To adapt the alphoidtetO-HAC [8] for CIN studies, the EGFP transgene cassette was inserted into a single loxP loading site of the HAC [13] in hamster HPRT-deficient Chinese Hamster Ovary (CHO) cells (Figure 3A, B, 2B). Here, HPRT1 is linked to cervical squamous intraepithelial neoplasia.