Copper stress proteomics highlights local adaptation of two strains of the model brown alga Ectocarpus siliculosus

Ectocarpus siliculosus is a cosmopolitan brown alga with capacity to thrive in copper enriched environments. Analysis of copper toxicity was conducted in two strains of E. siliculosus isolated from (i) an uncontaminated coast in southern Peru (Es32) and (ii) a copper polluted rocky beach in northern Chile (Es524). Es32 was more sensitive than Es524, with toxicity detected at 50 μg/L Cu, whereas Es524 displayed negative effects only when exposed to 250 μg/L Cu. Differential soluble proteome profiling for each strain exposed to sub‐lethal copper levels allowed to identify the induction of proteins related to processes such as energy production, glutathione metabolism as well as accumulation of HSPs. In addition, the inter‐strain comparison of stress‐related proteomes led to identify features related to copper tolerance in Es524, such as striking expression of a PSII Mn‐stabilizing protein and a Fucoxanthine chlorophyll a–c binding protein. Es524 also expressed specific stress‐related enzymes such as RNA helicases from the DEAD box families and a vanadium‐dependent bromoperoxidase. These observations were supported by RT‐qPCR for some of the identified genes and an enzyme activity assay for vanadium‐dependent bromoperoxidase. Therefore, the occurrence of two different phenotypes within two distinct E. siliculosus strains studied at the physiological and proteomic levels strongly suggest that persistent copper stress may represent a selective force leading to the development of strains genetically adapted to copper contaminated sites.     

Semantic knowledge influences prewired hedonic responses to odors

Background

Odor hedonic perception relies on decoding the physicochemical properties of odorant molecules and can be influenced in humans by semantic knowledge. The effect of semantic knowledge on such prewired hedonic processing over the life span has remained unclear.

Methodology/Principal Findings

The present study measured hedonic response to odors in different age groups (children, teenagers, young adults, and seniors) and found that children and seniors, two age groups characterized by either low level of (children) or weak access to (seniors) odor semantic knowledge, processed odor hedonics more on the basis of their physicochemical properties. In contrast, in teenagers and young adults, who show better levels of semantic odor representation, the role of physicochemical properties was less marked.

Conclusions/Significance

These findings demonstrate for the first time that the biological determinants that make an odor pleasant or unpleasant are more powerful at either end of the life span.     

An immunological method for quantifying antibacterial activity in Salmo salar (Linnaeus, 1758) skin mucus

Antimicrobial peptides (AMPs) are a pivotal component of innate immunity in lower vertebrates. The aim of this study was to develop an immunological method for quantifying AMPs in Salmo salar skin mucus. A known antimicrobial peptide derived from histone H1 previously purified and described from S. salar skin mucus (SAMP H1) was chemically synthesized and used to obtain antibodies for the quantification of the molecule via ELISA. Using skin mucus samples, a correlation of bacterial growth inhibition versus SAMP H1 concentration (ELISA) was established. The results provide the first evidence for quantifying the presence of active AMPs in the skin mucus of S. salar through the use of an immunological method.     

Karyotypic and molecular identification of laboratory stocks of the South American fruit fly Anastrepha fraterculus (Wied) (Diptera: Tephritidae)

The taxonomic status of the tephritid pest Anastrepha fraterculus (Wied.) is a controversial subject, mainly because of misinterpretation of the observed genetic variation. In this work, the different karyotypes and DNA polymorphism of a geographically defined population from Northeastern Argentina were studied, using derived stocks maintained in the laboratory during 25 generations. The karyotypes were analyzed using C-banding and N-banding techniques, while DNA analysis was performed through the DNA polymerase chain reaction (PCR). The variants isolated from both the wild Montecarlo population and the derived laboratory stocks were fully compatible and are present in other wild populations from South Brazil (lat 31 degrees 30' S) to Mid-Argentina (lat 34 degrees 30' S). Single-pair crosses among stocks carrying different chromosomal variants demonstrated the absence of isolation barriers. The polymorphic fragments isolated by RAPDs/PCR showed polymorphisms among stocks whereas the analysis of rDNA ITS1 exhibit a unique ITS1 length. Our results seem to indicate that all the examined variants belong to a single species with extended polymorphism and therefore do not support the hypothesis that the extended chromosomal polymorphism in A. fraterculus implies the existence of a complex of cryptic species.     

