Identification of chironomid species as natural reservoirs of toxigenic Vibrio cholerae strains with pandemic potential

Vibrio cholerae causes the fatal cholera diarrhea. Chironomids (Diptera; Chironomidae) are abundant in freshwater aquatic habitats and estuaries and are natural reservoirs of V. cholerae. Until now, only the non-O1/O139 serogroups of V. cholerae were identified in chironomids. Here, we explored whether chironomids are natural reservoirs of V. cholerae O1/O139 serogroups, which are associated with cholera endemics and pandemics. All four life stages of chironomids were sampled from two rivers, and a laboratory culture in Pune, India, and from a pond in Israel. In total, we analyzed 223 chironomid samples. The presence of V. cholerae O1/O139 serogroups was verified using molecular tools. Nine chironomid species were identified; of them, Chironomus circumdatus was the most abundant. The presence of V. cholerae serogroup O1 and the cholera toxin genes were detected in samples from all chironomid species. However, serogroup O139 was detected in only two chironomid species. Besides PCR to detect specific genes, a metagenomic analysis that was performed in three selected C. ramosus larvae, identified a list of virulence genes associated with V. cholerae. The findings provide evidence that chironomids are natural reservoirs of toxigenic V. cholerae O1/O139. Chironomid populations and V. cholerae show biannual peak patterns. A similar pattern is found for cholera epidemics in the Bengal Delta region. Thus, we hypothesize that monitoring chironomids in endemic areas of the disease may provide a novel tool for predicting and preventing cholera epidemics. Moreover, serogroup O139 was detected only in two chironomid species that have a restricted distribution in the Indian subcontinent, possibly explaining why the distribution of the O139 serogroup is limited.     

Aggregation of Human S100A8 and S100A9 Amyloidogenic Proteins Perturbs Proteostasis in a Yeast Model

Amyloid aggregates of the calcium-binding EF-hand proteins, S100A8 and S100A9, have been found in the corpora amylacea of patients with prostate cancer and may play a role in carcinogenesis. Here we present a novel model system using the yeast Saccharomyces cerevisiae to study human S100A8 and S100A9 aggregation and toxicity. We found that S100A8, S100A9 and S100A8/9 cotransfomants form SDS-resistant non-toxic aggregates in yeast cells. Using fluorescently tagged proteins, we showed that S100A8 and S100A9 accumulate in foci. After prolonged induction, S100A8 foci localized to the cell vacuole, whereas the S100A9 foci remained in the cytoplasm when present alone, but entered the vacuole in cotransformants. Biochemical analysis of the proteins indicated that S100A8 and S100A9 alone or coexpressed together form amyloid-like aggregates in yeast. Expression of S100A8 and S100A9 in wild type yeast did not affect cell viability, but these proteins were toxic when expressed on a background of unrelated metastable temperature-sensitive mutant proteins, Cdc53-1p, Cdc34-2p, Srp1-31p and Sec27-1p. This finding suggests that the expression and aggregation of S100A8 and S100A9 may limit the capacity of the cellular proteostasis machinery. To test this hypothesis, we screened a set of chaperone deletion mutants and found that reducing the levels of the heat-shock proteins Hsp104p and Hsp70p was sufficient to induce S100A8 and S100A9 toxicity. This result indicates that the chaperone activity of the Hsp104/Hsp70 bi-chaperone system in wild type cells is sufficient to reduce S100A8 and S100A9 amyloid toxicity and preserve cellular proteostasis. Expression of human S100A8 and S100A9 in yeast thus provides a novel model system for the study of the interaction of amyloid deposits with the proteostasis machinery.     

