Myogenesis: A View from Drosophila

Abstract

It may be apocryphal but there is a widely held belief among fly enthusiasts that the Drosophila larva has more muscles than a human being. Of course, it all depends on how you count the muscles, but it is undeniable that the Drosophila larva equips itself with a remarkably complex muscle pattern (Bate 1993; Abmayr et al. 1995). This pattern originates during a brief period of early development when the embryonic fly first subdivides its mesoderm into the progenitors of different internal structures and, thereafter, in a remarkable process whereby individual muscles are seeded and specified from the cells of the myogenic lineage. Recent work has fleshed out details of both these processes and reveals similarities and differences in the development of the muscles of flies and vertebrates. Like vertebrate embryos, flies divide their mesoderm into segmental units and the diversification of these units is influenced by signals such as TGFβ, Wnt, and Hh family members (Bate 1993; Lawrence et al. 1995; Wu et al. 1995; Azpiazu et al. 1996; Bate and Baylies 1996; Tajbakhsh and Cossu 1997). Myogenic lineages arise from these segmental units, and genes coding for components of the myogenic pathways have been remarkably conserved in many instances. However, there appear to be differences in the way in which these elements are deployed in flies and vertebrates. These differences may reflect a real divergence in the development of the musculature in two widely separated groups of animals, or alternatively, and perhaps more interestingly, they may represent variations in a common program that is, as yet, incompletely understood.