Characterization of an alarm pheromone secreted by amphibian tadpoles that induces behavioral inhibition and suppression of the neuroendocrine stress axis

Many species assess predation risk through chemical cues, but the tissue source, chemical nature, and mechanisms of production or action of these cues are often unknown. Amphibian tadpoles show rapid and sustained behavioral inhibition when exposed to chemical cues of predation. Here we show that an alarm pheromone is produced by ranid tadpole skin cells, is released into the medium via an active secretory process upon predator attack, and signals predator presence to conspecifics. The pheromone is composed of two components with distinct biophysical properties that must be combined to elicit the behavioral response. In addition to the behavioral response, exposure to the alarm pheromone caused rapid and strong suppression of the hypothalamo-pituitary-adrenal (HPA) axis, as evidenced by a time and dose-dependent decrease in whole body corticosterone content. Reversing the decline in endogenous corticosterone caused by exposure to the alarm pheromone through addition of corticosterone to the aquarium water (50 nM) partially blocked the anti-predator behavior, suggesting that the suppression of the HPA axis promotes the expression and maintenance of a behaviorally quiescent state. To our knowledge this is the first evidence for aquatic vertebrate prey actively secreting an alarm pheromone in response to predator attack. We also provide a neuroendocrine mechanism by which the behavioral inhibition caused by exposure to the alarm pheromone is maintained until the threat subsides.     

Spinopelvic pathways to bipedality: why no hominids ever relied on a bent-hip–bent-knee gait

Until recently, the last common ancestor of African apes and humans was presumed to resemble living chimpanzees and bonobos. This was frequently extended to their locomotor pattern leading to the presumption that knuckle-walking was a likely ancestral pattern, requiring bipedality to have emerged as a modification of their bent-hip-bent-knee gait used during erect walking. Research on the development and anatomy of the vertebral column, coupled with new revelations from the fossil record (in particular, Ardipithecus ramidus), now demonstrate that these presumptions have been in error. Reassessment of the potential pathway to early hominid bipedality now reveals an entirely novel sequence of likely morphological events leading to the emergence of upright walking.     

Responses of bullfrog tadpoles to hypoxia and predators

Low dissolved oxygen concentrations present numerous challenges for non-air-breathing aquatic organisms. Amphibian larvae and their predators can respond to oxygen levels by altering their behavior and physiology, but the ecological consequences of these responses are generally unknown. We conducted two laboratory experiments to study the effects of dissolved oxygen on respiratory behavior and susceptibility to predation of larval bullfrogs (Rana catesbeiana). In the first, we exposed small, lungless tadpoles to a predatory salamander larva (Ambystoma tigrinum) under high and low oxygen conditions. More tadpoles were consumed in high oxygen tanks than in low ones, presumably because salamanders remained near the surface in the low oxygen tanks while most tadpoles rested on the bottom. Tadpole activity depended on both oxygen and predator presence: swimming decreased after addition of salamanders under high oxygen, but increased under low oxygen. In the second experiment, we examined the effect of predator chemical cues on the air-breathing rate of large tadpoles with well-developed lungs under low oxygen conditions. In the presence of chemical cues produced by dragonfly larvae consuming bullfrog tadpoles, air-breathing and swimming were significantly reduced relative to controls. These experiments demonstrate the potential impact of dissolved oxygen on predator-prey interactions, and suggest that outcomes depend on the respiratory ecology of both predator and prey.     

Streamlining genomes: toward the generation of simplified and stabilized microbial systems

1. Download : Download high-res image (115KB)
2. Download : Download full-size image

Highlights? Top-down and bottom-up approaches to genome streamlining. ? Computational support for constructing and refactoring streamlined genomes. ? From genome engineering to metabolic reprogramming. ? Perspectives in applied genome engineering.     

Analysis of binding properties and specificity through identification of the interface forming residues (IFR) for serine proteases <Emphasis Type=Italic>in silico</Emphasis> docked to different inhibitors

Background  

Enzymes belonging to the same super family of proteins in general operate on variety of substrates and are inhibited by wide selection of inhibitors. In this work our main objective was to expand the scope of studies that consider only the catalytic and binding pocket amino acids while analyzing enzyme specificity and instead, include a wider category which we have named the Interface Forming Residues (IFR). We were motivated to identify those amino acids with decreased accessibility to solvent after docking of different types of inhibitors to sub classes of serine proteases and then create a table (matrix) of all amino acid positions at the interface as well as their respective occupancies. Our goal is to establish a platform for analysis of the relationship between IFR characteristics and binding properties/specificity for bi-molecular complexes.     

