Gene expression analysis and in vitro production procedures for bovine preimplantation embryos: Past highlights, present concepts and future prospects.

Over the past decades in vitro production (IVP) of bovine embryos has been significantly improved and in particular bovine IVP is now widely applied under field conditions. This in vitro technique provides new opportunities for cattle producers, particularly in the dairy industry, to overcome infertility and to increase dissemination of animals with high genetic merit. Improvements in OPU/IVP resulted in large-scale international commercialization. More than half a million IVP embryos are generated on the yearly basis demonstrating the enormous potential of this technology. These advances and the fact that bovine and human early development is remarkably similar have also prompted the use of bovine embryos as a model system to study early mammalian embryogenesis including humans. Despite all the improvements, embryos generated in vitro still differ from their in vivo derived counterparts. Embryos must adjust to multiple microenvironments at preimplantation stages. Consequently, maintaining or mimicking the in vivo situation in vitro will aid to improve the quality and developmental competence of the resulting embryo. The successful clinical application of the techniques in reproductive biotechnology requires both species-specific clinical skills and extensive laboratory experience. The recent advances in transcriptome profiling have also provided deeper insight into RNA expression and regulation at an unprecedented resolution. The development of these high-throughput DNA sequencing methods has resulted in new approaches for both mapping and quantifying transcriptomes. The aim of this review is therefore to summarize the available data related to gene expression analyses as well as in vitro embryo production procedures and to provide ideas about future concepts.