Evolution of segmentation genes in insects.

Systematic genetic analysis of the segmentation process in Drosophila has established a paradigm for the molecular control of the formation of metameric segments. However, it has been suggested that some of the mechanisms involved in this process in Drosophila are uniquely adapted to the syncytial mode of embryogenesis in such higher dipterans. A particularly contentious problem is the role of early segmentation genes in short-germ insects, in which development proceeds by sequential addition of segments in a cellular environment. However, analysis of the expression of presumptive homologs of segmentation genes in holometabolous short-germ insects suggests that they do indeed have a role in segmentation and that the Drosophila paradigm may be more widely applicable than is usually assumed. Most interestingly, these results suggest that the molecular mechanisms of pattern formation in noncellular and in cellular environments may not be as radically different as it is often thought to be.