BOC (Brother of CDO) and CDO (Cell Adhesion Molecule-related/Downregulated by Oncogenes) are cell surface receptors belonging to the Ig/Fibronectin type III (FNIII) repeat family. Both BOC and CDO have five Ig repeats and three FNIII repeats in their extracellular domains, an arrangement shared by ROBO axon guidance receptors. BOC and CDO are co-expressed in muscle precursor cells during development. BOC is also expressed in embryonic brain and may play a role in axon guidance. BOC and CDO have also been implicated in the Hedgehog signaling pathway.