viiPreface
Organogenesis, the generation of functional tissues and organs following an estab-
lished body plan during development, is a complex process that involves tissue self-
organization, cell–cell interactions, and the regulation of cell-signaling molecules
and cell movements. Various lineages of stem cells are produced and play central
roles in organ development. Stem cell research thus not only yields new fundamen-
tal insights into biology but also can contribute to the development of regenerative
medicine.
In the first generation of regenerative medicine, stem cell transplantation
approaches have been developed or are under development for diseases such as
hematopoietic malignancies, Parkinson’s disease, and myocardial infarction. The
second generation of regenerative medicine is tissue engineering using cell sheets
and cell aggregates of homogeneous cell populations such as skin, cartilage, and
bone. The next generation of regenerative therapy will be the development of fully
functioning bioengineered organs that can replace lost or damaged organs following
disease, injury, or aging. Efforts are now under way to develop bioengineering tech-
nologies to reconstruct fully functional organs in vitro through the precise arrange-
ment of several different cell types. Although attempts to make functional organs by
tissue engineering using scaffolds, cytokines, and various lineages of cells have
been made over the past several decades, clinical applications have remained
elusive.
In recent years, significant advances in techniques for organ regeneration, includ-
ing neuroectodermal, ectodermal, and endodermal organs, have been made using
three-dimensional stem cell culture in vitro by using various stem cell lineages and
pluripotent stem cells, such as embryonic stem cells and induced pluripotent stem
cells. Several groups have reported the generation of neuroectodermal and endoder-
mal organoids by harnessing the regulation of complex patterning signals during
embryogenesis and self-organization of pluripotent stem cells in three-dimensional
stem cell culture. Other groups have sought to generate functional organs that
develop by reciprocal epithelial and mesenchymal interactions using embryonic
organ inductive stem cells. Several groups have also reported the generation of
three-dimensional organoids/tissues by the reproduction of stem cells and their