fl-Tcf4 and dnTcf7 transcripts are the predominant Tcf/Lef1 family isoforms expressed in the intestine, which explains the opposite intestinal phenotypes in mice deleted of Tcf7l2 (lack of cycling stem cells) versus Tcf7 (intestinal polyposis) (8, 21, 22). Here, TCF7 is linked to gastrointestinal polyp.