Characterization of a cDNA encoding a putative chitinase from teratocytes of the endoparasitoid Toxoneuron nigriceps

Females of insect endoparasitoids inject substances along with the egg at oviposition, which can regulate or induce changes in a number of host physiological processes to benefit the developing parasitoid. These changes can be caused by substances such as venoms, calyx fluids, or symbiotic‐associated virus particles (polydnavirus), which are injected by females along with their eggs, and by substances secreted by parasitoid‐derived tissues (teratocytes) or the developing parasitoid larvae. Teratocytes (dissociated cells of the serosal membrane after parasitoid eclosion) release substances that have roles (i) in parasitoid nutrition, (ii) in the digestion of host tissues, and (iii) in the regulation of host development. Teratocytes of Toxoneuron nigriceps (Viereck) (Hymenoptera: Braconidae) have been implicated in the arrestment of the host development and in the regulation of circulating levels of host ecdysteroids. Here we describe the cDNA of a teratocyte‐secreted chitinase and its expression during parasitoid development, and discuss its putative role in this host–parasitoid association.     

Effect of fatigue on hamstring coactivation during isokinetic knee extensions

We examined the effect of fatigue of the quadriceps muscles on coactivation of the hamstring muscles and determined if the response is different between two isokinetic speeds in ten males and ten females with no history of knee pathology. Electromyographic data were recorded from the vastus lateralis and biceps femoris muscles during 50 maximal knee extensions at isokinetic speeds of 1.75 rad · s⁻¹ (100° · s⁻¹) and 4.36 rad · s⁻¹ (250° · s⁻¹). A greater degree of coactivation was apparent at the higher speed, but the increase in coactivation of the hamstring muscles was similar at both speeds. The results revealed that: (1) coactivation is greater at a higher isokinetic speed, and (2) coactivation increases during fatigue, but the rate of increase is independent of contraction velocity. Accepted: 15 June 1998     

Epidermal growth factor: Characteristics of specific binding in membranes from liver,placenta, and other target tissues

Epidermal growth factor, a 6,400-dalton polypeptide from the mouse submaxillary gland, binds specifically to cells and membranes derived from a variety of human, rat, mouse, and bovine tissues. Liver, placenta, skin, cornea, and cultured chondrocytes, Hela cells, and Chang liver cells bind large amounts of epidermal growth factor, whereas fat cells, resting and lectin-stimulated human peripheral lymphocytes, mouse thymocytes, cultured rat hepatoma cells, and mammary cells from virgin and pregnant mice bind little or no epidermal growth factor. The binding site for epidermal growth factor is distinct from receptors for other anabolic peptides such as insulin, nerve growth factor, and growth hormone. The binding of epidermal growth factor is rapid and reversible. The rate constant of association is approximately 10⁶ mole^?1 sec^?1, the rate constant of dissociation is about 6 × 10^?4 sec^?1, and the apparent equilibrium dissociation constant is about 10^?9m. Trypsin at low concentrations (50–200 μg/ml) destroys the receptor site for epidermal growth factor. The binding of epidermal growth factor by membranes is not accompanied by appreciable degradation of the peptide present in the medium or of that bound to the membranes. Use can be made of the high affinity and specificity of membranes for epidermal growth factor to measure by a competitive binding assay as little as 200 pg of EGF per ml (3 × 10^?11m).     

Structural and Biochemical Characterization of the Early and Late Enzymes in the Lignin β-Aryl Ether Cleavage Pathway from Sphingobium sp. SYK-6

