It is not yet known which, if any, of these substrates is cleaved to produce the key biochemical step in the initiation of apoptosis. Recently a novel heterodi-meric protein, DNA fragmentation factor (DFF), has been identified as a potential link between caspase-3 activation and DNA fragmentation. Caspase-3 cleaves DFF to produce an active factor that induces DNA fragmentation in isolated nuclei, and cleavage of DFF, in the absence of PARP cleavage, is sufficient to reproduce all the events of nuclear fragmentation observed during apoptosis. Whether DFF is present, and cleaved during apoptosis, in ovarian cells is not known. Since inhibitors of caspase-3 prevent apoptosis in granulosa cells, it is likely that caspase-3 is activated during follicular atresia. ventolin inhalers
The absence of detectable PARP and actin cleavage during induced follicular atresia in the present study may reflect a low level of caspase-3 activity that cleaves sufficient DFF to produce DNA fragmentation but is not extensive enough to produce detectable actin and PARP cleavage. Alternatively, since caspase-3 staining was detected only in granulosa cells of TUNEL-positive follicles, it is possible the cleaved PARP and actin extracted from those apoptotic granulosa cells would be diluted by the recovery of intact PARP or actin from other TUNEL-negative follicles. Although PARP and actin cleavage were probably not necessary for the activation of DNase I, it is possible that the degradation of these proteins could have other functions during luteal regression.