Fig. 1: Deletion of Mast4 leads to an amelogenesis imperfecta phenotype.

a–d Comparison of incisors from 6-week-old and 18-week-old WT and Mast4 KO mice. Bent maxillary and mandibular incisors were observed in Mast4 KO mice. The arrow indicates the peeled enamel in a maxillary incisor from a 6-week-old Mast4 KO mouse. e, f Micro-CT 3D reconstruction of the head of a Mast4 KO mouse shows that the incisor is severely curved. g, h Scanning electron microscopy (SEM) images of incisor enamel dissected planes. The outer enamel of Mast4 KO incisors was thicker than that of WT incisors. Decussated enamel rods were observed in the inner enamel layer of the WT incisor. The enamel rod arrangement was collapsed in the Mast4 KO incisor (arrows). i–n MAST4 localization in the WT incisor. The dotted lines indicate the boundary of the epithelial cell layer. i–k In incisors from 3-week-old mice, MAST4 was generally weakly expressed at the apical bud, but single cells with high MAST4 expression in the stem cell niche region were also detected. MAST4 was weakly expressed at proximal terminal web complexes (PTW) and moderately distal terminal web complexes (DTW) in secretory and maturation stage ameloblasts. l After 6 weeks, MAST4 expression extended to the apical side (asterisks). m MAST4 was localized to both sides (proximal and distal) of terminal web complexes and Tomes’ processes (TP) in secretory stage ameloblasts. n In the ameloblast maturation stage, MAST4 was observed at the ruffled border (RB) and terminal web complexes (PTW, DTW). E enamel, DTW distal terminal web complex, PTW proximal terminal web complex, TP Tomes’ process, RB ruffled border, Am ameloblast, SI stratum intermedium. Scale bars, g, h, 10 μm; l–n, 100 μm.