Differences in the incidence of apoptosis between in vivo and in vitro produced blastocysts of farm animal species: a comparative study.

This study compared the occurrence of cell death (apoptosis) in animal embryos developed in a lab (in vitro) and those developed naturally (in vivo). Despite both set of embryos being of high quality, there were more instances of cell death in the lab-developed ones. Particularly, the study also found that some signs of cell death were repeatedly found in the inner cell mass of lab-developed embryos, which could potentially explain lower embryo transfer success rates with these embryos.

Research Objectives and Methods

• The objective of the research was to investigate why in vitro produced embryos from various farm animals (equine, porcine, ovine, caprine, and bovine) have lower success rates in terms of pregnancies and births upon embryo transfer (ET) despite being of high morphological quality like their in vivo counterparts.
• The team used a comparative approach, examining both in vitro and in vivo produced embryos of the same species and focusing on the incidence of cell death (apoptosis) as a potential factor in their viability and success in ET.
• Cell death was detected by examining cell membrane damage, fragmented DNA and fragmented nuclei in selected embryos using Ethidium homodimer (EthD-1), terminal dUTP nick end labeling (TUNEL) and Hoechst 33342 staining.

Findings

• In general, cell death in these embryos was found to be low across all species examined.
• Blastomeres (an early stage cell in the embryo) in in vitro produced equine, porcine and bovine embryos showed a higher level of cell death compared to their in vivo counterparts.
• In particular, 4 out of the 29 lab-developed bovine blastocysts studied showed extensive cell death signs in their inner cell mass (ICM), a condition which is not compatible with a viable embryo.
• This higher cell death rate specifically in the ICM of in vitro developed embryos could possibly explain why they have lower ET outcomes.

Conclusion

• Despite the fact that morphologically high-quality blastocysts of several farm animal species present a significant difference in the percentage of cell death between in vitro and in vivo production, the incidence of this phenomenon at the blastocyst stage is low.
• This suggests that while a difference in occurrence of cell death exists and could contribute to the described difference in success rate, it isn’t extensive enough to fully account for the substantial difference in embryo viability observed between in vivo and in vitro produced blastocysts following ET.