Live imaging of targeted cell ablation in Xenopus:a new model to study demyelination and repair

Live imaging studies of the processes of demyelination and remyelination have so far been technically limited in mammals. We have thus generated a Xenopus laevis transgenic line allowing live imaging and conditional ablation of myelinating oligodendrocytes throughout the central nervous system (CNS). In these transgenic pMBP-eGFP-NTR tadpoles the myelin basic protein (MBP) regulatory sequences, specific to mature oligodendrocytes, are used to drive expression of an eGFP (enhanced green fluorescent protein) reporter fused to the E. coli nitroreductase (NTR) selection enzyme. This enzyme converts the innocuous pro-drug metronidazole (MTZ) to a cytotoxin. Using two-photon imaging in vivo, we show that pMBP-eGFP-NTR tadpoles display a graded oligodendrocyte ablation in response to MTZ, which depends on the exposure time to MTZ. MTZ-induced cell death was restricted to oligodendrocytes, without detectable axonal damage. After cessation of MTZ treatment, remyelination proceeded spontaneously, but was strongly accelerated by retinoic acid. Altogether, these features establish the Xenopus pMBP-eGFP-NTR line as a novel in vivo model for the study of demyelination/remyelination processes and for large-scale screens of therapeutic agents promoting myelin repair

Exploring nervous system transcriptomes during embryogenesis and metamorphosis in Xenopus tropicalis using EST analysis

<p>Abstract</p> <p>Background</p> <p>The western African clawed frog <it>Xenopus tropicalis </it>is an anuran amphibian species now used as model in vertebrate comparative genomics. It provides the same advantages as <it>Xenopus laevis </it>but is diploid and has a smaller genome of 1.7 Gbp. Therefore <it>X. tropicalis </it>is more amenable to systematic transcriptome surveys. We initiated a large-scale partial cDNA sequencing project to provide a functional genomics resource on genes expressed in the nervous system during early embryogenesis and metamorphosis in <it>X. tropicalis</it>.</p> <p>Results</p> <p>A gene index was defined and analysed after the collection of over 48,785 high quality sequences. These partial cDNA sequences were obtained from an embryonic head and retina library (30,272 sequences) and from a metamorphic brain and spinal cord library (27,602 sequences). These ESTs are estimated to represent 9,693 transcripts derived from an estimated 6,000 genes. Comparison of these cDNA sequences with protein databases indicates that 46% contain their start codon. Further annotation included Gene Ontology functional classification, InterPro domain analysis, alternative splicing and non-coding RNA identification. Gene expression profiles were derived from EST counts and used to define transcripts specific to metamorphic stages of development. Moreover, these ESTs allowed identification of a set of 225 polymorphic microsatellites that can be used as genetic markers.</p> <p>Conclusion</p> <p>These cDNA sequences permit <it>in silico </it>cloning of numerous genes and will facilitate studies aimed at deciphering the roles of cognate genes expressed in the nervous system during neural development and metamorphosis. The genomic resources developed to study <it>X. tropicalis </it>biology will accelerate exploration of amphibian physiology and genetics. In particular, the model will facilitate analysis of key questions related to anuran embryogenesis and metamorphosis and its associated regulatory processes.</p

Running GAGs: myxoid matrix in tumor pathology revisited: What’s in it for the pathologist?

Ever since Virchow introduced the entity myxoma, abundant myxoid extracellular matrix (ECM) has been recognized in various reactive and neoplastic lesions. Nowadays, the term “myxoid” is commonly used in daily pathological practice. But what do today’s pathologists mean by it, and what does the myxoid ECM tell the pathologist? What is known about the exact composition and function of the myxoid ECM 150 years after Virchow? Here, we give an overview of the composition and constituents of the myxoid ECM as known so far and demonstrate the heterogeneity of the myxoid ECM among different tumors. We discuss the possible role of the predominant constituents of the myxoid ECM and attempt to relate them to differences in clinical behavior. Finally, we will speculate on the potential relevance of this knowledge in daily pathological practice

