Promiscuous mitochondria in Cryptococcus gattii

Cryptococcus gattii is a primary pathogenic basidiomycetous yeast comprising four genotypic groups. Here we present data on two mitochondrial loci (MtLrRNA and ATP6 ). Two of the genotypic groups, namely amplified fragment length polymorphism (AFLP)5/VGIII and AFLP6/VGII, formed monophyletic lineages. The AFLP4/VGI genotypic group, however, possessed five different mitochondrial genotypes that did not form a monophyletic lineage. The majority of these isolates contained mitochondrial genomes that are partially identical to those found in isolates belonging to AFLP6/VGII, which is causing the ongoing and expanding Vancouver Island outbreak. Two out of four AFLP7/VGIV isolates contained an AFLP4/VGI allele of MtLrRNA. These observations are best explained by assuming a process of mitochondrial recombination. If this is true, mitochondrial recombination seems possible between cells belonging to different genotypic groups of C. gattii , especially between AFLP6/VGII or AFLP7/VGIV and AFLP4/VGI. We also have to assume that mitochondria, most likely, were transferred from cells belonging to AFLP6/VGII to AFLP4/VGI. As such a process of mitochondrial recombination is only possible after cell–cell conjugation, this may also allow the further exchange of genetic material, for example nuclear or plasmid in nature, between different genotypes of C. gattii . This may be relevant as it may provide a possible mechanism contributing to the modulation of virulence attributes of isolates, such as has been observed in the ongoing Vancouver Island outbreak of C. gattii .     

Quantifying the gender load: can population crosses reveal interlocus sexual conflict?

Six sister populations of Drosophila melanogaster kept under identical environmental conditions for greater than 600 generations were reciprocally crossed to investigate the incidence of population divergence in allopatry. Population crosses directly influenced fitness, mating frequency, and sperm competition patterns. Changes in both female remating rate and the outcome of male sperm competition (P1, P2) in response to foreign males were consistent with intersexual coevolution. Moreover, seven of the 30 crosses between foreign mates resulted in significant reductions in female fitness, whereas two resulted in significant increases, compared to local matings. This tendency for foreign males to reduce female fitness may be interpreted as evidence for either sexually antagonistic coevolution or the disruption of mutualistic interactions. However, instances in which female fitness improved via cohabitation with foreign males may better reveal sexual conflict, signalling release from the cost of interacting with locally adapted males. By this metric, female reproduction in D. melanogaster is strongly constrained by local adaptation by males, a situation that would promote antagonistic coevolution between the sexes. We conclude that sexual selection can promote population differentiation in allopatry and that sexual conflict is likely to have played a role in population differentiation in this study system.     

Surgical mask to prevent influenza transmission in households: a cluster randomized trial

Background

Facemasks and respirators have been stockpiled during pandemic preparedness. However, data on their effectiveness for limiting transmission are scarce. We evaluated the effectiveness of facemask use by index cases for limiting influenza transmission by large droplets produced during coughing in households.

Methodology and Principal Findings

A cluster randomized intervention trial was conducted in France during the 2008–2009 influenza season. Households were recruited during a medical visit of a household member with a positive rapid influenza A test and symptoms lasting less than 48 hours. Households were randomized either to the mask or control group for 7 days. In the intervention arm, the index case had to wear a surgical mask from the medical visit and for a period of 5 days. The trial was initially intended to include 372 households but was prematurely interrupted after the inclusion of 105 households (306 contacts) following the advice of an independent steering committee. We used generalized estimating equations to test the association between the intervention and the proportion of household contacts who developed an influenza-like illness during the 7 days following the inclusion. Influenza-like illness was reported in 24/148 (16.2%) of the contacts in the intervention arm and in 25/158 (15.8%) of the contacts in the control arm and the difference between arms was 0.40% (95%CI: −10% to 11%, P = 1.00). We observed a good adherence to the intervention. In various sensitivity analyses, we did not identify any trend in the results suggesting effectiveness of facemasks.

Conclusion

This study should be interpreted with caution since the lack of statistical power prevents us to draw formal conclusion regarding effectiveness of facemasks in the context of a seasonal epidemic.

Trial Registration

clinicaltrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00774774","term_id":"NCT00774774"}}NCT00774774     

Decoration of Outer Membrane Vesicles with Multiple Antigens by Using an Autotransporter Approach

Outer membrane vesicles (OMVs) are spherical nanoparticles that naturally shed from Gram-negative bacteria. They are rich in immunostimulatory proteins and lipopolysaccharide but do not replicate, which increases their safety profile and renders them attractive vaccine vectors. By packaging foreign polypeptides in OMVs, specific immune responses can be raised toward heterologous antigens in the context of an intrinsic adjuvant. Antigens exposed at the vesicle surface have been suggested to elicit protection superior to that from antigens concealed inside OMVs, but hitherto robust methods for targeting heterologous proteins to the OMV surface have been lacking. We have exploited our previously developed hemoglobin protease (Hbp) autotransporter platform for display of heterologous polypeptides at the OMV surface. One, two, or three of the Mycobacterium tuberculosis antigens ESAT6, Ag85B, and Rv2660c were targeted to the surface of Escherichia coli OMVs upon fusion to Hbp. Furthermore, a hypervesiculating ΔtolR ΔtolA derivative of attenuated Salmonella enterica serovar Typhimurium SL3261 was generated, enabling efficient release and purification of OMVs decorated with multiple heterologous antigens, exemplified by the M. tuberculosis antigens and epitopes from Chlamydia trachomatis major outer membrane protein (MOMP). Also, we showed that delivery of Salmonella OMVs displaying Ag85B to antigen-presenting cells in vitro results in processing and presentation of an epitope that is functionally recognized by Ag85B-specific T cell hybridomas. In conclusion, the Hbp platform mediates efficient display of (multiple) heterologous antigens, individually or combined within one molecule, at the surface of OMVs. Detection of antigen-specific immune responses upon vesicle-mediated delivery demonstrated the potential of our system for vaccine development.     

