Enamel formation in vitro in mouse molar explants exposed to amelogenin polypeptides ATMP and LRAP on enamel development.
OBJECTIVE
The enamel matrix contains amelogenin, leucine-rich amelogenin-polypeptide (LRAP), resulting from alternative splicing of the primary amelogenin-RNA transcript and tyrosine-rich amelogenin-polypeptide (TRAP), a proteolytic product of amelogenin. Presence of amelogenin-trityrosyl-motif peptide (ATMP) distinguishes TRAP from LRAP. The roles of these polypeptides in the formation of enamel remain to be elucidated.


METHODS
The mouse in vitro molar tooth-organ developed from bud stage (E16) was exposed to LRAP, ATMP, and mutated ATMP (T-ATMP, third proline replaced by threonine). The histology and morphometry of the explants on day-12 in culture was examined using Mallory's stain. Guanidine-HCl soluble protein concentrations of explants were compared.


RESULTS
The enamel width and protein solubility indicate that the explant on day-12 is comparable to postnatal molar on day-3 in vivo. The enamel of both untreated explants as well as that in vivo is fuchinophilic (acid fuchsin, AF+). ATMP reduced the ameloblast-height, accumulated AF+ spherules at the apical end of ameloblasts, and disrupted enamel-dentin bonding. T-ATMP abrogated deposition of AF+ material on the aniline blue positive (AB+) enamel matrix. LRAP reduced ameloblast-height, increased the enamel-width without disruption (at 17.25 nmol) and increased the density of AF+ dentinal tubules. AF+ substance from the tubules is released onto the surface of the dentin. The Guanidine-HCl-soluble protein is elevated in ATMP-treated explants but decreased in LRAP-treated explants.


CONCLUSIONS
Exogenous ATMP, T-ATMP and LRAP have divergent effects on developing enamel. Exogenous ATMP, but not LRAP, abrogates enamel-dentin bonding at 17.25 nmol. LRAP may play a role in the differentiation of ameloblasts, growth of enamel and formation of dentinal tubules.
Ravindranath
Rajeswari M H
RM
Center for Craniofacial Molecular Biology, School of Dentistry, University of Southern California, Los Angeles, CA 90033, USA. rravindr@usc.edu
Devarajan
Asokan
A
Bringas
Pablo
P
D000565:Ameloblasts / Q000187:drug effects; D020816:Amino Acid Motifs; D000818:Animals; D003743:Dental Enamel / Q000187:drug effects* / Q000196:embryology; D003746:Dental Enamel Proteins / Q000494:pharmacology*; D051379:Mice; D008963:Molar / Q000187:drug effects* / Q000196:embryology
D003746:Dental Enamel Proteins; C067432:leucine-rich amelogenin peptide; C084495:tyrosine-rich amelogenin polypeptide