In mammals, progressive activation of primordial follicles is essential for maintenance of the reproductive lifespan. Several reports have demonstrated that mitogen-activated protein kinases 3 and 1 (MAPK3/1)–mammalian target of rapamycin complex 1 (mTORC1) signaling in pre-granulosa cells promotes primordial follicle activation by increasing KIT ligand (KITL) expression and then stimulating phosphatidylinositol 3 kinase signaling in oocytes. However, the mechanism of mTORC1 signaling in the promotion of KITL expression is unclear. Immunofluorescence staining results showed that phosphorylated cyclic AMP response element-binding protein (CREB) was mainly expressed in pre-granulosa cells. The CREB inhibitor KG-501 and CREB knockdown by Creb siRNA significantly suppressed primordial follicle activation, reduced pre-granulosa cell proliferation and dramatically increased oocyte apoptosis. Western blotting results demonstrated that both the MAPK3/1 inhibitor U0126 and mTORC1 inhibitor rapamycin significantly decreased the levels of phosphorylated CREB, indicating that MAPK3/1–mTORC1 signaling is required for CREB activation. Furthermore, CREB could bind to the Kitl promoter region, and KG-501 significantly decreased the expression levels of KITL. In addition, KG-501 and CREB knockdown significantly decreased the levels of phosphorylated Akt, leading to a reduced number of oocytes with Foxo3a nuclear export. KG-501 also inhibited bpV (HOpic)-stimulated primordial follicle activation. Taken together, the results show that CREB is required for MAPK3/1–mTORC1 signaling-promoted KITL expression followed by the activation of primordial follicles.

在哺乳动物中，原始卵泡的逐步活化对于维持生殖寿命至关重要。几篇报道表明，前颗粒细胞中的雷帕霉素复合物1（mTORC1）信号转导的促分裂原活化蛋白激酶3和1（MAPK3 / 1）-哺乳动物靶标通过增加KIT配体（KITL）的表达进而刺激磷脂酰肌醇来促进原始卵泡的激活。 3卵母细胞中的激酶信号传导。但是，尚不清楚mTORC1信号在促进KITL表达中的机制。免疫荧光染色结果表明，磷酸化的环状AMP反应元件结合蛋白（CREB）主要在颗粒前颗粒细胞中表达。CREB抑制剂KG-501和CREB的抑制作用siRNA显着抑制了原始卵泡的活化，降低了颗粒前颗粒细胞的增殖，并显着增加了卵母细胞的凋亡。蛋白质印迹结果表明，MAPK3 / 1抑制剂U0126和mTORC1抑制剂雷帕霉素均显着降低了磷酸化CREB的水平，表明CREB激活需要MAPK3 / 1–mTORC1信号传导。此外，CREB可以与Kitl结合启动子区域和KG-501显着降低KITL的表达水平。此外，KG-501和CREB的敲低显着降低了磷酸化Akt的水平，从而导致Foxo3a核输出的卵母细胞数量减少。KG-501还抑制bpV（HOpic）刺激的原始卵泡活化。两者合计，结果表明CREB是MAPK3 / 1–mTORC1信号促进KITL表达，随后激活原始卵泡所必需的。