a 184-amino acid protein and bone morphogenic protein (Bmp) antagonist expressed during limb development in a region anterior to the zone of polarising activity (ZPA). Recent studies suggest that it acts as a signaling intermediate between sonic hedgehog (Shh) and fibroblast growth factor (Fgf). Belongs to the BMP antagonist gene family as Cerberus (head-inducing factor) and DAN (tumor suppressor)