Warfarin resistance in a French strain of rats

A warfarin‐resistant strain and a warfarin‐susceptible strain of wild rats (Rattus norvegicus) maintained in enclosures of the National Veterinary School of Lyon (France) were studied to determine the mechanism of the resistance to anticoagulant rodenticides. A low vitamin K epoxide reductase (VKOR) activity has been reported for many resistant rat strains. As recently suggested, mutations in the vitamin K epoxide reductase subunit 1 (VKORC1) gene are the genetic basis of anticoagulant resistance in wild populations of rats from various locations in Europe. Here we report, for our strain, one of the seven described mutations (Tyr139Phe) for VKORC1 in rats. In addition, a low expression of mRNA encoding VKORC1 gene is observed in resistant rats, which could explain their low VKOR activity. We calculated kinetic parameters of VKOR in the warfarin‐resistant and warfarin‐susceptible rats. The V_max and the K_m of the VKOR obtained in resistant rats were lowered by 57 and 77%, respectively, compared to those obtained in susceptible rats. As a consequence, the enzymatic efficiency (V_m/K_m) of the VKOR was similar between resistant and susceptible rats. This result could be a good explanation to the observation that no clinical signs of vitamin K deficiency was observed in the warfarin‐resistant strain, while a low VKOR activity was found. VKOR activity in warfarin‐resistant rats was poorly inhibited by warfarin (K_i for warfarin is 29 μM and 0.72 μM for resistant and susceptible rats, respectively). © 2005 Wiley Periodicals, Inc. J Biochem Mol Toxicol 19:379‐385, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jbt.20104     

The evolution of coloniality: the emergence of new perspectives

The evolution of group living remains an outstanding question in evolutionary ecology. Among the most striking forms of group living are the enormous assemblages of breeders that occur in many colonial marine birds and mammals, with some colonies containing more than a million individuals breeding in close contact. Coloniality is an evolutionary puzzle because individuals pay fitness costs to breed in high densities. Despite numerous potential benefits proposed to overcome these costs, we still lack a general framework to explain coloniality. Several new hypotheses involving breeding habitat and mate selection create promising approaches for studying this enigma.     

Ditch the niche – is the niche a useful concept in ecology or species distribution modelling?

In this first of three papers we examine the use of niche concepts in ecology and especially in species distribution modelling (SDM). This paper deliberately focuses on the lack of clarity found in the term ‘niche’. Because its meanings are so diverse, the term niche tends to create confusion and requires constant qualification. The literature houses many idiosyncratic ideas of what the niche is, but few examples where niche is more explanatory than the terminologies of population and community ecology or the statistical methods used to implement SDM analyses. In many cases the original (and inspirational) concepts are not directly applicable to our modern applications (e.g. set theory). There are some conceptual limitations found in individual definitions of niche (e.g. the fundamental niche concept), so it is perhaps understandable why more neutral terminology is becoming popular in SDM. An examination of the literature reveals a wide range of uncritical use of niche terminology. Our findings in this paper do not necessarily support the position of niche as a universally useful concept.     

Mathematical Modelling of Ca2+ Oscillations in Airway Smooth Muscle Cells

The action of different agonists such as acetylcholine on the membrane of airway smooth muscle cells may induce cytosolic Ca²⁺ oscillations which can be a part of the Ca²⁺ signalling pathway, eventually leading to cell contraction. The aim of the present study is to present a mathematical model of the possible effect of the initial Ca²⁺ distribution within the cell on the form and frequency of induced Ca²⁺ oscillations. It takes into account intracellular Ca²⁺ stores such as sarcoplasmic reticulum and cytosolic proteins as well as Ca²⁺ exchange across the plasma membrane. We are able to demonstrate a closer agreement of model predictions with observed Ca²⁺ traces for a significantly wider range of parameter values, as was previously reported. We show also that the total cellular Ca²⁺ content is an important system parameter especially because of the content in sarcoplasmic reticulum. At a total Ca²⁺ increase of about 20%, the oscillation frequency increases by 25%; also, damped oscillations become sustained. Cases are indicated in which such a situation could occur.     

