Alteration of Conserved Alternative Splicing in AMELX Causes Enamel Defects

Abstract

Tooth enamel is the most highly mineralized tissue in vertebrates. Enamel crystal formation and elongation should be well controlled to achieve an exceptional hardness and a compact microstructure. Enamel matrix calcification occurs with several matrix proteins, such as amelogenin, enamelin, and ameloblastin. Among them, amelogenin is the most abundant enamel matrix protein, and multiple isoforms resulting from extensive but wellconserved alternative splicing and postsecretional processing have been identified. In this report, we recruited a family with a unique enamel defect and identified a silent mutation in exon 4 of the AMELX gene. We show that the mutation caused the inclusion of exon 4, which is almost always skipped, in the mRNA transcript. We further show, by generating and characterizing a transgenic animal model, that the alteration of the ratio and quantity of the developmentally conserved alternative splicing repertoire of AMELX caused defects in enamel matrix mineralization.

Contribution of dental tissues to sex determination in modern human populations

“…Their findings, however, are supported by those obtained in genetic loci studies of human amelogenin; which appear to be the principal intermediaries of this interaction (Fincham et al, ; Salido, Yen, Koprivnikar, Yu, & Shapiro, ).The amelogenin is the main protein component of the organic matrix in enamel, and its genes are on both the X and Y chromosomes (Fincham, Moradian‐Oldak, & Simmer, ; Fincham et al, ). The quantitative and qualitative differences in their transcriptional products influence the proportions in which hard dental tissues are present (Salido et al, ; Schwartz and Dean, ), likewise genetic alterations of these genes cause different dental tissues defects (Cho et al, ; Hu et al, ).…”

Genes Regulating Immune Response and Amelogenesis Interact in Increasing the Susceptibility to Molar-Incisor Hypomineralization

“…The AMELX gene encodes the main organic component of enamel, amelogenin, which is secreted during the secretory phase in amelogenesis, and variations in this gene have also been associated with defects in enamel development [Cho et al, 2014;Kim et al, 2017]. The positive interactions observed for AMELX with immune response genes suggest an additive effect conferring greater susceptibility to MIH.…”

Enamel ribbons, surface nodules, and octacalcium phosphate in C57BL/6Amelx−/−mice andAmelx+/−lyonization

“…; Cho et al. ) (Appendix S1), which occurs in the absence of any phenotype except in enamel. A telltale phenotype of X‐linked AI is that heterozygous females often exhibit vertical bands of hypoplastic enamel alternating with bands of normal or less severely affected enamel, whereas affected males exhibit a uniformly thin layer of defective enamel.…”

“…In rodents there is only a single copy of the amelogenin gene (Amelx), and targeted interruption of this gene in mice resulted in an amelogenesis imperfecta phenotype (Gibson et al 2001). To date, 19 different genetic defects in AMELX have been reported to cause X-linked amelogenesis imperfecta (AI) (OMIM #301200) (Lagerstr€ om et al 1990(Lagerstr€ om et al , 1991Aldred et al 1992;Lench et al 1994;Lagerstrom-Fermer et al 1995;Lench and Winter 1995;Collier et al 1997;Hart et al 2000Hart et al , 2002Kindelan et al 2000;Ravassipour et al 2000;Sekiguchi et al 2001a,b;Greene et al 2002;Kim et al 2004;Kida et al 2007;Chan et al 2011;Lee et al 2011;Wright et al 2011;Cho et al 2014) (Appendix S1), which occurs in the absence of any phenotype except in enamel. A telltale phenotype of X-linked AI is that heterozygous females often exhibit vertical bands of hypoplastic enamel alternating with bands of normal or less severely affected enamel, whereas affected males exhibit a uniformly thin layer of defective enamel.…”

“…Overexpression of alternatively spliced amelogenin transcripts can be harmful. A splice junction mutation that increased the inclusion of the normally skipped Exon 4 resulted in X-linked amelogenesis imperfecta (Cho et al 2014). There have been many reports claiming the importance of selected amelogenin alternative splicing products, but the production of fully functional enamel in knock-in mice that only express the major amelogenin isoform argues otherwise.…”