Assessment of Differentiation Aspects by the Morphological Classification of Embryoid Bodies Derived from Human Embryonic Stem Cells

In general, the formation of embryoid bodies (EBs) is a commonly known method for initial induction of human embryonic stem cells (hESCs) into their derivatives in vitro. Despite the ability of EBs to mimic developmental processing, the specification and classifications of EBs are not yet well known. Because EBs show various differentiation potentials depending on the size and morphology of the aggregated cells, specification is difficult to attain. Here, we sought to classify the differentiation potentials of EBs by morphologies to enable one to control the differentiation of specific lineages from hESCs with high efficiency. To induce the differentiation of EB formation, we established floating cultures of undifferentiated hESCs in Petri dishes with hESC medium lacking basic fibroblast growth factor. Cells first aggregated into balls; similar to 10 days after suspension culture, some different types of EB morphology were present, which we classified as cystic-, bright cavity-, and dark cavity-type EBs. Next, we analyzed the characteristics of each type of EB for its capacity to differentiate into the 3 germ layers via multiplex polymerase chain reaction (PCR), real-time PCR, and immunocytochemistry. Our results indicated that most cells within the cystic EBs were composed of endoderm lineage populations, and both of the cavity EB types were well organized with 3 germ-layer cells. However, the differentiation capacity of the bright cavity EBs was faster than that of the dark cavity EBs. Thus, the bright cavity EBs in this study, which showed equal differentiation tendencies compared with other types of EBs, may serve as the standard for in vitro engineering of EBs. These results indicate that the classification of EB morphologies allows the estimation of the differentiation status of the EBs and may allow the delineation of subsets of conditions necessary for EBs to differentiate into specific cell types.