Changes in the Expression of Decoy Receptor 3 in Granulosa Cells during Follicular Atresia in Porcine Ovaries. Sugimoto M et al. During follicular development in mammalian ovaries, the majority of follicles undergo atresia. One of the characteristics of this process is apoptotic cell death in granulosa cells. Several death ligands and receptors, including Fas ligand (FasL) and Fas, have been detected in ovarian follicles and also demonstrated to be capable of inducing apoptosis in follicular cells. Decoy receptor 3 (DcR3) competes with Fas to bind FasL but lacks intracellular death domains, thus inhibiting the induction of apoptosis by the FasL/Fas system. In the present study, we examined the expression of putative porcine DcR3 (pDcR3) mRNA in porcine ovarian follicles. Total RNA was extracted from granulosa cells and thecal layer cells of tertiary follicles at healthy, early atretic and progressed atretic stages, and the expression of pDcR3 mRNA was demonstrated by reverse transcription-polymerase chain reaction (RT-PCR). The nucleic acid sequence in the coding region had 80% homology to that of human DcR3, and the deduced amino acid sequence was 73% identical to that of human DcR3. In an in situ hybridization experiment, pDcR3 mRNA expression was confirmed in granulosa and thecal layers, in both healthy and atretic follicles. Quantitative real time RT-PCR analysis showed that the expression of pDcR3 mRNA was weaker in granulosa cells of atretic follicles than those of healthy follicles. No notable changes were seen in the thecal layer cells. These results suggest that DcR3 plays a significant role in the regulation of apoptosis in granulosa cells, but not in thecal layer cells, during atresia.