Characterization of gastrulation-stage progenitor cells and their inhibitory crosstalk in human embryoid bodies

Human embryoid bodies (HEBs) are cell aggregates that are produced during the course of embryonic stem cell differentiation in suspension. Mature HEBs have been shown to contain derivatives of the three embryonic germ layers. In this study, using a combination of laser capture microscopy followed by DNA microarray analysis and cell sorting, we demonstrate that early HEBs are composed of three major cell populations. These cell populations can be defined by the expression of specific cell markers, namely: (i) OCT4⁺, REX1^-; (ii) NCAD⁺, OCT4^-; and (iii) EPOR ⁺, OCT4^-. By analyzing gene expression in embryonic tissues, these cell populations could respectively be assigned to the embryonic ectoderm, mesendoderm, and extraembryonic endoderm lineages. We show that the extraembryonic endoderm, which selectively expresses platelet-derived growth factor B (PDGF-B), negatively affects the mesendoderm lineage, which selectively expresses the receptor PDGFRA. Our analysis suggests that early HEBs are spatially patterned and that cell differentiation is governed by interactions between the different cell types.