Non-indigenous microorganisms in the Antarctic: assessing the risks

The Antarctic continent is frequently cited as the last pristine continent on Earth. However, this view is misleading for several reasons. First, there has been a rapid increase in visitors to Antarctica, with large increases at research bases and their environs and to sites of major tourist interest (e.g. historical sites and concentrations of megafauna). Second, although substantial efforts are made to avoid physical disturbance and contamination by chemical, human and other wastes at these sites, little has been done to prevent the introduction of non-indigenous microorganisms. Here, we analyse the extent and significance of anthropogenic introduction of microbial 'contaminants' to the Antarctic continent. We conclude that such processes are unlikely to have any immediate gross impact on microbiological community structure or function, but that increased efforts are required to protect the unique ecosystems of Antarctica from microbial and genetic contamination and homogenisation.     

Medical sequencing of candidate genes for nonsyndromic cleft lip and palate

Nonsyndromic or isolated cleft lip with or without cleft palate (CL/P) occurs in wide geographic distribution with an average birth prevalence of 1/700. We used direct sequencing as an approach to study candidate genes for CL/P. We report here the results of sequencing on 20 candidate genes for clefts in 184 cases with CL/P selected with an emphasis on severity and positive family history. Genes were selected based on expression patterns, animal models, and/or role in known human clefting syndromes. For seven genes with identified coding mutations that are potentially etiologic, we performed linkage disequilibrium studies as well in 501 family triads (affected child/mother/father). The recently reported MSX1 P147Q mutation was also studied in an additional 1,098 cleft cases. Selected missense mutations were screened in 1,064 controls from unrelated individuals on the Centre d'Étude du Polymorphisme Humain (CEPH) diversity cell line panel. Our aggregate data suggest that point mutations in these candidate genes are likely to contribute to 6% of isolated clefts, particularly those with more severe phenotypes (bilateral cleft of the lip with cleft palate). Additional cases, possibly due to microdeletions or isodisomy, were also detected and may contribute to clefts as well. Sequence analysis alone suggests that point mutations in FOXE1, GLI2, JAG2, LHX8, MSX1, MSX2, SATB2, SKI, SPRY2, and TBX10 may be rare causes of isolated cleft lip with or without cleft palate, and the linkage disequilibrium data support a larger, as yet unspecified, role for variants in or near MSX2, JAG2, and SKI. This study also illustrates the need to test large numbers of controls to distinguish rare polymorphic variants and prioritize functional studies for rare point mutations.     

Mutations remote from the human gonadotropin-releasing hormone (GnRH) receptor-binding sites specifically increase binding affinity for GnRH II but not GnRH I: evidence for ligand-selective, receptor-active conformations

The human gonadotropin-releasing hormone (GnRH) receptor is evolutionarily configured for high affinity binding of GnRH I ([Tyr(5),Leu(7),Arg(8)]GnRH) but at lower affinity for GnRH II ([His(5),Trp(7),Tyr(8)]GnRH). GnRH I is more potent in the activation of the G(q/11) protein in the gonadotrope; however, GnRH II is more potent in the stimulation of apoptosis and antiproliferative effects through activating G(i) protein-mediated signaling, implying that GnRH I and II selectively stabilize different receptor-active conformations that preferentially couple to different signaling pathways. Receptor activation involves ligand induction or conformational selection, but the molecular basis of the communication between ligand-binding sites and receptor allosteric sites remains unclear. We have sought conformational coupling between receptor-ligand intermolecular interactions and intramolecular interaction networks in the human GnRH receptor by mutating remote residues that induce differential ligand binding affinity shifts for GnRH I and II. We have demonstrated that certain Ala mutations in the intracellular segments of transmembrane domains 3 (Met(132)), 5 (Met(227)), 6 (Phe(272) and Phe(276)), and 7 (Ile(322) and Tyr(323)) of the human GnRH receptor allosterically increased ligand binding affinity for GnRH II but had little effect on GnRH I binding affinity. We examined the role of the three amino acids that differ in these two ligands, and we found that Tyr(8) in GnRH II plays a dominant role for the increased affinity of the receptor mutants for GnRH II. We propose that creation of a high affinity binding site for GnRH II accompanies receptor conformational changes, i.e."induced fit" or "conformational selection," mainly determined by the intermolecular interactions between Tyr(8) and the receptor contact residues, which can be facilitated by disruption of particular sets of receptor-stabilizing intramolecular interactions. The findings suggest that GnRH I and II binding may selectively stabilize different receptor-active conformations and therefore different ligand-induced selective signaling described previously for these ligands.     