There has been great progress in the development of technology for the conversion of lignocellulosic biomass to sugars and subsequent fermentation to fuels. However, plant lignin remains an untapped source of materials for production of fuels or high value chemicals. Biological cleavage of lignin has been well characterized in fungi, in which enzymes that create free radical intermediates are used to degrade this material. In contrast, a catabolic pathway for the stereospecific cleavage of β-aryl ether units that are found in lignin has been identified in Sphingobium sp. SYK-6 bacteria. β-Aryl ether units are typically abundant in lignin, corresponding to 50–70% of all of the intermonomer linkages. Consequently, a comprehensive understanding of enzymatic β-aryl ether (β-ether) cleavage is important for future efforts to biologically process lignin and its breakdown products. The crystal structures and biochemical characterization of the NAD-dependent dehydrogenases (LigD, LigO, and LigL) and the glutathione-dependent lyase LigG provide new insights into the early and late enzymes in the β-ether degradation pathway. We present detailed information on the cofactor and substrate binding sites and on the catalytic mechanisms of these enzymes, comparing them with other known members of their respective families. Information on the Lig enzymes provides new insight into their catalysis mechanisms and can inform future strategies for using aromatic oligomers derived from plant lignin as a source of valuable aromatic compounds for biofuels and other bioproducts.     

Fixing Content and Function in Neurobiological Systems: The Neuroethology of Electroreception

Are attributions of content and function determinate, or is there no fact of the matter to be fixed? Daniel Dennett has argued in favor of indeterminacy and concludes that, in practice, content and function cannot be fixed. The discovery of an electrical modality in vertebrates offers one concrete instance where attributions of function and content are supported by a strong scientific consensus. A century ago, electroreception was unimagined, whereas today it is widely believed that many species of bony fish, amphibians, sharks, skates, and rays possess this non-human sensory modality. A look at the history of science related to this discovery reveals a highly interdisciplinary endeavor, encompassing ethology, behavioral analysis, neuroscience, and evolutionary biology. While each area provides important evidence, none is sufficient on its own to fix content and function. Instead, I argue that an interdisciplinary, neuroethological approach is required to carry out such determinations. Further, a detailed consideration of biological research suggests that while content and function claims are empirically underdetermined and uncertain, there is insufficient reason to believe in an additional problem of indeterminism. In particular, Dennett's indeterminism arises from a research methodology -- logical adaptationism -- that generates evidence from only one of the areas of neuroethology. However, logical adaptationism does not reflect adaptationism as it is practiced in contemporary biology. I conclude that Dennett is faced with a dilemma: On the one hand, he can hold to logical adaptationism and the indeterminism that results from it, while giving up the relevance of his arguments to biological practice. On the other, he can embrace a more accurate version of adaptationism -- one which plays a role in a larger neuroethological framework -- but from which no strong indeterminacy claims follow.     

Stem demography and post-fire recruitment of a resprouting serotinous conifer

Abstract. The contribution of resprouts and seedling recruitment to post-fire regeneration of the South African fynbos conifer Widdringtonia nodiflora was compared eight months after wildfires in 1990. Stems on all trees were killed by fire but resprouting success was > 90 % at all but one site. A demographic study of burned skeletons revealed that prior to these fires, nearly all plants were multi-stemmed (4–9 stems/plant) and multi-aged, indicating continuous sprout production between fires. All stems were killed by these 1990 fires and at most sites > 90 % of the stems were burned to ground level. All diameter stems were susceptible to such incineration as, at most sites, there was no difference in average diameter of stems burned to ground level and those left standing. Individual genets usually had all ramets incinerated to ground level or all ramets charred, but intact, suggesting certain micro-sites burned hotter, whereas other sites were somewhat protected. Although not true of the 1990 fires, there was evidence that occasionally Widdring-tonia stems may survive fire. At one site, four of the 16 plants sampled had a burned stem twice as old as the oldest burned stem on the other 12 plants at the site, suggesting some stems had survived the previous fire (ca. 1970) and this conclusion was supported by fire-scars on these four stems that dated to ca. 1970. Based on the highly significant correlation between stem diameter and cone density left standing after the 1990 fires, we calculated that for most sites > 80 % of the initial cone crop was incinerated by fire. This is important because we observed a strong relationship between size of the canopy cone crop surviving fire and post-fire seedling recruitment. Under these conditions we hypothesize that sprouting confers a selective advantage to genets when fires cause heavy losses of seed. The infrequent occurrence of sprouting in the Cupressaceae suggests the hypothesis that resprouting is an apomorphic or derived trait in Widdringtonia. Data from this study suggests resprouting provides a selective advantage under severe fynbos fires, which are not only 'stand-replacing fires,’but also are intense enough to incinerate cone-bearing stems.     

