Cyst bank life-history model for a fairy shrimp from ephemeral ponds

1. Ephemeral wetland habitats provide a useful model system for studying how life‐history patterns enable populations to persist despite high environmental variation. One important life‐history trait of both plants and crustaceans in such habitats involves hatching/germination of only some of the eggs/seeds at any time. This bet‐hedging leads to the development of a bank composed of dormant propagules of many ages. 2. The San Diego fairy shrimp, Branchinecta sandiegonensis (Crustacea: Anostraca), a dominant faunal element of ephemeral ponds in San Diego, California, is a suitable organism for studying the consequences of highly fluctuating environmental conditions. As a result of large‐scale habitat loss, the species is also endangered, and this motivated our specific study towards understanding the hatching dynamics of its egg bank for planning conservation efforts such as pool restoration and re‐creation. 3. We formulated a matrix population model using egg age within the bank to study the relationship between adult survival and reproduction, and survival in and hatching from the egg bank. As vital rates for fairy shrimp are only poorly known, we generated 48 matrices with parameters encompassing ranges of likely values for the vital rates of B. sandiegonensis. We calculated population growth rates and eigenvalue elasticities both for a static model and a model with periodic reproductive failure. 4. The model shows that in good filling events, population growth rate is very high and the egg bank is increased dramatically. While population growth rate is insensitive to long‐term survival in the egg bank in our static deterministic model, it becomes sensitive to survival in the egg bank when a regime of periodically failed reproductive events is imposed. 5. Under favourable conditions, it was best for shrimp to hatch from eggs as soon as possible. However, under a regime where failed reproductive events were common, it was best to hatch after several pool fillings. Because conditions change from favourable to unfavourable unpredictably, variation in age within the egg bank appears to be critical for the persistence of the population. This attribute needs to be carefully considered when restoring or creating new pools for conservation purposes.     

TNFalpha-induced glutathione depletion lies downstream of cPLA(2) in L929 cells.

Both glutathione (GSH) depletion and arachidonic acid (AA) generation have been shown to regulate sphingomyelin (SM) hydrolysis and are known components in tumor necrosis factor alpha (TNFalpha)-induced cell death. In addition, both have hypothesized direct roles in activation of N-sphingomyelinase (SMase); however, it is not known whether these are independent pathways of N-SMase regulation or linked components of a single ordered pathway. This study was aimed at differentiating these possibilities using L929 cells. Depletion of GSH with L-buthionin-(S,R)-sulfoximine (BSO) induced 50% hydrolysis of SM at 12 h. In addition, TNF induced a depletion of GSH, and exogenous addition of GSH blocked TNF-induced SM hydrolysis as well as TNF-induced cell death. Together, these results establish GSH upstream of SM hydrolysis and ceramide generation in L929 cells. We next analyzed the L929 variant, C12, which lacks both cytosolic phospholipase A(2) (cPLA(2)) mRNA and protein, in order to determine the relationship of cPLA(2) and GSH. TNF did not induce a significant drop in GSH levels in the C12 line. On the other hand, AA alone was capable of inducing a 60% depletion of GSH in C12 cells, suggesting that these cells remain responsive to AA distal to the site of cPLA(2). Furthermore, depleting GSH with BSO failed to effect AA release, but caused a drop in SM levels, showing that the defect in these cells was upstream of the GSH drop and SMase activation. When cPLA(2) was restored to the C12 line by expression of the cDNA, the resulting CPL4 cells regained sensitivity to TNF. Treatment of the CPL4 cells with TNF resulted in GSH levels dropping to levels near those of the wild-type L929 cells. These results demonstrate that GSH depletion following TNF treatment in L929 cells is dependent on intact cPLA(2) activity, and suggest a pathway in which activation of cPLA(2) is required for the oxidation and reduction of GSH levels followed by activation of SMases.     

The Non-Immune RIP-kb Mouse is a Useful Host for Islet Transplantation,as the Diabetes is Spontaneous,Mild and Predictable

Chemically-induced diabetic mice and spontaneously diabetic NOD mice have been valuable as recipients for experimental islet transplantation. However, their maintenance often requires parenteral insulin. Diabetogenic chemicals can be cytotoxic to the host’s immune system and to other organs some of which are often used as the transplant site. Procurement of diabetic cohorts in the NOD mouse is problematic due to variability in the age of disease onset. We show that RIP-K^b mice, which spontaneously develop non-immune diabetes due to over-expression of the H-2K^b heavy chain in beta cells, offer many advantages as islet transplant recipients. Diabetes is predictable with a relatively narrow range of onset (4 wk) and blood glucose levels (23.0± 4.0 mmol/l for 39 males at 6 weeks of age). The diabetes is mild enough so that most diabetic mice can be maintained to 40 weeks of age without parenteral insulin. This consistency of diabetes avails that outcomes of intervention can be interpreted with confidence.     

