IADR Abstract Archives
Enamel Matrix Assembly and Posttranslational Amelogenin Processing During Enamel Development
Objectives: The developing tooth enamel matrix is a protein-rich environment that promotes long and parallel oriented enamel crystal growth. Here we have conducted studies to determine whether changes in matrix shape and organization during amelogenesis correspond to stages of enamel crystal nucleation and growth.
Methods: Here we have used transmission electron microscopy of two day postnatal mouse molar enamel and of E16 tooth organs cultured for 12 days to compare differences between intravesicular matrix structure in secretory ameloblasts, extracellular enamel matrix nanosphere subunit assemblies, and pericrystalline protein matrix of elongating enamel crystals. Western blot analysis of SDS and Guanidine extracted enamel proteins was used to compare loosely bound and mineral-associated protein fractions of developing porcine enamel organs, superficial and deep enamel layers.
Results: Transmission electron microscopy revealed a 2.5-fold difference in matrix subunit compartment dimensions between secretory vesicle and extracellular enamel protein matrix as well as conformational changes in matrix structure between vesicles, stippled materials, and pericrystalline matrix. Enamel crystal growth in organ culture revealed granular mineral deposits associated with the enamel matrix framework, and dramatic changes in enamel matrix configuration following the onset of enamel crystal formation. Western blot analysis demonstrated (i) a single, full-length amelogenin band in the enamel organ followed by 3kDa cleavage upon entry into the enamel layer, (ii) a close association of 8-16kDa C-terminal amelogenin cleavage products with the growing enamel apatite crystal surface, and (iii) a remaining pool of N-terminal amelogenin fragments loosely retained between the crystalline phases of the deep enamel layer.
Conclusions: In conclusion, our study suggests that cleavage of the amelogenin enamel matrix protein plays a key role in the patterning of the organic matrix framework as it affects enamel apatite crystal growth and habit. Funding by NIDCR grant DE018900 to TGHD is gratefully acknowledged.
Methods: Here we have used transmission electron microscopy of two day postnatal mouse molar enamel and of E16 tooth organs cultured for 12 days to compare differences between intravesicular matrix structure in secretory ameloblasts, extracellular enamel matrix nanosphere subunit assemblies, and pericrystalline protein matrix of elongating enamel crystals. Western blot analysis of SDS and Guanidine extracted enamel proteins was used to compare loosely bound and mineral-associated protein fractions of developing porcine enamel organs, superficial and deep enamel layers.
Results: Transmission electron microscopy revealed a 2.5-fold difference in matrix subunit compartment dimensions between secretory vesicle and extracellular enamel protein matrix as well as conformational changes in matrix structure between vesicles, stippled materials, and pericrystalline matrix. Enamel crystal growth in organ culture revealed granular mineral deposits associated with the enamel matrix framework, and dramatic changes in enamel matrix configuration following the onset of enamel crystal formation. Western blot analysis demonstrated (i) a single, full-length amelogenin band in the enamel organ followed by 3kDa cleavage upon entry into the enamel layer, (ii) a close association of 8-16kDa C-terminal amelogenin cleavage products with the growing enamel apatite crystal surface, and (iii) a remaining pool of N-terminal amelogenin fragments loosely retained between the crystalline phases of the deep enamel layer.
Conclusions: In conclusion, our study suggests that cleavage of the amelogenin enamel matrix protein plays a key role in the patterning of the organic matrix framework as it affects enamel apatite crystal growth and habit. Funding by NIDCR grant DE018900 to TGHD is gratefully acknowledged.
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