Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

CELL REPROGRAMMING AND PLURIPOTENT STEM CELLS
1257
CHROMATIN
REMODELING
HISTONE
MODIFICATION
HISTONE
VARIANTS
DNA
MODIFICATION
RNA
EXPRESSION
chromatin
remodelers
histone acetyl
transferases
histone variant
H3.3
DNA
demethylases
specific
IncRNAs
histone
deacetylases
histone variant
macroH2A
specific
miRNAs
specific histone
methyl transferases
histone
variant H2AZ
specific histone
demethylases
Figure 22–44 Factors that have been
observed to enhance reprogramming
efficiency. Emphasized here are those
factors that can alter chromatin states,
with those in the top three rows having
the most direct effects. An up arrow
indicates that reprogramming is increased
when the activity of the indicated factor
is increased; a down arrow indicates that
reprogramming is increased when the
activity of the indicated factor is decreased.
Thus, for example, increased activity of
histone acetyl transferases and increased
activity of histone deacetylases have
opposite effects, as expected from their
biochemical activities (see p. 196).
differentiation. After their long sojourn in culture, the ES cells or iPS cells and
their progeny can still read the signs at each branch in the highway and respond
as normal embryonic cells would. If ES or iPS cells are implanted directly into an
embryo at a later stage or into an adult tissue, however, they fail to receive the
MBoC6 n22.141/22.44
appropriate sequence of cues; their differentiation then is not properly controlled,
and they will often give rise to a tumor of the type known as a teratoma, containing
a mixture of cell types inappropriate to the site in the body.
In culture, by exposing the ES or iPS cell to an appropriate sequence of signal
proteins and growth factors, delivered with the right timing, it is possible to guide
the cell along a pathway that approximates a normal developmental pathway, so
as to convert it into one of the standard specialized adult cell types (Figure 22–45
and Movie 22.5). Success requires trial and error, but has now been achieved for
many different final specialized states, including neuronal, muscular, and intestinal
cell types. In a few cases, it has even been possible, by careful manipulation of
the culture conditions, to get ES or iPS cells to interact with one another so as to
construct an entire organ, albeit on a small scale (Figure 22–46).
Figure 22–45 Production of differentiated
cells from ES or iPS cells in culture.
These cells can be cultured indefinitely
as pluripotent cells when attached as a
monolayer to a dish. Alternatively they
can be detached and allowed to form
aggregates called embryoid bodies, which
causes the cells to begin to specialize.
Cells from embryoid bodies, cultured in
media with different factors added, can
then be driven to differentiate in various
ways. (Based on E. Fuchs and J.A. Segre,
Cell 100:143–155, 2000. With permission
from Elsevier.)
retinoic
acid
insulin, thyroid hormone
adipocyte
retinoic acid
neuron
macrophage colonystimulating
factor,
interleukin-3,
interleukin-1
cultured ES or
iPS cells
embryoid body
(about 1,000 cells)
dibutyryl cAMP,
retinoic acid
macrophage
fibroblast
growth
factor
fibroblast
growth factor 2,
epidermal
growth factor
fibroblast
growth factor 2,
platelet-derived
growth factor
smooth muscle cell
astrocytes
and oligodendrocytes