WNT1 and neoplasm: To characterize cells undergoing an active transcriptional response to expression of these transgenes, we crossed MMTV-Wnt1 and MMTV-ΔN89β-catenin lines to the Axin2-d2EGFP reporter mouse, isolated tumor MECs from the bitransgenic progeny and analyzed them for enhanced green fluorescent protein (EGFP) and CD24/CD49f expression by flow cytometry.