179 EFFECT OF SERUM DURING CULTURE ON DAY 14 ELONGATED BOVINE EMBRYOS

Abstract

It has been reported that the addition of serum to embryo culture media alters gene expression and triggers the development of large offspring syndrome. The objectives of this study were to determine gene expression levels in embryos cultured in the absence or presence of 5% calf serum and in vivo-derived (IVD) embryos and to determine the effects of serum on the length of elongated embryos. Abattoir-derived oocytes were obtained from a commercial provider and fertilized at 24 h of maturation with semen from a bull previously used for IVF. At 18 h post-insemination (hpi), embryos were denuded and groups of 15 presumptive zygotes were cultured in 30-μL drops of modified SOF medium with amino acids and 6 mg mL^–1 of BSA (mSOFaa). At 72 hpi, cleavage rate was assessed and embryos were randomly allocated into 2 treatments: mSOFaa without and with 5% calf serum. Embryos were then cultured to 168 hpi and blastocyst rates were assessed and recorded. Blastocysts (n = 5 to 10) from each treatment were transferred into synchronized recipients, and Day 14 embryos were recovered 7 days post-transfer. Embryos were photographed, measured, and immediately stored at –80°C in a minimal volume of PBS + 0.1% polyvinyl alcohol. Messenger RNA was isolated using a Dynabeads mRNA Direct Kit™ (Invitrogen, Carlsbad, CA), and reverse transcription was performed using an iScript™ cDNA Synthesis Kit (Bio-Rad Laboratories, Inc., CA). Quantitative PCR was performed to determine the transcript abundance for COX6A, IFNT1a, PLAC8, IGF2R, and GAPDH for each sample. The GAPDH was used as a reference gene, and gene expression was calculated as a ratio of expression levels between each gene of interest and GAPDH. Expression levels for each gene were determined from standard curves generated by serial dilutions of PCR amplicons starting with 0.4 pg/reaction. Blastocyst development rates were higher in embryos cultured with serum compared with the nonserum treatment (14.9 and 7.4% respectively; chi-square, P < 0.001). Lengths of elongated embryos from the serum (3395.3 ± 414.7 μm) and nonserum (2784 ± 741.8 μm) culture treatments differed from the IVD (6297.7 ± 677.2 μm) treatment (mean ± SE; ANOVA, P < 0.0052). There were no differences in the mean expression levels for COX6A, IFNT1a, PLAC8, and IGF2R across treatment groups, but in the serum treatment, 3 out 11 overexpressed IFNT1a, 4 out of 11 overexpressed IGF2R, and 2 out of 11 overexpressed PLAC8, defined as being 2 standard deviations above the mean of the IVD treatment for each respective gene. In the in vitro-produced nonserum and IVD treatments, overexpression by this definition was not observed. Although mean expression levels were not affected by culture with serum under these conditions, very high expression of IFNT1a, IGF2R, and PLAC8 was observed in some embryos cultured with serum, but not in embryos cultured without serum or IVD embryos.