The animal cap-the presumptive ectoderm of the blastula embryo-can differentiate into a variety of tissues belonging to the three germ layers following exposure to specific inducers. The "animal cap assay" was devised based on the pluripotency of presumptive ectodermal cells and enabled many important discoveries in the field of embryonic induction and cell differentiation. Using this system, investigators can test multiple factors in solution simultaneously to determine their inducing activities qualitatively, quantitatively, and synergistically. Furthermore, after dissociation and induction, reaggregated animal cap cells can be induced to form higher-order organs. This protocol details preoperative preparations, followed by the basic animal cap assay. Advanced protocols for the induction of kidney, pancreas, and heart are also described.
