The Small Alternatively Spliced Amelogenin LRAP Modulates Early Stage Ameloblast Differentiation
NAVAL MEDICAL RESEARCH UNIT (SAN ANTONIO) FORT SAM HOUSTON TX
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Amelogenesis is a regulated and sequential developmental cascade that results in expression of tissue specific gene products that form the enamel extracellular matrix. There remains considerable lack of knowledge regarding the precise mechanisms that control ameloblast differentiation and enamel matrix biomineralization. Amelogenins are the major protein product of ameloblasts and are comprised of multiple alternatively spliced isoforms that may function as structural molecules to regulate enamel crystal growth in addition to being signaling molecules that regulate cell differentiation. Hypothesis The small alternatively spliced amelogenin known as leucine rich amelogenin peptide LRAP functions to modulate ameloblast differentiation from pre-ameloblasts to terminal differentiation. Methods Transgenic mouse models that overexpressed LRAP in both a WT TgLRAP and an amelogenin null background TgLRAPAmelX Null were examined to determine if this alternatively spliced protein had a direct effect in vivo on ameloblast differentiation by assaying histomorphology, gene expression, and protein expression patterns in comparison to wild-type and amelogenin null mice. Biomineralization was further assessed with microCT and von Kossa staining. In vitro primary ameloblast lineage cells were transfected with LRAP to study early developmental effects. Results In vivo TgLRAP mice in the WT background showed a significant upregulation of enamel matrix gene products in preameloblasts with earlier and greater amelogenin protein expression in preiv secretory and secretory ameloblasts. Apoptosis was increased in secretory and transitional TgLRAP ameloblasts. Earlier mineral formation was also associated with the increased amelogenin expression. Downregulation of the master gene regulator SATB1 was also detected in pre-secretory and secretory ameloblasts.
- Genetic Engineering and Molecular Biology