The emergence of human gastrulation upon in vitro attachment

Abstract

While studied extensively in model systems, human gastrulation remains obscure. The scarcity of fetal biological material as well as ethical considerations limit our understanding of this process. Invitro attachment of natural blastocysts shed light on aspects of the second week of human development in the absence of the morphological manifestation of gastrulation. Stem cell-derived blastocyst models, blastoids, provide the opportunity to reconstitute pre- to post-implantation development invitro. Here we show that upon invitro attachment, human blastoids self-organize a BRA+ population and undergo gastrulation. Single-cell RNA sequencing of these models replicates the transcriptomic signature of the human gastrula. Analysis of developmental timing reveals that in both blastoid models and natural human embryos, the onset of gastrulation as defined by molecular markers, can be traced to timescales equivalent to 12days post fertilization. In all, natural human embryos and blastoid models self-organize primitive streak and mesoderm derivatives upon invitro attachment.