Host resistance and parasite virulence in greenfinch coccidiosis

The question why different host individuals within a population differ with respect to infection resistance is of fundamental importance for understanding the mechanisms of parasite-mediated selection. We addressed this question by infecting wild-caught captive male greenfinches with intestinal coccidian parasites originating either from single or multiple hosts. Birds with naturally low pre-experimental infection retained their low infection status also after reinfection with multiple strains, indicating that natural infection intensities confer information about the phenotypic ability of individuals to resist novel strains. Exposure to novel strains did not result in protective immunity against the subsequent infection with the same strains. Infection with multiple strains resulted in greater virulence than single-strain infection, indicating that parasites originating from different host individuals are genetically diverse. Our experiment thus demonstrates the validity of important but rarely tested assumptions of many models of parasite-mediated selection in a wild bird species and its common parasite.     

Gata3 is required for early morphogenesis and Fgf10 expression during otic development

Inner ear develops from an induced surface ectoderm placode that invaginates and closes to form the otic vesicle, which then undergoes a complex morphogenetic process to form the membranous labyrinth. Inner ear morphogenesis is severely affected in Gata3 deficient mouse embryos, but the onset and basis of the phenotype has not been known. We show here that Gata3 deficiency leads to severe and unique abnormalities during otic placode invagination. The invagination problems are accompanied often by the formation of a morphological boundary between the dorsal and ventral otic cup and by the precocious appearance of dorsal endolymphatic characteristics. In addition, the endolymphatic domain often detaches from the rest of the otic epithelium during epithelial closure. The expression of several cell adhesion mediating genes is altered in Gata3 deficient ears suggesting that Gata3 controls adhesion and morphogenetic movements in early otic epithelium. Inactivation of Gata3 leads also to a loss of Fgf10 expression in otic epithelium and auditory ganglion demonstrating that Gata3 is an important regulator of Fgf-signalling during otic development.     

Individual consistency and covariation of measures of oxidative status in greenfinches

Oxidative stress results from a mismatch between production of reactive oxygen species (ROS) and the organism's capacity to mitigate their damaging effects by building up sufficient antioxidant protection and/or repair mechanisms. Because ROS production is a universal consequence of cellular metabolism and immune responses, evolutionary animal ecologists have become increasingly interested in involvement of oxidative stress as a proximate mechanism responsible for the emergence of trade-offs related to the evolution of life-history and signal traits. Among the most practical problems pertinent to ecological research on oxidative stress is finding a combination of biomarkers of oxidative status that can be applied to typical wild animal models such as small birds, mammals, and reptiles. This study describes covariation and individual consistency of eight parameters of oxidative status in a small passerine bird, wild-caught captive greenfinch (Carduelis chloris). We measured two markers of plasma antioxidant potential--total antioxidant capacity (TAC) and oxygen radical absorbance (OXY)--and concentrations of one lipophilic (carotenoids) and two hydrophilic (uric acid and ascorbate) antioxidants in plasma. We also measured total glutathione (GSH) concentration and superoxide dismutase (SOD) activity in erythrocytes. Oxidative damage was assessed on the basis of plasma malondialdehyde (MDA) levels, measured by high-performance liquid chromatography. Plasma carotenoids, TAC, and erythrocyte GSH showed significant individual consistency over an 8-d period, indicating that those variables reflected more persistent differences between individuals than plasma OXY, MDA, and uric acid. We did not detect any strong or moderate correlations between the studied parameters, which suggests that all of these biomarkers contain potentially unique information. Injection of a synthetic mimetic of SOD and catalase--EUK-134--did not affect any of the parameters of oxidative status. Capability of phagocytes to produce oxidative burst was not associated with MDA, indicating that under our experimental conditions, ROS production by phagocytes was not a strong determinant of oxidative damage. Altogether these findings suggest that attempts to characterize oxidative balance should use a wide range of biomarkers, and further studies of oxidative status in wild animals may benefit from the experimental induction of oxidative stress.     

