BOC is a receptor-like, single pass membrane protein belonging to the cell surface molecule subfamily of the Immunoglobulin/fibronectin type-III repeat family within the immunoglobulin superfamily. It contains three fibronectin type-III domains and four Immunoglobulin-like C2-type domains in its extracellular region. The intracellular region of BOC is not required for proper function. BOC localizes to the cell membrane and is ubiquitously expressed with highest expression levels in skeletal muscle and small intestine. Its mRNA expression is down-regulated by Ras. BOC is involved in accelerating myoblast differentiation and is dependent on CDO for its activity. BOC and CDO are co-expressed in muscle precursors and are components of a receptor complex that mediates cell-cell interactions important in myogenesis. Overexpression of BOC results in enhanced differentiation of myoblast cells. In addition, BOC is a target and signaling component of the Shh pathway.