Essential for cartilage morphogenesis and joint formation. Inhibitor of bone morphogenetic proteins (BMP) signaling which is required for growth and patterning of the neural tube and somite (PubMed:9585504, PubMed:9603738). Inhibits chondrocyte differentiation through its interaction with GDF5 and, probably, GDF6 (By similarity). Homodimer. Interacts with GDF5; inhibits chondrocyte differentiation. Expressed in condensing cartilage and immature chondrocytes. Embryonic expression was first detected in the node at 7.5 dpc. By early somite stages, expression extends anteriorly along the entire length of the notochord and is expressed in the dorsal neural tube from the caudal hindbrain to the posterior-most region of the embryo. By the time cranial tube closure is completed expression is continuous along most of the dorsal midline of the neural tube, to its rostral termination at the base of the forebrain. Expression in the neural tube and caudal notochord remains unchanged during early organogenesis from 9.5 dpc to 10.5 dpc. Defects in Nog are the cause of a recessive lethal phenotype at birth. Multiple defects include a failure of neural tube closure, broad club-shaped limbs, loss of caudal vertebrae, a shortened body axis, and retention of a small vestigial tail. Belongs to the noggin family.