Methods for inducing embryoid body formation: in vitro differentiation system of embryonic stem cells.

When cultured in suspension without antidifferentiation factors, embryonic stem (ES) cells spontaneously differentiate and form three-dimensional multicellular aggregates called embryoid bodies (EBs). EBs recapitulate many aspects of cell differentiation during early embryogenesis, and play an important role in the differentiation of ES cells into a variety of cell types in vitro. There are several methods for inducing the formation of EBs from ES cells. The three basic methods are liquid suspension culture in bacterial-grade dishes, culture in methylcellulose semisolid media, and culture in hanging drops. Recently, the methods using a round-bottomed 96-well plate and a conical tube are adopted for forming EBs from predetermined numbers of ES cells. For the production of large numbers of EBs, stirred-suspension culture using spinner flasks and bioreactors is performed. Each of these methods has its own peculiarity; thus, the features of formed EBs depending on the method used. Therefore, we should choose an appropriate method for EB formation according to the objective to be attained. In this review, we summarize the studies on in vitro differentiation of ES cells via EB formation and highlight the EB formation methods recently developed including the techniques, devices, and procedures involved.