Noggin was originally identified based on its dorsalizing activity in Xenopus embryos. It was subsequently found to be a BMP binding protein that antagonizes BMP bioactivities. Mammalian Noggins were subsequently identified and cloned from human, mouse, and rat cDNA libraries. Mature mouse Noggin shares 99% and 83% amino acid sequence identity with human and Xenopus Noggin, respectively. Noggin has a complex pattern of expression during embryogenesis. In the adult, Noggin is expressed in the central nervous system and in several adult peripheral tissues such as lung, skeletal muscle, and skin.