BO***, also known as KAZALD1 (kazal-type serine protease inhibitor domain-containing protein 1), IGFBP-rP10, FKSG28 or FKSG40, is a 304 amino acid secreted extracellular matrix protein that promotes matrix assembly. BO*** is expressed in developing bones and odontoblasts in teeth, where it plays a role in osteoblast proliferation during bone formation and regeneration. BO*** is also expressed at high levels in spleen, and is found at lower levels in lung, skin, urinary bladder, brain, tongue, kidney and large intestine. Existing as two alternatively spliced isoforms, BO*** contains one Kazal-like domain, an IGFBP N-terminal domain and a single Ig-like C2-type (immunoglobulin-like) domain. The gene encoding BO*** maps to human chromosome 10, which contains over 800 genes and 135 million nucleotides. Cockayne syndrome, Cockayne syndrome and trisomy 10 are associated with defects in chromosome 10.