ABSTRACT
Stem cells are now believed to exist in virtually all parts of the human body and to contribute to tissue and organ development during all stages of life.1-8 The speci—c and unique responses required from stem cells are controlled by a vast number of growth factors, surrounding cells, and interactions with extracellular matrices.9,10 This microenvironment, called the “stem cell niche,” is crucial to stem cell fate determination and speci—es their responses to the environmental signals.11-20 Furthermore, stem cells are often considered to be truly pluri-or multipotent and
10.1 Introduction .................................................................................................. 259 10.2 Stem Cells .....................................................................................................260
