Figure 9.

A working model for a promyogenic cell surface complex. A complex of cell surface receptors and adhesion molecules found at sites of myoblast cell–cell contact includes CDO and BOC, which may function as a receptor for a yet-to-be identified ligand. CDO and BOC interact in cis with N- and M-cadherins, which bind β- and α-catenin. CDO and BOC also interact with neogenin, a receptor for netrin-3. Multiple signals appear to emanate from this complex, resulting in activation of myogenic bHLH and NFAT transcription factors and alteration of the actin cytoskeleton in preparation for fusion. Note that although cis dimers of cadherins are shown, no stoichiometry of complex formation between CDO, BOC and neogenin, or between these proteins and cadherins, is implied by the figure. Note also that the experiments that support this working model do not distinguish between the existence of a single complex containing each protein shown or multiple complexes in which some components may be mutually exclusive. See text for further details.