One of the most intriguing and important aspects of ES cell lines is their ability to differentiate into multiple mature somatic cell types in cell culture, when the appropriate stimuli are applied.
The most common method for initiating differentiation in culture is the formation of 3-D spherical, termed embryoid bodies (EBs) due to their similarity to post-implantation embryonic tissue in vivo. These structures contain derivatives of all three embryonic germ layers.
Figure 1. (a) Murine embryoid bodies, derived spontaneously from differentiating embryonic stem cells, floating in culture. (b) Sections of murine embryoid bodies after 8 days of differentiation, demonstrating the formation of endoderm on the outside of the bodies.
The incorporation of differentiated cells into higher-order structures will be essential for implants to be functional, and the acquisition of an appropriate 3-D structure may also further direct the maturation and specialization of differentiated cell types.
In addition to the potential for transplantation,such constructs could also provide extremely useful in vitro models to recapitulate the physiological state sufficiently for the evaluation of new drugs and identification of new therapeutic targets in tissue culture.