9727224 Martindale The Structure, Evolution, and Deployment of the Hox Cluster in a Basal Cnidarian Modern day animals exhibit a bewildering array of forms, or "body Plans." Classical biological approaches, such as paleontology and comparative embryology, have so far proved unable to elucidate the evolutionary transitions responsible for new body plans. Fortunately, molecular biology has revealed underlying evidence of continuity. For example, animals as divergent as mice and fruitflies have been found to use a common set of genes to establish their anterior-posterior axis during development. These genes, known as Hox genes, are important because they represent a conserved feature of development that is shared by animals whose body plans have diverged during evolution. Only by recognizing such conserved features can we hope to identify the evolution of novel mechanisms responsible for new body plans. We have recovered Hox genes from a sea anemone, a simple marine animal whose body plan is radically different from both mice and flies. Evidently, the Hox genes are very ancient and must have evolved prior to the evolutionary split between these highly divergent organisms, over 500 million years ago. Interestingly, sea anemones do not possess an anterior-posterior axis. This inconsistency raises two important questions: (1) What is the present-day role of Hox genes in animals such as sea anemones that lack an anterior-posterior axis? And (2) What does this reveal about the ancestral role of the Hox genes? Our research seeks to establish the role of Hox genes in the sea anemone by examining the chromosomal organization of these genes, and by determining where and when these genes are "turned-on" in the developing organism. In doing so, we expect to gain insight into the role of these genes during evolution and their significance for the evolution of animal body plans.
