Rapid Colorectal Adenoma Formation Initiated by Conditional Targeting of the Apc Gene

Familial adenomatous polyposis coli (FAP) is a disease characterized by the development of multiple colorectal adenomas, and affected individuals carry germline mutations in the APC gene. With the use of a conditional gene targeting system, a mouse model of FAP was created that circumvents the embryonic lethality of Apc deficiency and directs Apc inactivation specifically to the colorectal epithelium. IoxP sites were inserted into the introns around Apc exon 14, and the resultant mutant allele (Apc$^{580S}$) was introduced into the mouse germline. Mice homozygous for Apc$^{580S}$ were normal; however, upon infection of the colorectal region with an adenovirus encoding the Cre recombinase, the mice developed adenomas within 4 weeks. The adenomas showed deletion of Apc exon 14, indicating that the loss of Apc function was caused by Cre-IoxP-mediated recombination.