Research Paper Volume 8, Issue 2 pp 291—303

Figure 7. Possible pathways by which the FasL/Fas system facilitates oocyte aging. The sFasL released by cumulus cells activates Fas on the oocyte by activating NOX and increasing ROS. The activated Fas activates PLC-γ and caspase-8, which promote the production of IP₃ and the release of cytochrome c, respectively. Both IP₃ and cytochrome c interact with IP₃R, triggering Ca²⁺ release from endoplasmic reticulum into the cytoplasm. The cytoplasmic Ca²⁺ rises activate CaMKII and caspase-3. While the activated CaMKII causes cyclin B degradation, MPF inactivation and an increase in STAS, the activated caspase-3 facilitates further calcium releasing by truncating IP₃R, which activates more caspase-3 leading to oocyte fragmentation. On the other hand, the increase in STAS also facilitates oocyte fragmentation because a high MPF activity prevents caspase activation.