Fig. 4. Maintained Pax7 expression does not prevent the myogenic differentiation of satellite cells. To determine the effects of Pax7 expression on satellite-cell-derived myoblasts, plated myofibres were infected with retrovirus. After a further 72 hours of culture, immunostaining showed that the presence of Pax7, as shown by eGFP expression, did not affect proliferation of satellite-cell-derived progeny as shown by BrdU incorporation (a and b arrows). Similarly, cultures infected with pMSCV-IRES-eGFP (c,d) or pMSCV-Pax7-IRES-eGFP (e,f) were indistinguishable, showing that Pax7 did not alter MyoD expression (examples indicated with arrows). After 1 week of culture, many multinucleated satellite-cell-derived myotubes could be observed. Cultures infected with control pMSCV-IRES-eGFP showed that Pax7 protein was not present in eGFP⁺ myotubes, but was only maintained in single cells (g). By contrast, Pax7 protein was present in the nuclei of eGFP⁺ myotubes in pMSCV-Pax7-IRES-eGFP-infected cultures (h). As in myotubes from non-infected and control pMSCV-IRES-eGFP infected cultures, eGFP⁺ myotubes from cultures infected with pMSCV-Pax7-IRES-eGFP contained MyoD and myogenin (i-l). Bar, 60 µm (a,b); 30 µm (c-l).