When non-arthroplasty options either have failed or have a low likelihood of success, reverse shoulder arthroplasty provides reliable pain relief and return of shoulder function in patients with massive rotator cuff tears without arthritis at the time of short to intermediate-term follow-up.

CDO, a member of the Ig/fibronectin type III repeat subfamily of transmembrane proteins that includes the axon guidance receptor Robo, was identified by virtue of its down-regulation by the ras oncogene. We report here that one prominent site of cdo mRNA expression during murine embryogenesis is the early myogenic compartment (newly formed somites, dermomyotome and myotome). CDO is expressed in proliferating and differentiating C2C12 myoblasts and in myoblast lines derived by treating 10T1/2 fibroblasts with 5-azacytidine, but not in parental 10T1/2 cells. Overexpression of CDO in C2C12 cells accelerates differentiation, while expression of secreted soluble extracellular regions of CDO inhibits this process. Oncogenic Ras is known to block differentiation of C2C12 cells via downregulation of MyoD. Reexpression of CDO in C2C12/Ras cells induces MyoD; conversely, MyoD induces CDO. Reexpression of either CDO or MyoD rescues differentiation of C2C12/Ras cells without altering anchorage-independent growth or morphological transformation. CDO and MyoD are therefore involved in a positive feedback loop that is central to the inverse relationship between cell differentiation and transformation. It is proposed that CDO mediates, at least in part, the effects of cell–cell interactions between muscle precursors that are critical in myogenesis.

CDO is a cell surface receptor-like protein that positively regulates myogenic differentiation. Reported here is the identi®cation of BOC, which, with CDO, de®nes a newly recognized subfamily within the immunoglobulin superfamily. cdo and boc are coexpressed in muscle precursors in the developing mouse embryo. Like CDO, BOC accelerates differentiation of cultured myoblast cell lines and participates in a positive feedback loop with the myogenic transcription factor, MyoD. CDO and BOC form complexes in a cis fashion via association of both their ectodomains and their intracellular domains. A soluble fusion protein that contains the entire BOC ectodomain functions similarly to full-length BOC to promote myogenic differentiation, indicating that the intracellular region is dispensable for its activity in this system. Furthermore, a dominant-negative form of CDO inhibits the pro-myogenic effects of soluble BOC, suggesting that BOC is dependent on CDO for its activity. CDO and BOC are proposed to be components of a receptor complex that mediates some of the cell±cell interactions between muscle precursors that are required for myogenesis.

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