Origin and hierarchy of basal lamina-forming and -non-forming myogenic cells in mouse skeletal muscle in relation to adhesive capacity and Pax7 expression in vitro

As a novel approach to distinguish skeletal myogenic cell populations, basal lamina (BL) formation of myogenic cells was examined in the mouse compensatory enlarged plantaris muscles in vivo and in fiber-bundle cultures in vitro. MyoD + myogenic cells located inside the regenerative muscle fiber BL were laminin − but interstitial MyoD + cells were laminin + . This was also confirmed by electron microscopy as structural BL formation. Similar trends were observed in the fiber-bundle cultures including satellite cells and interstitial myogenic cells and laminin + myogenic cells predominantly showed non-adhesive (non-Ad) behavior with Pax7 − , whereas laminin − cells were adhesive (Ad) with Pax7 + . Moreover, non-Ad/laminin + and Ad/laminin − myotubes were also observed and the former type showed spontaneous contractions, while the latter type did not. The origin and hierarchy of Ad/Pax7 + /laminin − and non-Ad/Pax7 − /laminin + myogenic cells were also examined using skeletal muscle interstitium-derived CD34 + /45 − (Sk-34) and CD34 − /45 − (Sk-DN) multipotent stem cells, which were composed of non-committed myogenic cells with a few (