Stem Cells Find Their Own Way in Experiment
By Maggie Fox, Health and Science Correspondent
http://dailynews.yahoo.com/h/nm/20000601/sc/science_cells_1.html
WASHINGTON, June 1, 2000 (Reuters) - Swedish scientists said on Thursday
they found that adult stem cells, the seed cells from which all other
cells arise, can find their own way in the body.
They said their experiment shows that stem cells taken from both adults
and embryos are not only extraordinarily powerful, but can be controlled
and guided using the body's own systems.
But the experiment, described in a paper in the journal Science, will
not tip the balance either way in a U.S. battle over whether adult stem
cells are good enough substitutes for embryonic stem cells, whose use is
controversial.
"Embryonic stem cells remain the golden standard," Dr. Jonas Frisen, a
cell biologist at Sweden's Karolinska Institute, who led the study, said
in an interview conducted by e-mail.
Scientists hope that stem cells can be used eventually as tissue
transplants to help in diseases such as juvenile diabetes and
PARKINSON'S and perhaps someday as the basis of grow-your-own organ
transplants.
But research remains to be done and there are two sources of the cells
-- the adult body and embryos. Some groups in the United States oppose
the use of human embryonic stem cells because the embryo -- usually
taken from the leftovers of test-tube fertility efforts -- is destroyed
in the process of deriving them.
Scientists say both kinds of stem cell need to be tested because no one
knows if one will be more useful than the other.
"It is known that embryonic stem cells are totipotent, i.e. that they
can generate all cell types," Frisen said.
"This has not been described for any adult stem cells. What we now have
demonstrated is that they can generate very many cell types, but we do
not have evidence for them being able to give rise to all cell types."
In its experiment, Frisen's team took stem cells from the brains of
adult mice, genetically engineered them to carry a "marker" that could
be easily traced, and injected them into chick embryos.
In the chick embryos that survived and took up the stem cells, the
injected cells spread and grew to look identical to the surrounding,
native cells, they reported.
A similar experiment worked in mice, they said.
"The neural stem cells generated many different cell types, for example
in kidney, heart and liver," Frisen said.
They were struck by one particular finding -- beating hearts in the
mouse embryos contained normal-looking heart cells that were, in fact,
the product of the neural stem cells.
"These data demonstrate that the adult neural stem cells can integrate
into the developing chick and mouse embryo, give rise to embryonic cells
of various fates, and contribute to the generation of tissues and
organs," Frisen's team wrote.
But they did not find any of their marked cells in several places --
notably the bone marrow.
The next step is to find out how the stem cells that got into the heart
"knew" to become cardiac cells.
"The short answer is that we have no clue," Frisen said. "The neural
stem cells presumably respond to molecules secreted by their new
neighbors, but the nature of these signals is yet unknown to us."
Ihor Lemischka and colleagues at Princeton University and elsewhere
reported in the same issue of Science that they had set up a database of
the proteins made by hematopoietic stem cells -- the stem cells in the
bone marrow -- to screen for the factors that help determine what kind
of cells they give rise to and help stem cells in their apparent
immortality.
Copyright © 2000 Reuters Limited.
--
Judith Richards, London, Ontario, Canada
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