embryoid

Embryoid is a term used in developmental biology to describe embryo-like structures that can arise during the differentiation of pluripotent stem cells in culture or, in some contexts, during early embryogenesis. In modern stem cell research, embryoid bodies are the most common in vitro counterpart, serving as a practical model of early development.

Embryoid bodies are three-dimensional aggregates formed when embryonic stem cells or induced pluripotent stem cells are cultured under nonadherent or differentiating conditions. These aggregates spontaneously or with guidance differentiate into cell types representing derivatives of all three germ layers: ectoderm, mesoderm, and endoderm. Because of this, embryoid bodies are used to study pluripotency, lineage specification, and early developmental events, as well as to screen for teratogenic effects and to model certain aspects of disease.

Formation and characteristics of embryoid bodies typically involve placing pluripotent cells in suspension or in conditions that reduce self-renewal signals, enabling multilineage differentiation. They lack a defined anterior-posterior axis and often display cellular heterogeneity. Molecular and morphological markers across germ layers are used to assess their differentiation potential, though outcomes can be variable and are influenced by culture conditions and cell line.

Applications of embryoids and embryoid bodies include basic developmental biology research, regenerative medicine planning, toxicology screening, and disease modeling. Important limitations include their status as in vitro models that do not form complete, implantable embryos or extraembryonic tissues, as well as ethical and regulatory considerations surrounding pluripotent stem cell research.