Interactions between type of culture medium and addition of serum on development and gene expression of bovine blastocysts produced in vitro.

Serum is commonly added to culture medium to improve the production of bovine embryos in vitro. The main goals were to verify the actions of serum to increase blastocyst yield and test the hypothesis that fetal bovine serum alters blastocyst gene expression in a manner that could affect competence to establish pregnancy and dysregulate fetal development. Media used were synthetic oviduct fluid medium bovine embryo 2 (SOF-BE2) and a commercial medium from IVF Biosciences termed here as IVFB. Three experiments were conducted in which either adult or fetal bovine serum (10%, vol/vol) was added at day 1 or 5 of development. Overall, serum increased blastocyst production. Gene expression in blastocysts was measured in the experiment in which fetal bovine serum was added at day 5. Serum resulted in 215 differentially expressed genes for embryos cultured in SOF-BE2 and 194 genes for embryos cultured in IVFB (adjusted P value of <0.05 and a |log₂| fold change >1). Only 24 genes were regulated by serum similarly for both media, including several transcription factors, imprinted genes, PSAT1 implicated in fetal growth in mice, and genes dysregulated in cloned embryos. Serum largely eliminated differences in gene expression between media. Expression data on eight biomarker genes were also used to calculate an embryo competence index previously related to embryo survival. Serum lowered the embryo competence index for both media. In conclusion, actions of fetal bovine serum on the preimplantation embryo include changes in gene expression indicative of reduced embryo competence and possible alterations in fetal development.NEW & NOTEWORTHY Serum is commonly added to the culture medium to improve the production of bovine embryos in vitro, but its molecular consequences for the resultant embryo are unclear. Here, we showed that blastocysts produced in serum experienced changes in gene expression, including transcription factors and imprinted genes. An embryo competence index that predicts embryo's ability to establish pregnancy based on gene expression was reduced by serum, suggesting serum can reduce embryo survivability.