Abstract
The discovery of the vertebrate hox gene clusters and their structural and functional relationship to the Drosophila HOM-C cluster of homeotic genes revealed amazing similarities between the developmental mechanisms by which a major body axis is formed in vertebrates and those of many invertebrates, possibly encompassing all multicellular organisms. Recent data suggest that heart development in Drosophila also resembles vertebrate heart development in several fundamental aspects despite the drastic morphologic differences between them. The discovery of the homeobox gene tinman, which is expressed in the embryonic heart of Drosophila and is required for heart formation, made it possible to compare the determining factors of heart development between Drosophila and vertebrates. tinman has mouse, frog, and fish relatives with considerable sequence similarity, and one of these genes is also specifically expressed in the developing heart. It appears that embryologic orgins and morphogenic movements of heart progenitors, as well as gene expression patterns and possibly their functions, are similar in Drosophila and in vertebrates. If it is true that heart development is conserved between Drosophila and vertebrates, then Drosophila, once again, could serve as a model system for vertebrate development.
