Gene expression at different cell stages of in vitro-fertilized bovine embryos

Abstract

The birth rate of embryos produced in vitro (IVF) is still lower than that of embryos produced in vivo. Three major steps for the success of the IVF technique are maturation of immature oocytes, fertilization of matured oocytes, and culture of the resulting embryos. Studying mRNA expression in early embryonic development stages is important and can help to assess embryo quality and optimize production protocols in vitro. The current study aimed to determine the expression levels of developmentally important genes in different stages of bovine embryos produced in vitro. Cumulus-oocyte complexes (COCs) were collected from bovine ovaries and cultured in synthetic oviduct fluid (SOF) medium for 7 - 9 days. Embryos were collected at the time-points listed above, and mRNA expression of genes involved in pluripotency (OCT4), DNA methylation (DNMT1), apoptosis (BAX), and metabolism (GLUT1) and a heat shock protein (HSP70) was estimated from the 2-cell stage to the blastocyst stage of embryos. The results showed statistically significant differences in the relative abundance (RA) of OCT4, DNMT1, BAX, and GLUT1 gene transcripts among the different stages, whereas there were non-significant differences in the RA of HSP70 between these stages. In conclusion, gene expression levels differ among the developmental stages of embryos produced in vitro, possibly because of the timing of embryonic genome activation (EGA).