Immobilization of pectin fragments on solid supports: novel coupling by thiazolidine formation

As a prerequisite to solid-phase and sequence analyses and for the study of the fine structure of pectin, we have developed oriented and chemoselective methodologies to couple model pectin fragments onto a solid support. Polyethylene glycol polyacrylamide (PEGA) resins were selected due to their excellent swelling properties in a wide range of solvents, including water, and their easy accessibility to enzymes. Following appropriate derivatization of amino-terminated PEGA resins, oligomers of alpha-D-galacturonic acid (GalA), up to the trimer, were anchored to the support through their reducing end. In addition to reductive amination, the strategies included the formation of an oxime bond, a glycosyl hydrazide, and a pyroglutamyl ring. Further, we developed a new immobilization approach based on the formation of a thiazolidine ring. All methods proved efficient and did not require modification of the GalA oligomers prior to coupling. In addition, very mild conditions and few steps for derivatization of the support were required. Immobilization by thiazolidine ring and oxime bond formation were the preferred methods, given the stability of the linkages formed, their compatibility with aqueous solvents, the few number of steps required, and their potential for application to larger pectin fragments. Thiazolidine and pyroglutamyl anchoring were developed further by the insertion of a disulfide bond which allowed release of the saccharides under mild, selective conditions.     

Ephrins regulate the formation of terminal axonal arbors during the development of thalamocortical projections

The development of connections between thalamic afferents and their cortical target cells occurs in a highly precise manner. Thalamic axons enter the cortex through deep cortical layers, then stop their growth in layer 4 and elaborate terminal arbors specifically within this layer. The mechanisms that underlie target layer recognition for thalamocortical projections are not known. We compared the growth pattern of thalamic explants cultured on membrane substrates purified from cortical layer 4, the main recipient layer for thalamic axons, and cortical layer 5, a non-target layer. Thalamic axons exhibited a reduced growth rate and an increased branching density on their appropriate target membranes compared with non-target substrate. When confronted with alternating stripes of both membrane substrates, thalamic axons grew preferentially on their target membrane stripes. Enzymatic treatment of cortical membranes revealed that growth, branching and guidance of thalamic axons are independently regulated by attractive and repulsive cues differentially expressed in distinct cortical layers. These results indicate that multiple membrane-associated molecules collectively contribute to the laminar targeting of thalamic afferents. Furthermore, we found that interfering with the function of Eph tyrosine kinase receptors and their ligands, ephrins, abolished the preferential branching of thalamic axons on their target membranes, and that recombinant ephrin-A5 ligand elicited a branch-promoting activity on thalamic axons. We conclude that interactions between Eph receptors and ephrins mediate branch formation of thalamic axons and thereby may play a role in the establishment of layer-specific thalamocortical connections.     

Autoinhibition of X11/Mint scaffold proteins revealed by the closed conformation of the PDZ tandem

Members of the X11/Mint family of multidomain adaptor proteins are composed of a divergent N terminus, a conserved PTB domain and a pair of C-terminal PDZ domains. Many proteins can interact with the PDZ tandem of X11 proteins, although the mechanism of such interactions is unclear. Here we show that the highly conserved C-terminal tail of X11alpha folds back and inserts into the target-binding groove of the first PDZ domain. The binding of this tail occludes the binding of other target peptides. This autoinhibited conformation of X11 requires that the two PDZ domains and the entire C-terminal tail be covalently connected to form an integral structural unit. The autoinhibited conformation of the X11 PDZ tandem provides a mechanistic explanation for the unique target-binding properties of the protein and hints at potential regulatory mechanisms for the X11-target interactions.