IHH and cancer: Overexpression of CDON and GAS1 has been shown to induce apoptosis in cancer cell lines49,74 Forced expression of CDON in the chick neural tube resulted in an increase in apoptotic cells in the dorsal region where the level of SHH is lowest (Fig. 6d, f), consistent with previous findings50 and that co-expression with IHH suppressed the number of CDON-induced apoptotic cells in the dorsal region (Fig. 6d, f).