Do muscle founder cells exist in vertebrates?

Skeletal muscle is formed by the iterative fusion of precursor cells (myocytes) into long multinuclear fibres. Extensive studies of fusion in Drosophila embryos have lead to a paradigm in which myoblasts are divided into two distinct subtypes – founder and fusion-competent myoblasts (FCMs) – that can fuse to each other, but not among themselves. Only founder cells can direct the formation of muscle fibres, while FCMs act as a cellular substrate. Recent studies in zebrafish and mice have demonstrated conservation of the molecules originally identified in Drosophila, but an important question remains: is vertebrate fusion regulated by specifying myocyte subtypes? Stated simply: do vertebrate founder cells exist? In light of recent findings, we argue that a different regulatory mechanism has evolved in vertebrates.