The overall goal of this project is to identify and characterize intermediate calcium carriers which have a common mineralizing function in distantly related organism and to determine how carrier-bound calcium ions are utilized to form a crystalline mineral phase. As a working hypothesis, it is proposed that polyanionic macromolecules function as intermediate calcium carriers, i.e. that polyanions are charged with mineral ions intracellularly and are subsequently degraded at calcifying foci releasing mineral ions for crystal growth.
The specific aims are designed to test the carrier hypothesis in two homogeneous cell populations and in a complex metazoan tissue.
The first aim i s to identify and characterize the calcium-binding polyuronides that are apparently degraded at the mineralization front in coccolithophorid algae. The kinetics of polyuronide turnover will be analyzed to determine if there is a one-to-one correspondence between the number of calcium ions released via the degradation of these polyanions and the number of calcium ions deposited in the mineral phase.
The second aim i s to determine whether the spicule-forming primary mesenchyme cells derived from sea urchin embryos express a polyanionic calcium-binding phosphoprotein(s). If a protein with these properties is expressed, its calcium-binding capacity and rate of turnover will be analyzed in relation to the rate of calcium deposition in the spicules.
The third aim i s to examine the self-association of a bone phosphoprotein osteopontin in the presence of calcium, magnesium and phosphate ions. The purpose of this study is to determine whether osteopontin forms discrete aggregates containing sequestered Ca3 (PO4)2-like complexes similar to known calcium- carriers, e.g. casein.
The fourth aim i s to examine the distribution of phosphoproteins in the matrix of embryonic chick calvaria to determine whether matrix phosphoprotein is preferentially concentrated at mineralizing foci. This project is relevant to normal skeletal and pathological calcification processes.
| Marsh, M E; Munne, A M; Vogel, J J et al. (1995) Mineralization of bone-like extracellular matrix in the absence of functional osteoblasts. J Bone Miner Res 10:1635-43 |
| Marsh, M E; Chang, D K; King, G C (1992) Isolation and characterization of a novel acidic polysaccharide containing tartrate and glyoxylate residues from the mineralized scales of a unicellular coccolithophorid alga Pleurochrysis carterae. J Biol Chem 267:20507-12 |
| Marsh, M E (1990) Immunocytochemical localization of a calcium-binding phosphoprotein in hemocytes of heterodont bivalves. J Exp Zool 253:280-6 |
| Marsh, M E (1989) Binding of calcium and phosphate ions to dentin phosphophoryn. Connect Tissue Res 21:205-10;discussion 211 |
| Marsh, M E (1989) Binding of calcium and phosphate ions to dentin phosphophoryn. Biochemistry 28:346-52 |
| Marsh, M E (1989) Self-association of calcium and magnesium complexes of dentin phosphophoryn. Biochemistry 28:339-45 |
