Context-dependent genetic benefits of polyandry in a marine hermaphrodite

Numerous studies emphasize the potential indirect (genetic) benefits of polyandry in animals with resource-free mating systems. In this paper, we examine the potential for these benefits to fuel sexual selection and polyandry in the hermaphroditic ascidian Pyura stolonifera. Individuals were designated either sire (sperm producers) or dam (egg producers) at random and crossed in a North Carolina II breeding design to produce both paternal and maternal half siblings for our quantitative genetic analysis. We then partitioned the phenotypic variance in fertilization and hatching rates into additive and non-additive variance components. We found significant additive variance attributable to sire and dam effects at fertilization and hatching, suggesting the potential for selection to favour individuals carrying intrinsically 'good genes' for these traits. In separate analyses involving monandrous and polyandrous clutches, we found that both traits were elevated under polyandry, but the difference in hatching rates was due entirely to the difference in fertilization rates between treatments. When the hatching rates were standardized to account for variance at fertilization, there was no overall net benefit of polyandry for this trait. Despite this, we found that hatching success declined with increasing embryo densities, and that the slope of this decline was significantly greater in monandrous than polyandrous clutches. Hence, selection on embryo viability may still favour polyandry under restricted environmental conditions. Nevertheless, our results caution against interpreting elevated hatching success as an indirect genetic benefit of polyandry when variance in fertilization is not controlled.     

Substrate directs enzyme dynamics by bridging distal sites: UDP-galactopyranose mutase

UDP-Galactopyranose mutase (UGM) is a flavoenzyme that catalyzes interconversion of UDP-galactopyranose (UDP-Galp) and UDP-galactofuranose (UDP-Galf); its activity depends on FAD redox state. The enzyme is vital to many pathogens, not native to mammals, and is an important drug target. We have probed binding of substrate, UDP-Galp, and UDP to wild type and W160A UGM from K. pneumoniae, and propose that substrate directs recognition loop dynamics by bridging distal FAD and W160 sites; W160 interacts with uracil of the substrate and is functionally essential. Enhanced Trp fluorescence upon substrate binding to UGM indicates conformational changes remote from the binding site because the fluorescence is unchanged upon binding to W70F/W290F UGM where W160 is the sole Trp. MD simulations map these changes to recognition loop closure to coordinate substrate. This requires galactose-FAD interactions as Trp fluorescence is unchanged upon substrate binding to oxidized UGM, or binding of UDP to either form of the enzyme, and MD show heightened recognition loop mobility in complexes with UDP. Consistent with substrate-directed loop closure, UDP binds 10-fold more tightly to oxidized UGM, yet substrate binds tighter to reduced UGM. This requires the W160-U interaction because redox-switched binding affinity of substrate reverses in the W160A mutant where it only binds when oxidized. Without the anchoring W160-U interaction, an alternative binding mode for UDP is detected, and STD-NMR experiments show simultaneous binding of UDP-Galp and UDP to different subsites in oxidized W160A UGM: Substrate no longer directs recognition loop dynamics to coordinate tight binding to the reduced enzyme.     

Evidence for pH dependent Zn2+influx in K562 erythroleukemia cells: studies using ZnAF-2F fluorescence and 65Zn2+ uptake

Using both ZnAF-2F (a Zn2+ specific fluorophore) and 65Zn2+, we determined the rate of transporter mediated Zn2+ influx (presumably mediated by the SLC39A1 gene product, protein name hZIP1) under steady state conditions and studied the effects of extracellular acidification. When K562 erythroleukemia cells were placed in Zn2+ containing buffers (1-60 microM), the initial rate of 65Zn2+ accumulation mirrored the apparent rise in free intracellular Zn2+ concentrations sensed by ZnAF-2F. Therefore, newly transported Zn2+ equilibrated with the free intracellular Zn2+ pool sensed by ZnAF-2F. A new steady state with elevated free intracellular Zn2+ was established after about 30 min. An estimate of 11 microM for the Km and 0.203 nmol/mg/s for the Vmax were obtained for Zn2+ influx. 65Zn2+ uptake and ZnAF-2F fluorescent changes were inhibited by extracellular acidification (range tested: pH 8-6, IC50 = pH 6.34). The IC50 for proton effects was close to the pKa for histidine, suggesting conserved histidine residues present in SLC39A1 play a critical role in Zn2+ influx and are involved in the pH effect.     

Imaging of HIV-1 Envelope-induced Virological Synapse and Signaling on Synthetic Lipid Bilayers

