The transgene is designed with a bidirectional tetracycline operator between two cytomegalovirus (CMV) minimal promoters in the opposite orientation. One CMV promoter drives expression of hemagglutinin (HA)-tagged, modified rat transforming growth factor, beta receptor I gene, while the other drives expression of an enhanced green fluorescent protein sequence. Tgfbr1 is made constitutively active by the introduction of a T204D mutation. (J:213201)