Dynamic expression and regulation of Mage-D1 during tooth development in mice

To investigate the dynamic expression profile of mdanoma associated antigen D1 (Mage-D1) at different tooth development stages in mice after birth, and explore the effect of Mage-D1 knockout on tooth development in vivo.

C57-BL/6 wild-type suckling mice were grouped according to their age (1, 4, 7, 11 and 15 d after birth, n=3 in each group). Tissue samples were prepared and the developmental dynamics of the first mandibular molars in mice were observed by HE staining. Immunohistochemical staining was used to observe the expression of Mage-D1 as well as the homologous box genes Dlx1 and Msx1 at different stages of postnatal tooth development in mice. The Mage-D1 homozygous knockout mice (KO) and wild-type mice (WT) aged 1 and 3 months (n=6 in each group) were selected for phenotypic observation, and micro-CT scanning for mandible was performed to analyze the data of teeth and mandible.

Morphological observation showed that on postnatal day 1, the first mandibular molar was in the late bell-shaped stage without obvious hard tissue formation; on day 4, dentin and enamel alternatively formed and crown began to develop; on day 7, epithelial root sheaths shaped and root development initiated; on day 11, the enamel and crown dentin were almost completed, with the root about half developed; on day 15, the root of the tooth further developed, reaching more than 2/3, and the cementum was formed. Mage-D1 and the homeobox genes Dlx1 and Msx1 were positively expressed in both ameloblasts and odontoblasts of mice throughout the period from 1 d to 15 d after birth. As compared with WT mice, the body weight of KO mice was increased (P<0.05); though the number of teeth was the same in the 2 groups, the teeth appearance in KO group was slightly different, with incisors less stained and molars more easily worn. Scanning results indicated no significant difference in the density of teeth and alveolar bone.

Mage-D1, Dlx1 and Msx1 may contribute together to the formation of tooth enamel and dentin in mice, and the mice with Mage-D1 gene knockout present obesity signs and altered tooth phenotype.