Epiblast stem cells contribute new insight into pluripotency and gastrulation.

Gastrulation is the defining feature of metazoan development where it serves to apportion seemingly equivalent, pluripotent cells to specific fates. The three embryonic germ layers generated during gastrulation from the pluripotent epiblast including ectoderm, mesoderm, and definitive endoderm, contain the progenitors required to build all of the tissues of the developing organism. As a result, there is great interest in understanding the events that coordinate gastrulation. Because developing embryos in placental mammals are relatively inaccessible, stem cells are widely used for experimental and biochemical interrogation of these processes. Epiblast stem cells (EpiSCs) are grown from the post-implantation epiblast, which is the most proximal pluripotent tissue to the early somatic and germ cell precursors. Because EpiSCs can be propagated indefinitely in vitro as a stable state that recapitulates the properties of the post-implantation epiblast, they are uniquely positioned to provide novel insight into the developmental window where somatic and germ cell lineages are first established. Here we discuss the nature of EpiSCs and their significance in understanding gastrulation and cell specification in relationship to other pluripotent cell culture models.