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 (By similarity). Inhibits chondrocyte differentiation through its interaction with GDF5 and, probably, GDF6 (By similarity). Homodimer. Interacts with GDF5; inhibits chondrocyte differentiation. Prominently expressed in the CNS. High levels found in mitral and tufted cells in the olfactory bulb, piriform cortex of the brain and Purkinje cells in the cerebellum. Low level expression seen in the lung, skeletal muscle and skin. First detected at embryonic day 9 and in the brain, expression increases steadily from embryonic day 17 to postnatal day 19. Belongs to the noggin family.