在有胎盘的哺乳动物中，黄体对于妊娠的建立和维持有重要作用。黄体功能不足与复发性流产密切相关。迄今为止，仍然有约50%的复发性流产原因不明。Lgr4/5与黄体化激素受体的同源性预示着LGR4／5在雌性生殖系统中的作用，但是其功能一直未知。预实验结果表明，Lgr5缺失的黄体早衰，并导致妊娠终止。本课题拟研究Lgr4/5在黄体中的作用。核心假设是：Lgr4调控黄体生成；Lgr5维持黄体功能。本项目拟利用多种卵巢颗粒细胞特异性敲除小鼠模型，结合超数排卵模型和体外颗粒细胞培养，系统研究：（1）Lgr受体及配体在围排卵期卵巢中的动态表达模式；（2）Lgr4/5在颗粒细胞黄体化及孕酮合成中的作用及机制；（3）Lgr4/5在黄体形成和功能维持中的代偿机制；（4）Lgr4/5信号通路在黄体形成和功能维持中的新机制，以期进一步认识黄体化的分子基础，揭示新的由着床位点调控黄体功能的机制。

The ovarian corpus luteum (CL) is essential for the establishment and maintenance of pregnancy in all eutherian mammals. Failure to maintain functional CL is associated with recurrent pregnancy loss during early pregnancy. The exact causes for 50% of recurrent pregnancy failures are unknown. LGR4/5 proteins have been long suspected to be involved in female reproductive function, since their structures have high homology to those of follicle stimulating hormone receptor and luteinizing hormone receptor. In addition, both Lgr4 and Lgr5 are expressed in the CL. However, their function in this tissue still remains unknown. Our preliminary data using mice with luteal deletion of Lgr5 showed that the CL undergoes premature functional luteolysis which results in severely impaired fertility. The overall objective of this application is to study the role of Lgr4/5 in the CL. My central hypothesis is that Lgr5 plays a key role in the maintenance of functional CL and Lgr4 has a role in the formation of CL. Using multiple genetically modified mouse models with granulosa cell specific gene deletion, as well as superovulation mouse model and in vitro granulosa cell culture system, I will: (1)examine the dynamic expression of Lgr4/5 and their ligands RSPO1-4 in granulosa and luteal cells; (2) examine roles of Lgr4 and Lgr5 in luteinization and progesterone synthesis in matured CL; (3) examine the functional redundancy of Lgr4 and Lgr5 in luteinization and CL function maintenance; (4) explore unrecognized downstream targets of Lgr4/5 in the context of luteinization and steroid synthesis in CL. The proposed grant has the potential to reveal the mechanism by which Lgr4/5 regulate CL formation and function, and more importantly it may identify novel communication ways between implantation sites and CL during pregnancy.