Tg(Wap-tAg)1Gmn

The transgene consists of a 1600 bp DNA fragment containing the promoter of the mouse whey acidic protein gene joined to the SV40 early region, which includes the overlapping sequences encoding the SV40 large and small T-antigen genes. So that only the small t antigen is expressed, the 5' splice site of the large T antigen mRNA was modified by site-directed mutagenesis (CTGAG/GTATTT to CTGAA/GTCTT); this alteration entirely suppresses splicing of the transcript encoding the large T antigen without affecting the coding sequence of the small t antigen. RT-PCR and western blot analysis demonstrate high-level expression of the small t antigen mRNA and protein, respectively, in mammary gland epithelial (ME) cells of transgenic female mice during their first pregnancy that continues in the surviving ME cells after lactation ceases. Neither large T antigen mRNA nor protein is detectable in ME cells of these mice. (J:69711)