Gtwnt-5 a member of the wnt family expressed in a subpopulation of the nervous system of the planarian Girardia tigrina

Wnt proteins are a family of highly conserved secreted glycoproteins that regulate cell-to-cell interactions during embryogenesis. They act as signaling molecules and take part in many crucial decisions throughout the development of organisms ranging from Hydra to human. We have isolated and characterized the expression of a member of the Wnt family, Gtwnt-5 gene in the planarian Girardia tigrina. Planarians are free-living members (Class Turbellaria) of the Phylum Platyhelminthes. They are best known for their high regenerative capabilities. These organisms have an apparently simple central nervous system (CNS) from a morphological perspective, with cephalic ganglia in the dorsal anterior region and two ventral main nerve cords along the body. However, a large number of planarian neural genes have recently been identified and therefore it is possible to define different molecular and functional domains in the planarian brain. The present study shows expression of Gtwnt-5 in a subpopulation of the whole CNS of intact organisms, being activated during regeneration. Gtwnt-5 reveals a differential spatial pattern: the expression is preferentially found in the most external region of the CNS. In addition, a kind of iterative pattern has been observed at the ganglia level, suggesting that the planarian brain might not be a continuous structure but compartmented or regionalized. Gtwnt-5 signal is also detected at the sensors of the worm: at the auricle level and all around the cephalic periphery. All these data provide us with a new neural marker for the planarian brain, and can be used to follow regeneration of the CNS.     

Did My M.D. Really Go to University to Learn? Detrimental Effects of Numerus Clausus on Self-Efficacy,Mastery Goals and Learning

Exams with numerus clausus are very common in Medicine, Business Administration and Law. They are intended to select a predefined number of academic candidates on the basis of their rank rather than their absolute performance. Various scholars and politicians believe that numerus clausus policies are a vector of academic excellence. We argue, however, that they could have ironic epistemic effects. In comparison with selective policies based on criterion-based evaluations, selection via numerus clausus creates negative interdependence of competence (i.e., the success of some students comes at the expense of the others). Thus, we expect it to impair students’ sense of self-efficacy and—by extension—the level of mastery goals they adopt, as well as their actual learning. Two field studies respectively reported that presence (versus absence) and awareness (versus ignorance) of numerus clausus policies at University was associated with a decreased endorsement of mastery goals; this effect was mediated by a reduction in self-efficacy beliefs. Moreover, an experimental study revealed that numerus clausus negatively predicted learning; this effect was, again, mediated by a reduction in self-efficacy beliefs. Practical implications for the selection procedures in higher education are discussed.     

Identities in conflict: The Aboriginal question and the politics of recognition in Quebec

The will to have one's own particular identity universally acknowledged and respected is now one of the most significant determinants of the sociopolitical dynamic of contemporary modern societies. However, the actual recognition of difference is more often than not an unsatisfactory and disappointing experience for many of the groups and communities striving for that recognition. The recent experience of Canadian Aboriginal peoples is a case in point. This article looks at the struggle of Aboriginal nations for recognition in one particular region of Canada, the province of Quebec. Indeed, Quebec offers a revealing case‐study of the peculiarities of the politics of recognition. For over three decades now, the French‐speaking majority of Quebec has striven to assert its ethnocultural distinctiveness and laid claims to a special status within the Canadian political and constitutional framework. Today, both Quebecers and Aboriginals are recognition seekers within the Canadian polity. As a result, their relationship is inevitably marked by their respective but competing attempt to draw the attention of the Canadian state to their particular identity claims. In recent years, this has led to a highly conflictual dynamic which considerably strains any hope of social and cultural coexistence. The article examines the particularities of the politics of recognition in the Quebec context. Its objective is twofold. First, it should serve to shed some light on the manifestations of Aboriginal ethnonationalism in Canada. Secondly, it seeks to illustrate the limitations and paradoxical nature of the politics of recognition within a liberal framework.     

Cytoprotective effects of the antioxidant phytochemical indicaxanthin in β-thalassemia red blood cells

Antioxidant phytochemicals are investigated as novel treatments for supportive therapy in β-thalassemia. The dietary indicaxanthin was assessed for its protective effects on human β-thalassemic RBCs submitted in vitro to oxidative haemolysis by cumene hydroperoxide. Indicaxanthin at 1.0–10 μM enhanced the resistance to haemolysis dose-dependently. In addition, it prevented lipid and haemoglobin (Hb) oxidation, and retarded vitamin E and GSH depletion. After ex vivo spiking of blood from thalassemia patients with indicaxanthin, the phytochemical was recovered in the soluble cell compartment of the RBCs. A spectrophotometric study showed that indicaxanthin can reduce perferryl-Hb generated in solution from met-Hb and hydrogen peroxide (H₂O₂), more effectively than either Trolox or vitamin C.

