The "linker" region (amino acids 38-47) of the disintegrin elegantin is a novel inhibitory domain of integrin alpha5beta1-dependent cell adhesion on fibronectin: evidence for the negative regulation of fibronectin synergy site biological activity

Disintegrins are a family of potent inhibitors of cell-cell and cell-matrix adhesion. In this study we have identified a region of the disintegrin elegantin, termed the "linker domain" (amino acids 38-47), with inhibitory activity toward alpha(5)beta(1)-mediated cell adhesion on fibronectin (Fn). Using a chimeric structure-function approach in which sequences of the functionally distinct disintegrin kistrin were introduced into the elegantin template at targeted sites, a loss of inhibitory function toward alpha(5)beta(1)-mediated adhesion on Fn was observed when the elegantin linker domain was substituted. Subsequent analysis comparing the inhibitory efficacies of the panel of elegantin-kistrin chimeras toward CHO alpha(5) cell adhesion on recombinant Fn III(6-10) fragments showed that the loss of inhibitory activity associated with the disruption of the elegantin linker domain was dependent upon the presence of a functional Fn III(9) synergy site within the Fn III(6-10) substrate. This suggested that the elegantin linker domain inhibits primarily the activity of the Fn synergy domain in promoting alpha(5)beta(1) integrin-mediated cell adhesion. Construction of a cyclic peptide corresponding to the entire region of the elegantin linker domain showed that this domain has intrinsic alpha(5)beta(1) inhibitory activity comparable with the activity of the RGDS peptide. These data demonstrate a novel biological function for a disintegrin domain that antagonizes integrin-mediated cell adhesion.     

CCN3 controls 3D spatial localization of melanocytes in the human skin through DDR1

Melanocytes reside within the basal layer of the human epidermis, where they attach to the basement membrane and replicate at a rate proportionate to that of keratinocytes, maintaining a lifelong stable ratio. In this study, we report that coculturing melanocytes with keratinocytes up-regulated CCN3, a matricellular protein that we subsequently found to be critical for the spatial localization of melanocytes to the basement membrane. CCN3 knockdown cells were dissociated either upward to the suprabasal layers of the epidermis or downward into the dermis. The overexpression of CCN3 increased adhesion to collagen type IV, the major component of the basement membrane. As the receptor responsible for CCN3-mediated melanocyte localization, we identified discoidin domain receptor 1 (DDR1), a receptor tyrosine kinase that acts as a collagen IV adhesion receptor. DDR1 knockdown decreased melanocyte adhesion to collagen IV and shifted melanocyte localization in a manner similar to CCN3 knockdown. These results demonstrate an intricate and necessary communication between keratinocytes and melanocytes in maintaining normal epidermal homeostasis.     

Seasonal modulation of plasma antifreeze protein levels in Atlantic (Anarhichas lupus) and spotted wolffish (A. minor)

The Atlantic and spotted wolffish (Anarhichas lupus and A. minor, respectively) inhabit the cold waters of the northeast Atlantic Ocean. Although both species experience subzero water temperatures during winter, the Atlantic wolffish, which occupies shallower waters than the spotted wolffish, faces the greater threat of coming into contact with ice and freezing. This laboratory study was designed to determine whether these species differed in their abilities to resist freezing by examining the seasonal changes in blood plasma freezing points, antifreeze protein (AFP) activity and Na⁺ and Cl⁻ concentrations when exposed to seasonally cycling water temperatures and photoperiod. The plasma of both species showed distinct seasonal cycles in all parameters with the highest values occurring during the winter. However, of the two species, only the Atlantic wolffish produced sufficient AFP to protect the fish down to the freezing point of seawater (− 1.80 °C). The levels of AFP in the spotted wolffish were too low to impart any significant improvement in their resistance to freezing (approximately − 0.8 °C).When wolffish were maintained in warm water under a seasonally changing photoperiod, the amplitude of the seasonal cycle in AFP activity was greatly reduced, indicating that low water temperatures are necessary to maximize plasma AFP levels. However, despite being maintained in warm water, plasma levels of AFP activity began to increase over summer values at the same time of year as did the fish exposed to seasonally changing water temperatures. This suggests that photoperiod plays a major role in the timing of the annual AFP cycle.     

Structure and development of Nostoc strands in Leiosporoceros dussii (Anthocerotophyta): a novel symbiosis in land plants

The presence of Nostoc in longitudinally oriented schizogenous canals is a feature that separates Leiosporoceros from all other hornworts and represents a novel symbiotic arrangement in land plants. In surface view, Nostoc canals are visible as elongated, dichotomously branched blue-green strands. All other hornworts develop numerous discrete globose colonies through continuous production of mucilage clefts as avenues for multiple invasions within a single thallus. To elucidate the anatomy and development of the unusual Nostoc strands in Leiosporoceros, we examined sporeling development in culture and the structure of strands in field-collected plants using light and electron microscopy. Rosette-like sporelings have mucilage clefts scattered along swollen apices. All field specimens were strap-shaped, contained Nostoc, and lacked mucilage clefts. Nostoc strands are located in the center of the thallus and develop behind the apical cell by separation of the middle lamella between apical derivatives. Strands elongate and branch in synchrony with apical growth, and thus only a single invasion is required for strand production. Two distinct ultrastructural morphotypes in the collections suggest nonspecificity of Nostoc. We speculate that Nostoc enters the thallus in the sporeling stage through mucilage clefts, and once colonies are established, cleft production ceases.     

