Expression of Fas-Fas ligand system associated with atresia in murine ovary

We detected that Fas receptor (Fas) was expressed at transcriptional levels in oocytes/eggs and some granulosa cells of murine ovary, whereas, Fas ligand (FasL) was found to be strongly expressed in granulosa cells by means of in situ hybridisation. These results were supported by an indirect immunofluorescence (IIF) test with anti-Fas monoclonal antibody (mAb)/FasL Ab. The lysates from granulosa cells were precipitated by anti-FasL Ab, exhibiting a specific band at 40 kDa. When zona pellucida (ZP)-free eggs were incubated with granulosa cells in vitro, apoptosis (DNA fragmentation) was induced in the eggs, as detected by the terminal deoxynucleotide transferase mediated dUTP-nick end labelling (TUNEL) method. To examine whether FasL-bearing cells can induce apoptosis in eggs expressing Fas through molecular interaction between FasL and Fas, we employed a baculovirus expression system to generate FasL on the surface of Spodoptera frugiperda (Sf9) cells. The co-incubation of eggs with Autographa californica nuclear polyhedrosis virus (AcNPV) and FasL transfected Sf9 (Sf9-FasL) cells in vitro was performed and resulted in the induction of apoptosis in eggs as detected by the TUNEL method. Apoptosis was absent in eggs co-incubated with AcNPV-1393 transfected Sf9 (Sf9-1393) cells. Thus, ovarian atresia was suggested to be induced by molecular interaction between FasL on granulosa cells and Fas on oocytes/eggs during oogenesis.