Biomineralisation markers during a phase of active growth in Pinctada margaritifera

To search for the biochemical parameters involved in calcium and carbonate transport during crystal formation and biomineralisation in nacreous molluscs, the carbonic anhydrase activity, the levels of calciotropic hormones in hemolymph and in tissues and the circulating concentration of calcium were measured in pearl oysters (Pinctada margaritifera) during a phase of active growth. Activity of carbonic anhydrase in gill tissue increased linearly with age of the animals, while no age variation in activity was noted for the mantle. The circulating level of total calcium increased during the growth of the animals. Calciotropic hormones were radioimmunoassayed in gill, mantle and hemolymph. Only a calcitonin-gene related peptide (CGRP) could be detected and its concentration decreased as a function of growth, both in hemolymph and mantle. No variation in CGRP concentration with age was observed in gill tissue. Our data demonstrate that carbonic anhydrase and a molecule biologically and immunologically related to CGRP are involved during growth of the animals. In addition, this study shows the presence of three main calcium compartments, gill, hemolymph and mantle, involved in the biomineralisation process.