The evolution of insulin resistance in muscle of the glucose infused rat

Glucose infusion into rats causes skeletal muscle insulin resistance that initially occurs without changes in insulin signaling. The aim of the current study was to prolong glucose infusion and evaluate other events associated with the transition to muscle insulin resistance. Hyperglycemia was produced in rats by glucose infusion for 3, 5 and 8 h. The rate of infusion required to maintain hyperglycemia was reduced at 5 and 8 h. Glucose uptake into red quadriceps (RQ) and its incorporation into glycogen decreased between 3 and 5 h, further decreasing at 8 h. The earliest observed change in RQ was decreased AMPKα2 activity associated with large increases in muscle glycogen content at 3 h. Activation of the mTOR pathway occurred at 5 h. Akt phosphorylation (Ser⁴⁷³) was decreased at 8 h compared to 3 and 5, although no decrease in phosphorylation of downstream GSK-3β (Ser⁹) and AS160 (Thr⁶⁴²) was observed. White quadriceps showed a similar but delayed pattern, with insulin resistance developing by 8 h and decreased AMPKα2 activity at 5 h. These results indicate that, in the presence of a nutrient overload, alterations in muscle insulin signaling occur, but after insulin resistance develops and appropriate changes in energy/nutrient sensing pathways occur.     

Crystal structure of phosphotransacetylase from the methanogenic archaeon Methanosarcina thermophila

Phosphotransacetylase (Pta) [EC 2.3.1.8] is ubiquitous in the carbon assimilation and energy-yielding pathways in anaerobic prokaryotes where it catalyzes the reversible transfer of the acetyl group from acetyl phosphate to CoA forming acetyl CoA and inorganic phosphate. The crystal structure of Pta from the methane-producing archaeon Methanosarcina thermophila, representing the first crystal structure of any Pta, was determined by multiwavelength anomalous diffraction at 2.7 A resolution. In solution and in the crystal, the enzyme forms a homodimer. Each monomer consists of two alpha/beta domains with a cleft along the domain boundary, which presumably contains the substrate binding sites. Comparison of the four monomers present in the asymmetric unit indicates substantial variations in the relative orientation of the two domains and the structure of the putative active site cleft. A search for structural homologs revealed the NADP(+)-dependent isocitrate and isopropylmalate dehydrogenases as the only homologs with a similar two-domain architecture.     

TNF inhibited the apoptosis by activation of Akt serine/threonine kinase in the human head and neck squamous cell carcinoma

Tumour necrosis factor (TNF) is known to induce apoptosis, but recently, TNF was shown to promote cell survival, a process regulated by phosphatidylinositol-3-OH kinase (PI3K) and the NFkappaB pathway. In this study, we investigated the relationship between the molecules implicated in regulating TNF-induced cell survival and apoptosis induced by TNF in a human head and neck squamous cell carcinoma cell line (SAS), with special reference to the Akt pathway, one of the pathways related to cell survival. In SAS cells, TNF induced the phosphorylation of Akt at both Ser473 and Thr308, causing the activation of Akt, and also induced the phosphorylation and degradation of IkappaB (inhibitor of NFkappaB). This phosphorylation and degradation was inhibited by pretreating the cells with the PI3K inhibitors, wortmannin or LY294002. The apoptosis of SAS cells induced by TNF was dependent on the concentration: a high concentration of TNF, but not a low concentration, induced apoptosis within 30 h. However, a low concentration of TNF in the presence of wortmannin or LY294002 induced apoptosis. Furthermore, expression of the kinase-negative form of Akt, IKKalpha or IKKbeta, and the undegradable mutant of IkappaB, also induced apoptosis at low concentrations of TNF. When the SAS cells expressed constitutively activated Akt, apoptosis was not induced, even by high concentrations of TNF. These observations suggest that, in the SAS cell line, the PI3K-NFkappaB pathway contributes to TNF-induced cell survival and that inhibition of this pathway accelerates apoptosis.     

Meiotic cohesin STAG3 is required for chromosome axis formation and sister chromatid cohesion

The cohesin complex is essential for mitosis and meiosis. The specific meiotic roles of individual cohesin proteins are incompletely understood. We report in vivo functions of the only meiosis‐specific STAG component of cohesin, STAG3. Newly generated STAG3‐deficient mice of both sexes are sterile with meiotic arrest. In these mice, meiotic chromosome architecture is severely disrupted as no bona fide axial elements (AE) form and homologous chromosomes do not synapse. Axial element protein SYCP3 forms dot‐like structures, many partially overlapping with centromeres. Asynapsis marker HORMAD1 is diffusely distributed throughout the chromatin, and SYCP1, which normally marks synapsed axes, is largely absent. Centromeric and telomeric sister chromatid cohesion are impaired. Centromere and telomere clustering occurs in the absence of STAG3, and telomere structure is not severely affected. Other cohesin proteins are present, localize throughout the STAG3‐devoid chromatin, and form complexes with cohesin SMC1β. No other deficiency in a single meiosis‐specific cohesin causes a phenotype as drastic as STAG3 deficiency. STAG3 emerges as the key STAG cohesin involved in major functions of meiotic cohesin.