Résumé :
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Despite the fact that cardiac and skeletal muscles are structurally and functionally distinct, we show that a subset of skeletal muscles share common progenitors with the heart.It is established that somitic mesoderm is not the only source of skeletal muscle progenitors. Extraocular muscles, masticatory muscles, facial expression muscles, as well as some neck muscles, have been shown to originate from either the prechordal, cranial paraxial or occipital lateral plate mesoderm and do not derive from the somites. All of these muscles show a particular regulatory network, which does not involve Pax3, a key regulator of trunk myogenesis. These muscles however derive from progenitors that have expressed Isl1, an important regulator of cardiac development.We have investigated a possible clonal relationship between skeletal muscles and heart myocardium by using retrospective clonal analysis in the mouse embryo, in which a nlaacZ sequence, converted to functional nlacZ after a rare intragenic recombination event, is targeted to the _c-actin gene, expressed in all developing skeletal and cardiac muscle. We have first distinguished two head muscle lineages, which segregate early, both of which also contribute to the myocardium at the arterial pole of the heart. The first gives rise to masticatory muscles, and also contributes to myocardium of the right ventricle. The second lineage gives rise to muscles of facial expression and also contributes to outflow tract myocardium at the base of the arteries. Further sublineages distinguish myocardium at the base of the aorta or pulmonary trunk, with a clonal relationship to right or left head muscles, respectively. Our data also indicate that trapezius and sternocleidomastoid neck muscles belong to a distinct muscle lineage, which strikingly also contributes to myocardium at the venous pole of the heart.We thus establish lineage trees, that we correlate with genetic regulation, and link groups of skeletal muscles to different parts of the heart. This has implications for muscle-type specific myopathies.
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