BRIDGE, D.B.*; GORDON, A.A.; SHAFFER, A.L.; Elizabethtown College: Basal metazoans and the evolution of circulatory systems

Systems of fluid-bearing tubes or canals are present in colonial cnidarians as well as sponges. This raises the question of whether conserved mechanisms regulating the development of branching, fluid-bearing tubes arose early within the Metazoa. In vertebrates, the secreted protein vascular endothelial growth factor (VEGF) plays key roles in blood vessel development. During branching of a new blood vessel from an existing one, VEGF induces proliferation of endothelial cells and expression of proteases affecting the extracellular matrix. Among the cDNAs cloned and sequenced as part of the Hydra EST project is one encoding a homologue of VEGF. In situ hybridization with probes derived from this cDNA shows strong expression in the endoderm of the tentacles and peduncle. VEGF could thus potentially play a role in cell rearrangement during formation of narrow, tubular regions of the Hydra polyp. Increased expression of VEGF is also seen shortly after wounding, a result consistent with a role in remodeling the extracellular matrix. To determine whether a VEGF homologue plays a role in stolon branching in colonial hydrozoans, we plan to extend studies to the colonial species Podocoryna carnea.