Generation of trigenic pUHD-Tam67/MMTV-rtTA/MMTV-erbB2 mice and expression of the transgenes in mammary glands. A, bigenic pUHD-Tam67/MMTV-rtTA mice were generated by crossing heterozygous or homozygous pUHD-Tam67 mice with MMTV-rtTA mice. Offspring were screened by PCR of tail DNA. Identified bigenic pUHD-Tam67/MMTV-rtTA mice were crossed with MMTV-erbB2 mice. Offspring were screened for the presence of Tam67, rtTA, and erbB2 transgenes. B, five mice each were set for control or doxycycline treatment groups. The adult trigenic pUHD-Tam67/MMTV-rtTA/MMTV-erbB2 mice were fed either regular water or doxycycline-water for 2 wk, and then mammary glands were collected in tissue lysates for Western blot analysis. C, ErbB2, Flag-Tam67, rtTA, and β-actin were detected in mammary glands of control and doxycycline-treated mice by Western blotting with specific antibodies.