Carotenoid-based plumage coloration is not affected by vitamin E supplementation in male greenfinches

Carotenoid-based colours have become an important model of honest signalling as carotenoids are suggested to play vital roles in several physiological functions including antioxidants and immunostimulators, while they are also required for sexual displays. However, it has been recently suggested that carotenoid-based signals may be used mainly as reflectors of the systems that prevent their oxidation (mainly the amount of other non-pigmented antioxidants) rather than the antioxidative properties of carotenoids themselves. We tested this hypothesis by examining the effect of simultaneous supplementation of carotenoids and an uncoloured antioxidant—vitamin E—on the coloration of growing tail feathers in captive male greenfinches (Carduelis chloris chloris L.). While carotenoid supplementation enhanced the coloration of the feathers, manipulation of dietary vitamin E had no effect. Thus, our results do not support the idea that carotenoids are mainly used as indicators of the abundance of other antioxidants.     

Directionality of heart looping: effects of Pitx2c misexpression on flectin asymmetry and midline structures

The insulin-like growth factors (IGFs) are well known mitogens, both in vivo and in vitro, while functions in cellular differentiation have also been indicated. Here, we demonstrate a new role for the IGF pathway in regulating head formation in Xenopus embryos. Both IGF-1 and IGF-2, along with their receptor IGF-1R, are expressed early during embryogenesis, and the IGF-1R is present particularly in anterior and dorsal structures. Overexpression of IGF-1 leads to anterior expansion of head neural tissue as well as formation of ectopic eyes and cement gland, while IGF-1 receptor depletion using antisense morpholino oligonucleotides drastically reduces head structures. Furthermore, we demonstrate that IGF signaling exerts this effect by antagonizing the activity of the Wnt signal transduction pathway in the early embryo, at the level of beta-catenin. Thus, the IGF pathway is required for head formation during embryogenesis.     

Stabilization of bound polycyclic aromatic hydrocarbons by a pi-cation interaction

Proteins can use aromatic side-chains to stabilize bound cationic ligands through cation-pi interactions. Here, we report the first example of the reciprocal process, termed pi-cation, in which a cationic protein side-chain stabilizes a neutral aromatic ligand. Site-directed mutagenesis revealed that an arginine side-chain located in the deep binding pocket of a monoclonal antibody (4D5) is essential for binding the neutral polynuclear aromatic hydrocarbon benzo[a]pyrene. This Arg was very likely selected for in the primary response, further underscoring the importance of the pi-cation interaction for ligand binding, which should be considered in protein analysis and design when ligands include aromatic groups.     

Design, synthesis and properties of novel powerful antioxidants, glutathione analogues

Glutathione (GSH) is the major low-molecular weight antioxidant in mammalian cells. Thus, its analogues carrying similar and/or additional positive properties might have clinical perspectives. Here, we report the design and synthesis of a library of tetrapeptidic GSH analogues called UPF peptides. Compared to cellular GSH our designed peptidic analogues showed remarkably higher hydroxyl radical scavenging ability (EC(50) of GSH: 1,231.0 +/- 311.8 microM; EC(50) of UPF peptides: from 0.03 to 35 microM) and improved antiradical efficiency towards a stable alpha,alpha-diphenyl-beta-picrylhydrazyl (DPPH) radical. The best of UPF peptides was 370-fold effective hydroxyl radical scavengers than melatonin (EC(50): 11.4 +/- 1.0 microM). We also found that UPF peptides do not influence the viability and membrane integrity of K562 human erythroleukemia cells even at 200 microM concentration. Dimerization of GSH and UPF peptides was compared in water and in 0.9% saline solutions. The results, together with an earlier finding that UPF1 showed protective effects in global cerebral ischemia model in rats, suggest that UPF peptides might serve both as potent antioxidants as well as leads for design of powerful non-peptidic antioxidants that correct oxidative stress-driven events.