title: Maturation stage enamel malformations in Amtn and Klk4 null mice.
abstract: Amelotin (AMTN) and kallikrein-4 (KLK4) are secreted proteins specialized for enamel biomineralization. We characterized enamel from wild-type, Amtn(-/-), Klk4(-/-), Amtn(+/-)Klk4(+/-) and Amtn(-/-)Klk4(-/-) mice to gain insights into AMTN and KLK4 functions during amelogenesis. All of the null mice were healthy and fertile. The mandibular incisors in Amtn(-/-), Klk4(-/-) and Amtn(-/-)Klk4(-/-) mice were chalky-white and chipped. No abnormalities except in enamel were observed, and no significant differences were detected in enamel thickness or volume, or in rod decussation. Micro-computed tomography (μCT) maximum intensity projections localized the onset of enamel maturation in wild-type incisors distal to the first molar, but mesial to this position in Amtn(-/-), Klk4(-/-) and Amtn(-/-)Klk4(-/-) mice, demonstrating a delay in enamel maturation in Amtn(-/-) incisors. Micro-CT detected significantly reduced enamel mineral density (2.5 and 2.4gHA/cm(3)) in the Klk4(-/-) and Amtn(-/-)Klk4(-/-) mice respectively, compared with wild-type enamel (3.1gHA/cm(3)). Backscatter scanning electron microscopy showed that mineral density progressively diminished with enamel depth in the Klk4(-/-) and Amtn(-/-)Klk4(-/-) mice. The Knoop hardness of the Amtn(-/-) outer enamel was significantly reduced relative to the wild-type and was not as hard as the middle or inner enamel. Klk4(-/-) enamel hardness was significantly reduced at all levels, but the outer enamel was significantly harder than the inner and middle enamel. Thus the hardness patterns of the Amtn(-/-) and Klk4(-/-) mice were distinctly different, while the Amtn(-/-)Klk4(-/-) outer enamel was not as hard as in the Amtn(-/-) and Klk4(-/-) mice. We conclude that AMTN and KLK4 function independently, but are both necessary for proper enamel maturation.
authors.affiliation: Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, 1210 Eisenhower Pl., Ann Arbor, MI, USA 48108. Electronic address: nunezste@einstein.edu.
authors.forename: Stephanie M
authors.initials: SM
authors.lastname: Núñez
authors.affiliation: Department of Periodontics, School of Dentistry, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX 78240, USA. Electronic address: chuny@uthscsa.edu.
authors.forename: Yong-Hee P
authors.initials: YP
authors.lastname: Chun
authors.affiliation: Matrix Dynamics Group, Faculty of Dentistry, University of Toronto, 150 College Street, Fitzgerald Building, Toronto, ON M5S 3E2, Canada. Electronic address: b.ganss@utoronto.ca.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Ganss
authors.affiliation: Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, 1210 Eisenhower Pl., Ann Arbor, MI, USA 48108. Electronic address: yyhu@umich.edu.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Hu
authors.affiliation: Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, 1210 Eisenhower Pl., Ann Arbor, MI, USA 48108. Electronic address: ramelia@umich.edu.
authors.forename: Amelia S
authors.initials: AS
authors.lastname: Richardson
authors.affiliation: Department of Orthopaedics, RAYO, Carlisle Center for Bone and Mineral Imaging, School of Medicine, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX, USA. Electronic address: schmitzj@uthscsa.edu.
authors.forename: James E
authors.initials: JE
authors.lastname: Schmitz
authors.affiliation: Department of Orthopaedics, RAYO, Carlisle Center for Bone and Mineral Imaging, School of Medicine, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX, USA. Electronic address: fajardor@uthscsa.edu.
authors.forename: Roberto
authors.initials: R
authors.lastname: Fajardo
authors.affiliation: Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, 1210 Eisenhower Pl., Ann Arbor, MI, USA 48108; Department of Pediatric Dentistry, School and Hospital of Stomatology, Peking University, 22 South Avenue, Zhongguancun Haidian District, Beijing 100081, PR China. Electronic address: denyj78@163.com.
authors.forename: Jie
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, 1210 Eisenhower Pl., Ann Arbor, MI, USA 48108. Electronic address: janhu@umich.edu.
authors.forename: Jan C-C
authors.initials: JC
authors.lastname: Hu
authors.affiliation: Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, 1210 Eisenhower Pl., Ann Arbor, MI, USA 48108. Electronic address: jsimmer@umich.edu.
authors.forename: James P
authors.initials: JP
authors.lastname: Simmer
mesh_terms: D000566:Amelogenesis; D000818:Animals; D003743:Dental Enamel / Q000002:abnormalities* / Q000000981:diagnostic imaging; D003746:Dental Enamel Proteins / Q000235:genetics*; D007180:Incisor; D007610:Kallikreins / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D008855:Microscopy, Electron, Scanning; D008963:Molar; D014074:Tooth Calcification; D055114:X-Ray Microtomography
chemical_list: C507066:Amtn protein, mouse; D003746:Dental Enamel Proteins; D007610:Kallikreins; C120801:kallikrein 4
keywords: Ameloblasts; Amelotin; Kallikrein-4; Knoop hardness; Null mice; μCT