Matrix extracellular phosphoglycoprotein (also known as Osteoblast/osteocyte factor 45 or osteoregulin) has multiple functions, being involved in cell signalling, mineral homeostasis, and mineralization, as it plays a role in bone mineralization by osteoblasts and cartilage mineralization by chondrocytes [, , ]. It promotes renal phosphate excretion []and inhibits intestinal phosphate absorption [].This entry also includes Ovocleidin-116, the chicken orthologue, which is the major component of the eggshell matrix and is involved in eggshell calcification [].