy, besides Cornelia de Lange syndrome and Roberts syndrome, and shows that DDX11 functions at the interface between DNA repair and sister chromatid cohesion.     

Testicular morphology and expression of aromatase in testes of mice with the mosaic mutation (Atp7a mo-ms)

The aim of this study was to determine whether testicular cells of mice with the mosaic mutation, associated with abnormal copper metabolism, are able to aromatize androgens to estrogens, and what is the putative role of estrogens in the gonad of the mutant male. Mosaic is a lethal mutation; affected males usually die on about day 16. Those, which survive to reach sexual maturity, are valuable research subjects. In testes of young and adult mutants, histological analysis revealed the presence of many degenerating seminiferous tubules besides normal-looking ones. Additionally, high numbers of apoptotic germ cells were observed, especially in young mutants when compared with the controls. Positive immunostaining for aromatase was found in cultured Leydig cells and testicular sections of both control and mutant males. The intensity of immunostaining was always stronger in the mosaic mice. In both groups, Western-blot analysis revealed the presence of aromatase protein as a single band of approximately 55 kDa. In the mosaic males, levels of testosterone in cultured Leydig cells, whole testes, and in blood plasma were lower than in those of the respective controls. On the contrary, estradiol concentrations were always higher in the mutants. Both in vivo and in vitro studies indicate that morphological and functional changes in the testes of the mosaic mice mainly result from defective copper metabolism. The higher level of endogenous estrogens can additionally enhance morphological alterations within the testes. It seems also likely that excess estrogens may affect the survival rate of the mosaic males.     

Identification of the ryanodine receptor mutation I4743M and its contribution to diamide insecticide resistance in Spodoptera exigua (Lepidoptera: Noctuidae)

Insect ryanodine receptors (RyRs) are the targets of diamide insecticides. Two point mutations G4946E and I4790M (numbering according to Plutella xylostella, PxRyR) in the transmembrane domain of the insect RyRs associated with diamide resistance have so far been identified in three lepidopteran pests, P. xylostella, Tuta absoluta and Chilo suppressalis. In this study, we identified one of the known RyR target site resistance mutations (I4790M) in a field‐collected population of Spodoptera exigua. The field‐collected WF population of S. exigua exhibited 154 fold resistance to chlorantraniliprole when compared with the susceptible WH‐S strain. Sequencing the transmembrane domains of S. exigua RyR (SeRyR) revealed that the resistant WF strain was homozygous for the I4743M mutation (corresponding to I4790M in PxRyR), whereas the G4900E allele (corresponding to G4946E of PxRyR) was not detected. The 4743M allele was introgressed into the susceptible WH‐S strain by crossing WF with WH‐S, followed by three rounds of backcrossing with WH‐S. The introgressed strain 4743M was homozygous for the mutant 4743M allele and shared about 94% of its genetic background with that of the recipient WH‐S strain. Compared with WH‐S, the near‐isogenic 4743M strain showed moderate levels of resistance to chlorantraniliprole (21 fold), cyantraniliprole (25 fold) and flubendiamide (22 fold), suggesting that the I4743M mutation confers medium levels of resistance to all three diamides. Genetic analysis showed diamide resistance in the 4743M strain was inherited as an autosomal and recessive trait. Results from this study have direct implications for the design of appropriate resistance monitoring and management practices to sustainably control S. exigua.     

Novel Inhibitors of Staphylococcus aureus Virulence Gene Expression and Biofilm Formation

Staphylococcus aureus is a major human pathogen and one of the more prominent pathogens causing biofilm related infections in clinic. Antibiotic resistance in S. aureus such as methicillin resistance is approaching an epidemic level. Antibiotic resistance is widespread among major human pathogens and poses a serious problem for public health. Conventional antibiotics are either bacteriostatic or bacteriocidal, leading to strong selection for antibiotic resistant pathogens. An alternative approach of inhibiting pathogen virulence without inhibiting bacterial growth may minimize the selection pressure for resistance. In previous studies, we identified a chemical series of low molecular weight compounds capable of inhibiting group A streptococcus virulence following this alternative anti-microbial approach. In the current study, we demonstrated that two analogs of this class of novel anti-virulence compounds also inhibited virulence gene expression of S. aureus and exhibited an inhibitory effect on S. aureus biofilm formation. This class of anti-virulence compounds could be a starting point for development of novel anti-microbial agents against S. aureus.     

