Gastruloids

Gastruloids are embryo-like multicellular structures derived from pluripotent stem cells that model aspects of mammalian gastrulation in vitro. They are typically produced from mouse embryonic stem cells or human induced pluripotent stem cells and form three-dimensional aggregates. In culture, directed signaling cues—most commonly WNT pathway activation, along with NODAL and BMP signals—induce self-organizing patterning that resembles early embryonic development.

As they develop, gastruloids elongate and establish a posterior-like axis. They exhibit patterned germ layer formation, with mesoderm and endoderm precursors forming in specific domains and ectodermal tissues differentiating in more anterior regions. Reporter lines and lineage markers reveal a Brachyury (T)-expressing posterior domain and subsequent tissue differentiation reminiscent of the primitive streak stage. However, they do not form a structured placenta or yolk sac and lack certain embryonic structures present in vivo.

Limitations and scope should be noted. Gastruloids do not recapitulate the full embryo and lack maternal-fetal interactions. Variation between cell lines and culture conditions can affect reproducibility. They provide a reductionist model primarily for studying early patterning, cell fate decisions, and gene regulatory networks rather than complete development. In human models, research is governed by ethical guidelines and oversight to address concerns about embryo-like systems.

Applications of gastruloids include investigating gastrulation mechanisms, axis specification, and signaling cross-talk; studying congenital developmental disorders; screening compounds for effects on early development; and informing stem cell biology and regenerative medicine.

Gastruloids are related to the broader organoid field but focus on early gastrulation processes rather than organ maturation.