Many animals generate both intra- and extracellular calcium granule complexes in one or more of their tissues. Functions for these granules include the buffering of pH changes, storage of calcium, and binding of heavy metals as a detoxification system. Drs. Silverman and Dietz have found calcium phosphate based concretions located extracellularly in the connective tissues of the gill in freshwater unionids, and these concretions can amount to 50% of the gill dry weight. The five species examined to date demonstrate concretion mobilization during reproduction. The PIs have documented that during the mobilization of concretions, calcium is passed into the water channels of the gills and incorporated into the shells of developing embryos. This strategy of maternal nutritive support of (technically externally brooded) invertebrate larvae raises many questions of general interest. Specifically, the present proposal is aimed at understanding the mechanisms of synthesis and mobilization of the concretions and the mechanisms by which calcium is stored and then transferred to the embryos during shell formation. Elucidating the regulatory role of the concretion organic matrix, the inorganic structure of the concretions, and the cells producing concretions will lead to a better understanding of intracellular biomineralization processes in general. Calcium granules are produced in the gills of freshwater clams. These granules are composed of calcium and phosphate. The cells that produce the granules have been identified and are a good model system for intracellular mineralization processes. Drs. Silverman and Dietz will study the organic components of the granules, the inorganic structure of the granules, and the cells involved in mineralization. The PIs will study the regulatory role of organic molecules on the mineralization process. Understanding the mechanisms of clam calcium granule formation may lead to a better understanding of the biological processes involved in formation of mineralized structures.
