Mice hemizygous for the smMHC/Cre/eGFP transgene (smMHC^Cre/eGFP) are viable and fertile, with the smooth muscle myosin heavy chain (smMHC or Myh11) promoter directing bicistronic Cre and EGFP protein expression to smooth muscle cells during development as well as in the adult mouse. Hemizygotes from founder line SMCG2 (SM2^Cre/GFP) display intense EGFP fluorescence restricted to vascular and nonvascular smooth muscle, with strong concordance between cre expression and EGFP fluorescence (verifying the use of fluorescence as a marker for conditional gene recombination). When bred with mice containing a loxP-flanked sequence of interest, the resulting offspring can have Cre-mediated recombination of the flanked sequence in smooth muscle. Homozygotes are viable and fertile, with smaller litter sizes and a higher incidence of perinatal mortality. These smMHC/Cre/eGFP transgenic mice may be useful in studies utilizing "Cre-lox" technology or fluorescent protein expression in smooth muscle, especially separation of vascular myocytes from the surrounding cellular environment to isolate muscle specific adaptations or disease responses.

Considerations for experimental use: The donating investigator reports that the transgene is expressed in female germ cells and that Cre protein (or maternal RNA) may be passed to all embryos. If bred to males carrying a "floxed" allele, all offspring (cre-positive or cre-negative) may exhibit universal Cre-mediated recombination of the allele during early embryonic development. The donating investigator also reports transgene expression in the male germ line; post meiotic spermatagonia transiently express Cre recombinase with expression ending prior to fertilization. Therefore, Cre activity may be observed in all haploid male germ cells (cre-positive or cre-negative). If transgenic males also harbor "floxed" alleles in their genome, these loci may undergo universal Cre-mediated recombination in the sperm. As Cre activity ceases before fertilization, the resulting offspring exhibit no universal deletion affect on any "floxed" allele(s) of maternal origin. Because smMHC/Cre/eGFP transgene expression is observed in both maternal and paternal germlines, it is recommended to maintain the smMHC/Cre/EGFP transgenic colony without additional "floxed" mutations in their genome.