I want to do hESC differentiation with some TFs, which work at different stages. The ef1a promoter drive genes without control. Dox-TRE system can only control one stage? How to control different TF expression in several stages? For example, stage I express A and B, stage II express C and D, stage III express E and F. As I know oct4 promoter is huge, does it ok for Lentiviral Vectors?