Figure 7. Stabilization of β-catenin promotes SS18-SSX2–driven transformation of mesenchymal progenitors.

(A) Kaplan-Meier plot of the fraction without tumor among Prx1Cre^ERT2 mice bearing hSS2, Ctnnb1^ex3fl, or both conditional alleles (n = 7 for each; log rank test Z score = 3.83 and P < 0.001). (B) Posteroanterior radiographs of a control mouse and (C) a Prx1Cre^ERT2 hSS2 Ctnnb1^ex3fl mouse at 10 weeks of age, as well as posteroanterior photographs of the same (D and E, respectively), showing bulky tumorigenesis in periscapular regions (solid arrowheads) and forearms (open arrowheads) of the combination genotype mouse. (F) Gross dissection photograph and (G) GFP fluorescence image of the latter mouse. (H) H&E histology photomicrographs from sagittal sections through the elbow in a control mouse and (I) a combination genotype mouse, showing tumorigenesis from every bone surface along the ulna and radius (open arrowhead). (J) Higher-power H&E histology photomicrograph from a tumor arising along the periosteal surface of a Prx1Cre^ERT2 hSS2 Ctnnb1^ex3fl mouse at 10 weeks of age, showing classic SS features of staghorn-style hemangiopericytomatous vessels (solid arrowhead) and pseudoglandular structures (open arrowhead), along with (K) classic immunohistochemical staining images for cytoplasmic BCL2 and (L) nuclear TLE1. Scale bars: 100 μm (H–J); panel widths: 100 μm (K and L).