The integrative effects of behavior and morphology on amphibian movement

Animal movement and dispersal are key factors in population dynamics and support complex ecosystem processes like cross‐boundary subsidies. Juvenile dispersal is an important mechanism for many species and often involves navigation in unfamiliar habitats. For species that metamorphose, such as amphibians, this transition from aquatic to terrestrial environments involves the growth and use of new morphological traits (e.g., legs). These traits strongly impact the fundamental ability of an organism to move in novel landscapes, but innate behaviors can regulate choices that result in the realized movements expressed. By assessing the integrative role of morphology and behavior, we can improve our understanding of juvenile movement, particularly in understudied organisms like amphibians. We assessed the roles of morphological (snout‐vent length and relative leg length) and performance (maximal jump distance) traits in shaping the free movement paths, measured through fluorescent powder tracking, in three anuran species, Pacific treefrog (Hyliola regilla), Western toad (Anaxyrus boreas), and Cascades frog (Rana cascadae). We standardized the measurement of these traits to compare the relative role of species' innate differences versus physical traits in shaping movement. Innate differences, captured by species identity, were the most significant factor influencing movement paths via total movement distance and path sinuosity. Relative leg length was an important contributor but significantly interacted with species identity. Maximal jump performance, which was significantly predicted by morphological traits, was not an important factor in movement behavior relative to species identity. The importance of species identity and associated behavioral differences in realized movement provide evidence for inherent species differences being central to the dispersal and movement of these species. This behavior may stem from niche partitioning of these sympatric species, yet it also calls into question assumptions generalizing anuran movement behavior. These species‐level effects are important in framing differences as past research is applied in management planning.     

Level of Toll-like receptor agonist exposure differentially determines chemokine production in humans

Toll-like receptor (TLR) agonists, ubiquitously present in the environment, are key players in activating synthesis of cytokines and chemokines that control normal and pathophysiological processes, including multiple inflammatory diseases. TLR2 and TLR4 respond to bacterial cell wall products. We examined the impact of TLR activation on human immune capacity using stimuli ranging from the low levels seen in most environments to the high concentrations widely used for in vitro studies. Peripheral blood mononuclear cells from 117 healthy children were activated with lipopolysaccharide (TLR4 ligand) or peptidoglycan (TLR2 ligand) over a million-fold range of concentrations. Resulting interleukin-6, CCL2, and CCL22 production were quantified by ELISA. The intensity of cytokine production elicited was linearly related to the intensity of the stimulus up to maximal responses. In marked contrast, chemokine production was not linearly related to agonist concentration. Responses rose with increasing stimulation, and then were markedly reduced (40%-100%, p < 0.0001) in response to the high levels of TLR stimulation most commonly cited. Thus, the levels of TLR4 and TLR2 agonists typically used for in vitro interrogation of immune capacity yield results clearly distinct from those obtained using commonly occurring environmental levels of TLR ligands. These findings demonstrate the importance of utilizing TLR ligands at concentrations more closely mimicking environmental levels when assessing immune capacity.     

Probucol promotes endogenous antioxidant reserve and confers protection against reperfusion injury

The present study examines whether a subchronic probucol treatment of rats offers protection against ischemia-reperfusion (IR) injury in isolated perfused hearts. Sprague-Dawley rats were treated every second day per week with probucol (cumulative dose 120 mg/kg body mass, i.p.) for 4 weeks. In the probucol group, baseline myocardial antioxidant enzyme, glutathione peroxidase (GSHPx), activity was increased (p<0.05), whereas superoxide dismutase (SOD) and catalase (CAT) activities were not changed. Baseline oxidative stress, as indicated by the myocardial lipid peroxidation, was less (p<0.05) in the probucol group. Isolated hearts were subjected to 60 min global I and 20 min R. Recovery of the contractile function in globally ischemic hearts upon reperfusion was 36% in untreated group and 74% in the probucol group. After IR, GSHPx and CAT activities were significantly (p<0.05) higher in the probucol group compared with the control group, whereas SOD did not change. Lipid peroxidation owing to IR was significantly less in the probocol group. These data suggest that probucol treatment improves endogenous antioxidant reserve and protects against increased oxidative stress following IR injury.     