Automatic Detection of Attention Shifts in Infancy: Eye Tracking in the Fixation Shift Paradigm

This study measured changes in switches of attention between 1 and 9 months of age in 67 typically developing infants. Remote eye-tracking (Tobii X120) was used to measure saccadic latencies, related to switches of fixation, as a measure of shifts of attention, from a central stimulus to a peripheral visual target, measured in the Fixation Shift Paradigm. Fixation shifts occur later if the central fixation stimulus stays visible when the peripheral target appears (competition condition), than if the central stimulus disappears as the peripheral target appears (non-competition condition). This difference decreases with age. Our results show significantly faster disengagement in infants over 4 months than in the younger group, and provide more precise measures of fixation shifts, than behavioural observation with the same paradigm. Reduced saccadic latencies in the course of a test session indicate a novel learning effect. The Fixation Shift Paradigm combined with remote eye-tracking measures showed improved temporal and spatial accuracy compared to direct observation by a trained observer, and allowed an increased number of trials in a short testing time. This makes it an infant-friendly non-invasive procedure, involving minimal observational training, suitable for use in future studies of clinical populations to detect early attentional abnormalities in the first few months of life.     

High-resolution 3D quantitative analysis of caveolar ultrastructure and caveola-cytoskeleton interactions

Caveolae are characteristic invaginations of the mammalian plasma membrane (PM) implicated in lipid regulation, signal transduction and endocytosis. We have employed electron microscope tomography (ET) to quantify caveolae structure–function relationships in three-dimension (3D) at high resolution both in conventionally fixed and in fast-frozen/freeze-substituted (intact) cells as well as immunolabelled PM lawns. Our findings provide a detailed quantitative comparison of the average caveola dimensions for different cell types including tissue endothelial cells and cultured 3T3-L1 adipocytes. These studies revealed the presence of a spiked caveolar coat and a wide caveolar neck open to the extracellular milieu that is sensitive to conventional fixation; the neck region appeared to form a specialized microdomain with associated cytoplasmic material. In endothelial cells in situ in pancreatic islets of Langerhans, the diaphragm spanning the caveolar opening was clearly resolved by ET, and the involuted 3D topology of the cell surface mapped to measure the contribution of caveolar membranes to local increases in the surface area of the PM. The complexity of connections among caveolae and to the actin cytoskeleton and microtubules suggests that individual caveolae may be interconnected through a complex filamentous network to form a single functional unit.     

Habitat shifts in the evolutionary history of a Neotropical flycatcher lineage from forest and open landscapes

Background  

Little is known about the role ecological shifts play in the evolution of Neotropical radiations that have colonized a variety of environments. We here examine habitat shifts in the evolutionary history of Elaenia flycatchers, a Neotropical bird lineage that lives in a range of forest and open habitats. We evaluate phylogenetic relationships within the genus based on mitochondrial and nuclear DNA sequence data, and then employ parsimony-based and Bayesian methods to reconstruct preferences for a number of habitat types and migratory behaviour throughout the evolutionary history of the genus. Using a molecular clock approach, we date the most important habitat shifts.     

A ferroxidase encoded by FOX1 contributes to iron assimilation under conditions of poor iron nutrition in Chlamydomonas

When the abundance of the FOX1 gene product is reduced, Chlamydomonas cells grow poorly in iron-deficient medium, but not in iron-replete medium, suggesting that FOX1-dependent iron uptake is a high-affinity pathway. Alternative pathways for iron assimilation, such as those involving ZIP family transporters IRT1 and IRT2, may be operational.     

Genetic Diversity and Multihost Pathogenicity of Clinical and Environmental Strains of Burkholderia cenocepacia

