The reverse tetracycline-controlled transactivator rtTA2-S2 is toxic in mouse embryonic stem cells Vitezslav Bryja, Jiri Pachernik, Lukas Kubala, Ales Hampl and Petr Dvorak Reprod. Nutr. Dev., 43 6 (2003) 477-486 DOI: 10.1051/rnd:2004001