Expression data from Class 1 and Class 2 human Wilms tumors.

Oncogenic stabilizing mutations in the beta-catenin gene CTNNB1 are common in one class of human Wilms tumors. To model these tumors, we crossed mice carrying an inducible Cre recombinase (Rosa26-CreERT2) with a conditional gain-of-function beta-catenin allele (Ctnnb1Ex3flox). We obtained kidneys at embryonic day 13.5 and placed them in organ culture with tamoxifen. Multiple small tumors formed in the Ctnnb1∆Ex3 kidneys while the control kidneys developed normally. Immunostaining for Sall1, a marker of condensing metanephric mesenchyme, indicated that the tumors arise from this tissue compartment, analogous to the origin of human Wilms tumors. Expression profiling identified a set of induced genes overlapping with those up-regulated in human Wilms tumors with CTNNB1 mutations, including genes encoding feedback inhibitors of Wnt/beta-catenin signaling, the epithelial-mesenchymal transition (EMT) inducers, and the transcription factor E2-2 (ITF2/TCF4). A conditional deletion of E2-2 showed that this gene is important for growth of the nephroblastomas, in part via promoting an epithelial to mesenchymal transition downstream of beta-catenin. Given these cross-species validations, and genetic proof of the oncogenic function of a key downstream target gene, we expect that this rapid and efficient organ culture model will be useful for further studies to dissect and inhibit oncogenic Wnt/beta-catenin signaling. The expression of 8 Class 1 Wilms tumors was compared with 5 Class 2 Wilms tumors.