Figure 3. Lkb1-deficient stromal cells expand clonally during polyp development.

(A) Representative X-gal–stained antral sections from Lkb1^FspKO/FspKO;R26R-LacZ mice with increasing severity of polyposis at 3–4 months of age. Left: Macroscopically normal-looking gastric mucosa with local accumulation of Lkb1-deficient stroma. Middle: Larger expansion of Lkb1-deficient stroma with disorganized glands. Right: Antral polyp demonstrating stroma filled by Lkb1-deficient cells while epithelium remained entirely wild type. Scale bars: 100 μm. (B) Schematic presentation of R26R-Confetti allele. Cre-mediated recombination leads to excision of one of the 2-color cassettes and allows reorientation of the remaining cassette, resulting in the expression of 4 alternative fluorescent colors, nGFP, YFP, RFP, or mCFP (25). Cells expressing similar color are derived from a clonal origin. (C) Left: Low-magnification image of an Lkb1^FspKO/FspKO;R26R-Confetti polyp. Note large foci expressing similar fluorescent colors. Right: Zoom-in images of areas with RFP and nGFP/YFP stroma. Representative image is shown. Scale bar: 50 μm.