Sheep as a model for human ART: novel insights on phenotypic and epigenetic alteration in ART-derived sheep conceptuses.

Over 1% of babies born in Europe are conceived through Assisted Reproductive Technologies (ART). Retrospective data published by professional bodies as well as experimental data from research on animals have revealed a number of epi/genetic defects resulting from ART, especially from the most aggressive techniques, such as embryo biopsy, Ooplasm/Germinal/Vesicle Transfer, In Vitro Maturation and Cryopreservation. Such epi/genetic defects may have immediate phenotypic effects, or appear later in life, or even spill over the second generation. There is therefore a growing concern, not only amongst specialist practitioners, but the general public, over their potential side effects. Research on human embryos is forbidden in the majority of European Countries with the consequence that laboratory solutions to problems in human infertility are applied directly in the clinic, without the benefit of control studies in appropriate animal models. In order to address this dilemma, we have used sheep as animal model to monitor the phenotypic and epigenetic effects of in vitro embryo production and culture. The animal models we focus is sheep embryos because they are closer to human ones in term of their metabolism and key stages of preimplantation development like timing of zygotic genome activation, compaction and blastulation; moreover, sheep pregnancy has always been a golden model for human obstetricians. In this chapter we describe our studies of the early post implantation of ART derived foetuses, from day 20 to 28, which have been compared with similar age control ones, naturally conceived. ART foetuses are significantly retarded, and display a defective vascularization in correspondence of a rapid growth phase recorded at day 26. The lack of a angiogenetic support during this critical phase of development is verisimilarly responsible for their demise, which has been found to occur between day 24-26. [...]