TNKS and Menkes disease: We used the tankyrase inhibitor XAV939, a molecule that has been successfully used before in an organ culture set-up (31), to inhibit the β-catenin signalling pathway in urogenital ridge explant cultures (26), and found it to have a negative effect on MD formation in vitro, causing defects resembling the ones seen in mice with ablated β-catenin signalling (27,32,33).