Homeotic Gene Complexes are Similar in Flies and Mammals

Edward Lewis was long before his time. In the 1970s he summarized the results of his scientific work from several decades and formulated far-seeing theories on the function of homeotic genes in combination both with each other and with the co-linearity principle. Together with the discoveries made by Nüsslein-Volhard and Wieschaus, Lewis' pioneering work has had an enormous impact on our understanding of how evertebrate and vertebrate embryos develop. Other scientists have later found that the homeotic genes of Drosophila directly correspond to similar gene complexes in animals, all the way up to man. The Drosophila system has been an affluent source of knowledge for developmental biologists.

The homeotic genes (here called "HOM" genes) in Drosophila are clustered close to each other in the DNA, and they set a ground plan for embryonic development in the fly. Vertebrates also contain homeotic (HOX) genes. Here, we find four clusters, or complexes, of homeotic genes. These genes are closely related to the insect genes, their order in the DNA is the same, and their action during embryonal development follows the same order in time and space in the fly. Thus, the effects on the embryonic head-to-tail axis of these HOX genes largely follow the principles which Lewis' set up for the fly.

It is actually possible to transfer a HOX gene from man to the embryo of a fruit fly, where it is can perform some of the functions that the corresponding Drosophila gene normally executes. The location of our shoulders and hips on the vertebral column, for example, may be controlled by specific homeotic genes.