Résumé :
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The gene lethal (2) essential for life (lefl), the Drosophiila orthologue of _B-crystallin involved in Desminopathies in human, codes for small heat shock protein wit chaperon activity. lefl is expressed during Drosophila development in embryonic, larval and adult somatic and heart muscles. We investigated the role of lefl during sarcomeres assembly in larva by analyzing muscle-specific gain and loss of its function using GAL-4/UAS system. In muscles of 3rd instar larvae LEFL protein is mainly located on Z-disc and M line extensions linking sarcomeres with muscle membrane. It co-localizes with Vimentin-like and Lamin C proteins, which like Desmin in vertebrates, are intermediate filament proteins. Under attenuation of lefl expression a number of perturbations of muscle pattern occur, like splitting, lack of some muscles or incorrect muscle attachment. Moreover, it has been noticed that muscles of lefl-deficient larvae are shorter and narrower with smaller number o nuclei and sarcomeres. Ultrastuctural analyses confirmed altered sarcomeres organization showing mitochondria with barely visible mitochondrial crests and increased amount of glycogen between myofilaments. We also demonstrated by confocal microscopy analyzes that muscle-specific lefl knockdown causes altered arrangement of Vimentinlike protein indicating affected intermediate filament structure. We observed a meshwork-like organization of Vimentin-labeled filaments on the surface of myofibrils indicating that LEFL and Vimentin-like proteins interact. Thus, the mis-arrangement of intermediate filaments observed in muscles with attenuated lefl expression appears reminiscent of defects in human Desminopathies caused by mutations in _B-crystallin gene.Altogether our data provide evidence that intermediate filaments are part of sarcomeric structures in Drosophila muscles and support a view that fruit fly can be used as a model to study the genetic determinants of intermediate filaments linked myopathies.
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