THAMM, K.*; SEAVER, E.C.; University of Hawaii at Manoa; University of Hawaii at Manoa: Involvement of the Notch signaling pathway in the development of Capitella sp. I

Arthropods, chordates and annelids are the three segmented phyla in the animal kingdom. It is not yet clear if their common ancestor was segmented or if segmentation developed independently within each group. Recent molecular characterization of developmental pathways utilized in the formation of segments has been used as evidence to support homology of segments. Several hypotheses have been proposed to explain the number of times segmentation arose. Examination of Drosophila segmentation genes in vertebrates has not yielded any striking evidence for a common segmented ancestor of vertebrates and arthropods, but a recent article, which shows the involvement of Delta and Notch in the segmentation of the spider Cupiennius salei, supports the homology of segments. The Notch-Delta pathway plays a crucial role in the somitogenesis of chordates, but is not involved in the segmentation process of Drosophila. These results suggest that the lack of a role of Notch and Delta in the segmentation of Drosophila reflects developmental differences in the segmentation of Drosophila and more basal arthropods. To examine a possible ancestral function of the Notch-Delta pathway in segmentation, it is important to examine members of the third major phylum of segmented animals, the annelids. For our research we have been working with Capitella sp. I, a cosmopolitical polychaete, whose adult body plan shows an almost homonomous segmentation. We have already isolated the full open reading frame of Delta from this polychaete and fragments of the genes Notch and hairy. Initial results characterizing the expression pattern of Delta during larval development indicate that it has been recruited for multiple functions.