Demonstration of functional coupling between dopamine synthesis and its packaging into synaptic vesicles

We have previously shown that the membrane-associated form of the GABA-synthesizing enzyme, glutamate decarboxylase 65 (GAD₆₅), is activated by synaptic vesicle proton gradient-mediated protein phosphorylation. We now report that the rate-limiting enzyme in dopamine (DA) biosynthesis, tyrosine hydroxylase (TH), is regulated similarly to GAD₆₅. The membrane-associated form of TH (MTH) was activated by conditions favoring protein phosphorylation (e.g. ATP) and was inhibited by phosphatase (e.g. calf intestine phosphatase). Furthermore, the ATP-mediated activation of MTH was abolished by conditions that disrupted the proton gradient of synaptic vesicles, e.g. the presence of carbonyl cyanidem-chorophenylhydrazone, gramicidin, or the V-type ATPase inhibitor (bafilomycin), but not the P-type ATPase inhibitor (vanadate). Moreover, DA newly synthesized from tyrosine by MTH and membrane-associated aromatic amino acid decarboxylase was taken up preferentially rather than pre-existing DA. Therefore, the previously proposed model showing close coupling between GABA synthesis and GABA packaging into synaptic vesicles by vesicular GABA transporters is also applicable to the DA system. Hence, it is concluded that there is a general coupling mechanism between neurotransmitter synthesis and packaging of transmitter into synaptic vesicles.     

No reduction of female sexual receptivity following mating in a stalk‐eyed fly,Cyrtodiopsis dalmanni (Diptera: Diopsidae)

The level of female sexual receptivity is an important component of male and female reproductive success. In many insects, mating itself causes a sharp decline in female receptivity. This can be a direct result of the physical act of mating, or because of actions of sperm or seminal fluid proteins. The degree to which males can decrease female receptivity will directly affect their reproductive success, by altering the chance that their sperm will be used in fertilizations in the interval before the female mates again. In this study, we investigated the effect of mating on female receptivity in the sexually dimorphic stalk‐eyed fly, Cyrtodiopsis dalmanni. Our results showed no evidence for mating‐induced reductions in female receptivity. In addition, we found that matings with males that differed in eyespan did not cause differences in the level of female receptivity. There was also no evidence that females remated sooner when presented with large eyespan males. These results are surprising, given the indirect benefits that females gain from matings with large eyespan males. Finally we demonstrate that males do not appear to discriminate between females on the basis of female mating status.     

Cumulative solar irradiance and potential large-scale sea ice algae distribution off East Antarctica (30°E–150°E)

We present a computational model of the large-scale cumulative light exposure of sea ice in the Southern Ocean off East Antarctica (30°E–150°E). The model uses remotely sensed or modelled sea ice concentration, snow depth over sea ice, and solar irradiance data, and tracks sea ice motion over the season of interest in order to calculate the cumulative exposure of the ice field to photosynthetically active radiation (PAR). Light is the limiting factor to sea ice algal growth over winter and early spring, and so the results have implications for the estimation of algal biomass in East Antarctica. The model results indicate that highly light-exposed ice is restricted to within a few degrees of the coast in the eastern part of the study region, but extends much further north in the 30°E–100°E sector. The relative influences of sea ice motion, solar flux, and snow depth variations on interannual variations in model predictions were evaluated. The model estimates of cumulative PAR were found to correlate with satellite estimates of subsequent open-water chlorophyll-a concentration, consistent with the notion that sea ice algae can provide inocula for phytoplankton blooms.     

