Trait means and reaction norms: the consequences of climate change/invasion interactions at the organism level

How the impacts of climate change on biological invasions will play out at the mechanistic level is not well understood. Two major hypotheses have been proposed: invasive species have a suite of traits that enhance their performance relative to indigenous ones over a reasonably wide set of circumstances; invasive species have greater phenotypic plasticity than their indigenous counterparts and will be better able to retain performance under altered conditions. Thus, two possibly independent, but complementary mechanistic perspectives can be adopted: based on trait means and on reaction norms. Here, to demonstrate how this approach might be applied to understand interactions between climate change and invasion, we investigate variation in the egg development times and their sensitivity to temperature amongst indigenous and introduced springtail species in a cool temperate ecosystem (Marion Island, 46°54′S 37°54′E) that is undergoing significant climate change. Generalized linear model analyses of the linear part of the development rate curves revealed significantly higher mean trait values in the invasive species compared to indigenous species, but no significant interactions were found when comparing the thermal reaction norms. In addition, the invasive species had a higher hatching success than the indigenous species at high temperatures. This work demonstrates the value of explicitly examining variation in trait means and reaction norms among indigenous and invasive species to understand the mechanistic basis of variable responses to climate change among these groups.     

VGLUT2-dependent sensory neurons in the TRPV1 population regulate pain and itch

The natural response to itch sensation is to scratch, which relieves the itch through an unknown mechanism. Interaction between pain and itch has been frequently demonstrated, and the selectivity hypothesis of itch, based on data from electrophysiological and behavioral experiments, postulates the existence of primary pain afferents capable of repressing itch. Here, we demonstrate that deletion of vesicular glutamate transporter (VGLUT) 2 in a subpopulation of neurons partly overlapping with the vanilloid receptor (TRPV1) primary afferents resulted in a dramatic increase in itch behavior accompanied by a reduced responsiveness to thermal pain. The increased itch behavior was reduced by administration of antihistaminergic drugs and by genetic deletion of the gastrin-releasing peptide receptor, demonstrating a dependence on VGLUT2 to maintain normal levels of both histaminergic and nonhistaminergic itch. This study establishes that VGLUT2 is a major player in TRPV1 thermal nociception and also serves to regulate a normal itch response.     

The Disulfide Bonds in Glycoprotein E2 of Hepatitis C Virus Reveal the Tertiary Organization of the Molecule

Hepatitis C virus (HCV), a major cause of chronic liver disease in humans, is the focus of intense research efforts worldwide. Yet structural data on the viral envelope glycoproteins E1 and E2 are scarce, in spite of their essential role in the viral life cycle. To obtain more information, we developed an efficient production system of recombinant E2 ectodomain (E2e), truncated immediately upstream its trans-membrane (TM) region, using Drosophila melanogaster cells. This system yields a majority of monomeric protein, which can be readily separated chromatographically from contaminating disulfide-linked aggregates. The isolated monomeric E2e reacts with a number of conformation-sensitive monoclonal antibodies, binds the soluble CD81 large external loop and efficiently inhibits infection of Huh7.5 cells by infectious HCV particles (HCVcc) in a dose-dependent manner, suggesting that it adopts a native conformation. These properties of E2e led us to experimentally determine the connectivity of its 9 disulfide bonds, which are strictly conserved across HCV genotypes. Furthermore, circular dichroism combined with infrared spectroscopy analyses revealed the secondary structure contents of E2e, indicating in particular about 28% β-sheet, in agreement with the consensus secondary structure predictions. The disulfide connectivity pattern, together with data on the CD81 binding site and reported E2 deletion mutants, enabled the threading of the E2e polypeptide chain onto the structural template of class II fusion proteins of related flavi- and alphaviruses. The resulting model of the tertiary organization of E2 gives key information on the antigenicity determinants of the virus, maps the receptor binding site to the interface of domains I and III, and provides insight into the nature of a putative fusogenic conformational change.     

