Related article in January's issue of Discover magazine page 58:
(appologies if this has already been posted)
THE YEAR IN SCIENCE 1998
Medicine
Forever Young
Last year it was cloning. This year's blockbuster in
molecular sleight of hand was announced in November,
and it opens the door to some of the most far-out
scenarios of biology. Two labs--working on privately
funded research--reported that they had isolated human
embryonic stem cells, the primordial cells that give rise to
the many different tissues in our bodies. The most
far-reaching implication of the breakthrough is the
possibility of growing customized tissue to replace cells,
and eventually organs, lost to disease.
In the early stages of embryonic development, cells are undifferentiated, and over the course of development they are irreversibly cast into the roles of cells with specialized functions. What the two groups succeeded in doing was capturing undifferentiated human embryonic cells (such stem cells have already been isolated from several other animal species) and cultivating them in a
state of perpetual infancy. The researchers also found that
under various conditions the cells would grow into more
mature tissues resembling gut, neuron, and cartilage.
One group, led by James Thomson of the University of
Wisconsin, worked with embryos donated for research by
couples undergoing in vitro fertilization. After fertilization,
the egg cell divides, and over the course of several
divisions, it forms a blastocyst, a hollow sphere of cells
with a few cells clustered inside. The Wisconsin team
removed cells from within the blastocyst and coaxed them
to grow by using a technique they had developed while
working on monkey blastocysts. The other group--led by
John Gearhart at Johns Hopkins--isolated cells from
fetuses farther down the developmental pathway. From
five- to nine-week-old fetuses obtained from therapeutic
abortions, they isolated cells resembling germ cells, which
ultimately develop into eggs or sperm. The cells recovered
by both groups met the criteria for embryonic stem
cells--they could divide endlessly in an undifferentiated
state, and they could be prompted to mature into many
different kinds of cells.
But capturing and cultivating human embryonic stem cells is
just the first step. The real medical benefits will have to
wait until researchers can understand and accurately
manipulate the signals that produce specialized cells that
could replace diseased ones--say, neurons lost to
Parkinson's disease or defective islet cells in diabetics--and
then engineer versions that could be accepted by anyone.
By providing an endless supply of primitive cells,
embryonic stem cell technology could eliminate the need
for fetal tissue in experimental transplants. On the other
hand, it raises questions about the status of embryonic
tissue and whether it is right to appropriate such cells for
medical experimentation or treatment. Currently, the
government has banned federal funding for research on
human embryos or fetal tissue. The success of these new
techniques--and the medical benefits they might ultimately
yield--has reignited that debate. --Sarah Richardson
discover.com |
