Beginning with the Pax7tm1.2Sjc allele in which exon 2 was knocked out leaving a single loxP site, part of exon 1 was replaced with a cre/ERT2 (ESR1) fusion followed by an IRES-DsRed and an frt flanked neo cassette. Germ line, flp mediated recombination removed the neo cassette. The absence of full-length Pax7 protein expression was confirmed by western blot analysis on P10 tibialis anterior muscle extracts. Expression of the fusion cre/ERT2 protein was confirmed by a cross with a reporter line. DsRed fluorescence was not detectable by epifluorescence nor was DsRed protein by immunostaining.