114 PROGESTERONE CONCENTRATIONS DURING IVM AFFECT BOVINE OOCYTE QUALITY AT THE MOLECULAR LEVEL

Abstract

Progesterone (P4) is important for the developmental competence of cumulus–oocyte complexes (COC) used for in vitro maturation (IVM). In a recent study, we were able to show that circulating P4 concentrations had an effect on the molecular quality of COC recovered during repeated ovum pickup sessions, which might affect further development. (Schlüter et al. 2013 Reprod. Fertil. Dev. 25, 250). The aim of the present study was to determine the influence of different P4 concentrations during IVM on the molecular quality of bovine COC. The COC were collected from slaughterhouse ovaries and cultured as described recently (Stinshoff et al. 2011 Theriogenology 76, 1433–1441). The IVM medium was supplemented with 0, 50, 150, 300, and 450 ng mL^–1 P4. Ethanol served as vehicle control. After IVF with a bull of proven fertility, the presumptive zygotes were cultured in SOF under 5% oxygen (Stinshoff et al. 2011). Cleavage and developmental rates were determined at Day 3 and Day 7/8 (Day 0: IVF). Additionally, maturation rates were assessed. For mRNA analysis, immature and matured denuded COC (n = 5) were individually frozen at –80°C to analyse the relative transcript abundance using RT-qPCR. The transcripts studied play important roles during oocyte development [growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15), glucose transporter 1 (SCL2A1), hypoxia inducible factor 2α (HIF2α), nuclear progesterone receptor (PGR), progestin and adipoQ receptor 5 (PAQR5), progesterone receptor membrane component 1 and 2 (PGRMC1, PGRMC2)]. Data were tested using ANOVA followed by multiple pairwise comparisons using Tukey's test. A P-value of <0.05 was considered significant. The percentage of oocytes that reached the MII stage was similar in oocytes from all treatment groups (82.2–88.1%). Despite similar cleavage rates across all groups, the developmental rates did show significant differences. More embryos developed to the blastocyst stage stemming from oocytes cultured without any supplement or cultured only with alcohol compared to oocytes stemming from the group cultured with less than 50 ng mL^–1 P4 (25.4 ± 5.7 and 27.9 ± 7.2 v. 15.8 ± 2.6). The relative abundance of SCL2A1, BMP15, and PGRMC1transcripts in single oocytes did not show differences related to the supplementation of the IVM medium, whereas GDF9, HIF2α, and PAQR5 mRNA was reduced in oocytes of all groups compared with immature ones. The PGR and PGRMC2 transcripts were increased in matured oocytes of the control group and the vehicle control group (PGRMC2). In summary, supplementation of the IVM medium with different P4 concentrations had an effect on the molecular quality of oocytes after IVM, which might affect further development.

The financial support of the FBF (Förderverein Biotechnologieforschung) e.V. is gratefully acknowledged.