Abstract: A method and system for controlling the expression of transgene products in specific tissues in a transgenic animal is provided. The method comprises: a) providing a fist transgenic parent animal whose genome comprises an F transgene comprising an exogenous gene operatively linked to a promoter that is upregulated by a transactivator protein; b) providing a second transgenic parent animal whose genome comprises i) a second transgene, comprising a second promoter that is downregulated by the transactivator protein and operatively linked to an antisense gene that encodes a sequence which inhibits or reduces processing of the F transgene transcript; and ii) a third transgene comprising a tissue specific promoter operatively linked to a gene encoding the transactivator protein; and c) breeding the first transgenic parent animal with the second transgenic parent animal to provide a transgenic offspring animal whose genome comprises the three transgenes.