The transposon containing an unspecified hybrid actin promoter driving expression of red fluorescent protein (RFP) flanked by piggyBac-specific left and right terminal sequences was co-injected with a piggyBac-containing transgene to mobilize the transposon. The transposon inserted into intron 3 of the gene, resulting in overexpression in homozygous mutant mice. RT-PCR of whole embryos and embryonic kidneys of E12.5 homozygous and heterozygous mice detected an increase in expression levels compared to that in wild type mice.