Cell adhesion molecule-related, down-regulated by oncogenes (CDON), also known as CDO, is an Ig superfamily member, is a component of a cell surface receptor that positively regulates skeletal myogenesis. Brother of CDO (BOC) is a cell surface receptor that derives its name from the structurally related protein, CDON. They are components of a cell surface receptor that positively regulates myogenesis in vitro. Expression of Cdo and Boc in myoblast cell lines is downregulated by the ras oncogene, and forced re-expression of either Cdo or Boc can override ras-induced inhibition of myogenic differentiation. CDO and BOC play a role in the inverse relationship between differentiation and transformation of cells in the skeletal muscle lineage. CDON binds to Bnip-2 and JLP, scaffold proteins for Cdc42 and p38alpha/beta MAPK, respectively. The Bnip-2/Cdc42 and JLP/p38alpha/beta complexes associate in a CDON-dependent manner, resulting in Bnip-2/Cdc42-dependent p38alpha/beta activation and stimulation of cell differentiation. It is proposed that CDO mediates, at least in part, the effects of cell-cell interactions between muscle precursors that are critical in myogenesis.