Abstract
Genetic diseases that affect tooth enamel are grouped under the classification amelogenesis imperfecta. Human pedigrees and experiments on transgenic and null mice have all demonstrated that mutations to the secreted proteins amelogenin, enamelin, and enamelysin result in visibly, structurally, or mechanically defective enamel. In an attempt to better define a physiologic function for ameloblastin during enamel formation, we have produced transgenic mice that misexpress the ameloblastin gene. These transgenic animals exhibit imperfections in their enamel that is evident at the nanoscale level. Specifically, ameloblastin overexpression influences enamel crystallite habit and enamel rod morphology. These findings suggest enamel crystallite habit and rod morphology are influenced by the temporal and spatial expression of ameloblastin and may implicate the role of the ameloblastin gene locus in the etiology of a number of undiagnosed autosomally dominant cases of amelogenesis imperfecta.
Highlights
In 1996 a new member of the non-amelogenin, non-enamelin class of enamel proteins was simultaneously characterized by three different groups of investigators, two groups using rat incisors and one group using porcine teeth
These data suggest that ameloblastin has a significant physiologic role to play in enamel formation, and ameloblastin should be considered as a candidate gene when discussing the genetics of amelogenesis imperfecta
The mouse X-chromosomal-derived amelogenin promoter is used to drive the expression of the ameloblastin gene that is marked as a transgene by the presence of the c-Myc epitope
Summary
In 1996 a new member of the non-amelogenin, non-enamelin class of enamel proteins was simultaneously characterized by three different groups of investigators, two groups using rat incisors and one group using porcine teeth. The human enamelysin gene maps to chromosome 11q22.3, and no linkage data yet have implicated enamelysin to an amelogenesis imperfecta phenotype, enamelysin null animals do have defective enamel and a weakened dentin enamel junction (13). We targeted ameloblastin overexpression to ameloblasts by generating transgenic animals in which ameloblastin expression was under the control of the ameloblast-specific amelogenin promoter With this transgenic animal model we provide evidence that altering the expression profile of ameloblastin has an adverse effect on enamel formation that results in imperfect enamel. These data suggest that ameloblastin has a significant physiologic role to play in enamel formation, and ameloblastin should be considered as a candidate gene when discussing the genetics of amelogenesis imperfecta
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