An in vitro model of the interaction between the extra-embryonic lineages of the peri-implantation human embryo

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Theme: Bioscience for HealthThe signalling pathways that govern peri-implantation morphogenesis in the primate embryo are not fully understood. In the mouse embryo, a signalling centre known as the Anterior Visceral endoderm (AVE) secretes a number of Nodal and Wnt antagonists (e.g Lefty, Dkk1, Cer1), leading to the formation of a gradient of Nodal and Wnt activity across the AP axis of the embryo. Interestingly, AVE-like cells have been identified in the cynomolgus monkey hypoblast. These AVE-like cells secrete WNT and BMP antagonists, whereas cytotrophoblast and amniotic cells secrete WNT3A and BMP4, respectively. This suggests that the two extraembryonic lineages of the primate embryo may act to create a gradient of WNT and BMP gradient across the epiblast, which may in turn orchestrate amnion formation and also even gastrulation. Given the technical and ethical hurdles associated with the culture of human embryos post-implantation, this project seeks to model the interaction between the human extraembryonic and the embryonic lineages in vitro using stem cell lines representative of each. Via Activin A, WNT and LIF treatment of human pluripotent stem cells (hPSCs), we sought to derive a human hypoblast-like stem cell line from hPSCs representative of a pre-implantation pluripotent state: a "naïve" pluripotent state. This is because the hypoblast is specified from the pre-implantation ICM. For this, both the "Rset" cell line and the human extended potential pluripotent stem cell (hEPSC) line were used. We also sought to determine whether a hypoblast-like cell could be derive from the conventional human embryonic stem cell (hESC), which have a "primed" pluripotent state more similar to the post-implantation epiblast, and thus ascertain the influence that different pluripotent states has on amenability of a hPSC towards hypoblast-specification. We also seek to model the interaction between these ACL-treated hPSCs and hESCs in an attempt to model epiblast-hypoblast crosstalk, finding that ACL-treated hESCs act to prevent hESC differentiation via both WNT and BMP signalling inhibition.