[Comparative properties of myogenesis in invertebrates and in lower and higher vertebrates]

Development of the muscle system in invertebrates (on the example of nematode Caenorhabditis elegans and Drosophila) and vertebrates (fish, birds, and mammals) demonstrates a number of common patterns at the level of molecular and genetic control mechanisms but also a number of distinctive features. C. elegans muscle is formed from several cells of different origin at the earliest developmental stages, while inductive interactions play a critical role in Drosophila: the mesoderm, which is a source of muscle formation, receives the inductive signals from the neighboring ectoderm as expression of Dpp and Hh genes. In vertebrates, the induction and commitment of cells to the myogenic lineage are promoted by morphogenetic signals from the neighboring notochord (as expression of Shh gene) and neural tube (as expression of Wnt and Shh genes). The inductive signals entering the mesoderm are related to the subsequent activation of genes encoding protein transcription factors of bHLH gene family and analogs. These include hlh-1 and CeTwi in C. elegans; Twi and nau in Drosophila; and MyoD, Myf5, myogenin, and MRF4 in vertebrates. The diversity of myosin isoforms in different animals is provided by either gene duplication or alternative splicing of particular genes.