Scientists identify embryonic stem cells by appearance alone
CAMBRIDGE, Mass. (August 27, 2007) Some scientific results are hard
to spot, especially in genetic research. Often scientists are unable
to physically see if the gene they inserted into a cell has produced
the desired trait. To overcome this problem researchers use various
genetic markers that contain pieces of foreign DNA that cause cells
to, for example, glow when exposed to ultraviolet light.
But scientists in the lab of Whitehead Member Rudolf Jaenisch didn't
have to resort to these genetic markers in their latest experiment
because the results were easy to see. Building on their widely
publicized June Nature paper, which demonstrated that it's possible
to convert specialized mouse skin cells into unspecialized stem
cells, Whitehead postdoctoral researchers Alexander Meissner and
Marius Wernig have now identified successfully reprogrammed cells by
looks alone.
Their findings, which appear online in the journal Nature
Biotechnology on Aug. 27, bring human stem cell therapies a step
closer to reality. Before reprogramming can be applied to our own
species to generate custom embryonic stem cells, scientists must be
able to accomplish it without altering the DNA of the cells
involved. "This eliminates one of the major hurdles to reprogramming
human cells," says Jaenisch, who is also an MIT professor of
biology. "If we overcome the other obstacles, this approach could one
day provide custom human embryonic stem cells for use in therapy."
"This eliminates one of the major hurdles to reprogramming human
cells," says Jaenisch, who is also an MIT professor of biology. "If
we overcome the other obstacles, this approach could one day provide
custom human embryonic stem cells for use in therapy."
Last spring, Wernig and Meissner relied on genetic markers to
identify successfully reprogrammed cells. This required them to work
with fibroblasts from a genetically modified mouse. The mouse was
grown from embryonic stem cells that contained foreign DNA coding for
antibiotic resistance. The scientists had strategically inserted
these foreign DNA "markers" at particular points along the genome,
next to genes expressed only in embryonic stem cells. All of the
cells (including fibroblasts) in the resulting mouse contained the
markers.
In the original experiment, the researchers took fibroblasts from the
tail of this mouse and infected them with a special virus containing
four genes (Oct4, Sox2, c-myc, and Klf4) capable of converting the
cells to an embryonic state. Genes typically active in embryonic stem
cells roared to life, triggering the adjacent foreign DNA to provide
antibiotic resistance. Thus only fully reprogrammed cells survived
exposure to an antibiotic, which allowed the scientists to isolate
them.
"When we conducted the original experiment, we noticed that many of
the infected cells had already started to change shape before the
markers were activated," says Wernig.
So they set up a new experiment to test if visual identification
alone would work. Indeed, they were able to separate the reprogrammed
cells from ordinary fibroblasts under a microscope, based on several
physical differences. Fibroblasts are big and flat. Embryonic stem
cells are small, round and form tight colonies.
"We've shown that there's no need to use markers to isolate
successfully reprogrammed cells," says Meissner. "This significantly
simplifies this approach in mice, as we can now work with ordinary
fibroblasts.
But another hurdle remains before the technique can be applied to
human cells.
The scientists are now working to eliminate the virus from the
reprogramming process. Jaenisch believes they will eventually succeed
and points out that the technique could eventually yield a bountiful
supply of custom human embryonic stem cells for use in therapy.
Meissner and Wernig successfully reprogrammed about 0.5 percent of
the fibroblasts. Given that there are millions of cells in a typical
skin biopsy (researchers used skin from either the end of the tail or
from the ear of the mouse), that translates into thousands of stem
cells, each one capable of developing into any cell type of the body
Written by Eric Bland.
****
Rudolf Jaenisch's primary affiliation is with Whitehead Institute of
Biomedical Research, where his laboratory is located and all his
research is conducted. He also is a professor of biology at
Massachusetts Institute of Technology.
****
Full Citation:
Nature Biotechnology, online edition, August 27, 2007
"Direct Reprogramming of Genetically Unmodified Fibroblasts into
Pluripotent Stem Cells"
Authors: Alexander Meissner(1*)
(1,2)
*These authors contributed equally to this work.
(1) Whitehead Institute for Biomedical Research, Cambridge,
Massachusetts
(2) Department of Biology, Massachusetts Institute of Technology,
Cambridge, Massachusetts
Whitehead Institute for Biomedical Research is a nonprofit,
independent research and educational institution. Wholly independent
in its governance, finances and research programs, Whitehead shares a
close affiliation with Massachusetts Institute of Technology through
its faculty, who hold joint MIT appointments.
http://www.wi.
«¤»¥«¤»§«¤»¥«¤»§«¤»¥«¤»«¤»¥«¤»§«¤»¥«¤»§«¤»¥«
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
StemCells subscribers may also be interested in these sites:
Children's Neurobiological Solutions
http://www.CNSfoundation.org/
Cord Blood Registry
http://www.CordBlood.com/at.cgi?a=150123
The CNS Healing Group
http://groups.yahoo.com/group/CNS_Healing
____________________________________________
«¤»¥«¤»§«¤»¥«¤»§«¤»¥«¤»«¤»¥«¤»§«¤»¥«¤»§«¤»¥«
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch format to Traditional
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe
__,_._,___
