Both WT and Gpa33−/− mice exhibited activation of the WNT pathway, shown by elevated β-catenin protein (supplementary material Fig. S4A) and upregulated expression of the WNT target genes, CD44 and Lgr5, in tumours compared to normal epithelium (supplementary material Fig. S4B), consistent with CTNNB (encoding β-catenin) being a known AOM target. Here, GPA33 is linked to infectious otitis media.