Endemic Foci of the Tick-Borne Relapsing Fever Spirochete Borrelia crocidurae in Mali,West Africa,and the Potential for Human Infection

Background

Tick-borne relapsing fever spirochetes are maintained in endemic foci that involve a diversity of small mammals and argasid ticks in the genus Ornithodoros. Most epidemiological studies of tick-borne relapsing fever in West Africa caused by Borrelia crocidurae have been conducted in Senegal. The risk for humans to acquire relapsing fever in Mali is uncertain, as only a few human cases have been identified. Given the high incidence of malaria in Mali, and the potential to confuse the clinical diagnosis of these two diseases, we initiated studies to determine if there were endemic foci of relapsing fever spirochetes that could pose a risk for human infection.

Methodology/Principal Findings

We investigated 20 villages across southern Mali for the presence of relapsing fever spirochetes. Small mammals were captured, thin blood smears were examined microscopically for spirochetes, and serum samples were tested for antibodies to relapsing fever spirochetes. Ornithodoros sonrai ticks were collected and examined for spirochetal infection. In total, 11.0% of the 663 rodents and 14.3% of the 63 shrews tested were seropositive and 2.2% of the animals had active spirochete infections when captured. In the Bandiagara region, the prevalence of infection was higher with 35% of the animals seropositive and 10% infected. Here also Ornithodoros sonrai were abundant and 17.3% of 278 individual ticks tested were infected with Borrelia crocidurae. Fifteen isolates of B. crocidurae were established and characterized by multi-locus sequence typing.

Conclusions/Significance

The potential for human tick-borne relapsing fever exists in many areas of southern Mali.     

Role of the Actin Ala-108–Pro-112 Loop in Actin Polymerization and ATPase Activities

Actin plays fundamental roles in a variety of cell functions in eukaryotic cells. The polymerization-depolymerization cycle, between monomeric G-actin and fibrous F-actin, drives essential cell processes. Recently, we proposed the atomic model for the F-actin structure and found that actin was in the twisted form in the monomer and in the untwisted form in the filament. To understand how the polymerization process is regulated (Caspar, D. L. (1991) Curr. Biol. 1, 30–32), we need to know further details about the transition from the twisted to the untwisted form. For this purpose, we focused our attention on the Ala-108–Pro-112 loop, which must play crucial roles in the transition, and analyzed the consequences of the amino acid replacements on the polymerization process. As compared with the wild type, the polymerization of P109A was accelerated in both the nucleation and the elongation steps, and this was attributed to an increase in the frequency factor of the Arrhenius equation. The multiple conformations allowed by the substitution presumably resulted in the effective formation of the collision complex, thus accelerating polymerization. On the other hand, the A108G mutation reduced the rates of both nucleation and elongation due to an increase in the activation energy. In the cases of polymerization acceleration and deceleration, each functional aberration is attributed to a distinct elementary process. The rigidity of the loop, which mediates neither too strong nor too weak interactions between subdomains 1 and 3, might play crucial roles in actin polymerization.     

Toxicity of microcystin from cyanobacteria growing in a source of drinking water

Microcystin-LR (MC-LR) is a cyanobacterial heptapeptide that presents acute and chronic hazards to animal and human health. The morphological changes in mitochondria are the primary effect induced by MC-LR leading to cell death. We investigated the toxicity of cyanobacterial microcystin-containing extract (CEM) on the respiratory complex of mammalian mitochondria from Bos taurus. Cyanobacterial blooms of Microcystis aeruginosa were harvested from Sulejow Reservoir, a source of drinking water in central Poland. The concentration of microcystin-LR (MC-LR(CEM)) in CEM extract was determined by high-performance liquid chromatography (HPLC). Commercially available microcystin-LR (Sigma) was used as a standard (MC-LR(S)); both standard and CEM extract were incubated with mitochondria in different doses and time of exposure. MC-RL(CEM) at 1 nM, maximal acceptable dose of microcystin (WHO) in drinking water, provoked activation of cytochrome c oxidase complex in mitochondria. We suggest that it might be considered as a defensive signal of mitochondria against low concentration of a toxic compound. In contrast 1 iM MC-RL(CME) inhibited the activity of mitochondrial oxidase complex much stronger than the same concentration of standard MC-RL(S) (58% vs. 87% of control activity, P<0.05), and this may cause a similar effect to long-term consumption of water. In conclusion, we affirm that CEM extract is highly toxic, and mitochondria could be used as an indicator of this toxicity in vivo, especially during long-term consumption of water from reservoirs where microcystin is produced.