| The isolation of human embryonic stem cells (hESC) has provided avenues to learn about the earliest events in embryonic development. Trophoblast differentiation has been studied from transformed trophoblast cell lines, placental tumor cells, and primary cultures of fresh placental tissue. The main limitation of these models is that the cells have already undergone differentiation into trophoblasts and therefore the earliest lineage decisions have already been made. Therefore, the use of hESC provides a valuable tool to study trophoblast lineage differentiation.;The formation of aggregates of hESC, termed embryoid bodies (EBs), is a useful platform to study cell-cell contact as well as cell-ECM interactions that influence hESC differentiation. The fetal mesenchyme and endothelial cells are the first non-trophoblastic cells that come into contact with the trophoblast cells of the placenta. Therefore, placental fibroblasts were added to the EB model to form an aggregate EB. The placental fibroblasts provide cues that induce elevated placental hormone secretion in the heterotypic aggregates, compared to EBs not incorporating the fibroblasts.;Evaluating non-cellular influences on differentiation, contact with the ECM has been shown to induce trophoblast outgrowth from EBs in 2 dimensional and even more so, in 3 dimensional cultures. The studies presented here demonstrate that, culturing EBs in a collagen matrix provides the appropriate cues to induce an extravillous phenotype in EB-derived trophoblasts. Further gene expression analysis of EB-derived trophoblast outgrowths confirmed this phenotype. Additionally, genes involved in the focal adhesion kinase pathway were highlighted as potential players associated with the extravillous trophoblast phenotype of EB-derived outgrowths. Finally, in vivo, extravillous trophoblasts migrate from the placental cell columns into the maternal decidua, and remodel the maternal spiral arterioles. EB-derived trophoblasts migrate in vitro and enhanced migration is evident in the presence of an endothelial cell monolayer. This migration is enhanced by IL-8, but IL-8 alone does not seem to be a critical component of this enhancement. The results from these experiments further define differentiation with the EB-derived trophoblast model, and provide a platform for further investigation of trophoblast differentiation and function derived from hESC serving as embryonic surrogates. |
