Noggin belongs to a group of diffusible proteins which bind to ligands of the TGF-beta family and regulate their activity by inhibiting their access to signaling receptors. Noggin was originally identified as a BMP-4 antagonist whose action is critical for proper formation of the head and other dorsal structures. Consequently，Noggin has been shown to modulate the activities of other BMPs including BMP-2,-7,-13，and -14. Targeted deletion of Noggin in mice results in prenatal death and recessive phenotype displaying a severely malformed skeletal system. Conversely，transgenic mice over-expressing Noggin in mature osteoblasts display impaired osteoblastic differentiation，reduced bone formation，and severe osteoporosis.
