Several members of the bone morphogenetic protein (BMP) family of secreted signaling molecules are also expressed in stripes at sites where joints will form, including those encoded by the genes Gdf5, Gdf6, Gdf7, Bmp2, and Bmp4 (Storm and Kingsley 1996; Wolfman et al. 1997; Francis-West et al. 1999; Settle et al. 2003).