The Complement System in Sea Urchins and the Evolution of the Vertebrate Complement Cascades

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Abstract 9603086 Smith The aim of this investigation is to understand the complement system of the purple sea urchin, Strongylocentrotus purpuratus, an ancient and primitive organism, that may elucidate the origin and evolution of the complement cascade in higher vertebrates. This investigator has identified, in the immune cells of this sea urchin, two putative complement components. One is a gene encoding a protein (SpC3) with significant similarity to the vertebrate complement C3, the central component of the complement cascades in higher vertebrates, and the other gene codes for a protein (SpCR) with similar domains or functional modules that are characteristic of complement receptors or complement regulatory proteins. The research in this proposal is aimed at understanding this complement system. The sequence analysis of SpC3 and SpCr genes will be completed and from this the encoded protein sequences deduced. The expression patterns of these two genes in sea urchin cells and tissues will be determined. Changes in gene and protein expression in coelomocytes responding to immune challenges will also be examined. Experiments will be done to see whether SpC3 functions as an opsonin and SpCR functions as a complement receptor or a complement regulatory protein. This proposal is designed to address the evolution of deuterostome immunity through investigations of the newly identified sea urchin complement system. This system will further our understanding of the mechanisms involved in the sea urchin immune response and will help define the primitive functions that still operate in higher vertebrates. ***