Regulation of Apoptosis and Differentiation by p53 in Human ...

CHAPTER 1: Introduction
1.1- HUMAN EMBRYONIC STEM CELLS
The excitement and controversy surrounding the potential role of human embryonic
stem cells in transplantation therapy have often overshadowed their potentially
more important use as a basic research tool for understanding the
development and function of human tissue (Xu et al, 2002).
Human embryonic stem cell lines (hESC) are established from the inner cell mass (ICM) of the
blastocyst and differentiate into all cell lineages of the body (Figure 1.1). They were first derived
in 1998 by James Thomson’s group in the University of Wisconsin-Madison, USA (Thomson et
al., 1998) and have enormous potential as a source of cells for cell replacement therapies and as
a model for early human development (Hoffman and Carpenter, 2005). In fact, hESC represent a
useful experimental system that provides access to stages of the human life cycle that were
previously inaccessible to experimentation (Pera and Trounson, 2004). Conversely, better
understanding of stem cell basic biology will help to improve maintenance and differentiation
protocols for manipulating hESC, thus enabling the dissection of some developmental diseases
and advancement of more effective treatments. Moreover, because hESC and their derivatives
are diploid, they are more attractive than the transformed cell lines for drug screening and
disease modeling.
Two important features of embryonic stem cells (ESC) are their self-renewal capacity (they can
be maintained and expanded in culture) and pluripotency (they can differentiate to give rise to
mesoderm, endoderm and ectoderm as well as germ cells). Unlike human embryonic carcinoma
cell lines (hECC, the transformed counterpart of hESC), hESC can conserve a normal karyotype
if cultured under appropriate conditions.
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