During final maturation (between LH surge and ovulation) in vivo, a switch from oestradiol to progesterone dominance within the follicle is well described. The aim was to mimic the in vivo situation during in vitro maturation via the supplementation of different gonadotropins. Groups of 30 cumulus-oocyte complex (abattoir-derived ovaries) were matured in TCM 199 plus different gonadotropins (eCG/hCG; FSH/LH, each in 0.05 or 0.01 IU; only FSH 0.05 IU; without gonadotropins) using a standard protocol without oil overlay. In Experiment 1, denuded oocytes were collected at 0 h (immature) and after 24 h of in vitro maturation (IVM; exhibit first polar body). In Experiment 2, oocytes were collected at different time points [0 (immature), 4, 8, 12, 16, 20, and 24 h] after IVM in eCG/hCG-supplemented medium. They were individually stored at −80°C until analyses. Transcripts of developmental competence (BMP15, GDF9, ZAR1), glucose or steroid metabolism (G6PD, STAR), and progesterone receptors (PGR, PGRMC1/2) were examined in individual oocytes via quantitative RT-PCR (n = 5). For statistical analyses, 1-way ANOVA followed by a Tukey test was used. Relative abundance of BMP15 transcripts was significantly lower (P ≤ 0.05) in oocytes of the group matured for 24 h with FSH/LH 0.01 IU, FSH 0.05 IU, and without gonadotropins than in immature oocytes. Relative amount of G6PD and PGRMC2 mRNA was significantly lower (P ≤ 0.05) in mature oocytes of the group with FSH/LH 0.01 IU, FSH 0.05 IU, and without gonadotropins than in immature ones. Relative abundance of GDF9, STAR, and ZAR1 transcripts was significantly lower (P ≤ 0.05) in oocytes of the group with eCG/hCG, FSH/LH 0.01 IU, FSH 0.05 IU, and without gonadotropins compared with immature oocytes. Relative abundance of PGR mRNA was significantly higher (P ≤ 0.05) in mature oocytes of the group with eCG/hCG than in immature oocytes, FSH/LH 0.01IU, FSH 0.05 IU, and without gonadotropins (Experiment 1). Relative amount of GDF9 transcripts was significantly lower (P ≤ 0.05) in mature oocytes collected after 24 h than in immature ones. Relative abundance of PGR mRNA was significantly higher (P ≤ 0.05) in oocytes collected after 20 and 24 h of IVM than in immature ones. Relative amount of ZAR1 transcripts was significantly lower (P ≤ 0.05) in oocytes collected after 16, 20, and 24 h of IVM than in immature oocytes; likewise, they were significantly lower (P ≤ 0.05) in oocytes collected after 12, 16, 20, and 24 h than in oocytes collected after 4 h of IVM. Relative amount of STAR mRNA was significantly lower (P ≤ 0.05) in oocytes collected after 24 h than in immature ones, and significantly lower (P ≤ 0.05) in oocytes collected after 16, 20, and 24 h than in oocytes collected after 4 h of IVM (Experiment 2). The results suggest a down-regulation of most transcripts during the period of IVM with different gonadotropin supplements with exception of PGR. Furthermore, most transcripts follow a timely regulated mRNA expression pattern during the entire IVM period.
We gratefully acknowledge the financial support of the German Research Foundation (DFG; FOR 1369, WR 154/3–1).
mRNA expression pattern of selected candidate genes differs in bovine oviductal epithelial cells in vitro compared with the in vivo state and during cell culture passages