Using specific techniques to determine the presence of paricular cell surface
markers that are typically produced by undifferentiated cells.
Examining the chromosomes under a microscope. This is a method to assess
whether the chromosomes are damaged or if the number of chromosomes has
changed. It does not detect genetic mutations in the cells.
Determining whether the cells can be re-grown, or subcultured, after freezing,
thawing, and re-plating.
Testing whether the human embryonic stem cells are pluripotent by l) allowing the
cells to differentiate spontaneously in cell culture.' 2) manipulating the cells so they
will differentiate to form cells characteristic of the three germ layers; or 3) injecting
the cells into a mouse with a suppressed immune system to test for the formation of
a benign tumor called a teratoma. Since the mouse's immune system is suppressed,
the injected human stem cells are not rejected by the mouse immune system and
scientists can observe growth and differentiation of the human stem cells.
Teratomas t5T)ically contain a mixture of many differentiated or partly
differentiated cell types—an indication that the embryonic stem cells are capable of
differentiating into multiple cell types. As long as the embryonic stem cells in
culture are grown under appropriate conditions, they can remain undifferentiated
(unspecialized). But if cells are allowed to clump together to form embryoid bodies,
they begin to differentiate spontaneously. They can form muscle cells, nerve cells,
and many other cell tjTpes. Although spontaneous differentiation is a good
indication that a culture of embryonic stem cells is healthy, it is not an efficient way
to produce cultures of specific cell types.