Pathogen specific, IRF3-dependent signaling and innate resistance to human kidney infection

The mucosal immune system identifies and fights invading pathogens, while allowing non-pathogenic organisms to persist. Mechanisms of pathogen/non-pathogen discrimination are poorly understood, as is the contribution of human genetic variation in disease susceptibility. We describe here a new, IRF3-dependent signaling pathway that is critical for distinguishing pathogens from normal flora at the mucosal barrier. Following uropathogenic E. coli infection, Irf3(-/-) mice showed a pathogen-specific increase in acute mortality, bacterial burden, abscess formation and renal damage compared to wild type mice. TLR4 signaling was initiated after ceramide release from glycosphingolipid receptors, through TRAM, CREB, Fos and Jun phosphorylation and p38 MAPK-dependent mechanisms, resulting in nuclear translocation of IRF3 and activation of IRF3/IFNβ-dependent antibacterial effector mechanisms. This TLR4/IRF3 pathway of pathogen discrimination was activated by ceramide and by P-fimbriated E. coli, which use ceramide-anchored glycosphingolipid receptors. Relevance of this pathway for human disease was supported by polymorphic IRF3 promoter sequences, differing between children with severe, symptomatic kidney infection and children who were asymptomatic bacterial carriers. IRF3 promoter activity was reduced by the disease-associated genotype, consistent with the pathology in Irf3(-/-) mice. Host susceptibility to common infections like UTI may thus be strongly influenced by single gene modifications affecting the innate immune response.     

Molecular systematics and morphological character evolution of the Condamineeae (Rubiaceae)

? Premise of the study: The Condamineeae have in previous molecular studies been shown to be part of an early-divergent clade within the subfamily Ixoroideae, together with the tribes Calycophylleae, and Hippotideae, and genera of the former Cinchoneae and Rondeletieae. Generic relationships within this clade have, however, remained largely unresolved. ? Methods: In this study, the systematics of the Condamineeae was further examined by phylogenetic reconstruction of six cpDNA regions and one nrDNA region using parsimony and Bayesian Markov chain Monte Carlo inference. Morphological character evolution within the tribe was assessed by ancestral state reconstruction using likelihood optimization of characters onto Bayesian trees. ? Key results: Calycophylleae appears polyphyletic. "Hippotideae" is monophyletic but nested within the Condamineeae. The phylogenetic hypotheses presented support a resurrection of the genera Holtonia, Schizocalyx, and Semaphyllanthe. Furthermore, Bathysa is found to be polyphyletic, Tresanthera is found nested within Rustia, and the taxonomically disputed genus Dialypetalanthus is here shown to be sister to a Bothriospora-Wittmackanthus clade. Morphological ancestral state reconstructions indicate that protogyny have evolved at least two times within the tribe and that indehiscent fruits, loculicidal fruit dehiscence, and intrapetiolar stipules have evolved independently several times. The occurrence of calycophylls (leaf-like calyx lobes), poricidal anthers, and winged seeds also appear homoplastic within the tribe. ? Conclusions: A diagnosis and delimitation of the tribe Condamineeae is presented, with taxonomic proposals to synonymize Tresanthera and to transfer several species of Bathysa as well as Phitopis to a resurrected Schizocalyx.     

Investigation of Chlamydiaceae in semen and cauda epididymidis and seroprevalence of Chlamydophila abortus in breeding bulls

Background

Reproductive disorders associated with chlamydial infection have been reported worldwide in cattle and there are indications of potential venereal transmission.

Methods

Semen samples from 21 dairy bulls and cauda epididymidis tissue samples from 43 beef bulls were analysed for chlamydial agent by real-time polymerase chain reaction (PCR) including an internal amplification control (mimic). Additionally, presence of antibodies against Chlamydophila (Cp.) abortus among the bulls was investigated with the commercial Pourquier^® ELISA Cp. abortus serum verification kit.

Results

No chlamydial agent was detected by PCR in either the semen samples or in the tissue samples. Additionally, no antibodies against Cp. abortus were detected.

Conclusions

The results suggest that Cp. abortus is very rare, or absent in Swedish bulls and thus the risk for venereal transmission of chlamydial infection through their semen is low. However, because Chlamydophila spp. infection rates seem to differ throughout the world, it is essential to clarify the relative importance of transmission of the infection through semen on cattle fertility.     

