In Tet-Off Systems, the basal state is maintained in the presence of doxycycline (Dox), and induced by its withdrawal. Tet-On Systems are activated in the presence of Dox. System induction produces high-level transcription of EGFP-Medaka polycystic kidney disease 1 (Pkd1) delta N from TRE promotor. Transgene: Medaka polycystic kidney disease 1 (Pkd1) gene, EGFP, pTRE2hyg.