Identification and characterization of a stable intermediate in photosystem I assembly in tobacco

Photosystem I (PSI) is the most efficient bioenergetic nanomachine in nature and one of the largest membrane protein complexes known. It is composed of 18 protein subunits that bind more than 200 co‐factors and prosthetic groups. While the structure and function of PSI have been studied in great detail, very little is known about the PSI assembly process. In this work, we have characterized a PSI assembly intermediate in tobacco plants, which we named PSI*. We found PSI* to contain only a specific subset of the core subunits of PSI. PSI* is particularly abundant in young leaves where active thylakoid biogenesis takes place. Moreover, PSI* was found to overaccumulate in PsaF‐deficient mutant plants, and we show that re‐initiation of PsaF synthesis promotes the maturation of PSI* into PSI. The attachment of antenna proteins to PSI also requires the transition from PSI* to mature PSI. Our data could provide a biochemical entry point into the challenging investigation of PSI biogenesis and allow us to improve the model for the assembly pathway of PSI in thylakoid membranes of vascular plants.     

A simple trogocytosis-based method to detect, quantify, characterize and purify antigen-specific live lymphocytes by flow cytometry, via their capture of membrane fragments from antigen-presenting cells

We have developed a method exploiting the phenomenon of trogocytosis to detect lymphocytes reacting specifically with target cells by flow cytometry. Trogocytosis is a process by which lymphocytes capture fragments of the plasma membrane from the antigen-presenting cells (APCs) expressing their cognate antigen. For this method, a label (such as a fluorescent lipid or biotin) is first incorporated in the membrane of APCs. These labeled cells are then co-cultured for a few hours with a population of cells containing the lymphocytes to be detected. After this period of stimulation, lymphocytes that have performed trogocytosis are identified by their acquisition of the label initially present on the APC membrane using flow cytometry. A major advantage of this method is its compatibility with the simultaneous detection of phenotypic and/or functional markers on the lymphocytes. Furthermore, cells can be recovered alive and active after detection of trogocytosis, and are therefore available for further characterization or even conceivably for therapeutic purposes.     

Staphylococcus epidermidis in Orthopedic Device Infections: The Role of Bacterial Internalization in Human Osteoblasts and Biofilm Formation

Background

Staphylococcus epidermidis orthopedic device infections are caused by direct inoculation of commensal flora during surgery and remain rare, although S. epidermidis carriage is likely universal. We wondered whether S. epidermidis orthopedic device infection strains might constitute a sub-population of commensal isolates with specific virulence ability. Biofilm formation and invasion of osteoblasts by S. aureus contribute to bone and joint infection recurrence by protecting bacteria from the host-immune system and most antibiotics. We aimed to determine whether S. epidermidis orthopedic device infection isolates could be distinguished from commensal strains by their ability to invade osteoblasts and form biofilms.

Materials and Methods

Orthopedic device infection S. epidermidis strains (n = 15) were compared to nasal carriage isolates (n = 22). Osteoblast invasion was evaluated in an ex vivo infection model using MG63 osteoblastic cells co-cultured for 2 hours with bacteria. Adhesion of S. epidermidis to osteoblasts was explored by a flow cytometric approach, and internalized bacteria were quantified by plating cell lysates after selective killing of extra-cellular bacteria with gentamicin. Early and mature biofilm formations were evaluated by a crystal violet microtitration plate assay and the Biofilm Ring Test method.

Results

No difference was observed between commensal and infective strains in their ability to invade osteoblasts (internalization rate 308+/−631 and 347+/−431 CFU/well, respectively). This low internalization rate correlated with a low ability to adhere to osteoblasts. No difference was observed for biofilm formation between the two groups.

