2026 Theses Doctoral

Engineering human and non-human primate embryogenesis in vitro

Zhang, Miaoci

Early human development unfolds through a series of tightly coordinated lineage decisions and morphogenetic events, yet many of the most informative stages remain inaccessible to direct study because peri- and post-implantation embryos are difficult to investigate experimentally and are subject to major technical and ethical constraints. As a result, the molecular and cellular mechanisms that govern early embryonic–extraembryonic interactions, chorion formation, and post-implantation morphogenesis remain incompletely understood. This dissertation addresses that gap by developing stem cell-based models of the nascent chorion and peri- to post- implantation embryo, with the goal of defining how embryonic and extraembryonic lineages emerge, interact, and organize during early development within a broader primate framework.

Chapter 1 reviews early human embryogenesis and its in vitro reconstruction, with particular emphasis on peri- and post-implantation development, extraembryonic lineage formation, and current stem cell-based embryo models. In Chapter 2, I establish a HIPPO-guided model of human trophectoderm and chorion formation. Using transient naïve resetting, chemically defined differentiation, 3D organoid culture, quantitative imaging, and bulk and single-cell transcriptomic analyses, I show that transient naïve resetting followed by HIPPO suppression is sufficient to initiate the human trophectoderm program and generate chorion organoids with key features of nascent chorionic villus organization.

In Chapter 3, I extend this framework to a comparative primate setting. Using human and chimpanzee pluripotent stem cells, directed differentiation, fluorescent lineage reporters, flow cytometry, quantitative imaging, and 3D assembloid culture, I show that transient naïve-reset cells can generate hypoblast- and extraembryonic mesoderm-like populations and can be assembled into multicompartment primate assembloid models that recapitulate key domains of the post- implantation human and chimpanzee embryo.

These studies demonstrate that the framework can be implemented in both human and chimpanzee systems, enabling comparative analysis of conserved and species-specific features of early primate embryogenesis. Chapter 4 synthesizes these findings and outlines future directions for extending culture duration, improving molecular benchmarking, and using these systems to study embryonic–extraembryonic interactions and placental/embryo development.

Together, this work provides experimentally accessible platforms for engineering early primate embryogenesis in vitro. More broadly, it lays a foundation for mechanistic studies of chorion development, post‑implantation morphogenesis, placentation, and early pregnancy loss, and advances stem cell–based embryo models as a versatile framework for probing the earliest stages of human and primate development.