Essential Cell Biology 5th edition

716 CHAPTER 20 Cell Communities: Tissues, Stem Cells, and Cancer
Figure 20–40 Mouse ES cells can be
induced to differentiate into specific cell
types in culture. ES cells are harvested
from the inner cell mass of an early mouse
embryo and can be maintained indefinitely
as pluripotent stem cells in culture. If they
are allowed to aggregate (not shown)
and are then exposed to the appropriate
extracellular signal molecules, in the correct
sequence and at the right time, these cells
can be induced to differentiate into specific
cell types of interest (Movie 20.6). (Based
on data from E. Fuchs and J.A. Segré, Cell
100:143–155, 2000.)
cells of inner cell mass
fat cell
neuron
cultured ES cells
macrophage
early embryo
(blastocyst)
heart muscle cell
glial cells
Figure 10−28). ES cells can also be induced, by the appropriate extracellular
signal molecules, to differentiate in culture into a large variety of cell
types (Figure 20–40).
Cells with properties similar to those of mouse ES cells can also be derived
from early human embryos, and these cells can be induced to differentiate
into a variety of cell types as illustrated in Figure 20–40. In principle,
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human ES cells provide a potentially inexhaustible supply of cells that
might be used for the replacement or repair of mature human tissues that
are damaged. For example, experiments in mice suggest that it should be
possible to use cells derived from human ES cells to replace the skeletal
muscle fibers that degenerate in victims of muscular dystrophy, the nerve
cells that die in patients with Parkinson’s disease, the insulin-secreting
cells that are destroyed by the immune system in type 1 diabetics, and
the cardiac muscle cells that die during a heart attack. Perhaps one day it
might even become possible to grow entire organs from human ES cells
by a recapitulation of embryonic development, as we discuss shortly.
There are, however, many hurdles to be cleared before such dreams can
become reality. One major problem concerns immune rejection: if the
transplanted cells are genetically different from the cells of the patient
into whom they are grafted, they are likely to be rejected and destroyed
by the immune system. Beyond the practical scientific difficulties, there
have been ethical concerns about the use of human embryos to produce
human ES cells. One way around both of these problems is to generate
human pluripotent cells in another way, as we now discuss.
Induced Pluripotent Stem Cells Provide a Convenient
Source of Human ES-like Cells
It is now possible to produce pluripotent stem cells without the use
of embryos. Differentiated cells can be taken from an adult mouse or
human tissue, grown in culture, and reprogrammed into an ES-like state
by artificially driving the expression of a set of three or four transcription