Using N-ethyl-N-nitrosourea (ENU), an ENAM mutation mouse model [40] showed AI-like phenotypes in the incisors and molars. Ameloblasts in ENAM null mice develop atypical features that include the absence of a Tomes’ process, an expanded endoplasmic reticulum, an apparent loss of polarity, and a pooling of extracellular matrix in all directions, including between ameloblasts

and the stratum intermedium. Ameloblast apoptosis has been observed in these mice starting in the secretory stage and with no apparent alteration in cell proliferation. In the absence of ENAM, ameloblasts undergo pathological changes early in the secretory stage, tooth surface detachment, apoptosis, and ectopic calcification formation, both outside and inside the dystrophic enamel organ [41]. Furthermore, ENAM null mice have alveolar MEK inhibitor clinical trial bone height reduction [42], indicating that ENAM may be important for calcification and bone formation. β-Catenin/LEF1 is a key transcriptional complex involved in tooth development and bone formation via Wnt. The 5′-flanking region of the mouse ENAM gene contains two conserved LEF1 responsive elements that may augment its transcriptional Protease Inhibitor Library cost activity. Further, Wnt/β-Catenin signaling might function

in ENAM expression by direct interactions through these two elements of the ENAM gene in ameloblast-like cells [43]. Amelotin (AMTN) is an enamel matrix protein originally identified by the differential display PCR assays of various micro-dissected dental organ cell types obtained from incisor teeth. The predicted translated protein sequence is unique and shows a significant homology only with its human ortholog. The AMTN gene second in mice and humans displays a similar exon–intron structure and is located in loci on chromosomes 5 and 4, respectively.

AMTN mutations are associated with various forms of AI. AMTN mRNA expression is restricted to the maturation stage of ameloblasts in developing murine molars and incisors. In addition, the AMTN protein is efficiently secreted from cultured transfected cells, indicating that AMTN is an extracellular matrix molecule produced by ameloblasts [44]. In addition, the AMTN gene is conserved in mammals, while it is absent in fish, birds, and amphibians [45]. AMTN expression is detected in a transient fashion during ameloblast differentiation in molars. The expression level declines at the time of tooth eruption. Prominent AMTN expression in the maturation stage of ameloblasts in continuously erupting incisors persists into adulthood, whereas AMEL, AMBN, and ENAM are predominantly found during the early secretory stage. Furthermore, odontogenic ameloblast-associated amyloid in Pindborg tumors and kallikrein 4 expression in ameloblasts’ maturation stage were found to parallel that of AMTN.