Thus, hydra occupies a strategic position for the analysis of issues concerning the evolution of the mechanisms governing pattern formation. Over the last ten years inroads have been made in gaining an understanding of these developmental processes at a molecular level. To explore the issue of evolutionary conservation of genes regulating development, we looked for hydra homologues of transcription factors known to regulate patterning and cell fate processes in vertebrates and arthropods. The expression patterns of some of them suggest a conservation of function between hydra and organisms that arose later in evolution such as vertebrates and arthropods. And, Cnash, a hydra member of the achaete-scute class of bHLH genes plays a role in cell fate decisions in the interestitial cell lineage as do members of this class in the developmentment of the peripheral nervous system in vertebrates and Drosophila.
Current efforts are in three directions.
At first glance the head of a hydra has little in common with a head of an insect or a vertebrate. Yet, heads of all these animals have similar functions with respect to ingestion of food, the concentration of sensory organs, and a high density of neurons, which in more complex organisms is part of the central nervous system. This suggests that a set of genes and developmental mechanisms for forming a head may have been invented early in evolution, and basically maintained ever since. To explore this issue further, the presence and role of homologues other genes known to also be involved in head patterning, such as emx and Lim-1, will be examined in hydra. Subsequently, efforts will be made to determine the relationship among these genes.