Growing through predation windows: effects on body size development in young fish

The degree to which growth in early life stages of animals is regulated via density‐dependent feedbacks through prey resources is much debated. Here we have studied the influence of size‐ and density‐dependent mechanisms as well as size‐selective predation pressure by cannibalistic perch Perca fluviatilis on growth patterns of young‐of‐the‐year (YOY) perch covering several lakes and years. We found no influence of initial size or temperature on early body size development of perch. In contrast, there was a negative relationship between reproductive output and the length of YOY perch at five weeks of age. However, rather than an effect of density‐dependent growth mediated via depressed resources the relationship was driven by positive size‐selective cannibalism removing large individuals. Hence, given a positive correlation between the density of victims and predation pressure by cannibals, size‐dependent interactions between cannibals and their victims may wrongly be interpreted as patterns of density‐dependent growth in the victim cohort. Overall, our results support the view that density‐dependent resource‐limitation in early life stages is rare. Still, patterns of density‐dependent growth may emerge, but from variation in size‐selective predation pressure rather than density as such. This illustrates the importance of taking overall population demography and predatory interactions into account when studying growth patterns among recruiting individuals.     

Sequestration of the Aβ Peptide Prevents Toxicity and Promotes Degradation In Vivo

Protein aggregation, arising from the failure of the cell to regulate the synthesis or degradation of aggregation-prone proteins, underlies many neurodegenerative disorders. However, the balance between the synthesis, clearance, and assembly of misfolded proteins into neurotoxic aggregates remains poorly understood. Here we study the effects of modulating this balance for the amyloid-beta (Aβ) peptide by using a small engineered binding protein (Z_Aβ3) that binds with nanomolar affinity to Aβ, completely sequestering the aggregation-prone regions of the peptide and preventing its aggregation. Co-expression of Z_Aβ3 in the brains of Drosophila melanogaster expressing either Aβ₄₂ or the aggressive familial associated E22G variant of Aβ₄₂ abolishes their neurotoxic effects. Biochemical analysis indicates that monomer Aβ binding results in degradation of the peptide in vivo. Complementary biophysical studies emphasize the dynamic nature of Aβ aggregation and reveal that Z_Aβ3 not only inhibits the initial association of Aβ monomers into oligomers or fibrils, but also dissociates pre-formed oligomeric aggregates and, although very slowly, amyloid fibrils. Toxic effects of peptide aggregation in vivo can therefore be eliminated by sequestration of hydrophobic regions in monomeric peptides, even when these are extremely aggregation prone. Our studies also underline how a combination of in vivo and in vitro experiments provide mechanistic insight with regard to the relationship between protein aggregation and clearance and show that engineered binding proteins may provide powerful tools with which to address the physiological and pathological consequences of protein aggregation.     

Structure of the extracellular portion of CD46 provides insights into its interactions with complement proteins and pathogens

The human membrane cofactor protein (MCP, CD46) is a central component of the innate immune system. CD46 protects autologous cells from complement attack by binding to complement proteins C3b and C4b and serving as a cofactor for their cleavage. Recent data show that CD46 also plays a role in mediating acquired immune responses, and in triggering autophagy. In addition to these physiologic functions, a significant number of pathogens, including select adenoviruses, measles virus, human herpes virus 6 (HHV-6), Streptococci, and Neisseria, use CD46 as a cell attachment receptor. We have determined the crystal structure of the extracellular region of CD46 in complex with the human adenovirus type 11 fiber knob. Extracellular CD46 comprises four short consensus repeats (SCR1-SCR4) that form an elongated structure resembling a hockey stick, with a long shaft and a short blade. Domains SCR1, SCR2 and SCR3 are arranged in a nearly linear fashion. Unexpectedly, however, the structure reveals a profound bend between domains SCR3 and SCR4, which has implications for the interactions with ligands as well as the orientation of the protein at the cell surface. This bend can be attributed to an insertion of five hydrophobic residues in a SCR3 surface loop. Residues in this loop have been implicated in interactions with complement, indicating that the bend participates in binding to C3b and C4b. The structure provides an accurate framework for mapping all known ligand binding sites onto the surface of CD46, thereby advancing an understanding of how CD46 acts as a receptor for pathogens and physiologic ligands of the immune system.