New reactive polymer for protein immobilisation on sensor surfaces

Immobilisation of biorecognition elements on transducer surfaces is a key step in the development of biosensors. The immobilisation needs to be fast, cheap and most importantly should not affect the biorecognition activity of the immobilised receptor. A novel protocol for the covalent immobilisation of biomolecules containing primary amines using an inexpensive and simple polymer is presented. This tri-dimensional (3D) network leads to a random immobilisation of antibodies on the polymer and ensures the availability of a high percentage of antibody binding sites. The reactivity of the polymer is based on the reaction between primary amines and thioacetal groups included in the polymer network. These functional groups (thioacetal) do not need any further activation in order to react with proteins, making it attractive for sensor fabrication. The novel polymer also contains thiol derivative groups (disulphide groups or thioethers) that promote self-assembling on a metal transducer surface. For demonstration purposes the polymer was immobilised on Au Biacore chips. The resulting polymer layer was characterised using contact angle meter, atomic force microscopy (AFM) and ellipsometry. A general protocol suitable for the immobilisation of bovine serum albumin (BSA), enzymes and antibodies such as polyclonal anti-microcystin-LR antibody and monoclonal anti-prostate specific antigen (anti-PSA) antibody was then optimised. The affinity characteristics of developed immunosensors were investigated in reaction with microcystin-LR, and PSA. The calculated detection limit for analytes depended on the properties of antibodies. The detection limit for microcystin-LR was 10 ngmL(-1) and for PSA 0.01 ngmL(-1). The non-specific binding of analytes to synthesised polymers was very low. The polymer-coated chips were stored for up to 2 months without any noticeable deterioration in their ability to react with proteins. These findings make this new polymer very promising for the development of low-cost, easy to prepare and sensitive biosensors.     

Association of Body Mass and Brain Activation during Gastric Distention: Implications for Obesity

Background

Gastric distention (GD), as it occurs during meal ingestion, signals a full stomach and it is one of the key mechanisms controlling food intake. Previous studies on GD showed lower activation of the amygdala for subjects with higher body mass index (BMI). Since obese subjects have dopaminergic deficits that correlate negatively with BMI and the amygdala is innervated by dopamine neurons, we hypothesized that BMI would correlate negatively with activation not just in the amygdala but also in other dopaminergic brain regions (midbrain and hypothalamus).

Methodology/Principal Findings

We used functional magnetic resonance imaging (fMRI) to evaluate brain activation during GD in 24 healthy subjects with BMI range of 20–39 kg/m². Using multiple regression and cross-correlation analyses based on a family-wise error corrected threshold P = 0.05, we show that during slow GD to maximum volumes of 500 ml and 700 ml subjects with increased BMI had increased activation in cerebellum and left posterior insula, and decreased activation of dopaminergic (amygdala, midbrain, hypothalamus, thalamus) and serotonergic (pons) brain regions and anterior insula, regions that were functionally interconnected with one another.

Conclusions

The negative correlation between BMI and BOLD responses to gastric distention in dopaminergic (midbrain, hypothalamus, amygdala, thalamus) and serotonergic (pons) brain regions is consistent with disruption of dopaminergic and serotonergic signaling in obesity. In contrast the positive correlation between BMI and BOLD responses in posterior insula and cerebellum suggests an opposing mechanism that promotes food intake in obese subjects that may underlie their ability to consume at once large food volumes despite increasing gastric distention.     

Identification of endangered Hawaiian ducks (Anas wyvilliana), introduced North American mallards (A. platyrhynchos) and their hybrids using multilocus genotypes

Hawaiian ducks (Anas wyvilliana), or koloa, are endemic to the Hawaiian Islands and are listed as a federal and state endangered species. Hybridization between koloa and introduced mallards (A. platyrhynchos) is believed to be a primary threat to the recovery of koloa. We evaluated the utility of two sets of nuclear markers (microsatellite loci and amplified fragment length polymorphisms) and a variable portion of the mitochondrial DNA control region to distinguish among koloa, mallards, and hybrids. We show that microsatellite and AFLP markers can be used to distinguish between koloa and mallard-koloa hybrids with a high degree of confidence. For all but one of the putative koloa in our sample, the posterior probability of belonging to the koloa category was >0.90. Similarly all but one of the mallard-koloa hybrids were assigned to the hybrid category with posterior probabilities >0.98. Subsets of markers led to poorer resolution among koloa, mallard and hybrid categories. Among a sample of 61 koloa, hybrids and mallards, we found 25 different mtDNA haplotypes, belonging to two groups of haplotypes (A and B) identified previously in mallards and their relatives. All putative koloa samples exhibited group B haplotypes, of which 65% comprised one haplotype, while the rest were divided among four haplotypes. All Hawai’i mallard samples exhibited haplotypes that belonged to group A. Hybrids and California mallards exhibited haplotypes belonging to both groups, but a majority were of group A, suggesting that hybridization may more commonly involve mating between Hawai’i mallard females and koloa males.     