Proteinaceous infectious behavior in non-pathogenic proteins is controlled by molecular chaperones

External stresses or mutations may cause labile proteins to lose their distinct native conformations and seek alternatively stable aggregated forms. Molecular chaperones that specifically act on protein aggregates were used here as a tool to address the biochemical nature of stable homo- and hetero-aggregates from non-pathogenic proteins formed by heat-stress. Confirmed by sedimentation and activity measurements, chaperones demonstrated that a single polypeptide chain can form different species of aggregates, depending on the denaturing conditions. Indicative of a cascade reaction, sub-stoichiometric amounts of one fast-aggregating protein strongly accelerated the conversion of another soluble, slow-aggregating protein into insoluble, chaperone-resistant aggregates. Chaperones strongly inhibited seed-induced protein aggregation, suggesting that they can prevent and cure proteinaceous infectious behavior in homo- and hetero-aggregates from common and disease-associated proteins in the cell.     

Expansion-repression mechanism for scaling the Dpp activation gradient in Drosophila wing imaginal discs

Maintaining a proportionate body plan requires the adjustment or scaling of organ pattern with organ size. Scaling is a general property of developmental systems, yet little is known about its underlying molecular mechanisms. Using theoretical modeling, we examine how the Dpp activation gradient in the Drosophila wing imaginal disc scales with disc size. We predict that scaling is achieved through an expansion-repression mechanism [1] whose mediator is the widely diffusible protein Pentagone (Pent). Central to this mechanism is the repression of pent expression by Dpp signaling, which provides an effective size measurement, and the Pent-dependent expansion of the Dpp gradient, which adjusts the gradient with tissue size. We validate this mechanism experimentally by demonstrating that scaling requires Pent and further, that scaling is abolished when pent is ubiquitously expressed. The expansion-repression circuit can be readily implemented by a variety of molecular interactions, suggesting its general utilization for scaling morphogen gradients during development.     

Semaphorin3A regulates axon growth independently of growth cone repulsion via modulation of TrkA signaling

Regulation of axon growth is a critical event in neuronal development. Nerve growth factor (NGF) is a strong inducer of axon growth and survival in the dorsal root ganglia (DRG). Paradoxically, high concentrations of NGF are present in the target region where axon growth must slow down for axons to accurately identify their correct targets. Semaphorin3A (Sema3A), a powerful axonal repellent molecule for DRG neurons, is also situated in their target regions. NGF is a modulator of Sema3A-induced repulsion and death. We show that Sema3A is a regulator of NGF-induced neurite outgrowth via the TrkA receptor, independent of its growth cone repulsion activity. First, neurite outgrowth of DRG neurons is more sensitive to Sema3A than repulsion. Second, at concentrations sufficient to significantly inhibit Sema3A-induced repulsion, NGF has no effect on Sema3A-induced axon growth inhibition. Third, Sema3A-induced outgrowth inhibition, but not repulsion activity, is dependent on NGF stimulation. Fourth, Sema3A attenuates TrkA-mediated growth signaling, but not survival signaling, and over-expression of constitutively active TrkA blocks Sema3A-induced axon growth inhibition, suggesting that Sema3A activity is mediated via regulation of NGF/TrkA-induced growth. Finally, quantitative analysis of axon growth in vivo supports the possibility that Sema3A affects axon growth, in addition to its well-documented role in axon guidance. We suggest a model whereby NGF at high concentrations in the target region is important for survival, attraction and inhibition of Sema3A-induced repulsion, while Sema3A inhibits its growth-promoting activity. The combined and cross-modulatory effects of these two signaling molecules ensure the accuracy of the final stages in axon targeting.     

Light-dependent fluorescence in the coral Galaxea fascicularis

The concept of ecological stoichiometry has been useful for understanding nutrient dynamics in aquatic food webs; however, the majority of studies have focused on autotrophic systems, leaving detritus-based food webs largely understudied. In addition, most detritus-based studies have explored enrichment in high-gradient, low-nutrient systems, despite the fact that many of the streams most likely to face enrichment (those surrounded by agriculture) are low-gradient and contain inherently higher dissolved nutrient concentrations due to differences in soil type, geomorphology, and atmospheric deposition. Constraints on consumer growth due to consumer-resource imbalances have been documented in these low-nutrient streams, but the extent to which consumer growth may be limited in higher-nutrient, detritus-based streams is unknown. We investigated the impact of dissolved nutrients (N and P) on mayfly growth, using artificial streams simulating a high-nutrient detritus-based system. Mayflies were reared and sampled under two total nutrient concentrations, one meant to mimic a more natural undisturbed (ambient) watershed and one to mimic a disturbed (enriched) watershed. Under each of these conditions two N:P ratios (low and high) were tested. The low N:P treatments produced higher mayfly growth under both ambient and enriched conditions, showing that nutrient limitation can occur even in high-nutrient streams.     

