阐明成牙本质细胞分化的分子机制是认识牙发育过程和实现牙本质再生的关键。申请人前期研究发现同源盒基因Lhx8通过表观修饰抑制Dspp等成牙本质细胞终末分化关键基因表达，维持细胞增殖和未分化的前体状态。申请人进一步预实验显示：组蛋白甲基转移酶Suv39h1在牙源性间充质中的表达谱与Lhx8高度相似，且与Lhx8具有强相互作用；干涉Suv39h1显著阻断Lhx8对成牙本质细胞终末分化的抑制。据此，我们提出科学假说：Lhx8通过募集Suv39h1在表观遗传水平调控牙发育进程。本项目将通过牙胚原位杂交、牙胚重组和细胞学等实验，明确牙发育早期，Lhx8是否通过与Suv39h1相互作用，将其募集到Dspp，Col1a1，Msx1/2等成牙本质细胞终末分化关键基因的启动子区，导致局部H3K9me3修饰和基因表达抑制，维持牙源性间质细胞的前体细胞状态和增殖分化平衡。本研究有望揭示牙发育的表观遗传新机制。

Elucidation of the exact molecular mechanism controlling odontoblast differentiation process is one of fundamental works to fully understand the tooth development and to successfully achieve dentin regeneration. Our previous work has demonstrated that homeobox gene Lhx8 plays a critical role in the maintenance of cell proliferation and progenitor status via epigenetic suppression of key odontoblast differentiation genes, such as Dspp. Our further pilot studies revealed that Suv39h1, a key histone epigenetic modification enzyme, displayed a highly similar expression pattern with that of Lhx8 in the dental mesenchyme. Importantly, we found that Lhx8 showed strong physical interaction with Suv39h1, and knock-down of Suv39h1 significantly blocked the odontoblast terminal differentiation suppression induced by Lhx8. Based on these previous results, we hypothesize that Lhx8 epigenetically regulates the balance of cell proliferation and differentiation via recruiting Suv39h1. In this project, we will further investigate whether Lhx8 interact with Suv39h1 and determine whether Lhx8 can mediate recruitment of Suv39h1 to the promoters of key genes (Dspp, Col1a1, and Msx1/2) controlling odontoblast terminal differentiation and induce tri-methylation of H3K9 of these genes, which therefore will sustain the suppression and the progenitor status of dental mesenchyme cells. Such epigenetic suppression will therefore control the delicate balance between proliferation and differentiation of dental mesenchyme cells. Our study will provide a novel epigenetic insight into molecular mechanisms of tooth development.