Résumé :
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Communication n° 484. Muscle Progenitor Cells (MPCs; Myf5+) and their ancestors in mice are born in the dorsal (epaxial) and ventral (hypaxial) lips of the somite dermomyotome (DM) epithelium. Pax3 and Pax7 mark essentially all cells in the DM. The DM assures a continued source of MPCs until this epithelium dissociates. In the somite, MPCs give rise to precursor cells (myoblasts) which form the first (post-mitotic) skeletal mass, the myotome. We are interested in how the skeletal muscle stem cell pool is retained throughout development. One mode of stem cell self-renewal is via asymmetric divisions. Several cell fate determinants, such as Numb, have been implicated in binary cell fate choices during asymmetric cell divisions, but the mechanisms involved in generating cell diversity in vertebrates remains largely unknown. To assess how stem cells and progenitor cells in the DM are maintained, we investigated the orientations of cell divisions using immuno-histochemistry on sections and wholemount. Our analysis shows that divisions in the plane of the DM are rare and that the dividing nuclei are preferentially located on the apical side of the DM epithelium. Immunostainings with Numb antibody localise this determinant to the apical surface of the DM. In parallel, using a transgenic approach, we directed the expression of Numb-GFP and H2B-mRFP to the epaxial DM lip using an enhancer from the Myf5 gene. This should allow us to analyse live Numb-GFP segregation with respect to the dynamics of the division in the DM, as well as the consequences of Numb over expression on cell fate decisions.
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