14.30-14.45 Claudia Gerri
‘A conserved mechanism initiates trophectoderm differentiation in human, bovine and mouse embryos prior to blastocyst formation’
Current understanding of cell specification in early mammalian preimplantation development has mainly relied on mouse studies, where the first lineage specification event occurs at the morula stage with the differentiation of placental progenitors, which constitute the trophectoderm (TE). At subsequent developmental stages, the remaining cells will form the inner cell mass (ICM), which is comprised of precursor cells of the embryo proper and yolk sac. Notably, recent gene expression analyses suggest that factors involved in lineage specification in the mouse may not be conserved in other mammals, including human and bovine. Here, we examined the evolutionary conservation of a morphokinetic and molecular cascade initiating TE segregation in mouse, bovine and human embryos using a comparative embryology approach. Importantly, we discovered that the expression pattern of key lineage specifiers involved in TE initiation is conserved among all three species. Specifically, outer cells acquire a distinct apico-basal cell polarity during compaction and show nuclear expression of the Hippo signaling pathway effector YAP1 and of the transcription factor GATA3 at morula stage. We also demonstrate that inhibition of aPKC, a key cell polarity factor, impairs TE initiation at the morula stage in mouse, bovine and human embryos. Altogether, our comparative embryology analysis refines the current model of early lineage specification in human preimplantation embryos and indicates a conserved mechanism of TE initiation.