title: Ameloblastin-rich enamel matrix favors short and randomly oriented apatite crystals.
abstract: Molecular evolution studies suggest that amelogenin (AMELX), the principal component of the mammalian enamel matrix, emerged considerably later than ameloblastin (AMBN), and enamelin. Here, we created a transgenic mouse model to ask the question how a conceivable basal enamel lacking AMELX and enriched in the more basal AMBN might compare with recent mouse enamel. To answer this question we overexpressed AMBN using a keratin 14 (K14) promoter and removed AMELX from the genetic background by crossbreeding with amelx(-/-) mice. Enamel coverings of amelx(-/-) mice and of the squamate Iguana iguana were used for comparison. Scanning electron microscopic analysis documented that AMBN transgenic (TG) × amelx(-/-) mouse molars were covered by a 5 μm thin 'enameloid' layer resembling the thin enamel of the Iguana squamate. Transmission electron microscopy revealed that the enamel of developing AMBN TG × amelx(-/-) mouse molars contained short (approximately 70 nm) and randomly oriented crystals, while WT controls, AMBN overexpressors, and AMELX(-/-) mice all featured elongated and parallel oriented crystals measuring between 300 and 600 nm in average length. Together, these studies illustrate that AMBN promotes the growth of a crystalline enamel layer with short and randomly oriented crystals, but lacks the ability to facilitate the formation of long and parallel oriented apatite crystals.
authors.affiliation: Brodie Laboratory for Craniofacial Genetics, University of Illinois at Chicago, Chicago, IL, USA.
authors.forename: Xuanyu
authors.initials: X
authors.lastname: Lu
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Ito
authors.forename: Ashok
authors.initials: A
authors.lastname: Kulkarni
authors.forename: Carolyn
authors.initials: C
authors.lastname: Gibson
authors.forename: Xianghong
authors.initials: X
authors.lastname: Luan
authors.forename: Thomas G H
authors.initials: TG
authors.lastname: Diekwisch
mesh_terms: D000566:Amelogenesis; D053523:Amelogenin / Q000737:chemistry* / Q000235:genetics; D000818:Animals; D001031:Apatites / Q000737:chemistry*; D003460:Crystallization; D003743:Dental Enamel / Q000737:chemistry* / Q000648:ultrastructure*; D003746:Dental Enamel Proteins / Q000737:chemistry* / Q000235:genetics; D019143:Evolution, Molecular; D005260:Female; D015870:Gene Expression; D006801:Humans; D007076:Iguanas / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D011401:Promoter Regions, Genetic
chemical_list: C490890:Ambn protein, mouse; D053523:Amelogenin; C507200:Amelx protein, mouse; D001031:Apatites; D003746:Dental Enamel Proteins