Fig. 1.

Gene activation or deletion by Cre recombinase. Cre recombinase deletes DNA that is flanked by loxP sites. (A) Fusion-gene activation by tissue-specific Cre. Removal of a silenced STOP cassette by Cre allows for expression of the Pax3-Fkhr fusion gene (Keller et al., 2004b). (B) Gene activation by CreER activity. Addition of tamoxifen activates CreER, allowing for removal of the silenced loxP-STOP-loxP cassette. This results in expression of the oncogene SYT-SSX2 (Haldar et al., 2007). (C) Gene deletion via Cre recombinase. Cre activity removes the p53 gene flanked by two loxP sites (Jonkers et al., 2001).