Sources and Functions of Defenses Against Solar UV Radiationand Photooxidative Stress in Sea Urchins

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9316426 Shick The regulation of defenses against solar ultraviolet radiation-induced photooxidative stress will be studied in sea urchins. Like other marine organisms, sea urchins contain mycosporine-like amino acids (MAAs) which absorb environmentally relevant wavelengths of UV. Various seaweeds eaten by sea urchins are rich in MAAs, and preliminary chromatographic analyses indicate concordance between the MAA levels in seaweed and in sea urchin tissues, especially ovaries. Controlled maintenance of sea urchins on seaweeds lacking or rich in MAAs confirms dietary accumulation of MAAs in the urchins' ovaries, and provides an experimental means to fortify the eggs with these presumptive UV defenses. Published documentation of a UV-protective effect of MAAs is largely circumstantial. Thus, a major objective of the proposed research is to test directly whether MAAs protect echinoid eggs and larvae from exposure to natural and simulated solar UV. If the hypothesis that MAAs do confer protection against UV radiation is correct, dietary fortification of sea urchin ovaries should confer a greater resistance to UV in eggs and larvae; therefore, effects of acute UV exposure on pyrimidine dimer formation in DNA, fertilization, development, and larval survival will be assessed in MAA-rich and MAA-deficient individuals. A comparative study in this project is aimed at determining whether different exposures to solar UV radiation are associated with qualitative and quantitative differences in MAA content. MAA composition and content in a Maine species of sea urchin will be compared with those in a sympatric sand dollar. The sea urchin species matures and spawns in late winter; thus gamete maturation and larval development take place under relatively low levels of UV exposure. In contrast, the sand dollar is mature and spawns repeatedly from June through October, so its eggs and larvae are exposed to higher seasonal UV radiation than the winter- spawning se a urchin and may require more robust photooxidative defenses. The results of this study will have implications for the mechanism of accumulation and effectiveness of natural photooxidative defenses in marine food chains. This is a genuine concern because of deterioration of the protective ozone layer, where boreal marine organisms have evolved under relatively low solar UV exposure. The research may also have importance in the search for natural (dietary) antioxidants, some of which may be active as inhibitors of tumor promotion in human cells. ***