Résumé :
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Non-satellite cells are known to possess myogenic potential and can participate in muscle regeneration, however, their precise position, origin and relationship to satellite cells remain unclear. During postnatal growth, PW1/Peg3, a gene co-expressed with Pax7 in satellite cells, is also expressed in a sub-population of muscle resident interstitial cells, termed PICs (PW1 interstitial cells). In primary cultures, we readily obtain PW1+/Pax7+/MyoD+ cells (myoblasts) but fail to obtain PW1+/Pax7- cells (PICs). We therefore sought to isolate PICs by FACS using stem cell markers. We obtain a population of Sca1+/CD34+ cells that is highly enriched for PICs, distinct from the Sca1-/CD34+ satellite cells. In culture, PICs predominantly acquire a smooth muscle identity but do show spontaneous skeletal myogenic conversion. When PICs are co-cultured with satellite cells, they become PW1+/Pax7+/MyoD+, indistinguishable from satellite cells. In the Pax7 mutant, we note a marked increase in the PIC population. In culture, purified Pax7 mutant satellite cells show pronounced myogenic capacity. In contrast, Pax7 mutant PICs cannot spontaneously convert to the myogenic lineage, suggesting that Pax7 is required to recruit PICs to the satellite cell pool. Injection of labelled PICs into injured muscle reveals participation in myogenesis as well as repopulation of the PICs revealing stem cell properties in vivo. Taken together, these results demonstrate the existence of a substantial and previously unidentified population of resident postnatal skeletal muscle stem cells.
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