PRDC (protein related to DAN and Cerberus) is a secreted cysteine knot-containing BMP antagonist belonging to the Cerberus/DAN (CAN) family. Mammalian CAN family members, including Gremlin, Dan, Cerberus, COCO, SOST, and USAG-1, have the conserved 6 cysteine residues that form a cysteine knot, and two additional cysteine residues located in the loops of the cysteine knot, which form an additional intrasubunit disulfide bond. PRDC acts as a specific BMP antagonist, binding to and blocking signaling induced by BMP-2 or -4, but not Activin or TGF-beta. Thus, PRDC expression in the ovary could be involved in follicular development by antagonizing the inhibitory effects of BMPs on FSH stimulation of progesterone