Preservation of winter social dominance status in Brent Geese Branta bernicla bernicla within and across winters

Dominant and subordinate individuals in a group may benefit from the stability of the social dominance organisation, avoiding excessive waste of time and energy in aggressive interactions and reducing injury risks. Nevertheless, the likely evolutionary incentive for individuals to become, and furthermore to stay, dominant may destabilise such dominance hierarchies. In this context, the relative importance of fixed (e.g. sex, morphological size) and fluctuating (e.g. body condition, mating status, reproductive success, social unit size) traits influencing the establishment and preservation of dominance relationships could play a key role in group structure. We investigated the relative role of fixed and fluctuating traits on social status in Dark-bellied Brent Geese Branta bernicla bernicla which form large fairly unstable groups both within and across winters. We compared individual dominance scores of ringed Brent Geese during four consecutive winters. Brent Geese conserved their dominance score within a given winter irrespective of their age but were generally unable to conserve it across consecutive winters. As winter dominance scores correlated best with social unit size, dominance status thus appeared to be mostly a by-product of a fluctuating trait: breeding success in the previous summer. When we considered only adults that had the same social unit size during two consecutive winters, we observed a significant preservation of dominance scores. This result suggests that a fixed trait such as sex or morphological size may still play a role in setting dominance status.     

ICEEc2, a New Integrative and Conjugative Element Belonging to the pKLC102/PAGI-2 Family,Identified in Escherichia coli Strain BEN374

The diversity of the Escherichia coli species is in part due to the large number of mobile genetic elements that are exchanged between strains. We report here the identification of a new integrative and conjugative element (ICE) of the pKLC102/PAGI-2 family located downstream of the tRNA gene pheU in the E. coli strain BEN374. Indeed, this new region, which we called ICEEc2, can be transferred by conjugation from strain BEN374 to the E. coli strain C600. We were also able to transfer this region into a Salmonella enterica serovar Typhimurium strain and into a Yersinia pseudotuberculosis strain. This transfer was then followed by the integration of ICEEc2 into the host chromosome downstream of a phe tRNA gene. Our data indicated that this transfer involved a set of three genes encoding DNA mobility enzymes and a type IV pilus encoded by genes present on ICEEc2. Given the wide distribution of members of this family, these mobile genetic elements are likely to play an important role in the diversification of bacteria.The fantastic diversity of the Escherichia coli species has been known for a long time. With modern sequencing strategies, the molecular bases of this diversity are now being unraveled (49). Analyzing the genome of 20 E. coli strains, Touchon et al. recently showed that only a minority of genes, approximately 1,900 genes, were shared by all E. coli strains and constituted the core genome of the E. coli species (50). Additionally, the total number of genes found in all E. coli strains, the pan-genome, is an order of magnitude larger than this core genome (50). The non-core genome of a strain, also called flexible gene pool, is therefore made of a wide diversity of genes. This genetic diversity of the E. coli species translates into a diversity of phenotypic properties. While most E. coli strains are commensal of the gastrointestinal tract of humans and warm-blooded animals, a significant number are responsible for different diseases in humans and animals (22), including extraintestinal infections in chickens; strains isolated from such cases are designated by the term APEC for avian pathogenic E. coli (10).This diversity arises from frequent horizontal gene transfers of mobile genetic elements such as transposons, plasmids, phages, genomic islands, or integrative and conjugative elements (ICEs) (11, 21, 34). Among these mobile genetic elements, ICEs have a particular place as they share properties with both plasmids, genomic islands, and transposons; they can be defined as elements that encode all the necessary machineries that allow their excision from the chromosome, their transfer to a recipient strain, and their integration into the recipient strain''s genome (5, 6, 46, 54). Well-known representatives of this class of genetic elements include Tn916 discovered in Enterococcus faecalis, the conjugative transposon CTnDOT in Bacteroides thetaiotaomicron, ICEKp1 in Klebsiella pneumoniae, SXT/R391-related elements, PFGI-1 in Pseudomonas fluorescens, and the clc element in Pseudomonas sp. strain B13 as well as ICEBs1 in Bacillus subtilis and ICEEc1 in the E. coli strain ECOR31 (1, 39, 44, 46, 54). Typically, ICEs contain at least three modules that are required for key steps in the ICE''s life cycle: an excision/integration module, a transfer module, and a regulation module (54). Besides these, ICEs often contain cargo regions that confer on their host a diverse array of properties, such as virulence properties (ICEEc1), antibiotic resistance (SXT), or degradation of chemical compounds (clc). Because of their self-transfer abilities and their diverse accessory gene repertoires, ICEs are very likely to play a major role in bacteria evolution (46).A new family of ICEs has recently gained interest and was named the pKLC102/PAGI-2 family. The first element of this family, the clc element, was discovered in Pseudomonas sp. strain B13 and confers on the bacteria the possibility to degrade aromatic compounds (42). The transfer of this element was discovered long before its complete sequence was characterized (16). Other members of this family include several elements present in Pseudomonas strains such as PAGI-1 and PAGI-2 as well as the pKLC102 element first considered to be a plasmid but later on shown to be an ICE because of its ability to integrate into the chromosome of its host (23, 52). pKLC102/PAGI-2 elements share a set of core genes (33) and, like most ICEs and genomic islands, are all integrated downstream of tRNA genes (26, 52). The transfer between strains has been demonstrated, albeit with different frequencies, for only a few members, such as the clc element, Pseudomonas aeruginosa pathogenicity island 1 (PAPI-1), and ICEHin1056 from Haemophilus influenzae (20, 37, 41); this transfer involves the type IV pilus (20), the integrase (40), and in some cases the formation of a circular intermediate of the excised ICE (24).In order to identify new accessory genes of APEC strains, we previously described tRNA loci in the E. coli genome that could represent potential insertion sites for new genomic islands (18). We had already used this strategy to characterize the AGI-3 region that is involved in the virulence of an avian pathogenic E. coli strain and that confers the ability to grow on fructooligosaccharides (7, 43). During this tRNA screening, we showed that genomic islands might potentially be present downstream of the tRNA genes argW, leuX, pheU, pheV, selC, serU, and thrW in several APEC strains.In this report, we describe the identification of a new genomic island located downstream of pheU in the APEC strain BEN374. This region, which we named ICEEc2, was fully sequenced, and its properties were analyzed in detail; ICEEc2 is a new ICE found in E. coli and belongs to the pKLC102/PAGI-2 family described above.     

