Hello, i am facing a problem with transgenic mice. I am using mice with inducible gene expression of a human transgene upon Doxycycline. These mice have aMHCre/R26 promoter with a floxed stop cassette which drives the expression of rtTA after removal of stop cassette from Cre, and Tre promoter which drives the expression of the gene of interest after rtTA binding ( with Doxycycline). The problem i am facing is that i see expression of the gene in both Cre positive and Cre negative mice and in all the tissues, not only in the heart. It seems that Cre doesn’t drive the tissue specificity overexpression. Does anyone have an idea of what is happening? Thanks.