Identification and characterization of a eukaryotically encoded rubredoxin in a cryptomonad alga

We have identified an open reading frame with homology to prokaryotic rubredoxins (rds) on a nucleomorph chromosome of the cryptomonad alga Guillardia theta. cDNA analysis let us propose that the rd preprotein has an NH(2)-terminal extension that functions as a transit peptide for import into the plastid. Compared to rds found in non-photosynthetic prokaryotes or found in bacteria that exhibit an anoxigenic photosynthesis apparatus, nucleomorph rd has a COOH-terminal extension, which shows high homology exclusively to the COOH-termini of cyanobacterial rds as well as to a hypothetical rd in the Arabidopsis genome. This extension can be divided into a putative membrane anchor and a stretch of about 20 amino acids with unknown function linking the common rd fold to this anchor. Overexpression of nucleomorph rd in Escherichia coli using a T7 RNA polymerase/promotor system resulted in a mixture of iron-containing holorubredoxin and zinc-substituted protein. Preliminary spectroscopic studies of the iron form of nucleomorph rd suggest the existence of a native rd-type iron site. One-dimensional nuclear magnetic resonance spectroscopy of recombinant Zn-rd suggests the presence of a stable tertiary fold similar to that of other rd structures determined previously.     

Importance of grazing and soil acidity for plant community composition and trait characterisation in coastal dune grasslands

Question: Does grazing by large herbivores affect species composition or community‐wide variation in plant functional traits? Location: Dune grasslands at the Belgian coast. Methods: Plant cover and soil data were collected in 146 plots that were randomly selected at 26 grazed and ungrazed grassland sites. Plant community composition was assessed by Detrended Correspondence Analysis and mean values of plant trait categories were calculated across the plots. Results: Differentiation of plant composition and community‐wide plant trait characteristics was largely determined by grazing, soil acidity and their interaction. In ungrazed situations, a clear floristic distinction appears between acidic (non‐calcareous) and alkaline (calcareous) grasslands. In grazed situations, these floristic differences largely disappeared, indicating that grazing results in a decrease of natural variation in species composition. At higher soil pH, a larger difference in plant community composition and community‐wide plant traits was observed between grazed and ungrazed plots. In ungrazed situations, shifts in plant functional traits along the acidity gradient were observed. Conclusions: Grazing is responsible for shifts in plant community composition, and hence a decrease in plant diversity among grasslands at opposing acidity conditions in coastal dune grasslands. Therefore, care should be taken when introducing grazing as a system approach for nature conservation in dune grasslands as it may eliminate part of the natural variation in plant diversity along existing abiotic gradients.     

Image-guided navigation for the control interstitial laser therapy of vascular malformations in the head and neck region]

Laser-induced interstitial thermal therapy (LITT) is a proven minimally invasive surgical technique for the treatment of haemangiomas and vascular malformations, and various tumours. The intra-lesion application of thermal energy destroys regional tissue. The percutaneous placement of the laser fibre for photocoagulation is done without the benefit of direct visual control. Image-data-based LITT was performed in patients (five procedures) with extensive venous malformations in the maxillofacial area. The system comprised a specially developed Nd:YAG laser fibre introducer set used in conjunction with fused high-resolution computed tomography, and magnetic resonance image-data--based surgical navigation. In all cases, follow-up examination clearly showed a diminishment in tumour volume, and all patients reported significant subjective improvement. The results suggest that navigation-guided LITT can be performed safely, preserving vital structures from collateral thermal damage.     

Predicting future community composition from random soil seed bank sampling – evidence from a drained lake bottom

Questions: What is the accuracy and reliability of the commonly used random soil sampling methodology for predicting seedling density, species richness and composition of the emerging seedling community? Location: Lake Kraenepoel, western Belgium. Methods: We compared density, species composition and observed and rarefactioned species richness of the seedling community emerging on a soft water lake bed exposed after drainage with the seedling community germinating in the laboratory from random soil samples in the same plots. Results: Seedling density did not differ between the two methods and there was a significant correlation between seedling density on the exposed lake bed and in the soil samples. This indicates that future seedling density can be reliably predicted based on soil sampling, in particular for the most abundant species. The most frequently occurring and abundant species among the seedlings in the soil samples were also the most frequent and abundant species germinating on the exposed lake bed. In contrast, species richness was much higher on the exposed lake bed than in the soil samples, and this difference was still significant for annual species after correction for differences in sampling intensity by rarefaction. We found no correlation between the number of species retrieved by the two methods. Although seedlings of rare and target species emerged on the lake bed, random soil sampling clearly failed to detect seeds of most of these species. Conclusions: Random soil sampling at a commonly used intensity and using the standard germination conditions can accurately predict future total seedling density and the density of the most abundant species. However, the method is not reliable for predicting the probability of establishment of populations of uncommon species. When executing a seed bank study, sampling intensity and germination conditions need to be adapted to the nature and the level of detail of the research question to be answered.     

Foraging for mates in the hyperparasitic wasp, Dendrocerus carpenteri: impact of unfavourable weather conditions and parasitoid age

Males of the aphid hyperparasitoid Dendrocerus carpenteri (Curtis) were attracted by a sex pheromone released by conspecific females. The intensity of this cue, and thus female attractiveness, depended both on the female's mating status and her age. Only virgin females younger than 2 h were consistently recognized as mates by foraging males. Male age did not influence foraging and mating success. Empty mummies, from which females had emerged within the previous 10 min were attractive to males and examined intensively. Rain reduced the searching success of males, although the host plant Vicia faba provided sheltered places. Wind did not reduce mating success but prevented both sexes from leaving the host plant. Since the time of female attractiveness seems to be very limited, wind may have an enormous effect on the mating success of D. carpenteri in the field and thus on the population dynamics of this species. Received: 5 October 1998 / Accepted: 16 December 1998     

Heterogeneous genetic invasions of three insecticide resistance mutations in Indo‐Pacific populations of Aedes aegypti (L.)

