Parasite-mediated intraguild predation as one of the drivers of co-existence and exclusion among invasive and native amphipods (Crustacea)

Parasitism is emerging as one of the forces determining the outcome of biological invasions. Using field survey and laboratory experiments, we investigate parasitism as one of the factors mediating the interactions among invasive and native amphipods. An extensive survey (100 sites) of a small British island, revealed the native Gammarus duebeni celticus to be parasitised by the muscle wasting microsporidian Pleistophora mulleri and the acanthocephalan duck parasite Polymorphus minutus, the introduced European Gammarus pulex only by P. minutus and the North American Crangonyx pseudogracilis by neither. While Gammarus spp. were widespread in rivers (one or both species present in 64% of sites), C. pseudogracilis had a restricted distribution (7% of sites) and always co-occurred with Gammarus spp. In contrast, Gammarus spp. were absent from all pond/reservoir sites, with C. pseudogracilis present in over 90%. While the negative association of C. pseudogracilis with Gammarus spp. undoubtedly results from factors such as physico-chemical tolerance and predation as C. pseudogracilis can be heavily predated by Gammarus spp., it was notable that C. pseudogracilis co-occurred with Gammarus spp. more frequently when the latter were parasitised. Laboratory experiments clearly showed that predation on C. pseudogracilis was greatly diminished when G. d. celticus was parasitised by P. mulleri and G. pulex by P. minutus. Our study provides evidence that parasitism, by mediating a key interspecific interaction, is one of an array of interacting factors that may have a role in driving patterns of exclusion and co-existence in natives and invaders.     

Human salivary gland branching morphogenesis: morphological localization of claudins and its parallel relation with developmental stages revealed by expression of cytoskeleton and secretion markers

Development of salivary glands is a highly complex and dynamic process termed branching morphogenesis, where branched structures differentiate into mature glands. Tight junctions (TJ) are thought to play critical roles in physiological functions of tubular organs, contributing to cell polarity and preventing lateral movement of membrane proteins. Evidence demonstrated that claudins are directly involved in TJ formation and function. Using immunohistochemistry and immunofluorescence we have mapped the distribution of claudins-1, 2, 3, 4, 5, 7 and 11 and compared it with the expression of differentiation markers in human salivary glands obtained from foetuses ranging from weeks 4 to 24 of gestation. Expression of all claudins, except claudin-2 was detected in the various phases of human salivary gland development, up to fully mature salivary gland. The expression of all claudins increased according to the progression of salivary gland maturation evidenced by the classical markers-cytokeratin 14, cytokeratin low molecular weight, smooth muscle actin and human secretory component. Tight junction proteins-claudins appear to be important in the final shape and physiological functions of human salivary glands and are parallel related with markers of salivary gland differentiation.     

Biased competition through variations in amplitude of <Emphasis Type="Italic">γ</Emphasis>-oscillations

Experiments in visual cortex have shown that the firing rate of a neuron in response to the simultaneous presentation of a preferred and non-preferred stimulus within the receptive field is intermediate between that for the two stimuli alone (stimulus competition). Attention directed to one of the stimuli drives the response towards the response induced by the attended stimulus alone (selective attention). This study shows that a simple feedforward model with fixed synaptic conductance values can reproduce these two phenomena using synchronization in the gamma-frequency range to increase the effective synaptic gain for the responses to the attended stimulus. The performance of the model is robust to changes in the parameter values. The model predicts that the phase locking between presynaptic input and output spikes increases with attention.     

NS-kNN: a modified <Emphasis Type="Italic">k</Emphasis>-nearest neighbors approach for imputing metabolomics data

Introduction

A common problem in metabolomics data analysis is the existence of a substantial number of missing values, which can complicate, bias, or even prevent certain downstream analyses. One of the most widely-used solutions to this problem is imputation of missing values using a k-nearest neighbors (kNN) algorithm to estimate missing metabolite abundances. kNN implicitly assumes that missing values are uniformly distributed at random in the dataset, but this is typically not true in metabolomics, where many values are missing because they are below the limit of detection of the analytical instrumentation.

Objectives

Here, we explore the impact of nonuniformly distributed missing values (missing not at random, or MNAR) on imputation performance. We present a new model for generating synthetic missing data and a new algorithm, No-Skip kNN (NS-kNN), that accounts for MNAR values to provide more accurate imputations.

