Fig. 6. Model of the two-step myoblast fusion process. The cell-cell recognition is mediated by Duf in the founder/precursor cells (yellow) and Sns in the fusion-competent myoblasts (orange). The first fusion step crucially depends on Mbc and Loner (Chen and Olson, 2003; Erickson et al., 1997). The second fusion step is characterised by formation of prefusion complexes, electron-dense plaques and membrane breakdown (Doberstein et al., 1997). This requires proper function of Rols, Blow and Kette. In this process, blow, kette and sns¹⁵ mutants are involved at different times. Kette acts during the formation of the electron-dense plaques shortly after Blow.