ERM, an ETS transcription factor, is expressed in granulosa and cumulus cells and serves as a transcriptional regulator of the cyclooxygenase-2. Eo J et al. PEA3, ER81, and ERM are members of PEA3 subfamily of E26 transformation-specific (ETS) transcription factors which are known to influence a host of biological processes. We previously showed that ERM, expressed in Sertoli cells, plays a crucial role in maintaining spermatogonial stem cell niche in the mouse testis. However, it is not yet known whether PEA3 family members are expressed in the ovary or play any role in ovarian functions. Here we show that ERM and PEA3 are expressed in mouse ovaries in granulosa and cumulus cells during folliculogenesis. Both ERM and PEA3 mRNAs are also detected in cumulus-oocyte-complexes (COCs) and in denuded oocytes. Notably, PEA3 is highly expressed in the cumulus cells of ovulated COCs at 16 hr post-hCG. Cyclooxygenase-2 (COX-2), a rate-limiting enzyme for prostaglandin synthesis, is critical for oocyte maturation and ovulation. Since several putative ETS-binding sites (EBS) are present in the COX-2 promoter, we examined whether ERM influences COX-2 transcriptional activity. Indeed, we found that addition of ERM increases the transcriptional activity of the 3.2-kb mCOX-2 promoter by 2.5 fold in luciferase reporter assays. Collectively, the results show that PEA3 and ERM are expressed in granulosa and cumulus cells during folliculogenesis and ovulation, suggesting they influence cellular events in the ovary by regulating downstream genes such as COX-2.