A TECHNIQUE FOR DETECTING MATRIX PROTEINS IN THE CRYSTALLINE SPICULE OF THE SEA-URCHIN EMBRYO

The presence of proteins associated with the CaCO3-containing biocryst als found in a wide variety of marine organisms is well established. I n these organisms, including the primitive skeleton (spicule) of the s ea urchin embryo, the structural and functional role of these proteins either in the biomineralization process or in control of the structur al features of the biocrystals is unclear, Recently, one of the matrix proteins of the sea urchin spicule, SM 30, has been shown to contain a carbohydrate chain (the 1223 epitope) that has been implicated in th e process whereby Ca2+ is deposited as CaCO3, Because an understanding of the localization of this protein, as well as other proteins found within the spicule, is central to understanding their function, we und ertook to develop methods to localize spicule matrix proteins in intac t spicules, using immunogold techniques and scanning electron microsco py, Gold particles indicative of this matrix glycoprotein could not be detected on the surface of spicules that had been isolated from embry o homogenates and treated with alkaline hypochlorite to remove any ass ociated membranous material, However, when isolated spicules were etch ed for 2 min with dilute acetic acid (10 mM) to expose more internal r egions of the crystal, SM 30 and perhaps other proteins bearing the 12 23 carbohydrate epitope were detected In the calcite matrix, These res ults, indicating that these two antigens are widely distributed in the spicule, suggest that this technique should be applicable to any matr ix protein for which antibodies are available.