Nations throughout the Indo‐Pacific region use pyrethroid insecticides to control Aedes aegypti, the mosquito vector of dengue, often without knowledge of pyrethroid resistance status of the pest or origin of resistance. Two mutations (V1016G + F1534C) in the sodium channel gene (Vssc) of Ae. aegypti modify ion channel function and cause target‐site resistance to pyrethroid insecticides, with a third mutation (S989P) having a potential additive effect. Of 27 possible genotypes involving these mutations, some allelic combinations are never seen whereas others predominate. Here, five allelic combinations common in Ae. aegypti from the Indo‐Pacific region are described and their geographical distributions investigated using genome‐wide SNP markers. We tested the hypothesis that resistance allele combinations evolved de novo in populations versus the alternative that dispersal of Ae. aegypti between populations facilitated genetic invasions of allele combinations. We used latent factor mixed‐models to detect SNPs throughout the genome that showed structuring in line with resistance allele combinations and compared variation at SNPs within the Vssc gene with genome‐wide variation. Mixed‐models detected an array of SNPs linked to resistance allele combinations, all located within or in close proximity to the Vssc gene. Variation at SNPs within the Vssc gene was structured by resistance profile, whereas genome‐wide SNPs were structured by population. These results demonstrate that alleles near to resistance mutations have been transferred between populations via linked selection. This indicates that genetic invasions have contributed to the widespread occurrence of Vssc allele combinations in Ae. aegypti in the Indo‐Pacific region, pointing to undocumented mosquito invasions between countries.     

SECRETION OF LIPASES IN THE DIGESTIVE TRACT OF THE CRICKET Gryllus bimaculatus

Little is known concerning the sites and the ratios of the lipase secretions in insects, therefore we undertook an examination of the lipase secretion of fed and unfed adult female Gryllus bimaculatus. The ratio of triacylglyceride lipase, diacylglyceride lipase, and phosphatidylcholine lipase secreted by fed females in the caecum and ventriculus is 1:1.4:0.4. These activities decrease in the caecum by 30–40% in unfed females. The total lipase activity (TLA) in the caecum is about 10 times that in the ventriculus. Minimal lipase secretion occurs before and during the final moult, and remains at this level in unfed crickets, indicating a basal secretion rate. In 2‐day‐old fed females, about 10% of the TLA in the entire gut is found in the crop, about 70% in the caecum, 20% in the ventriculus, and 3% in the ileum. Lipases in the ventriculus are recycled back to the caecum and little is lost in the feces. Oleic acid stimulated in vitro lipase secretion, but lipids did not. Feeding stimulated lipase secretion, starvation reduced lipase secretion, but this does not prove a direct prandal regulation of secretion, because feeding also induced a size and volume increase of the caecum.     

TFF3 and EGF induce different migration patterns of intestinal epithelial cells in vitro and trigger increased internalization of E-cadherin.

BACKGROUND/AIMS: TFF3, a member of the TFF (trefoil factor family) peptides, and epidermal growth factor (EGF) actively support the repair of mucosal barriers, particularly during restitution. The aim of this study was to compare the motogenic effects of TFF3 and EGF. METHODS: The influence of recombinant human TFF3 (dimeric form) and EGF on the migration of IEC-18 cells was characterized in an in vitro restitution model (scratch wound assay) with the help of time-lapse video microscopy, morphometry, and immunocytochemistry including confocal laser scanning microscopy. RESULTS: TFF3- and EGF-treated cells re-populated the wounded area via different migration patterns; TFF3 treatment resulted in the formation of continuous sheets of migrating cells with only a few gaps. In contrast, EGF-treated cells formed a network of migrating cells (often with a fibroblast-like morphology) with numerous gaps and only punctual contacts. TFF3 and EGF treatment also changed the localization of E-cadherin indicating endocytotic recycling and/or degradation of E-cadherin. CONCLUSION: TFF3, in contrast to EGF, enhanced a collective cell migration ensuring a precise coverage of the re-populated area avoiding gaps.     

nAChR‐induced octopamine release mediates the effect of nicotine on a startle response in Drosophila melanogaster

Biogenic amines (BAs) play a central role in the generation of complex behaviors in vertebrates and invertebrates, including the fly Drosophila melanogaster. The comparative advantages of Drosophila as a genetic model to study the contribution of BAs to behaviors stumble upon the difficulty to access the fly brain to ask relevant physiological questions. For instance, it is not known whether the activation of nicotinic acetylcholine receptors (nAChRs) induces the release of BAs in fly brain, a phenomenon associated to several behaviors in vertebrates. Here, we describe a new preparation to study the efflux of BAs in the adult fly brain by in vitro chronoamperometry. Using this preparation we show that nAChR agonists including nicotine induce a fast, transient, dose‐dependent efflux of endogenous BAs, an effect mediated by α‐bungarotoxin‐sensitive nAChRs. By using different genetic tools we demonstrate that the BA whose efflux is induced by nAChR activation is octopamine (Oct). Furthermore, we show that the impairment of a mechanically induced startle response after nicotine exposure is not observed in flies deficient in Oct transmission. Thus, our data show that the efflux of BAs in Drosophila brain is increased by nAChR activation as in vertebrates, and that then AChR‐induced Oct release could have implications in a nicotine‐induced behavioral response.