A collection of 54 clinical and agricultural isolates of Burkholderia cenocepacia was analyzed for genetic relatedness by using multilocus sequence typing (MLST), pathogenicity by using onion and nematode infection models, antifungal activity, and the distribution of three marker genes associated with virulence. The majority of clinical isolates were obtained from cystic fibrosis (CF) patients in Michigan, and the agricultural isolates were predominantly from Michigan onion fields. MLST analysis resolved 23 distinct sequence types (STs), 11 of which were novel. Twenty-six of 27 clinical isolates from Michigan were genotyped as ST-40, previously identified as the Midwest B. cenocepacia lineage. In contrast, the 12 agricultural isolates represented eight STs, including ST-122, that were identical to clinical isolates of the PHDC lineage. In general, pathogenicity to onions and the presence of the pehA endopolygalacturonase gene were detected only in one cluster of related strains consisting of agricultural isolates and the PHDC lineage. Surprisingly, these strains were highly pathogenic in the nematode Caenorhabditis elegans infection model, killing nematodes faster than the CF pathogen Pseudomonas aeruginosa PA14 on slow-kill medium. The other strains displayed a wide range of pathogenicity to C. elegans, notably the Midwest clonal lineage which displayed high, moderate, and low virulence. Most strains displayed moderate antifungal activity, although strains with high and low activities were also detected. We conclude that pathogenicity to multiple hosts may be a key factor contributing to the potential of B. cenocepacia to opportunistically infect humans both by increasing the prevalence of the organism in the environment, thereby increasing exposure to vulnerable hosts, and by the selection of virulence factors that function in multiple hosts.The betaproteobacterium Burkholderia cenocepacia, 1 of now 17 classified species belonging to the Burkholderia cepacia complex (BCC), is ubiquitous and extremely versatile in its metabolic capabilities and interactions with other organisms (38, 40, 57, 58). Strains of B. cenocepacia are pathogens of onion and banana plants, opportunistic pathogens of humans, symbionts of numerous plant rhizospheres, contaminants of pharmaceutical and industrial products, and inhabitants of soil and surface waters (14, 29, 33, 34, 37, 45). Originally described as a pathogen of onions (8), organisms of the BCC emerged in the past 3 decades as serious human pathogens, capable of causing devastating chronic lung infections in persons with cystic fibrosis (CF) or chronic granulomatous disease (21, 24, 28). Infections due to BCC are a serious concern to CF patients due to their inherent antibiotic resistance and high potential for patient-to-patient transmission (23). Although 16 of the BCC species have been recovered from respiratory secretions of CF patients in many countries (46, 58), B. cenocepacia has been the most common species isolated in North America, detected in 50% of 606, 83% of 447, and 45.6% of 1,218 patients in recent studies (35, 46, 52).The epidemiology of infectious disease caused by B. cenocepacia appears to involve patient-to-patient spread of genetically distinct lineages. B. cenocepacia lineages, such as ET12, Midwest, and PHDC, have been identified from large numbers of individuals in disease outbreaks in North America and Europe (11, 32, 54). A recently developed multilocus sequence typing (MLST) scheme has been shown to be a reliable epidemiologic tool for differentiating between the five subgroups (IIIA to IIIE) of B. cenocepacia, and strains representing three of these subgroups (IIIA, IIIB, and IIID) have been recovered from CF patients (2). Outside of the patient-to-patient transmission of clonal lineages, the mode of acquisition of strains causing sporadic cases of B. cenocepacia in CF patients remains unclear, although environmental sources are a logical reservoir for infection. Previously, an isolate of B. cenocepacia indistinguishable from the PHDC epidemic clonal lineage by using standard typing methods (e.g., repetitive-sequence-based PCR, randomly amplified polymorphic DNA, pulsed-field gel electrophoresis) was detected in an agricultural soil sample (34). Similarly, three distinct MLST sequence types containing both clinical and environmental (plant and soil) B. cenocepacia isolates were identified (1). These findings suggest that natural populations of B. cenocepacia in soil or associated with plants are a potential reservoir for the emergence of new human pathogenic lineages.Experimental models for the study of virulence potential and traits of B. cenocepacia include mouse and rat models with genetic defects allowing chronic lung infections to be established (e.g., see reference 48). Nematode (Caenorhabditis elegans), alfalfa (Medicago sativa), and onion (Allium cepa) models have also been routinely utilized for the identification of virulence factors (5, 29, 31). C. elegans has been extensively used to study the pathogenesis and virulence factors of a wide variety of bacterial and fungal pathogens (9, 15, 42, 51, 56). In several pathogens, including Pseudomonas (56) and Burkholderia (20), putative virulence factors important for the pathogenesis in mammalian systems (15, 51) have been identified using the C. elegans model. The C. elegans model might be limited in the detection of host-specific virulence factors; however, several attributes, such as small size and rapid development, make it an excellent whole animal model for pathogenesis research (16, 51).The evidence that individual strains of B. cenocepacia can be pathogenic to both plants and humans and are prevalent in various environmental niches has provoked particular interest in elucidating the clinical pathogenic potential of environmental isolates. The basis of this study was to examine whether genetically related B. cenocepacia strains exhibit shared characteristics that contribute to their pathogenicity in multiple hosts and to examine the potential for circulating environmental isolates to emerge as new clinical pathogens. Here, we tested the degree of virulence in animal (nematode) and plant (onion) infection models, the production of antifungal activity, and the genetic relatedness of clinical and environmental B. cenocepacia subgroup IIIB strains predominantly isolated from Michigan.