Recombinase mediated cassette exchange was used to insert a tetO, CAG regulated EGFP followed by a short hairpin RNAi specific for the Brachyury (T) gene followed by a PGK promoter into the Gt(ROSA)26Sortm1Bgh allele. The tetracycline silencer prevents expression of both the reporter and the shRNAi until mice are treated with doxycycline.