Tomographic imaging of collagen-mineral interaction: implications for osteogenesis imperfecta

The novel method of high voltage electron microscopic tomography (3D) has been applied for the first time to examine ultrastructural features and spatial relations between collagen fibrils and mineral crystals in a mouse mutant (oim/oim) which replicates a moderate to severe form of osteogenesis imperfecta. The animal produces collagen consisting of the alpha1(I) homotrimer and has a brittle calcified skeleton. Three-dimensional image reconstructions of the Achilles tendons, which were found to mineralize in the mutant mice, revealed that their composite crystals were different in their structural appearance and spatial association with collagen compared to that determined in normal calcified tissues. These results indicate that the nature of the organic matrix of a mineralizing tissue critically influences the formation, structure, and location of the constituent mineral and, further, the data are interpreted as suggesting that the unusual structural and organizational interaction between mineral and collagen underlies the inherent brittleness and weakness of calcification in this model of osteogenesis imperfecta.