Thursday, September 12, 2002
United Press International
By STEVE MITCHELL, Medical Correspondent
Scientists have discovered there is no single gene that gives a stem cell the ability to transform into different cell types in the body, but rather it is a combination of more than 200 little-known genes being turned on in concert.
They also found adult stem cells derived from bone marrow express more of the same genes as other adult cells than embryonic stem cells. This suggests these adult stem cells are not as versatile as embryonic stem cells and may not have the same potential for treating disease, principal investigator of the study Douglas Melton, a molecular biologist at Harvard University, told United Press International Wednesday.
This is an important difference because some people, groups and legislators have opposed embryonic stem cell research on moral and religious grounds as it requires the destruction of embryos to obtain the stem cells. Scientists have pursued embryonic stem cells because they have the potential to replace damaged tissues in diseases ranging from Parkinson's to diabetes.
Embryonic stem cell opponents have argued adult stem cells should be used because they have the same potential as embryonic stem cells but can be harvested from certain tissues in adults without the destruction of embryos.
The current study, however, rejects these ideas and calls into question all the studies that have claimed to have gotten adult stem cells to transform into other cell types to treat disease, Melton said.
Many scientists question those results, and this now gives researchers a way to check whether they started with adult stem cells or some other type of cell because they now know which genes to look for that would indicate adult stem cells, Melton said.
George Daley, a biologist who studied stem cells at the Whitehead Institute for Biomedical Research in Cambridge, Mass., told United Press International one possible conclusion from the data is that adult stem cells are not as versatile as embryonic stem cells but he noted he would like to see further research before he makes a definitive conclusion.
Melton's research also found adult stem cells obtained from the brain are more like embryonic stem cells than they are other brain cells. This suggests embryonic stem cells may default into brain cells and bodes well for using these cells to replace damaged tissue in brain disorders such as Alzheimer's and Parkinson's, Melton and his colleagues write in the Sept. 12 issue of Science Express, the online version of the journal Science.
The finding that more than 200 genes give stem cells their amazing ability to transform into different cell types is also notable because many of these genes previously were unrecognized.
Daley said: "This is an important first effort to understand stem cells at the genetic level. It points out how little we really know about them since almost half the genes that are expressed in stem cells are completely unknown and uncharacterized."
"From a scientific perspective I look at that and say that is very, very cool," Daley said. It means stem cells are "a unique class of cells that have very unusual properties" and studying these genes could have enormous implications, he added.
In the study, Melton's team isolated from mice embryonic stem cells and two types of adult stem cells -- one found in the bone marrow and another found in the brain. They monitored gene expression in the different cell types and found 216 genes were important to their "stemness" but the genes were different from one stem cell type to the others.
The findings could be used to understand which genes to turn on in adult stem cells to make them more like embryonic stem cells, Melton said.
It also gives scientists a better understanding of what to look for when searching for these stem cells, he said, noting adult stem cells are suspected of occurring in various places in the body, such as the pancreas and the heart, but they have not been found there yet.
"This gives a genetic definition and will make it easier to look for them and find them," he said.
(Reported by UPI medical correspondent Steve Mitchell in Washington.)
Copyright 2002 by United Press International