Codistribution analysis of elastin and related fibrillar proteins in early vertebrate development.

Elastin is an extracellular matrix protein found in adult and neonatal vasculature, lung, skin and connective tissue. It is secreted as tropoelastin, a soluble protein that is cross-linked in the tissue space to form an insoluble elastin matrix. Cross-linked elastin can be found in association with several microfibril-associated proteins including fibrillin-1, fibrillin-2 and fibulin-1 suggesting that these proteins contribute to elastic fiber assembly, structure or function. To date, the earliest reported elastin expression was in the conotruncal region of the developing avian heart at 3.5 days of gestation. Here we report that elastin expression begins at significantly earlier developmental stages. Using a novel immunolabeling method, the deposition of elastin, fibrillin-1 and -2 and fibulin-1 was analyzed in avian embryos at several time points during the first 2 days of development. Elastin was found at the midline associated with axial structures such as the notochord and somites at 23 h of development. Fibrillin-1 and -2 and fibulin-1 were also expressed at the embryonic midline at this stage with fibrillin-1 and fibulin-1 showing a high degree of colocalization with elastin in fibers surrounding midline structures. The expression of these genes was confirmed by conventional immunoblotting and mRNA detection methods. Our results demonstrate that elastin polypeptide deposition occurs much earlier than was previously appreciated. Furthermore, the results suggest that elastin deposition at the early embryonic midline is accompanied by the deposition and organization of a number of extracellular matrix polypeptides. These filamentous extracellular matrix structures may act to transduce or otherwise stabilize dynamic forces generated during embryogenesis.     

Overexpression of IL-10 in C2D Macrophages Promotes a Macrophage Phenotypic Switch in Adipose Tissue Environments

Adipose tissue macrophages are a heterogeneous collection of classically activated (M1) and alternatively activated (M2) macrophages. Interleukin 10 (IL-10) is an anti-inflammatory cytokine, secreted by a variety of cell types including M2 macrophages. We generated a macrophage cell line stably overexpressing IL-10 (C2D-IL10) and analyzed the C2D-IL10 cells for several macrophage markers after exposure to adipocytes compared to C2D cells transfected with an empty vector (C2D-vector). C2D-IL10 macrophage cells expressed more CD206 when co-cultured with adipocytes than C2D-vector cells; while the co-cultured cell mixture also expressed higher levels of Il4, Il10, Il1β and Tnf. Since regular C2D cells traffic to adipose tissue after adoptive transfer, we explored the impact of constitutive IL-10 expression on C2D-IL10 macrophages in adipose tissue in vivo. Adipose tissue-isolated C2D-IL10 cells increased the percentage of CD206⁺, CD301⁺, CD11c⁻CD206⁺ (M2) and CD11c⁺CD206⁺ (M1b) on their cell surface, compared to isolated C2D-vector cells. These data suggest that the expression of IL-10 remains stable, alters the C2D-IL10 macrophage cell surface phenotype and may play a role in regulating macrophage interactions with the adipose tissue.     

Influence of Fuels,Weather and the Built Environment on the Exposure of Property to Wildfire

Wildfires can pose a significant risk to people and property. Billions of dollars are spent investing in fire management actions in an attempt to reduce the risk of loss. One of the key areas where money is spent is through fuel treatment – either fuel reduction (prescribed fire) or fuel removal (fuel breaks). Individual treatments can influence fire size and the maximum distance travelled from the ignition and presumably risk, but few studies have examined the landscape level effectiveness of these treatments. Here we use a Bayesian Network model to examine the relative influence of the built and natural environment, weather, fuel and fuel treatments in determining the risk posed from wildfire to the wildland-urban interface. Fire size and distance travelled was influenced most strongly by weather, with exposure to fires most sensitive to changes in the built environment and fire parameters. Natural environment variables and fuel load all had minor influences on fire size, distance travelled and exposure of assets. These results suggest that management of fuels provided minimal reductions in risk to assets and adequate planning of the changes in the built environment to cope with the expansion of human populations is going to be vital for managing risk from fire under future climates.