Shortcut to making stem cells
2008-10-13 22:21
Washington - Researchers trying to find
ways to transform ordinary skin cells into powerful stem cells
said on Sunday they found a shortcut by "sprinkling" a chemical
onto the cells.
Adding the chemical allowed the team at the Harvard Stem
Cell Institute in Massachusetts to use just two genes to
transform ordinary human skin cells into more powerful induced
pluripotent stem cells or iPS cells.
"This study demonstrates there's a possibility that instead
of using genes and viruses to reprogramme cells, one can use
chemicals," said Dr Doug Melton, who directed the study
published in the journal Nature Biotechnology.
Melton said Danwei Huangfu, a postdoctoral researcher in
his lab, developed the new method.
"The exciting thing about Danwei's work is you can see for
the first time that you could sprinkle chemicals on cells and
make stem cells," Melton, a Howard Hughes Medical Institute
Investigator, said in a statement.
Stem cells are the body's master cells, giving rise to all
the tissues, organs and blood. Embryonic stem cells are
considered the most powerful kinds of stem cells, as they have
the potential to give rise to any type of tissue.
Doctors hope to someday use them to transform medicine.
Melton, for instance, wants to find a way to regenerate the
pancreatic cells destroyed in type 1 diabetes and perhaps cure
that disease.
Inserting genes
But pluripotent stem cells such as the embryonic cells are
difficult to make, requiring the use of an embryo or cloning
technology. Many people also object to their use, and several
countries, including the United States, limit funding for such
experiments.
In the past year, several teams of scientists have reported
finding a handful of genes that can transform ordinary skin
cells into iPS cells, which look and act like embryonic stem
cells.
To get these genes into the cells, they have had to use
retroviruses, which integrate their own genetic material into
the cells they infect. This can be dangerous and can cause
tumors and perhaps other effects.
Last month US researchers did the same thing using a
harmless virus called an adenovirus, but the method was not
efficient.
And last week, Shinya Yamanaka of Kyoto University
in Japan, who discovered iPS cells in mice, used a loop of
genetic material called a plasmid to reformat the cells.
Huangfu tried treating the cells first with valproic acid.
After she did this, it only took two of the four usual genes to
reprogram the cells into iPS cells, she reported.
This is good because the other two genes usually needed can
promote cancer.
Reprogramming
The Melton team used retroviruses to carry the two genes in
but suggest they might not be necessary.
"These results support the possibility of reprogramming
through purely chemical means, which would make therapeutic use
of reprogrammed cells safer and more practical," they wrote in
their report.
Huangfu said the valproic acid unravelled the chromatin -
the physical structure of the chromosomes - making it possible
to get in and alter the DNA more easily.
"We may need two types of chemicals, one to loosen the
chromatin structure, and one to reprogramme. We are looking for
that reprogramming chemical, and it should be possible to find
it eventually," she said.