IGFBP-rP10 (IGF binding protein-related protein 10; also Kazal-type serine protease inhibitor domain-contain protein 1 and BONO1) is a 37kD (predicted), secreted member of the IGFBP superfamily. It is expressed by osteoblasts and odontoblasts, is associated with regions of mineralization, and stimulates the proliferation of osteoblasts in vitro. Mature human IGFBP-rP10 is 274 aa in length. It contains an IGF binding domain (aa49-124), a follistatin-like serine protease inhibitor region (aa125-168) and a C2-type Ig-like domain (aa172-269). There is one splice variant that shows a 70 aa substitution for aa184-304. Mature human IGFBP-rP10 is 87% aa identical to mouse IGFBP-rP10.