Review: Overview of the transcriptomic landscape in bovine blastocysts and elongated conceptuses driving developmental competence.

In cattle, pregnancy loss due to early embryonic mortality is a major concern that significantly impacts reproductive efficiency. Given the economic importance of cattle in livestock productivity, much research has been carried out to comprehend the regulatory mechanisms underlying this early embryo loss. Thus, understanding the molecular principles behind the reciprocal communication between the maternal uterus and the developing conceptus is paramount. Measurement of mRNA expression through a variety of techniques is widely used to unravel the complex and dynamic interaction between these two players. Development of high-throughput technologies, such as microarrays and RNA sequencing, have allowed global quantification of the full range of expressed mRNA, or transcriptome, of a biological sample. Therefore, numerous investigators have applied one or the other method to study the bovine embryo transcriptome at different developmental checkpoints and under different conditions. The goal of this article was to review studies involving the use of high-throughput techniques to study the transcriptome of the bovine embryo from the blastocyst (∼day 7) to the elongating conceptus stage (∼days 13-16) in terms of developmental capacity and the impact of procedures for in vitro embryo production. Furthermore, the differentially expressed genes reported by each study and enriched pathways were compared to determine common terms. The studies described here highlight differences in the transcriptome (i) between blastocysts with divergent ability to sustain a pregnancy, (ii) between age-matched elongated conceptuses with divergent developmental fates, and (iii) between blastocysts and elongated conceptuses produced in vitro or in vivo. Comparison between these works, supported by other studies involving transcriptomic data integration presented at the end of this review, highlights the involvement of pathways related to energy metabolism in embryonic competence, which may be altered because of the procedures involved in the in vitro production of embryos.