Rotational Moulding of Thermosets: Understanding of a Reactive Forming Process

L'auteur Abbas TCHARKHTCHI faisait parti en 2008 du Laboratoire d’Ingénierie des Matériaux (LIM). Depuis 2010, le LIM a fusionné avec deux autres unités de recherche en un seul laboratoire intitulé PIMM (Procédés et Ingénierie en Mécanique et Matériaux). Il fait parti du groupe de recherche : Procédés et Performance des Polymères et Composites.Physical and chemical transformations of polyurethane thermoset are studied by means of thermal analysis, infrared spectrophotometer and dynamic rheology. Gel point, which limits the material flow, is given as a function of conversion and as a function of time by kinetic law. Glass transition corresponding to a dramatic transformation of the material is also explored and connected to conversion and time. These ex situ characterizations are then exploited in terms of rotational moulding process parameters to improve the understanding and thus the control of the process. Therefore in situ thermal analyses are handled to confirm first results. Final parts thickness distribution is examined as a quantitative parameter of process quality. Finally, as a perspective, ultrasonic response is also studied as a new way to follow material evolution directly in the forming mould

Insights from Xenopus genomes.

International audienceAmphibians have been used since the 19th century as vertebrate models for the experimentalist. Since 50 years or so, Xenopus laevis is the most widely used anuran amphibian research organism. However, because it is a pseudo-tetraploid species, its genetics has been lagging behind. Contemporary studies shift their focus to the only Xenopus species known to be diploid, the small African tropical clawed frog Xenopus tropicalis. A complete genome project is undertaken, with genetic and physical mapping going alongside cDNA and genome sequencing. Currently, X. tropicalis is the most distantly related vertebrate species to humans that still exhibits long-range synteny. Much of amphibian genetics can be learned from this genomic undertaking, and could shed light on fascinating biological processes such as embryogenesis, regeneration and metamorphosis. Moreover, Xenopus species are exciting models for the study of gene duplication because new species can evolve through allopolyploidization, a type of genome duplication that can result from hybridization among species. The current genomic resources for Xenopus briefly described here, combined with the practical experimental advantages of this non-mammalian vertebrate model, make it ideally suited for systematic functional genomic studies

Sulfadoxine-pyrimethamine susceptibilities and analysis of the dihydrofolate reductase and dihydropteroate synthase of Plasmodium falciparum isolates from Cote d'Ivoire

Over a 2-year study period, three methods [a test of therapeutic efficacy, an in-vitro assay, and sequencing of the parasites' dihydrofolate-reductase (dhfr) and dihydropteroate-synthase (dhps) genes] were used to monitor sulfadoxine-pyrimethamine (SP) resistance in the Plasmodium falciparum strains infecting young children near Abidjan, the largest city in Cote d'Ivoire. Overall, 118 children aged < 5 years and infected with P. falcipartan were treated with SP. Twenty-one (23.5%) of the 89 children who completed the 14 days of follow-up were categorized as therapeutic failures. When P. falcipartan isolates from the 61 children with adequate parasitaemias were investigated in the in-vitro assay, 24 (39.5%) were found to be highly resistant to pyrimethamine, each having a median inhibitory concentration (IC50) of at least 2000 nm. Polymorphism analysis of gene fragments of 118 P. falciparum isolates (one from each child enrolled in the study) revealed that 46 (39%) of the isolates had mutant dhfr and 111 (94%) had mutant dhps. The mutations mainly affected DHFR codon 108 (39% of the isolates) and DHPS codons 436 (65%), 437 (52%) and 613 (27%). Of the 37 DHFR mutant isolates from children who completed follow-up, 21 were from children with therapeutic failure, indicating that mutant DHFR was associated with resistance to pyrimethamine in vivo (kappa=0.61). A mutant dhfr genotype was also found to be strongly associated with resistance to pyrimethamine in vitro (kappa=0.79). There was, however, little evidence of an association between SP efficacy and dhps genotype (kappa=0.04). Resistance to SP appears to be an increasing problem in southern Cote d'Ivoire and one which may now justify a change away from this drug combination as the first- or second-line treatment for P. falciparum malaria in this area