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. 2021 Jun 13;10(6):1491. doi: 10.3390/cells10061491

Figure 3.

Figure 3

Pre-granulosa cells initiate the activation of primordial follicles through mTORC1–KITL in pre-granulosa cells and KIT Y719–PI3K in oocytes. In dormant follicles (left), the mTORC1 signaling in pre-granulosa cells is suppressed, and only a low level of KITL is expressed by pre-granulosa cells, which is insufficient to activate KIT Y719 on oocytes. KIT Y719 is not phosphorylated and the intraoocyte PI3K signaling is suppressed in this situation. In growing follicles (right), activated mTORC1 signaling in the pre-granulosa cells leads to enhanced production of KITL that binds to c-kit and subsequently activates the intraoocyte PI3K signaling through phosphorylation of KIT Y719. Activated PI3K signaling in oocytes awakens the dormant oocytes.