Expression of interferon regulatory factor-1 in the mouse cumulus-oocyte complex is negatively related with oocyte maturation

OBJECTIVE We found previously that interferon regulatory factor (Irf)-1 is a germinal vesicle (GV)-selective gene that highly expressed in GV as compared to metaphase II oocytes. To our knowledge, the function of Irf-1 in oocytes has yet to be examined. The present study was conducted to determine the relationship between retinoic acid (RA) and RA-mediated expression of Irf-1 and the mouse oocyte maturation. METHODS Immature cumulus-oocyte-complexes (COCs) were collected from 17-day-old female mice and cultured in vitro for 16 hours in the presence of varying concentrations of RA (0-10 µM). Rate of oocyte maturation and activation was measured. Gene expression was measured by quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) and cytokine secretion in the medium was measured by Bio-Plex analysis. Apoptosis was analyzed by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. RESULTS The rates of oocyte maturation to metaphase II and oocyte activation increased significantly with RA treatment (10 nM-1 µM). With 100 nM RA treatment, lowest level of Irf-1 mRNA and cumulus cell's apoptosis was found. Among 23 cytokines measured by Bio-Plex system, the substantial changes in secretion of tumor necrosis factor-α, macrophage inflammatory protein-1β, eotaxin and interleukin-12 (p40) from COCs in response to RA were detected. CONCLUSION We concluded that the maturation of oocytes and Irf-1 expression are negatively correlated, and RA enhances the developmental competence of mouse immature oocytes in vitro by suppressing apoptosis of cumulus cells. Using a mouse model, results of the present study provide insights into improved culture conditions for in vitro oocyte maturation and relevant cytokine production and secretion in assisted reproductive technology.