The fDTR transgene was designed with a loxP-flanked alkaline phosphatase-polyadenylation signal upstream of a human diphtheria toxin receptor (DTR; heparin-binding epidermal growth factor-like growth factor (HBEGF)) under the transcriptional control of the murine calcium/calmodulin-dependent protein kinase II alpha (CamKIIalpha) promoter. Lines A and B were generated with line B exhibiting reduced expression compared with line A. (J:197654)