CD36 signals to the actin cytoskeleton and regulates microglial migration via a p130Cas complex

The pattern recognition receptor CD36 initiates a signaling cascade that promotes microglial activation and recruitment to beta-amyloid deposits in the brain. In the present study we identify the focal adhesion-associated proteins p130Cas, Pyk2, and paxillin as novel members of the tyrosine kinase signaling pathway downstream of CD36 and show that assembly of this complex is essential for microglial migration. In primary microglia and macrophages exposed to beta-amyloid, the scaffolding protein p130Cas is rapidly tyrosine-phosphorylated and co-localizes with CD36 to membrane ruffles contemporaneous with F-actin polymerization. These beta-amyloid-stimulated events are not detected in CD36 null cells and are dependent on CD36 activation of Src family tyrosine kinases. Fyn, a Src kinase known to interact with CD36, co-precipitates with p130Cas and is an essential upstream intermediate in the signaling pathways leading to phosphorylation of the p130Cas substrate domain. Furthermore, the p130Cas-interacting kinase Pyk2 and the cytoskeletal adapter protein paxillin also demonstrate CD36-dependent phosphorylation, identifying these focal adhesion molecules as additional members of this beta-amyloid signaling cascade. Disruption of this p130Cas complex by small interfering RNA silencing inhibits p44/42 mitogen-activated protein kinase phosphorylation and microglial migration, illustrating the importance of this pathway in microglial activation and recruitment. Together, these data are the first to identify the signaling cascade that directly links CD36 to the actin cytoskeleton and, thus, implicates it in diverse processes such as cellular migration, adhesion, and phagocytosis.     

The Hemolymph of the ascidian Styela plicata (Chordata-Tunicata) contains heparin inside basophil-like cells and a unique sulfated galactoglucan in the plasma

The hemolymph of ascidians (Chordata-Tunicata) contains different types of hemocytes embedded in a liquid plasma. In the present study, heparin and a sulfated heteropolysaccharide were purified from the hemolymph of the ascidian Styela plicata. The heteropolysaccharide occurs free in the plasma, is composed of glucose ( approximately 60%) and galactose ( approximately 40%), and is highly sulfated. Heparin, on the other hand, occurs in the hemocytes, and high performance liquid chromatography of the products formed by degradation with specific lyases revealed that it is composed mainly by the disaccharides DeltaUA(2SO(4))-1-->4-beta-d-GlcN(SO(4)) (39.7%) and DeltaUA(2SO(4))-1-->4-beta-d-GlcN(SO(4))(6SO(4)) (38.2%). Small amounts of the 3-O-sulfated disaccharides DeltaUA(2SO(4))-1-->4-beta-d-GlcN(SO(4))(3SO(4)) (9.8%) and DeltaUA(2SO(4))-1-->4-beta-d-GlcN(SO(4))(3SO(4))(6SO(4)) (3.8%) were also detected. These 3-O-sulfated disaccharides were demonstrated to be essential for the binding of the hemocyte heparin to antithrombin III. Electron microscopy techniques were used to characterize the ultrastructure of the hemocytes and to localize heparin and histamine in these cells. At least five cell types were recognized and classified as univacuolated and multivacuolated cells, amebocytes, hemoblasts, and granulocytes. Immunocytochemistry showed that heparin and histamine co-localize in intracellular granules of only one type of hemocyte, the granulocyte. These results show for the first time that in ascidians, a sulfated galactoglucan circulates free in the plasma, and heparin occurs as an intracellular product of a circulating basophil-like cell.     

