转录因子Six1/Six2通过BMP信号通路调控上下颌突铰链区发育在颌骨黏连发生中的作用机制

颌骨黏连为罕见的颅颌面先天畸形，病因不明。课题组发现转录因子Six1/Six2缺失可导致上下颌骨黏连。上下颌分化异常与颌骨黏连关系密切。课题组前期研究证明Six1、Six2在上下颌连接区上皮表达，参与调控上下颌分化，为研究颌骨黏连提供重要切入点，但机制不清。预实验进一步发现，Six1/Six2缺失导致BMP信号通路表达异常，而Bmp4缺失可挽救Six1/Six2缺失导致的颌骨黏连。因此，在前期研究基础上，结合文献提出假设：Six1/Six2通过BMP信号通路调控上下颌分化，在颌骨黏连中发挥重要作用；课题组拟构建Six1/Six2f/fK14Cre小鼠模型，证实上皮中Six1、Six2对上下颌分化的调控作用，进一步构建体外表达缺失细胞系，结合体内外研究，利用ChIP等相关分子生物学技术系统阐明Six1/Six2对BMP通路的调控机制，为颌骨黏连病因研究提供实验依据，为临床研究提供潜在靶点。

Syngnathia, a rare but severe human congenital defect, is characterized by bony fusion of the mandible to the maxilla. However, the genetic mechanisms are remained unknown. Here we present evidence that Six1 and Six2, who encode closely related transcription factors, exhibit partly overlapping patterns of expression in the developing mouse embryonic maxillary and mandibular processes. We found that Six1-/-Six2-/- mutant mice were born with syngnathia. Moreover, whereas Six1-/- mice exhibited partial bony fusion of maxilla and zygoma, Six1-/-Six2+/- mice exhibited significantly increased penetrance of the bony fusion malformation. Our research found ectopic Bmp4, Msx1 expression at the maxillary-mandibular junction area in Six1-/-, Six1-/-Six2+/-, Six1-/-Six2-/- mice. Genetically inactivating 1 allele of Bmp4 significantly reduced the penetrance of bony fusion malformation in both Six1-/- and Six1-/-Six2+/- embryos, indicating that Six1 and Six2 regulate BMP signaling pathway to pattern facial structures. Furthermore, we show that neural crest-specific inactivation of Six1 in Six2-/- embryos only resulted in bone agenesis without syngnathia. Thus, comes our hypothesis, Six1 and Six2 in epithelium function partly redundantly to control maxillary and mandibular processes development by regulating BMP signaling pathway. This project plans to construct a Six1f/fSix2f/fK14Cre mouse model, to confirm the regulatory effect of Six1 and Six2 in the epithelium on jaw differentiation. By combining in vitro and in vivo studies, using ChIP and other related molecular biological technology systems, the regulatory mechanism of Six1/Six2 on the BMP pathway will be elucidated, and provides the experimental basis for the study of the cause of syngnathia and presents potential targets for clinical research.