Collectively our results demonstrate that indicaxanthin can be incorporated into the redox machinery of β-thalassemic RBC and defend the cell from oxidation, possibly interfering with perferryl-Hb, a reactive intermediate in the hydroperoxide-dependent Hb degradation. Opportunities of therapeutic interest for β-thalassemia may be considered.     

Bioinformatic and biochemical evidence for the identification of the type III secretion system needle protein of Chlamydia trachomatis

Chlamydia spp. express a functional type III secretion system (T3SS) necessary for pathogenesis and intracellular growth. However, certain essential components of the secretion apparatus have diverged to such a degree as to preclude their identification by standard homology searches of primary protein sequences. One example is the needle subunit protein. Electron micrographs indicate that chlamydiae possess needle filaments, and yet database searches fail to identify a SctF homologue. We used a bioinformatics approach to identify a likely needle subunit protein for Chlamydia. Experimental evidence indicates that this protein, designated CdsF, has properties consistent with it being the major needle subunit protein. CdsF is concentrated in the outer membrane of elementary bodies and is surface exposed as a component of an extracellular needle-like projection. During infection CdsF is detectible by indirect immunofluorescence in the inclusion membrane with a punctuate distribution adjacent to membrane-associated reticulate bodies. Biochemical cross-linking studies revealed that, like other SctF proteins, CdsF is able to polymerize into multisubunit complexes. Furthermore, we identified two chaperones for CdsF, termed CdsE and CdsG, which have many characteristics of the Pseudomonas spp. needle chaperones PscE and PscG, respectively. In aggregate, our data are consistent with CdsF representing at least one component of the extended Chlamydia T3SS injectisome. The identification of this secretion system component is essential for studies involving ectopic reconstitution of the Chlamydia T3SS. Moreover, we anticipate that CdsF could serve as an efficacious target for anti-Chlamydia neutralizing antibodies.     

Effects of chronic exposure to cadmium- or lead-enriched environments on ionic currents of identified neurons inLymnaea stagnalis L.

Summary 1. Voltage-activated ionic currents of three identified neurons ofLymnaea stagnalis L. were compared in control snails and in animals having been exposed to a cadmium- or lead-enriched environment for 2 weeks. We determined the presence, amplitude, and changes, if any, in the current-voltage characteristics of calcium and potassium currents in each of the three neurons from each of the three groups of animals. Finally, we have compared the effects of acute administration of Cd²⁺ or Pb²⁺ on neurons from control and chronically exposed animals.2. Chronic exposure to cadmium resulted in a near doubling of the high voltage-activated calcium current.3. No differences were found in the effects of acute application of Cd²⁺ or Pb²⁺ on neurons of pretreated and control animals. Cadmium was a potent blocker of the Ca current in either case, while lead caused only a 20% inhibition of the Ca current in neurons of both control and lead-exposed animals.4. Potassium currents were affected in both Cd²⁺- and Pb²⁺-exposed animals. While the sustained outward current was not influenced noticeably, the fast K current was affected in different ways in different neurons. Some did not show this current in the controls but expressed it in neurons from the exposed animals. Other neurons showed the current in the controls and its depression in exposed animals. Acute application of cadmium did not modulate the K current, but lead enhanced the peak amplitude of the transient K current in neurons of both exposed and control snails.     

The growth suppressing gas1 product is a GPI-linked protein

Growth arrest specific (gas) 1 gene product is expressed in non-transformed fibroblasts in response to stimuli driving cells into Go phase. Gas1 has been demonstrated to inhibit cell proliferation when over-expressed in proliferating fibroblasts. This activity depends on a function of the p53 protein independent of its transactivating ability. To better define the pathway leading from Gas1, which is located on the plasma membrane, to p53, we have undertaken a detailed characterization of its topology. We demonstrate that the protein undergoes cotranslational modifications in the endoplasmic reticulum, consisting of signal peptide cleavage, N-linked glycosylation and glycosyl-phosphatidylinositol anchor addition. Immunoelectron microscopy shows that, in its mature form, Gas1 is randomly distributed over the outer leaflet of the plasma membrane and that upon antibody-induced clustering it relocalizes to caveolae.