The expression of E7 is required for the maintenance of high-grade cervical dysplasia and cervical cancer in Bi-L E7/K5-tTA bitransgenic mice. Shown in all panels are images of sections of the endocervices from bitransgenic mice expressing E7 for the indicated duration. A, composite images at ×10 magnification of sections of the endocervix stained with H&E. Insets, ×40 magnification of cancers in mice receiving no doxycycline (left) or 3 d of doxycycline (middle). B, images at ×40 magnification of sections from the endocervical epithelium stained with H&E, illustrating a region of high-grade dysplasia observed in a bitransgenic mouse receiving no doxycycline (left) and the regression of high-grade dysplasia on treatment of bitransgenic mice with doxycycline for 3 d (middle) or 1 mo (right). C and D, immunohistochemical analysis of BrdUrd (C) and MCM7 (D) in the endocervical epithelium of mice receiving no doxycycline (left), 3 d of doxycycline (middle), or 1 mo of doxycycline (right). The black line delineates the basement membrane. Insets, results from tumors from the same animals.