Effects of follicle stimulating hormone (FSH) and amphiregulin (AREG) on meiosis dynamics of oocytes undergoing in vitro maturation

Oocyte meiosis is arrested at prophase I during early folliculogenesis, and is resumed after the ovulatory LH surge, which induces germinal vesicle breakdown (GVBD) and progression of nuclear maturation to metaphase II (MII). Resumption of nuclear maturation is associated with decreases in oocyte transcription/translation and intracellular communication within the cumulus-oocyte complex. Therefore, precocious meiosis resumption may compromise oocyte fertility. The influences of LH in ovulatory follicles and of FSH during in vitro maturation (IVM) are mediated by EGF-like growth factors, including amphiregulin (AREG), which are produced by mural granulosa and cumulus cells. Recent studies suggest that replacement of FSH by AREG in IVM may improve oocyte developmental competence. This study aimed to assess meiosis dynamics in oocytes cultured with FSH or AREG. We tested the hypothesis that the direct stimulation with AREG speeds up nuclear maturation. Cumulus-oocyte complexes (COCs) were aspirated from bovine ovaries obtained at a slaughterhouse, and submitted to IVM for 6 hours in TCM 199 supplemented with BSA (0.4%), amikacin (75µg/mL), pyruvate (22µg/mL) and FSH (1µL/mL; n=81) or AREG (100ƞg/mL; n=59). After culture, oocytes were denuded, fixed in paraformaldehyde 4%, stained with Hoechst 33342 and examined under a fluorescence microscope to assess meiosis progression. Data were transformed to arcsine and groups compared by the Student t test, considering values of P<0.05 as significant. Supplementation with AREG resulted in a lower percentage of germinal vesicle oocytes (39.12% ± 6.6% vs. 61.06 ± 5.12; P=0.04) and a higher percentage of oocytes in MI (23.59% ± 5.5 vs. 9.93 ± 1.04; P = 0.04) in comparison with FSH. The percentage of oocytes at GVBD did not differ between treatments (P = 0.1). The present data indicate that AREG induces nuclear maturation more rapidly than FSH. Keywords: oocyte maturation, meiosis, AREG, FSH, cattle. Acknowledgements: CAPES, FAPESP, CNPq.