Résumé :
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Communication n° 681. The pleckstrin homology domain-containing protein CKIP-1 was isolated in a yeast two-hybrid screen using CK2 alpha as bait. CKIP-1 is expressed in several human normal tissues, including brain, placenta, lung and heart. Its expression is higher in skeletal muscle. CKIP-1 is expressed at low level in proliferating C2C12 myoblast cells and its expression is upregulated upon induction of differentiation in parallel with myogenin, suggesting a role of CKIP-1 in this process. Ectopic expression of CKIP-1 in these C2C12 cells first promoted their proliferation and then stimulated their differentiation, thus mimicking exogenous IGF addition. Moreover, silencing of CKIP-1 by RNA interference abolished proliferation and delayed differentiation. Interference with the PI3-K signaling impeded CKIP-1 effect on myoblast differentiation. Thus, these data argue for CKIP-1 implication in IGF-PI3-K regulated muscle differentiation. This also suggests that CKIP-1 could be involved in skeletal muscle development. We are investigating his potential role in in vivo myogenesis in zebrafish that has proven to be a good model for studying early steps of myogenesis as well as pathological muscle development. Using whole-mount in situ hybridization technique, we are studying CKIP-1 expression pattern in developing embryos and comparing it with key myogenic regulators such as Pax-3, Pax-7, MyoD, Myf-5 and myogenin. Then, we will determine the consequences of either a down or upregulation of CKIP-1 expression on skeletal muscle development. CKIP-1 knock down expression will be realized by injection of either morpholino-oligonucleotides directed against the 5'-untranslated region of CKIP-1 mRNA or expression of a dominant negative mutant of CKIP-1.
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