Germ layer induction in ESC--following the vertebrate roadmap.

Controlled differentiation of pluripotential cells takes place routinely and with great success in developing vertebrate embryos. It therefore makes sense to take note of how this is achieved and use this knowledge to control the differentiation of embryonic stem cells (ESCs). An added advantage is that the differentiated cells resulting from this process in embryos have proven functionality and longevity. This unit reviews what is known about the embryonic signals that drive differentiation in one of the most informative of the vertebrate animal models of development, the amphibian Xenopus laevis. It summarizes their identities and the extent to which their activities are dose-dependent. The unit details what is known about the transcription factor responses to these signals, describing the networks of interactions that they generate. It then discusses the target genes of these transcription factors, the effectors of the differentiated state. Finally, how these same developmental programs operate during germ layer formation in the context of ESC differentiation is summarized. Copyright 2007 by John Wiley & Sons, Inc.