Apoptosis in rodent peri-implantation embryos: differential susceptibility of inner cell mass and trophectoderm cell lineages--a review.

Inner cell mass (ICM) and trophectoderm cell lineages diverge early in cleavage in response to a complex combination of cellular and molecular determinative events. The resulting differences in metabolic requirements, cell positioning and micro-environments are considered as some of the major causes underlying the differential sensitivity of ICM and trophectoderm cell lines to embryotoxic agents. In most instances, ICM cells appear less resistant to disruption than trophectoderm cells, and past observations suggest that over-stimulation of apoptosis is probably one of the mechanisms leading to selective ICM depletion at the blastocyst stage. Disproportionate deficiency in this lineage below a certain threshold level may then prevent the ICM core from providing sufficient prefetal stem cells during gastrulation and from sending regulatory signals to the trophectoderm, leading to compromised post-implantation development. The aim of this review article is to discuss the above observations and to show the value of the impact of hyperglycaemia on blastocyst metabolism and development as an exciting model for further studies.