The Blue Crab Exoskeleton-A Model System for Studying the Control of Biomineralization

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Mineralized structures are found in most groups of animals. Biominerals are associated with bones, teeth, sponge spicules, and shells of molluscs, crustaceans and echinoderms to name but a few. Biomineralization is also associated with such pathological conditions as atherosclerosis, kidney stones and tumors. In most groups the minerals are salts of calcium and in all cases the minerals are associated with organic molecules. The organic molecules are involved in initiating, guiding and regulating the growth of the mineral crystals in all of these systems. These organic molecules are often proteins. Recently, Dr. Roer and others have found that some of these proteins associated with biomineralization have sugars attached to them and are referred to as glycoproteins. It is also becoming apparent that changes in the sugars associated with the glycoproteins may play a role in controlling biomineralization.He has chosen the exoskeleton of the blue crab, Callinectes sapidus, as a model system for studying the role of glycoproteins in controlling biomineralization. The crab is ideal for such studies, in large part, because crabs must molt in order to grow. In preparation for the molt, crabs form the outer layers of their new exoskeleton beneath the old one. The new shell must stay soft until the crab emerges from the old shell and expands. Only then does the new shell begin to harden. He thus has a tissue that is incapable of mineralizing at one point in time which then turns on mineralization within one to three hours after it molts. This phenomenon allows him to analyze the tissue in both states and understand the changes in the glycoproteins that are responsible for turning on mineralization. These results will have general application to other mineralizing tissues.