FasL-induced apoptosis in bovine oocytes via the Bax signal

The factor associated suicide (Fas) and its ligand (FasL) signaling is an important regulatory pathway of apoptosis in mammalian follicles. However, whether apoptosis in bovine oocytes is regulated by the Fas–FasL signaling pathway remains unknown. In this study, localization of Fas and FasL in immature oocytes and FasL in cumulus cells were examined using immunofluorescence staining. In addition, exogenous FasL was added to an in vitro culture system to investigate apoptotic changes in bovine oocytes, using annexin-V and terminal uridine nick-end labeling staining, and real-time quantitative polymerase chain reaction. In this study, Fas was expressed in immature oocytes, whereas FasL was expressed in cumulus cells, but not in immature oocytes; annexin–V- and terminal uridine nick-end labeling-positive rates of oocytes treated with 2, 10, or 50 ng/mL FasL were higher than those of control oocytes (P < 0.05); and oocytes from the three treatment groups had higher expression levels of Fas and B cell lymphoma/leukemia-2 associated X than those in the control group (P < 0.05). Taken together, we concluded that the Fas–FasL signaling pathway was involved in regulation of bovine oocyte apoptosis, perhaps related to B cell lymphoma/leukemia-2 associated X upregulation.