Résumé :
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During embryogenesis, the skeletal muscle is constituted by myogenic progenitor cells. But around birth, foetal muscle progenitor cells adopt a satellite cell position, becoming embedded within the basal lamina in close contact to the muscle fibers. Importantly during this transition, in addition to this morphological change, the emerging satellite cells enter quiescence, a molecular state poorly characterized in vivo. After the transition (during the post-natal growth), in response to injury a subset of the satellite cells become activated, proliferate and either fuse to form multinucleated myotubes. Moreover, the satellite cells are able to re-establish a residual pool of quiescent satellite cells that have the capability of supporting additional rounds of growth/regeneration: they are able to self-renew. The satellites cells are the adult myogenic stem cells. We are interested in identifying new molecular pathways involved in the transition from a proliferating population to a quiescent post-natal progenitor cell population. Pax3 is a paired-homeobox transcription factor expressed in muscle progenitor cells throughout development, including post-natal satellite cells. We used a previously generated Pax3GFP/+ allele (Relaix et al., 2005), which provides direct and efficient access to the Pax3-expressing muscle progenitor cells through FACS-sorting. We have performed expression profiling of Pax3GFP/+ cells during development and in early post-natal muscle progenitor cells and identified factors specifically regulated during specification of muscle satellite cells. Results and validation of the screen as well as functional analysis of novel candidate genes will be presented. Here, the Ephrin pathway will be discussed and observed in the ex vivo model of the isolated fibers.
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