<Emphasis Type="Italic">Euphyllia paradivisa</Emphasis>, a successful mesophotic coral in the northern Gulf of Eilat/Aqaba,Red Sea

Mesophotic coral ecosystems (MCEs) host a thriving community of biota that has remained virtually unexplored. Here we report for the first time on a large population of the endangered coral species Euphyllia paradivisa from the MCEs of the Gulf of Eilat/Aqaba (GOE/A), Red Sea. The mesophotic zone in some parts of the study site harbors a specialized coral community predominantly comprising E. paradivisa (73 % of the total coral cover), distributed from 36 to 72 m depth. Here we sought to elucidate the strict distribution but high abundance of E. paradivisa in the MCEs at the GOE/A. We present 4 yr of observations and experiments that provide insight into the physiological plasticity of E. paradivisa: its low mortality rates at high light intensities, high competitive abilities, successful symbiont adaptation to the shallow-water environment, and tolerance to bleaching conditions or survival during prolonged bleaching. Despite its ability to survive under high irradiance in shallow water, E. paradivisa is not found in the shallow reef of the GOE/A. We suggest several factors that may explain the high abundance and exclusivity of E. paradivisa in the MCE: its heterotrophic capabilities; its high competition abilities; the possibility of it finding a deep-reef refuge there from fish predation; and its concomitant adaptation to this environment.     

Response of the tooth-periodontal ligament-bone complex to load: A microCT study of the minipig molar

One strategy evolved by teeth to avoid irreversible damage is to move and deform under the loads incurred during mastication. A key component in this regard is the periodontal ligament (PDL). The role of the bone underlying the PDL is less well defined. We study the interplay between the PDL and the underlying alveolar bone when loaded in the minipig. Using an Instron loading device we confirmed that the force-displacement curves of the molars and premolars of relatively fresh minipig intact mandibles are similar to those obtained for humans and other animals. We then used this information to obtain 3D images of the teeth before and after loading the tooth in a microCT such that the load applied is in the third linear part of the force displacement curve. We observed that at many locations there is a complimentary topography of the cementum and alveolar bone surface, strongly suggesting an active interplay between the tooth and the bone during mastication. We also observed that the loaded tooth does not come into direct contact with the underlying bone surface. A highly compressed layer of PDL is present between the tooth and the bone. The structure of the bone in the upper furcation region has a unique appearance with little obvious microstructure, abundant pores that have a large size range and at many locations the bone at the PDL interface has a needle-like shape. We conclude that there is a close interaction between the tooth, the PDL and the underlying alveolar bone during mastication. The highly compressed PDL layer that separates the tooth from the bone may fulfill a key shock absorbing function.     

A galling aphid furnishes its home with a built-in pipeline to the host food supply

Galling insects modify the developmental pathways of their host plants and create a protected and favourable microhabitat for their offspring. Galling aphids reproduce in their galls and the resulting clones often comprise hundreds of individuals. We followed the histological changes in the host Pistacia palaestina (Anacardiaceae) induced by the galling aphid Geoica wertheimae (Aphidoidea, Pemphigidae: Fordinae). We showed that the leaf tissues are altered in the gall in a way that gives the aphids easy access to the vascular system from which they obtain their nourishment. Specifically, the cuticle that lines the normal leaf epidermal cells is absent on the surface of the inner gall cavity, and the normal palisade cells are replaced by parenchymatous tissue with numerous wide latex ducts. Associated with these ducts, many new sieve tubes (phloem elements) are formed just a few cell layers below the inner gall surface. This arrangement enables the hundreds of aphids to feed simultaneously and continuously in the gall throughout the summer.