title: Enamelin (Enam) is essential for amelogenesis: ENU-induced mouse mutants as models for different clinical subtypes of human amelogenesis imperfecta (AI).
abstract: Amelogenesis imperfecta (AI) is a group of commonly inherited defects of dental enamel formation, which exhibits marked genetic and clinical heterogeneity. The genetic basis of this heterogeneity is still poorly understood. Enamelin, the affected gene product in one form of AI (AIH2), is an extracellular matrix protein that is one of the components of enamel. We isolated three ENU-induced dominant mouse mutations, M100395, M100514 and M100521, which caused AI-like phenotypes in the incisors and molars of the affected individuals. Linkage analyses mapped each of the three mutations to a region of chromosome 5 that contained the genes encoding enamelin (Enam) and ameloblastin (Ambn). Sequence analysis revealed that each mutation was a single-base substitution in Enam. M100395 (Enam(Rgsc395)) and M100514 (Enam(Rgsc514)) were putative missense mutations that caused S to I and E to G substitutions at positions 55 and 57 of the translated protein, respectively. Enam(Rgsc395) and Enam(Rgsc514) heterozygotes showed severe breakage of the enamel surface, a phenotype that resembled local hypoplastic AI. The M100521 mutation (Enam(Rgsc521)) was a T to A substitution at the splicing donor site in intron 4. This mutation resulted in a frameshift that gave rise to a premature stop codon. The transcript of the Enam(Rgsc521) mutant allele was degraded, indicating that Enam(Rgsc521) is a loss-of-function mutation. Enam(Rgsc521) heterozygotes showed a hypomaturation-type AI phenotype in the incisors, possibly due to haploinsufficiency of Enam. Enam(Rgsc521) homozygotes showed complete loss of enamel on the incisors and the molars. Thus, we report here that the Enam gene is essential for amelogenesis, and that mice with different point mutations at Enam may provide good animal models to study the different clinical subtypes of AI.
authors.affiliation: Mouse Functional Genomics Research Group, Tsukuba, Ibaraki, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Masuya
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Shimizu
authors.forename: Hideki
authors.initials: H
authors.lastname: Sezutsu
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Sakuraba
authors.forename: Junko
authors.initials: J
authors.lastname: Nagano
authors.forename: Aya
authors.initials: A
authors.lastname: Shimizu
authors.forename: Naomi
authors.initials: N
authors.lastname: Fujimoto
authors.forename: Akiko
authors.initials: A
authors.lastname: Kawai
authors.forename: Ikuo
authors.initials: I
authors.lastname: Miura
authors.forename: Hideki
authors.initials: H
authors.lastname: Kaneda
authors.forename: Kimio
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Junko
authors.initials: J
authors.lastname: Ishijima
authors.forename: Takahide
authors.initials: T
authors.lastname: Maeda
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Gondo
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Noda
authors.forename: Shigeharu
authors.initials: S
authors.lastname: Wakana
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Shiroishi
mesh_terms: D000566:Amelogenesis / Q000235:genetics; D000567:Amelogenesis Imperfecta / Q000235:genetics* / Q000473:pathology; D000595:Amino Acid Sequence; D000818:Animals; D002874:Chromosome Mapping; D003746:Dental Enamel Proteins / Q000235:genetics* / Q000378:metabolism; D004195:Disease Models, Animal; D005038:Ethylnitrosourea; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D012333:RNA, Messenger / Q000378:metabolism; D017422:Sequence Analysis, DNA
chemical_list: D003746:Dental Enamel Proteins; D012333:RNA, Messenger; C038456:tuftelin; D005038:Ethylnitrosourea