All-trans retinoic acid and basic fibroblast growth factor synergistically direct pluripotent human embryonic stem cells to extraembryonic lineages

Human embryonic stem cells (hESCs) can be used to model the cellular and molecular mechanisms that underlie embryonic development. Understanding the cellular mechanisms and pathways involved in extraembryonic (ExE) differentiation is of great interest because of the important role of this process in maternal health and fertility. Fibroblast growth factor 2 (FGF-2) is widely used to maintain the self-renewal of hESCs and induced pluripotent stem cells, while all trans retinoic acid (RA) is used to facilitate the directed differentiation of hESCs. Here, we monitored the RA induced differentiation of hESCs to the ExE lineage with and without FGF-2 over a 7-day period via global transcriptional profiling. The stemness markers POU5F1, NANOG and TDGF1 were markedly downregulated, whereas an upregulation of the ExE markers KRT7, CGA, DDAH2 and IGFBP3 was observed. Many of the differentially expressed genes were involved in WNT and TGF-β signaling. RA inactivated WNT signaling even in the presence of exogenous FGF-2, which that promotes the maintenance of the pluripotent state. We also show that BMP4 was upregulated and that RA was able to modulate the TGF-β signaling pathway and direct hESCs toward the ExE lineage. In addition, an epigenetic study revealed hypermethylation of the DDAH2, TDGF1 and GATA3 gene promoters, suggesting a role for epigenetic regulation during ExE differentiation. These data reveals that the effect of RA prevails in the presence of exogenous FGF-2 thus resulting in the direction of hESCs toward the ExE lineage.