Metabolomics‐driven quantitative analysis of ammonia assimilation in E. coli

Despite extensive study of individual enzymes and their organization into pathways, the means by which enzyme networks control metabolite concentrations and fluxes in cells remains incompletely understood. Here, we examine the integrated regulation of central nitrogen metabolism in Escherichia coli through metabolomics and ordinary‐differential‐equation‐based modeling. Metabolome changes triggered by modulating extracellular ammonium centered around two key intermediates in nitrogen assimilation, α‐ketoglutarate and glutamine. Many other compounds retained concentration homeostasis, indicating isolation of concentration changes within a subset of the metabolome closely linked to the nutrient perturbation. In contrast to the view that saturated enzymes are insensitive to substrate concentration, competition for the active sites of saturated enzymes was found to be a key determinant of enzyme fluxes. Combined with covalent modification reactions controlling glutamine synthetase activity, such active‐site competition was sufficient to explain and predict the complex dynamic response patterns of central nitrogen metabolites.     

Local population density and group composition influence the signal‐preference relationship in Enchenopa treehoppers (Hemiptera: Membracidae)

Many animals exhibit social plasticity – changes in phenotype or behaviour in response to experience with conspecifics that change how evolutionary processes like sexual selection play out. Here, we asked whether social plasticity arising from variation in local population density in male advertisement signals and female mate preferences influences the form of sexual selection. We manipulated local density and determined whether this changed how the distribution of male signals overlapped with female preferences – the signal preference relationship. We specifically look at the shape of female mate preference functions, which, when compared to signal distributions, provide hypotheses about the form of sexual selection. We used Enchenopa binotata treehoppers, a group of plant‐feeding insects that exhibit natural variation in local densities across individual host plants, populations, species and years. We measured male signal frequency and female preference functions across the density treatments. We found that male signals varied across local social groups, but not according to local density. By contrast, female preferences varied with local density – favouring higher signal frequencies in denser environments. Thus, local density changes the signal–preference relationship and, consequently, the expected form of sexual selection. We found no influence of sex ratio on the signal–preference relationship. Our findings suggest that plasticity arising from variation in local group density and composition can alter the form of sexual selection with potentially important consequences both for the maintenance of variation and for speciation.     

Spacing and movement in the green porcelain crab Petrolisthes armatus: evidence for male competition and mate guarding

The green porcelain crab, Petrolisthes armatus, is a common invasive species on inter-tidal oyster reefs in the South Atlantic Bight whose behavior is largely unknown. We assessed the effects of the presence of opposite-sex conspecifics on adult crab spacing at a low density to infer potential mate acquisition behaviors. Adult crabs held in all-male, all-female, and mixed-sex treatments were observed twice daily over five days to determine nearest-neighbor (NN) distances and relative activity. Males in the mixed-sex treatment with the shortest NN distances (NN₁) were most commonly (1) closest to females, and, when compared to NN₁ males in the all-male treatment, were (2) closer to their NN and (3) had lower activity levels. Female movement did not differ between treatments. Percent ovigerous females at the end of trials were higher in the mixed-sex treatment, reflecting mating activity, which when observed, involved inter-molt females. Mate guarding, rather than pure-searching behavior, was the mating behavior most consistent with observed spacing and movement patterns.