Effect Of Core Transcription Factor Runx2 In Mouse Enamel Biomineralization

Aims of study:As an osteoblast-specific transcription factor, Runx2 plays an important role in the development of bones.Runx2 significantly expressed in developing enamel maturation ameloblasts.However,its specific function is not clear yet.The purposes of this study are as the followings:(1) To observe the temporal and spatial expression pattern of transcription factor Runx2 during mouse molars development;(2)To study the function of Runx2 in the teeth grew of mouse through conditional knockout.Material and methods:(1)Immunohistochemistry technique was used to examine the expression of Runx2 during the development of mice molars.(2)Amelx-Cre,K14-Cre, Runx2loxp/loxp pconditional knockout mice were generated and analysed by IHC,SEM,stereomicroscope,Micro X-ray,Micro-uCT,HE staining and RT-PCR,to further study the function of Runx2 in enamel development.Results:In the first molars of PN1 mice, Runx2 expression was not detected in secretory stage ameloblasts ;At PN5,Runx2 significantly expressed in ameloblast nucleus in the cusp which was secreted by enamel matrix,while in neighboring secreted ameloblast nucleus,it had a weakly expression;At PN10,in the first molars,Runx2 expressed weakly in the secreted ameloblast nuclears near the collar;While its expression significantly enhanced in transition ameloblasts and continue until maturity stage.Therefore, we speculate that Runx2 involved in the maturity stage of enamel development.Compared with the wild type(Runx2loxp/loxp)mice,in the mutant mice(Amelx-Cre;Runx2loxp/loxp), Runx2 gene was not specificly deleted in ameloblasts,and there were no significant differences on the teeth surface.While compared with the mutant mice(K14-Cre; Runx2loxp/loxp), Runx2 gene was specifically deleted in the early epithelial cells; It was not discovered in ameloblast nuclears,and the enamel surface had seriously adverse mineralization phenotypes;In the tips of six month mice incisors,the enamel was partially missing,and molars lost normal shapes,tips weared seriously,while enamel matrix protein content increased significantly.Conclusion:(1)Runx2 protein had obviously expression in the maturation ameloblasts,suggesting that Runx2 may be involved in the maturation development of enamel.(2) In the mutant mice(Amelx-Cre; Runx2loxp/loxp), the partially missing of Runx2 gene did not cause enamel dysplasia, we suspect that there may be some kinds of compensation in place of the missing matrix Runx2 gene function,causing adverse enamel mineralization.(3)In the mutant mice(K14-Cre, Runx2loxp/loxp), the specifically knockout Runx2 gene at the early epithelial cells,caused ameloblasts losing Runx2 gene expression and adverse enamel mineralization,which indicated that Runx2 gene plays an important role in the development and mineralization of enamel.