Transmission of white sturgeon iridovirus in Kootenai River white sturgeon Acipenser transmontanus

It is thought that white sturgeon iridovirus (WSIV) is transmitted vertically from adult white sturgeon Acipenser transmontanus to progeny, and that wild adults are carriers of this virus. Based on this assumption, egg disinfection trials were initiated using wild Kootenai River white sturgeon. Over 2 consecutive years, post-fertilized eggs were disinfected with iodine at concentrations ranging from 0 to 400 ppm. Eggs were incubated and progeny were reared on either de-chlorinated municipal or Kootenai River water. Juvenile sturgeon (mean weight 3.0 g) from these treatment groups were then subjected to a density stress (15 or 20 g(-1)) to manifest WSIV disease in individuals harboring the virus. In Year 1, mortality in all groups ranged from 6 to 37% and the use of municipal water was shown to significantly improve survival. However, WSIV infection was not detected in fish from any of the treatment groups or controls, and therefore did not contribute to the observed mortality. In Year 2, all treatment and control groups reared on Kootenai River water tested positive for WSIV infection and exhibited mortality ranging from 59 to 94%, but fish from groups reared on municipal water did not test positive for WSIV infection. This shows that that vertical transmission did not occur in this study. Horizontal transmission played a significant role in WSIV infection, but the lack of infection in Year 1 suggests a cyclic occurrence of the virus in the Kootenai River system. Although survival tended to be better in iodine-treated groups, the effects of iodine treatment in relation to WSIV transmission remain unknown. An important finding is that not all wild white sturgeon broodstock yield WSIV-positive progeny.     

Polychlorinated Biphenyl (PCB)-Degrading Bacteria Associated with Trees in a PCB-Contaminated Site

The abundance, identities, and degradation abilities of indigenous polychlorinated biphenyl (PCB)-degrading bacteria associated with five species of mature trees growing naturally in a contaminated site were investigated to identify plants that enhance the microbial PCB degradation potential in soil. Culturable PCB degraders were associated with every plant species examined in both the rhizosphere and root zone, which was defined as the bulk soil in which the plant was rooted. Significantly higher numbers of PCB degraders (2.7- to 56.7-fold-higher means) were detected in the root zones of Austrian pine (Pinus nigra) and goat willow (Salix caprea) than in the root zones of other plants or non-root-containing soil in certain seasons and at certain soil depths. The majority of culturable PCB degraders throughout the site and the majority of culturable PCB degraders associated with plants were identified as members of the genus Rhodococcus by 16S rRNA gene sequence analysis. Other taxa of PCB-degrading bacteria included members of the genera Luteibacter and Williamsia, which have not previously been shown to include PCB degraders. PCB degradation assays revealed that some isolates from the site have broad congener specificities; these isolates included one Rhodococcus strain that exhibited degradation abilities similar to those of Burkholderia xenovorans LB400. Isolates with broad congener specificity were widespread at the site, including in the biostimulated root zone of willow. The apparent association of certain plant species with increased abundance of indigenous PCB degraders, including organisms with outstanding degradation abilities, throughout the root zone supports the notion that biostimulation through rhizoremediation is a promising strategy for enhancing PCB degradation in situ.     

Local stream habitat variables predicted from catchment scale characteristics are useful for predicting fish distribution

South-east Queensland (Australia) streams were described by 21 local habitat variables that were chosen because of their potential association with fish distribution. An Assessment by a Nearest Neighbour Analysis (ANNA) model used large-scale variables that are robust to human influence to predict what the values of each of the 21 local habitat variables at each site would be without modification from human activity. The ANNA model used elevation, stream order, distance from source and longitude to predict the local habitat variables; other candidate predictor variables (mean rainfall, latitude and catchment area) were not found to be useful. The ANNA model was able to predict five of the 21 local habitat variables (average width, sand (%), cobble (%), rocks (%) and large woody debris) with an R ² of at least 0.2. The observed values of these five local habitat variables were used to model the distributions of individual fish species. The species distribution models were developed using logistic regression based on a subset of the data (some of the data were withheld for model validation) and a forward stepwise model selection procedure. There was no difference in predictive performance of fish distribution models for model predictions based on observed values and model predictions based on ANNA predicted values of local habitat variables in the withheld data (p-value = 0.85). Therefore, it is possible to predict the suitability of sites as habitat for given fish species using estimated (estimates based on large-scale variables) natural values of local habitat variables.     

Silica in grasses as a defence against insect herbivores: contrasting effects on folivores and a phloem feeder

1. Silica, deposited as opaline phytoliths in the leaves of grasses, constitutes 2-5% of dry leaf mass, yet its function remains unclear. It has been proposed that silica may act as an antiherbivore defence by increasing the abrasiveness and reducing the digestibility of grass leaves, although there is little direct experimental evidence to support this. 2. We investigated the effects of manipulated silica levels on the abrasiveness of the leaves of five grass species. We also examined the effects of silica levels on the feeding preferences, growth performance and digestion efficiency of two folivorous insects and one phloem-feeding insect. 3. Silica addition resulted in increases to leaf abrasiveness in four of the five grass species studied. Silica addition also deterred feeding by both folivores and reduced their growth rates and digestion efficiency. 4. These effects resulted in lower pupal mass of the lepidopteron larvae Spodoptera exempta and compensatory feeding by the orthopteran, Schistocerca gregaria. In contrast, silica had no effects on the feeding preference or the population growth of the phloem feeder, Sitobion avenae. 5. Our results demonstrate that silica is an effective defence against folivorous insects, both as a feeding deterrent, possibly mediated by increased abrasiveness, and as a digestibility reducer. The effects of silica on pupal mass and development time may impact on herbivore fitness and exposure to natural enemies. 6. These results are the first demonstration of a direct effect of silica on the abrasiveness of grasses and the adverse impact of silica on herbivore preference and performance.