SEAVER, Elaine C; University of Hawaii: Development of the segmented polychaete body plan

The evolution of a segmented body plan in the Bilateria has been a much debated topic. Current efforts to resolve this issue focus on comparisons of molecular components of developmental pathways involved in segment formation from disparate taxa such as flies, mice and fish. The presence of shared components is cited as evidence supporting homologies. The molecular pathway of segment formation is poorly understood in annelids, one of the major segmented clades. We have taken a candidate gene approach to identify molecular components of segmentation genes as defined in Drosophila and other arthropods as well as members of the vertebrate somitogenesis cascade in polychaete annelids. The expression patterns of a number of these genes have been analyzed during segment formation in the polychaete Capitella sp. I , Chaetopterus, and Hydroides elegans. We have also begun to extend our studies to include other related lophotrochozoan taxa such as myzostomids, and unsegmented taxa such as the sipunculid Themiste lageniformis. The expression of these genes will be discussed with respect to their putative developmental roles in segmentation.