Assessing pre‐implantation embryo development in mice provides a rationale for understanding potential adverse effects of ART and PGD procedures

Abstract

Although the molecular events controlling human pre-implantation development remain unclear, mechanisms have been identified by analyzing these stages in mice. Through this approach, considerable insight has been gained into the events that operate to determine the first two cell fate decisions, occurring from zygote formation to the blastocyst prior to implantation. These mechanisms are related to cell polarization, cell division, cell-cell contact, and cell spatial position. Two developmental stages are essential for these processes to proceed adequately. Firstly, the second polar body must anchor to the external membrane during the first mitotic divisions of the embryo as its position is strongly biased to determine the plane of polarity. This in turn has important influence on the fate of the early blastomeres. Secondly, in the transition from the 8- to 16-cell stage, the cells that will form the inner cell mass are determined. Moreover, analyses performed on human oocytes and embryos have identified similar processes to those reported in mice and thus are evolutionarily conserved. Therefore, the understanding of mice pre-implantation embryo development provides a rationale to interpret current results of potential long-term adverse outcomes of Assisted Reproductive Technologies and Pre-implantation Genetic Diagnosis (PGD).

Fertilization and Cleavage Axes Differ In Primates Conceived By Conventional (IVF) Versus Intracytoplasmic Sperm Injection (ICSI)

“…Foremost among these are questions regarding which events are essential for the union of sperm and egg DNA within the activated zygote, as well as the consequences of different ART approaches, especially IVF as compared to ICSI, on the resultant embryo 1–6 . Notwithstanding the impressive literature on murine reproduction 7–11 , many differences between rodents and primates, especially in centriole and centrosome transmission 12–15 , preclude relevant conclusions. While human zygotes are investigated noninvasively, especially with the adoption of commercial time-lapse imaging systems, the earliest events during fertilization may not be captured in these systems, particularly during conception by ICSI.…”