An assessment of false discovery rates and statistical significance in label-free quantitative proteomics with combined filters

Background  

Many studies have provided algorithms or methods to assess a statistical significance in quantitative proteomics when multiple replicates for a protein sample and a LC/MS analysis are available. But, confidence is still lacking in using datasets for a biological interpretation without protein sample replicates. Although a fold-change is a conventional threshold that can be used when there are no sample replicates, it does not provide an assessment of statistical significance such as a false discovery rate (FDR) which is an important indicator of the reliability to identify differentially expressed proteins. In this work, we investigate whether differentially expressed proteins can be detected with a statistical significance from a pair of unlabeled protein samples without replicates and with only duplicate LC/MS injections per sample. A FDR is used to gauge the statistical significance of the differentially expressed proteins.     

Molluscum Contagiosum in a Pediatric American Indian Population: Incidence and Risk Factors

Background

Molluscum contagiosum virus (MCV) causes an innocuous yet persistent skin infection in immunocompetent individuals and is spread by contact with lesions. Studies point to atopic dermatitis (AD) as a risk factor for MCV infection; however, there are no longitudinal studies that have evaluated this hypothesis.

Methods

Outpatient visit data from fiscal years 2001–2009 for American Indian and Alaska Native (AI/AN) children were examined to describe the incidence of molluscum contagiosum (MC). We conducted a case-control study of patients <5 years old at an Indian Health Service (IHS) clinic to evaluate dermatological risk factors for infection.

Results

The incidence rate for MC in children <5 years old was highest in the West and East regions. MC cases were more likely to have a prior or co-occurring diagnosis of eczema, eczema or dermatitis, impetigo, and scabies (p<0.05) compared to controls; 51.4% of MC cases had a prior or co-occurring diagnosis of eczema or dermatitis.

Conclusions

The present study is the first demonstration of an association between AD and MC using a case-control study design. It is unknown if the concurrent high incidence of eczema and MC is related, and this association deserves further investigation.     

Palmitoylation and trafficking of GAD65 are impaired in a cellular model of Huntington's disease

HD (Huntington's disease) is caused by an expanded polyQ (polyglutamine) repeat in the htt (huntingtin protein). GABAergic medium spiny neurons in the striatum are mostly affected in HD. However, mhtt (mutant huntingtin)-induced molecular changes in these neurons remain largely unknown. The present study focuses on the effect of mhtt on the subcellular localization of GAD (glutamic acid decarboxylase), the enzyme responsible for synthesizing GABA (γ-aminobutyric acid). We report that the subcellular distribution of GAD is significantly altered in two neuronal cell lines that express either the N-terminus of mhtt or full-length mhtt. GAD65 is predominantly associated with the Golgi membrane in cells expressing normal htt; however, it diffuses in the cytosol of cells expressing mhtt. As a result, vesicle-associated GAD65 trafficking is impaired. Since palmitoylation of GAD65 is required for GAD65 trafficking, we then demonstrate that palmitoylation of GAD65 is reduced in the HD model. Furthermore, overexpression of HIP14 (huntingtin-interacting protein 14), the enzyme responsible for palmitoylating GAD65 in vivo, could rescue GAD65 palmitoylation and vesicle-associated GAD65 trafficking. Taken together, our data support the idea that GAD65 palmitoylation is important for the delivery of GAD65 to inhibitory synapses and suggest that impairment of GAD65 palmitoylation by mhtt may lead to altered inhibitory neurotransmission in HD.     

Metabolomic analysis of citrus infection by 'candidatus liberibacter' reveals insight into pathogenicity

Huanglongbing (HLB), considered the most serious citrus disease in the world, is associated with the nonculturable bacterium 'Candidatus Liberibacter asiaticus' (Las). Infection of citrus by this pathogen leads to reduced plant vigor and productivity, ultimately resulting in death of the infected tree. It can take up to two years following initial infection before outward symptoms become apparent, making detection difficult. The existing knowledge gap in our understanding of Las and its pathogenesis leading to HLB has stymied development of treatments and methods to mitigate the pathogen's influence. To evaluate the influence of Las on fruit quality in both symptomatic and asymptomatic fruit, and gain further insight into the pathogenesis of the disease, a (1)H NMR metabolomics investigation, complemented with physicochemical and analyte-specific analyses, was undertaken. Comparison of the juice obtained from oranges gathered from Las(+) (symptomatic and asymptomatic) and Las(-) (healthy) trees revealed significant differences in the concentrations of sugars, amino and organic acids, limonin glucoside, and limonin. This study demonstrates differing metabolic profiles in the juice of oranges from Las(+) and Las(-) and proposes how Las may be able to evade citrus defense responses.