Molecular Basis for the Dual Function of Eps8 on Actin Dynamics: Bundling and Capping

Actin capping and cross-linking proteins regulate the dynamics and architectures of different cellular protrusions. Eps8 is the founding member of a unique family of capping proteins capable of side-binding and bundling actin filaments. However, the structural basis through which Eps8 exerts these functions remains elusive. Here, we combined biochemical, molecular, and genetic approaches with electron microscopy and image analysis to dissect the molecular mechanism responsible for the distinct activities of Eps8. We propose that bundling activity of Eps8 is mainly mediated by a compact four helix bundle, which is contacting three actin subunits along the filament. The capping activity is mainly mediated by a amphipathic helix that binds within the hydrophobic pocket at the barbed ends of actin blocking further addition of actin monomers. Single-point mutagenesis validated these modes of binding, permitting us to dissect Eps8 capping from bundling activity in vitro. We further showed that the capping and bundling activities of Eps8 can be fully dissected in vivo, demonstrating the physiological relevance of the identified Eps8 structural/functional modules. Eps8 controls actin-based motility through its capping activity, while, as a bundler, is essential for proper intestinal morphogenesis of developing Caenorhabditis elegans.     

Linking Morphological and Behavioural Defences: Prey Fish Detect the Morphology of Conspecifics in the Odour Signature of their Predators