Evidence for direct roles of two additional factors, SECp43 and soluble liver antigen, in the selenoprotein synthesis machinery

Selenocysteine (Sec) is inserted into selenoproteins co-translationally with the help of various cis- and trans-acting factors. The specific mechanisms of Sec biosynthesis and insertion into protein in eukaryotic cells, however, are not known. Two proteins, SECp43 and the soluble liver antigen (SLA), were previously reported to interact with tRNA([Ser]Sec), but their functions remained elusive. Herein, we report that knockdown of SECp43 in NIH3T3 or TCMK-1 cells using RNA interference technology resulted in a reduction in the level of methylation at the 2'-hydroxylribosyl moiety in the wobble position (Um34) of Sec tRNA([Ser]Sec), and consequently reduced glutathione peroxidase 1 expression. Double knockdown of SECp43 and SLA resulted in decreased selenoprotein expression. SECp43 formed a complex with Sec tRNA([Ser]Sec) and SLA, and the targeted removal of one of these proteins affected the binding of the other to Sec tRNA([Ser]Sec). SECp43 was located primarily in the nucleus, whereas SLA was found in the cytoplasm. Co-transfection of both proteins resulted in the nuclear translocation of SLA suggesting that SECp43 may also promote shuttling of SLA and Sec tRNA([Ser]Sec) between different cellular compartments. Taken together, these data establish the role of SECp43 and SLA in selenoprotein biosynthesis through interaction with tRNA([Ser]Sec) in a multiprotein complex. The data also reveal a role of SECp43 in regulation of selenoprotein expression by affecting the synthesis of Um34 on tRNA([Ser]Sec) and the intracellular location of SLA.     

Repellency and toxicity of mint oil granules to red imported fire ants (Hymenoptera: Formicidae)

Repellency and toxicity of 2% mint oil granules were evaluated against worker red imported fire ants. Solenopsis invicta Buren, in a series of laboratory and field experiments. In continuous exposure experiments, LT50 values ranged from 1.2 h with 164.8 mg/cm2 of 2% mint oil granules to 15.3 h with 1.65 mg/cm2 of granules. LT50 values declined exponentially with increasing rate of mint oil granules. Limited exposure to 164.8 mg/cm2 mint oil granules resulted in > 50% knock down (KD) after 30 min; however, there was no KD at 15 min. Twenty-four hour mortality increased linearly with increasing exposure time. Mean repellency of worker red imported fire ants ranged from 49.2 +/- 5.4% for 0 mg/cm2 (untreated control) of mint oil granules at 30 min to 100% for 147.8 mg/cm2 of mint oil granules at 3 h. Repellency increased with increasing milligrams per square centimeter of mint oil granules and exposure time. In field tests, 100% of mounds opened and treated with mint oil granules were abandoned 5 d after treatment and ants had relocated or formed satellite mounds by 2 d after treatment. Unopened mounds treated topically with mint oil granules were not abandoned, but ants formed satellite mounds 2 d after treatment. Mint oil granules could provide another tool for red imported fire ant integrated pest management, particularly in situations in which conventional insecticides would be inappropriate.     

Socialized medicine: Individual and communal disease barriers in honey bees

Honey bees are attacked by numerous parasites and pathogens toward which they present a variety of individual and group-level defenses. In this review, we briefly introduce the many pathogens and parasites afflicting honey bees, highlighting the biology of specific taxonomic groups mainly as they relate to virulence and possible defenses. Second, we describe physiological, immunological, and behavioral responses of individual bees toward pathogens and parasites. Third, bees also show behavioral mechanisms for reducing the disease risk of their nestmates. Accordingly, we discuss the dynamics of hygienic behavior and other group-level behaviors that can limit disease. Finally, we conclude with several avenues of research that seem especially promising for understanding host–parasite relationships in bees and for developing breeding or management strategies for enhancing honey bee health. We discuss how human efforts to maintain healthy colonies intersect with similar efforts by the bees, and how bee management and breeding protocols can affect disease traits in the short and long term.     

Genotype-by-Diet Interactions Drive Metabolic Phenotype Variation in Drosophila melanogaster

