ABSTRACT
INTRODUCTION Stem cells have the capacity for self-renewal and the ability to differentiate to various cell lineages. Thus, they represent an important building block for regenerative medicine and tissue engineering. Current research focuses on the possible exploitation of stem cells in medicine and their potential to offer a range of effective treatments for various diseases. A variety of stem cells, ranging from embryonic, bone marrow, endogenous, and amniotic fluid have been investigated andmay prove useful as novel alternatives for organ regeneration both in vitro and in vivo. ESCs are pluripotent cells derived from the inner cell mass of the early mammalian embryo. Because of their plasticity and potentially unlimited capacity for self-renewal, ESCs have generated tremendous interest both as models for developmental biology and as possible tools for regenerative medicine. This excitement has been attenuated, however, by scientific, political, and ethical considerations. To exploit this potential, it is essential to be able to control ESC differentiation and to direct the development of these cells along specific pathways. Embryology has offered important insights into key pathways regulating ESC differentiation, resulting in advances in modeling gastrulation in vitro and in the efficient induction of endoderm, mesoderm, and ectoderm, and many of their downstream derivatives. This has led to the identification of new multipotential progenitors for the hematopoietic, neural, and cardiovascular lineages and to the development of protocols for the efficient generation of a broad spectrum of cell types including hematopoietic cells, cardiomyocytes, oligodendrocytes, dopamine neurons, and immature pancreatic b-cells. The next challenge will be to demonstrate the functional utility of these cells, both in vitro and in preclinical models of human disease.