Human immunodeficiency virus type 1 (HIV-1) infection occurs most efficiently via cell to cell transmission^2,10,11. This cell to cell transfer between CD4⁺ T cells involves the formation of a virological synapse (VS), which is an F-actin-dependent cell-cell junction formed upon the engagement of HIV-1 envelope gp120 on the infected cell with CD4 and the chemokine receptor (CKR) CCR5 or CXCR4 on the target cell ⁸. In addition to gp120 and its receptors, other membrane proteins, particularly the adhesion molecule LFA-1 and its ligands, the ICAM family, play a major role in VS formation and virus transmission as they are present on the surface of virus-infected donor cells and target cells, as well as on the envelope of HIV-1 virions^1,4,5,6,7,13. VS formation is also accompanied by intracellular signaling events that are transduced as a result of gp120-engagement of its receptors. Indeed, we have recently showed that CD4⁺ T cell interaction with gp120 induces recruitment and phosphorylation of signaling molecules associated with the TCR signalosome including Lck, CD3ζ, ZAP70, LAT, SLP-76, Itk, and PLCγ¹⁵.In this article, we present a method to visualize supramolecular arrangement and membrane-proximal signaling events taking place during VS formation. We take advantage of the glass-supported planar bi-layer system as a reductionist model to represent the surface of HIV-infected cells bearing the viral envelope gp120 and the cellular adhesion molecule ICAM-1. The protocol describes general procedures for monitoring HIV-1 gp120-induced VS assembly and signal activation events that include i) bi-layer preparation and assembly in a flow cell, ii) injection of cells and immunofluorescence staining to detect intracellular signaling molecules on cells interacting with HIV-1 gp120 and ICAM-1 on bi-layers, iii) image acquisition by TIRF microscopy, and iv) data analysis. This system generates high-resolution images of VS interface beyond that achieved with the conventional cell-cell system as it allows detection of distinct clusters of individual molecular components of VS along with specific signaling molecules recruited to these sub-domains.     

Prevention of LPS-Induced Microglia Activation,Cytokine Production and Sickness Behavior with TLR4 Receptor Interfering Peptides

The innate immune receptor Toll-like 4 (TLR4) is the receptor activated by lipopolysaccharide (LPS), and TLR4-LPS interaction is well known to induce an innate immune response, triggering sickness behavior. Within the brain, TLR4 is highly expressed in brain microglia, and excessive inflammation resulting from activation of this pathway in the brain has been implicated in depressive disorders and neurodegenerative pathologies. We hypothesized that blocking LPS-induced activation of TLR4 would prevent downstream immune signaling in the brain and suppress the induction of sickness behavior. We used interfering peptides to block TLR4 activation and confirmed their efficacy in preventing second messenger activation and cytokine production normally induced by LPS treatment. Further, these peptides blocked morphological changes in microglia that are typically induced by LPS. We also demonstrated that intraperitoneal (i.p.) injection of Tat-TLR4 interfering peptides prevented LPS-induced sickness behavior, as assessed in home cage behavior and with the intracranial self-stimulation paradigm. These newly synthesised peptides inhibit TLR4 signaling thereby preventing changes in behavior and motivation caused by inflammatory stimuli. These peptides highlight the roll of TLR4 and microglia morphology changes in sickness behavior, and thus may be of therapeutic value in limiting the deleterious impact of excessive inflammation in specific CNS pathologies.     

Stress impacts telomere dynamics

Telomeres are DNA-protein complexes at the ends of chromosomes that control genomic integrity but appear to become shorter with age and stress. To test whether stress causes telomere attrition, we exposed the offspring of wild-caught house mice (Mus musculus) to stressful conditions and examined the changes in telomere length over six months. We found that females exposed to males and reproductive stress (either with or without crowding) had significantly shorter telomeres than controls, and males exposed to crowding stress had shorter telomeres than males that were not crowded. Our results indicate that stress alters telomere dynamics, causing attrition and hindering restoration, and these effects are sex dependent. Telomeres may thus provide a biomarker for assessing an individual's cumulative exposure or ability to cope with stressful conditions.     

Environment‐dependent variation in selection on life history across small spatial scales

Variation in life‐history traits is ubiquitous, even though genetic variation is thought to be depleted by selection. One potential mechanism for the maintenance of trait variation is spatially variable selection. We explored spatial variation in selection in the field for a colonial marine invertebrate that shows phenotypic differences across a depth gradient of only 3 m. Our analysis included life‐history traits relating to module size, colony growth, and phenology. Directional selection on colony growth varied in strength across depths, while module size was under directional selection at one depth but not the other. Differences in selection may explain some of the observed phenotypic differentiation among depths for one trait but not another: instead, selection should actually erode the differences observed for this trait. Our results suggest selection is not acting alone to maintain trait variation within and across environments in this system.     

An estimation of Canadian population exposure to cosmic rays from air travel

Based on air travel statistics in 1984, it was estimated that less than 4 % of the population dose from cosmic ray exposure would result from air travel. In the present study, cosmic ray doses were calculated for more than 3,000 flights departing from more than 200 Canadian airports using actual flight profiles. Based on currently available air travel statistics, the annual per capita effective dose from air transportation is estimated to be 32 μSv for Canadians, about 10 % of the average cosmic ray dose received at ground level (310 μSv per year).     

EVOLUTIONARY CONSTRAINTS AND THE MAINTENANCE OF INDIVIDUAL SPECIALIZATION THROUGHOUT SUCCESSION

Constraints on life‐history traits, with their close links to fitness, are widely invoked as limits to niche expansion at most organizational levels. Theoretically, such constraints can maintain individual specialization by preventing adaptation to all niches available, but empirical evidence of them remains elusive for natural populations. This problem may be compounded by a tendency to seek constraints involving multiple traits, neglecting their added potential to manifest in trait expression across environments (i.e., within reaction norms). By replicating genotypes of a colonial marine invertebrate across successional stages in its local community, and taking a holistic approach to the analysis of ensuing reaction norms for fitness, we show the potential for individual specialization to be maintained by genetic constraints associated with these norms, which limit the potential for fitness at one successional stage to improve without loss of fitness at others. Our study provides new insight into the evolutionary maintenance of individual specialization in natural populations and reinforces the importance of reaction norms for studying this phenomenon.