Fig. 4.

Increased numbers of pituitary progenitor/stem cells and an elevated proliferation rate underlie the formation of the murine tumors. (A) Total numbers of progenitor/stem cells (colony-forming cells) are significantly elevated in the Hesx1^Cre/+;Ctnnb1^+/lox(ex3) pituitaries relative to controls from late gestation to adulthood (n = 5–8 pituitaries per stage). (B) Time-lapse microscopy frames showing the formation of a colony from a single progenitor/stem cell (arrowhead, Upper left). (C) Time-lapse microscopy showing that the proliferation rate of pituitary progenitor/stem cells is increased in Hesx1^Cre/+;Ctnnb1^+/lox(ex3) mutant (Lower row) relative to Ctnnb1^+/lox(ex3) control pituitaries (Upper row). (D) Representative examples of lineage trees indicating faster division times in the double heterozygotes. (E) Photographs of tissue culture plates containing fixed and hematoxylin-stained colonies demonstrate the presence of higher numbers and overall larger colonies in the Hesx1^Cre/+;Ctnnb1^+/lox(ex3) pituitaries (Right) relative to Ctnnb1^+/lox(ex3) controls (Left). (F) Expression of mutant β-catenin in committed progenitors (Pit1-Cre;Ctnnb1^+/lox(ex3)) (Left) or terminally differentiated hormone-producing cells (Gh-Cre;Ctnnb1^+/lox(ex3) (Center) and Prl-Cre;Ctnnb1^+/lox(ex3)) (Right) is not tumorigenic, and pituitaries from adult mice are normal. (Scale bars: 100 μm.)