Predation is a strong selective force acting on both morphology and behaviour of prey animals. While morphological defences (e.g. crypsis, presence of armours or spines or specific body morphologies) and antipredator behaviours (e.g. change in foraging or reproductive effort, or hiding and fleeing behaviours) have been widely studied separately, few studies have considered the interplay between the two. The question raised in our study is whether antipredator behaviours of a prey fish to predator odours could be influenced by the morphology of prey conspecifics in the diet of the predator. We used goldfish (Carassius auratus) as our test species; goldfish exposed to predation risk significantly increase their body depth to length ratio, which gives them a survival advantage against gape‐limited predators. We exposed shallow‐bodied and deep‐bodied goldfish to the odour of pike (Esox lucius) fed either form of goldfish. Deep‐bodied goldfish displayed lower intensity antipredator responses than shallow‐bodied ones, consistent with the hypothesis that individuals with morphological defences should exhibit less behavioural modification than those lacking such defences. Moreover, both shallow‐ and deep‐bodied goldfish displayed their strongest antipredator responses when exposed to the odour of pike fed conspecifics of their own morphology, indicating that goldfish are able to differentiate the morphology of conspecifics through predator diet cues. For a given individual, predator threat increases as the prey become more like the individual eaten, revealing a surprising level of sophistication of chemosensory assessment by prey fish.     

Endothelium and myocyte cellular insulin receptor alterations in a rat model of myocardial infarction

Ischemic heart disease is considered to be one of the leading causes of death in adults. While extensive research on mechanisms contributing to the pathogenesis of myocardial infarction (MI) has been underway, it is not known whether insulin receptor characteristics and postreceptor signaling have been fully addressed as yet. Present work attempts to investigate whether the remodeling process effectively induces alteration(s) in insulin-binding characteristics at the coronary endothelium and cardiomyocytes using a rat heart model of MI. MI was induced by ligation of the left anterior descending coronary artery of adult male Sprague-Dawley rats. Two animal groups were used in the study: (i) sham-operated CHAPS-untreated and CHAPS-treated, and (ii) MI CHAPS-untreated and MI CHAPS-treated. A physical model describing 1:1 stoichiometry of reversible insulin binding to its receptors present on the endothelium and at cardiomyocytes after CHAPS treatment was considered for data analysis. Quantitation of the collected effluents after heart perfusion, the inlet at the aortic and outlet at the coronary sinus sites, were curve fitted using a first-order Bessel function, which determines the binding constants (k(n)), the reversible constant (k(-n)), the dissociation constant (k(d) = k(-n)/k(n)), and the residency time constant (tau = 1/k(-n)). In addition, hearts were excised, separated into right and left ventricles, and individually weighed, and areas of infarcted regions were measured. Results of the MI group showed significant increases in relative heart mass, left ventricle mass, and right ventricle mass normalized to total body mass. MI induced severe ischemia and irreversible myocardial injury as assessed by planimetry and histologic studies. The data showed differences in insulin receptor affinities at the endothelial and cardiac myocytes in the sham and in the MI-operated rats. The observed reduction in the binding affinity of insulin at the myocyte postinfarction may explain the pathogenic role of insulin in ischemic heart disease and, hence, resistance. Therefore, insulin administration during and post MI might be cardioprotective.     

Lipopolysaccharides of bacterial pathogens from the genus Yersinia: a mini-review

This review summarizes the state of knowledge on the composition and structure of the lipopolysaccharides (LPS) from three species of Yersinia known to produce disease in humans: Y. pseudotuberculosis, Y. enterocolitica and Y. pestis. We also mention recent data on the genome sequence of Yersinia pestis and the role of LPS in relation to the virulence of this bacteria.     

The beta-thymosin/WH2 domain; structural basis for the switch from inhibition to promotion of actin assembly

The widespread beta-thymosin/WH2 actin binding domain has versatile regulatory properties in actin dynamics and motility. beta-thymosins (isolated WH2 domain) maintain monomeric actin in a "sequestered" nonpolymerizable form. In contrast, when repeated in tandem or inserted in modular proteins, the beta-thymosin/WH2 domain promotes actin assembly at filament barbed ends, like profilin. The structural basis for these opposite functions is addressed using ciboulot, a three beta-thymosin repeat protein. Only the first repeat binds actin and possesses the function of ciboulot. The region that shows the strongest interaction with actin is an amphipathic N-terminal alpha helix, present in all beta-thymosin/WH2 domains, which recognizes the ATP bound actin structure and uses the shear motion of actin linked to ATP hydrolysis to control polymerization. Crystallographic ((1)H, (15)N), NMR, and mutagenetic data reveal that the weaker interaction of the C-terminal region of beta-thymosin/WH2 domain with actin accounts for the switch in function from inhibition to promotion of actin assembly.