Methods

We compare the imputation errors of the original kNN algorithm using two distance metrics, NS-kNN, and a recently developed algorithm KNN-TN, when applied to multiple experimental datasets with different types and levels of missing data.

Results

Our results show that NS-kNN typically outperforms kNN when at least 20–30% of missing values in a dataset are MNAR. NS-kNN also has lower imputation errors than KNN-TN on realistic datasets when at least 50% of missing values are MNAR.

Conclusion

Accounting for the nonuniform distribution of missing values in metabolomics data can significantly improve the results of imputation algorithms. The NS-kNN method imputes missing metabolomics data more accurately than existing kNN-based approaches when used on realistic datasets.

     

In Vitro Studies on the Putative Function of N-acetylaspartate as an Osmoregulator

Efflux and tissue content of N-acetylaspartate (NAA) and amino acids were evaluated from cultured and acutely prepared hippocampal slices in response to changes in osmolarity. The osmoregulator taurine, but not NAA, was lost from both types of slices after moderate reductions in extracellular osmolarity (−60 mOsm) for 10–48 h. Hypoosmotic shock (−166 mOsm) for 5 min resulted in unselective efflux of several amino acids from acutely prepared slices. Notably, the efflux of taurine, but not NAA, was prominent also after the shock. Efflux of NAA was markedly enhanced by NMDA and high K⁺, in particular after the stimulation period. The high K⁺-mediated efflux was decreased by high extracellular osmolarity and a NMDA-receptor antagonist. The results indicate that NAA efflux can be induced by a sudden non-physiological decrease in extracellular osmolarity but not by prolonged more moderate changes in osmolarity. The mechanisms behind the efflux of NAA by high K⁺ are complex and may involve both swelling and activation of NMDA-receptors.     

Characterization of Upstream Sequences of the <Emphasis Type=Italic>LOJ</Emphasis> Gene Leads to Identification of a Novel Enhancer Element Conferring Lateral Organ Junction-Specific Expression in <Emphasis Type=Italic>Arabidopsis thaliana</Emphasis>

Isolation and characterization of promoters are important in understanding gene regulation and genetic engineering of crop plants. Earlier, a pentatricopeptide repeat protein (PPR) encoding gene (At2g39230), designated as Lateral Organ Junction (LOJ) gene, was identified through T-DNA promoter trapping in Arabidopsis thaliana. The upstream sequence of the LOJ gene conferred on the reporter gene a novel LOJ-specific expression. The present study was aimed at identifying and characterizing the cis-regulatory motifs responsible for tissue-specific expression in the −673 and +90 bases upstream of the LOJ gene recognized as LOJ promoter. In silico analysis of the LOJ promoter revealed the presence of a few relevant regulatory motifs and a unique feature like AT-rich inverted repeat. Deletion analysis of the LOJ promoter confirmed the presence of an enhancer-like element in the distal region (−673/−214), which stimulates a minimal promoter-like sequence in the −424/−214 region in a position and orientation autonomous manner. The −136/+90 region of the LOJ promoter was efficient in driving reporter gene expression in tissues like developing anthers and seeds of Arabidopsis. A positive regulation for the seed- and anther-specific expression module was contemplated within the 5′ untranslated region of the LOJ gene. However, this function was repressed in the native context by the lateral organ junction-specific expression. The present study has led to the identification of a novel lateral organ junction-specific element and an enhancer sequence in Arabidopsis with potential applications in plant genetic engineering.     

Germination responses of three grassland species differ between native and invasive origins

The germination stage is critical in plant life-history and is also a key process during the expansion of species’ ranges into new environments. In this study we investigated the germination patterns of three plant species (Achillea millefolium, Hieracium pilosella and Hypericum perforatum) that are invasive to New Zealand (NZ) and native to Central Europe. We asked whether the species show differences in germination temperature requirements, germination speed and maximum germination rates, and thus, whether they display evidence of adaptation to different conditions in the invasive range. Seeds from three populations per species and region were subjected to three different temperature regimes to compare germination rates among origins and across temperature conditions. For Achillea millefolium and Hypericum perforatum, germination rates were significantly higher for invasive NZ provenances than for native German ones. Seeds from invasive populations of all three species displayed increased maximum germination at medium temperature conditions when compared to native populations, which indicates altered germination strategies in the invaded range. Changes in temporal development patterns were most conspicuous for invasive Hieracium pilosella and Hypericum perforatum populations. These findings imply that adaptation in germination patterns towards different climatic conditions in invasive populations has occurred. Our study emphasises the importance of the germination stage during plant invasion and its role in explaining range expansion of these species.     