The rising prevalence of complex disease suggests that alterations to the human environment are increasing the proportion of individuals who exceed a threshold of liability. This might be due either to a global shift in the population mean of underlying contributing traits, or to increased variance of such underlying endophenotypes (such as body weight). To contrast these quantitative genetic mechanisms with respect to weight gain, we have quantified the effect of dietary perturbation on metabolic traits in 146 inbred lines of Drosophila melanogaster and show that genotype-by-diet interactions are pervasive. For several metabolic traits, genotype-by-diet interactions account for far more variance (between 12 and 17%) than diet alone (1–2%), and in some cases have as large an effect as genetics alone (11–23%). Substantial dew point effects were also observed. Larval foraging behavior was found to be a quantitative trait exhibiting significant genetic variation for path length (P = 0.0004). Metabolic and fitness traits exhibited a complex correlation structure, and there was evidence of selection minimizing weight under laboratory conditions. In addition, a high fat diet significantly increases population variance in metabolic phenotypes, suggesting decreased robustness in the face of dietary perturbation. Changes in metabolic trait mean and variance in response to diet indicates that shifts in both population mean and variance in underlying traits could contribute to increases in complex disease.METABOLIC syndrome (MetS) is a complex disease that is promoted by interactions between genetic and environmental effects (O''Rahilly and Farooqi 2006), and seems to be increasing in prevalence in response to a transition from traditional toward Westernized lifestyles (Lee et al. 2004; Schulz et al. 2006). MetS is a constellation of metabolic symptoms including insulin resistance, abdominal obesity, and dyslipidemia, and is predictive of cardiovascular disease and type-2 diabetes (Alberti et al. 2006). The condition has reached epidemic proportions in many Westernized countries (Isomaa et al. 2001; Ford and Giles 2003; Lorenzo et al. 2003; Alberti et al. 2006). Not all individuals are susceptible to the deleterious effects of a Westernized lifestyle, but some individuals are very sensitive to the effects of their environment (Schulz et al. 2006).We argued previously that environmental perturbation contributes to the recent increases in chronic disease in Westernized societies by exposing cryptic genetic variation, a phenomenon that may be particularly evident in metabolic syndrome (Gibson 2009). Increases in complex disease after an environmental shift can be caused by both a change in the population mean or increased variance in a predisposing underlying trait, or endophenotype, causing a larger portion of the population to exceed a disease threshold (Gibson and Reed 2008). Endophenotypes can be molecular, such as rate of uptake of glucose into cells, but also include visible disease covariates, such as body mass. The transition from traditional diets and lifestyles may have perturbed our metabolic homeostasis, thereby promoting increased susceptibility to, and in turn prevalence of, obesity, hyperlipidemia, diabetes, and cardiovascular illness.The complexity of genetic and environmental interactions leads to major challenges in successful disease treatment and prevention strategies, in that it is very difficult to accurately model the relative contributions of nature and nurture to disease susceptibility in a human population. Dietary factors have been demonstrated to interact with specific genetic variants to increase the risk of metabolic disease in humans (Corella and Ordovas 2005; Ordovas 2006; Corella et al. 2009; Warodomwichit et al. 2009), but the relative contribution of overall genotype and environmental effects on human variation is difficult to determine. Modeling population level genotype-by-environment interactions using a model organism like Drosophila can compensate for the research challenges of parameter estimation in human populations.Drosophila share great homology to humans in a number of systems including central metabolism, insulin-signaling pathways, and organs responsible for physiological homoeostasis (e.g., heart, liver, and kidney) (Rizki 1978; Bodmer 1995; Nation 2002; Rulifson et al. 2002; Denholm et al. 2003; Wessells et al. 2004). It has been shown that Drosophila with ablated insulin-producing neurons have elevated hemolymph trehalose levels, considered to parallel a diabetic phenotype (Rulifson et al. 2002). Loss of insulin signaling also restores normal rhythmicity of adult heart rate in old flies (Wessells et al. 2004), providing a link between the obesity and cardiac components of MetS. We have used 146 natural genetic isolates of Drosophila melanogaster to model the relative contributions of genetics, diet, and other environmental effects on the MetS-like phenotypes of larval weight gain, blood sugar concentration, lipid storage, and survival. Individuals from each of these genetic lines were raised on four different diets: their normal lab food, a calorie restricted (0.75% glucose) food, a high (4%) glucose food, and a high fat diet containing (3%) coconut oil.Using this approach, we sought evidence pertaining to two major hypotheses. There are six general types of phenotypic reaction scenarios that a genetically variable population can exhibit in response to an environmental transition: (1) no phenotypic variation in response to genetic or environmental factors, (2) genetic variation in mean phenotype but no change across environments, (3) an additive change in phenotypic mean across genotypes between environments, (4) an interaction effect between genetic and environment leading to a crossing of line means, and (5) a decrease or (6) an increase in variance in the new environment (Gibson and Vanhelden 1997). First, we considered whether the predominant source of metabolic variation within a Drosophila population is genetic, environmental, or the interaction between genetic and environmental effects. Our null was that none of these factors significantly influence weight gain or other phenotypes (scenario 1 above), but it was expected that genetic variation would be prevalent. The more fundamental issue is which of two alternate hypotheses apply: that dietary effects are essentially additive across genotypes (3) or that they are largely genotype dependent (4), possibly also with contributions of behavior and the external environment. Second, we considered whether the transition from a standard laboratory diet to a perturbing diet would change the environmental and/or genetic variance observed in the population: a decrease (5) indicating physiological limitation to the variation or an increase (6) indicating decanalization of the metabolic phenotypes due to loss of physiological buffering.