Conclusion

Osteoblast invasion and biofilm formation levels failed to distinguish S. epidermidis orthopedic device infection strains from commensal isolates. This study provides the first assessment of the interaction between S. epidermidis strains isolated from orthopedic device infections and osteoblasts, and suggests that bone cell invasion is not a major pathophysiological mechanism in S. epidermidis orthopedic device infections, contrary to what is observed for S. aureus.     

The GCP3-interacting proteins GIP1 and GIP2 are required for γ-tubulin complex protein localization, spindle integrity, and chromosomal stability

Microtubules (MTs) are crucial for both the establishment of cellular polarity and the progression of all mitotic phases leading to karyokinesis and cytokinesis. MT organization and spindle formation rely on the activity of γ-tubulin and associated proteins throughout the cell cycle. To date, the molecular mechanisms modulating γ-tubulin complex location remain largely unknown. In this work, two Arabidopsis thaliana proteins interacting with gamma-tubulin complex protein3 (GCP3), GCP3-interacting protein1 (GIP1) and GIP2, have been characterized. Both GIP genes are ubiquitously expressed in all tissues analyzed. Immunolocalization studies combined with the expression of GIP-green fluorescent protein fusions have shown that GIPs colocalize with γ-tubulin, GCP3, and/or GCP4 and reorganize from the nucleus to the prospindle and the preprophase band in late G2. After nuclear envelope breakdown, they localize on spindle and phragmoplast MTs and on the reforming nuclear envelope of daughter cells. The gip1 gip2 double mutants exhibit severe growth defects and sterility. At the cellular level, they are characterized by MT misorganization and abnormal spindle polarity, resulting in ploidy defects. Altogether, our data show that during mitosis GIPs play a role in γ-tubulin complex localization, spindle stability and chromosomal segregation.     

Mapping of Bancroftian Filariasis in Cameroon: Prospects for Elimination

BackgroundLymphatic filariasis (LF) is one of the most debilitating neglected tropical diseases (NTDs). It still presents as an important public health problem in many countries in the tropics. In Cameroon, where many NTDs are endemic, only scant data describing the situation regarding LF epidemiology was available. The aim of this study was to describe the current situation regarding LF infection in Cameroon, and to map this infection and accurately delineate areas where mass drug administration (MDA) was required.MethodologyThe endemicity status and distribution of LF was assessed in eight of the ten Regions of Cameroon by a rapid-format card test for detection of W. bancrofti antigen (immunochromatographic test, ICT). The baseline data required to monitor the effectiveness of MDA was collected by assessing microfilariaemia in nocturnal calibrated thick blood smears in sentinel sites selected in the health districts where ICT positivity rate was ≥ 1%.Conclusion/significanceICT card test results showed that LF was endemic in all the Regions and in about 90% of the health districts surveyed. All of these health districts qualified for MDA (i.e. ICT positivity rate ≥ 1%). Microfilariaemia data collected as part of this study provided the national program with baseline data (sentinel sites) necessary to measure the impact of MDA on the endemicity level and transmission of LF important for the 2020 deadline for global elimination.     

Tetramerization Is a Conserved Feature of the Virion-Associated Protein in Plant Pararetroviruses

All plant pararetroviruses belong to the Caulimoviridae family. This family contains six genera of viruses with different biological, serological, and molecular characteristics. Although some important mechanisms of viral replication and host infection are understood, much remains to be discovered about the many functions of the viral proteins. The focus of this study, the virion-associated protein (VAP), is conserved among all members of the group and contains a coiled-coil structure that has been shown to assemble as a tetramer in the case of cauliflower mosaic virus. We have used the yeast two-hybrid system to characterize self-association of the VAPs of four distinct plant pararetroviruses, each belonging to a different genus of Caulimoviridae. Chemical cross-linking confirmed that VAPs assemble into tetramers. Tetramerization is thus a common property of these proteins in plant pararetroviruses. The possible implications of this conserved feature for VAP function are discussed.