A landscape of shifting-mosaic steady state in Lassen Volcanic National Park,California

It is generally perceived that landscape patterns or textures in a given protected area are spatially stationary. The findings of this study suggest that this common perception is only partially correct. Over the course of 52 years, equilibrium in landscape shifting was detected using digital data for the Lassen Volcanic National Park (USA). Vertical aerial photographs taken of the park in 1941 were geo-referenced with the digital orthophoto quarter quadrangle (DOQQ) images of the same area from 1993 to identify landscape compositions and to measure change. Spatial analysis was used to observe pattern changes over time. The results suggested that landscape development maintained equilibrium while patches were in various stages of a successional sequence. The total area of each landscape component held steady, although over time patches throughout the landscape changed—a shifting-mosaic steady state (SMSS). These findings reflect the limitations of contemporary environmental conservation theory. They also suggest the importance of considering landscape change in policies that currently govern park planning and management.     

Long-term population dynamics in a Mediterranean aquatic snake

A review of several long-term studies has recently suggested that snakes might be declining in large parts of the world. Additional data from other long-term studies are therefore urgently needed in order to assess the generalities of such suggested declines. Based on a 20-year study, we analyzed demographic data on adult dice snakes (Natrix tessellata) studied in central Italy between 1985 and 2004. Both male and female dice snakes were relatively long-lived, with no significant differences in longevity between the sexes. Individual males and females were observed over a maximum of 10 and 14 years, respectively. However, the among-year recapture rates between the year the snakes were initially captured and the subsequent year (i.e., year 1 to year 2) was significantly lower (45%) than the among-year recapture rates during subsequent years (74%; i.e., year 2 to year 3), suggesting that a large proportion of the snakes at first capture were in fact not resident within our study area, and hence many snakes were migrating in and out of our 2-km stream study site, with no inter-sexual difference in dispersal rates. Sex ratio was virtually equal if we consider the study period as a whole. Significant annual fluctuations were, however, observed through the study. In 1985–1990, 1993–1995, 1998 and 1999 the sex ratio was male-biased, whereas in 2000–2004 female-biased. In terms of both survival and recapture probabilities, model selection showed that Akaike’s information criterion favored the model incorporating body size, with the model incorporating year having an intermediate likelihood, and the model with sex included being the most disfavored. Total population number estimates suggest an average 86 adult individuals along the 2 km of stream with only minor annual variations. However, a significant decrease in the number of males occurred during the last 6 years of our study. Thus, further monitoring of this population is warranted in light of the decline of snake populations reported recently.     

Inflammation-associated S100 proteins: new mechanisms that regulate function

This review focuses on new aspects of extracellular roles of the calgranulins. S100A8, S100A9 and S100A12 are constitutively expressed in neutrophils and induced in several cell types. The S100A8 and S100A9 genes are regulated by pro- and anti-inflammatory mediators and their functions may depend on cell type, mediators within a particular inflammatory milieu, receptors involved in their recognition and their post-translational modification. The S100A8 gene induction in macrophages is dependent on IL-10 and potentiated by immunosuppressive agents. S100A8 and S100A9 are oxidized by peroxide, hypochlorite and nitric oxide (NO). HOCl generates intra-chain sulfinamide bonds; stronger oxidation promotes cross-linked forms that are seen in human atheroma. S100A8 is >200-fold more sensitive to oxidative cross-linking than low-density lipoprotein and may reduce oxidative damage. S100A8 and S100A9 can be S-nitrosylated. S100A8–SNO suppresses mast cell activation and inflammation in the microcirculation and may act as an NO transporter to regulate vessel tone in inflammatory lesions. S100A12 activates mast cells and is a monocyte and mast cell chemoattractant; a G-protein-coupled mechanism may be involved. Structure–function studies are discussed in relation to conservation and divergence of functions in S100A8. S100A12 induces cytokines in mast cells, but not monocytes/macrophages. It forms complexes with Zn²⁺ and, by chelating Zn²⁺, S100A12 significantly inhibits MMPs. Zn²⁺ in S100A12 complexes co-localize with MMP-9 in foam cells in atheroma. In summary, S100A12 has pro-inflammatory properties that are likely to be stable in an oxidative environment, because it lacks Cys and Met residues. Conversely, S100A8 and S100A9 oxidation and S-nitrosylation may have important protective mechanisms in inflammation.