The cyclic AMP cascade is altered in the fragile X nervous system

Fragile X syndrome (FX), the most common heritable cause of mental retardation and autism, is a developmental disorder characterized by physical, cognitive, and behavioral deficits. FX results from a trinucleotide expansion mutation in the fmr1 gene that reduces levels of fragile X mental retardation protein (FMRP). Although research efforts have focused on FMRP's impact on mGluR signaling, how the loss of FMRP leads to the individual symptoms of FX is not known. Previous studies on human FX blood cells revealed alterations in the cyclic adenosine 3', 5'-monophosphate (cAMP) cascade. We tested the hypothesis that cAMP signaling is altered in the FX nervous system using three different model systems. Induced levels of cAMP in platelets and in brains of fmr1 knockout mice are substantially reduced. Cyclic AMP induction is also significantly reduced in human FX neural cells. Furthermore, cAMP production is decreased in the heads of FX Drosophila and this defect can be rescued by reintroduction of the dfmr gene. Our results indicate that a robust defect in cAMP production in FX is conserved across species and suggest that cAMP metabolism may serve as a useful biomarker in the human disease population. Reduced cAMP induction has implications for the underlying causes of FX and autism spectrum disorders. Pharmacological agents known to modulate the cAMP cascade may be therapeutic in FX patients and can be tested in these models, thus supplementing current efforts centered on mGluR signaling.     

Obesity and impairment in psychosocial functioning in women: the mediating role of eating disorder features

Objective: The objective was to test the hypothesis that, in women, the association between obesity and impairment in psychosocial functioning is mediated by levels of weight and shape concerns and/or binge‐eating frequency. Research Methods and Procedures: Self‐report measures of eating disorder psychopathology, mental health functioning, subjective quality of life in the psychological and social domains, and days “out‐of‐role” associated with any (physical or mental) health problem, were completed by a community sample of women classified as obese (BMI ≥30 kg/m², n = 639) or non‐obese (BMI <30 kg/m², n = 4253). For each of the dependent measures, regression models were used to test the hypothesis of mediation by comparing the strength of the relationship between independent and dependent variables with and without inclusion of the putative mediator in the regression model. Results: On each measure, the conditions for perfect mediation were satisfied when weight or shape concerns acted as the putative mediator, indicating that there was no association between obesity and functional impairment after controlling for weight or shape concerns. In contrast, associations between obesity and impairment in psychosocial functioning remained highly significant when binge‐eating frequency was the putative mediator. Discussion: The findings suggest that in women, weight and shape concerns are an important mediator of the relationship between obesity and impairment in psychosocial functioning, whereas binge eating may not be of primary importance. A greater focus on body acceptance in obesity treatment may be indicated.     

Changes in purine specificity in tandem GAF chimeras from cyanobacterial cyaB1 adenylate cyclase and rat phosphodiesterase 2

The C-terminal catalytic domains of the 11 mammalian phosphodiesterase families (PDEs) are important drug targets. Five of the 11 PDE families contain less well-characterized N-terminal GAF domains. cGMP is the ligand for the GAF domains in PDEs 2, 5, 6 and 11, and cAMP is the ligand for PDE10. Structurally related tandem GAF domains signalling via cAMP are present in the cyanobacterial adenylate cyclases cyaB1 and cyaB2. Because current high-resolution crystal structures of the tandem GAF domains of PDE2 and cyaB2 do not reveal how cNMP specificity is encoded, we generated chimeras between the tandem GAF domains of cyaB1 and PDE2. Both bind the ligand in the GAF B subdomains. Segmental replacements in the highly divergent beta1-beta3 region of the GAF B subdomain of cyaB1 by the corresponding PDE2 regions switched signalling from cAMP to cGMP. Using 10 chimeric constructs, we demonstrated that, for this switch in purine specificity, only 11% of the sequence of the cyanobacterial GAF B needs to be replaced by PDE2 sequences. We were unable, however, to switch the purine specificity of the PDE2 tandem GAF domain from cGMP to cAMP in reverse constructs, i.e. by replacement of PDE2 segments with those from the cyaB1 GAF tandem domain. The data provide a novel view on the structure-function relationships underlying the purine specificity of cNMP-binding GAF domains and indicate that, as potential drug targets, they must be characterized structurally and biochemically one by one.