Figure 5.

Model of the functional contributions of the SCAR and WASp pathways to myoblast fusion in Drosophila embryos. A SCAR-complex-dependent morphological transition underlies the acquisition of migratory behaviour by myoblasts, which are now able to attach to founder cells and/or myotubes. Upon the initiation of fusion, the SCAR complex is again used to promote the formation of pores in the apposed cell membranes. Once initial pores are formed, Wsp, recruited by D-WIP, mediates pore expansion, presumably through forces derived from Arp2/3-based actin polymerization. Note, an alternative model for the contribution of the two pathways has been recently proposed (Berger et al, 2008; see supplementary information online for further discussion). D-WIP, D-WASp-interacting protein; FC, founder cell; FCM, fusion-competent myoblast; SCAR, suppressor of cyclic AMP receptor; WASp, Wiskott–Aldrich syndrome protein.