The transgene contains the following elements: the CAG promoter, a loxP site, a cat (chloramphenicol acetyltransferase) gene and polyA signal sequences, a second loxP site, and a mouse Trim8 cDNA and polyA signal sequences. This transgene allele normally expresses the cat gene: only after cre-mediated removal of the cat gene will it express the Trim8 gene. Four mouse lines (1-4) were established and line 4, which has the highest increase in Trim8 peptide expression after induction, was selected for further study.