Accelerated evolutionary rate of housekeeping genes in tunicates.

International audiencePhylogenomics has recently revealed that tunicates represent the sister-group of vertebrates in the newly defined clade Olfactores. However, phylogenomic and comparative genomic studies have also suggested that tunicates are characterized by an elevated rate of molecular evolution and a high degree of genomic divergence. Despite the recurrent interest in the group, the picture of tunicate peculiar evolutionary dynamics is still fragmentary, as it mainly lies in studies focusing on only a few model species. In order to expand the available genomic data for the group, we used the high-throughput 454 technology to sequence the partial transcriptome of a previously unsampled tunicate, Microcosmus squamiger. This allowed us to get further insights into tunicate-accelerated evolution through a comparative analysis based on pertinent phylogenetic markers, i.e., a core of 35 housekeeping genes conserved across bilaterians. Our results showed that tunicates evolved on average about two times faster than the other chordates, yet the degree of this acceleration varied extensively upon genes and upon lineages. Appendicularia and Aplousobranchia were detected as the most divergent groups which were also characterized by highly heterogeneous substitution rates across genes. Finally, an estimation of the d (N)/d (S) ratio in three pairs of closely related taxa within Olfactores did not reveal strong differences between the tunicate and vertebrate lineages suggesting that for this set of housekeeping genes, the accelerated evolution of tunicates is plausibly due to an elevated mutation rate rather than to particular selective effects

Recovered and recycled Kraft fibers as reinforcement of PP composites

Recycled Kraft fibers coming from old sacs were used for the preparation of polypropylene (PP) composites. Composites up to 50 wt.% of reinforcement were obtained and maleated polypropylene (MAH-PP) was used as coupling agent for improving the fiber-matrix compatibility and adhesion. In the present work, the mechanical properties of the obtained composites as well as the evaluation of interfacial behavior are studied. The results discussion is based on the analysis of the mechanical properties of composites, measurements of surface polarity, specific surface, fiber dimensions, spectroscopic and microscopic analysis. Different adhesion mechanisms at fiber-matrix interface must be presumed depending on the existence of MAH-PP coupling agent, as revealed the analysis of the modification reaction and the conducted proofs. The results showed that the addition of maleated polypropylene favored the incorporation of the relatively high amounts of this natural reinforcement and promoted the stress transfer inside the composite. Thus, an increase up to 50 wt.% of recycled Kraft fibers increased two times the ultimate tensile strength of the non-reinforced matrix. Additionally, the intrinsic mechanical properties of recycled Kraft fibers are deduced by means of modified rule of mixtures and compared to those available in the literature. Finally, an approach of the industrial competitiveness of these fibers, daily present in the market, with respect to E fiberglass is carried out. For this reason a comparison between the mechanical properties and the final cost of PP composites from recycled Kraft fibers or E fiberglass has been considered. © 2007 Elsevier B.V. All rights reserved.Fil: Vilaseca, F.. Universidad de Girona; EspañaFil: Méndez, J.A.. Universidad de Girona; EspañaFil: López J.P.. Universidad de Girona; EspañaFil: Vallejos, María Evangelina. Universidad de Girona; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Materiales de Misiones. Universidad Nacional de Misiones. Facultad de Ciencias Exactas Químicas y Naturales. Instituto de Materiales de Misiones; ArgentinaFil: Barberà, L.. Universidad de Girona; EspañaFil: Pèlach, M.A.. Universidad de Girona; EspañaFil: Turon, X.. Universidad de Girona; EspañaFil: Mutjé, P.. Universidad de Girona; Españ

Évolution des personnels et des laboratoires

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Évolution des personnels et des laboratoires

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Porifera. In: Invertebrate Histology

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