22 DECEMBER 2005
you
think the news media don't cover science enough, now is the season to
rejoice. Stem cells have been in the headlines lately almost as much
as torture and Tom DeLay.
Alas, as with Tom and torture, the news is mostly bad. Major steps toward using stem cells to cure disease have turned out to be not so sure-footed as originally reported. Ethical transgressions and possibly even fraudulent findings have stained the stem cell field. Such loss of credibility can be lethal for research already stringently restricted by a government serving those who are religiously opposed to such research to begin with.
But before burying research on stem cells, it might be worth remembering why so many scientists have praised it. Stem cells derived from embryos are the ultimate utility players in the game of life, believed to be able to assume any position in the body's multiple tissues. An embryonic stem cell is like a child with aptitude for any profession; its training diverts it to one job or another as it matures. In principle, such stem cells could become fully functioning members of any body tissue's cellular repertoire.
Therefore, scientists have surmised, stem cells could help rebuild diseased organs or perform other important roles where a body's cells are defective or damaged. Because of their versatility, stem cells have been proclaimed to be potential cures for everything from arthritis to Alzheimer's.
So far, though, promise has exceeded production, and scientists are still in the early stages of figuring out how to make stem cells perform their potential magic. Allegations of fraud make stem cells' benefits seem even farther from fruition.
But in the end, fraud and politics don't matter nearly as much as biology. Fraudulent science leads nowhere and eventually dissolves from its own lack of substance. And stem cell success will ultimately depend not on what is supported by government, but what is allowed by nature.
Problem is, the most promising method of making stem cells involves harvesting cells from human embryos, acquired via in vitro fertilization methods or by cloning a cell from an existing animal, the way scientists cloned Dolly the sheep. (In this case, the process is called "therapeutic cloning," as its purpose is to make cells for therapy, not to reproduce animals.) And there's no guarantee that these methods, especially cloning, will be able to produce cells that are genetically correct for use in people.
Clones supposedly are genetically identical copies of the original. And Dolly's DNA was the same as the DNA from the cell of her "mother." But DNA is not the whole genetic story. Genes themselves are made of DNA, but how the genes work depend on chemical attachments to the DNA double helix and the chemical packaging that holds the DNA in place inside a cell's nucleus. These "epigenetic" factors help determine which genes are active -- producing proteins or other important chemicals -- and which genes are silent, doing nothing.
Thus the body's chemistry is controlled not by genes alone, but by genes as modified by these epigenetic changes. And epigenetic markings on DNA are altered throughout life by interactions with the environment.
Just as the DNA genome is a catalog of all the genes, the "epigenome" is the list of all the alterations in that pristine catalog. In the epigenomic version of the catalog, some of the pages are flagged for ready reading, other pages are stuck together and rendered unreadable. Over time, two identical catalogs (such as identical twins) can become very different books.
"Epigenetic marks can be described as marks of experience; they contribute to differentiating us from our younger selves," write researchers Peter Jones of the University of Southern California and Robert Martienssen of Cold Spring Harbor Laboratory in New York.
In fact, no genome is ever pristine, not even at birth. Some epigenetic modifications of the genome can be passed on from one generation to the next. Cloned embryos are likely to possess a whole slew of non-normal epigenetic modifications, and so stem cells derived from such embryos may be susceptible to serious problems, including a propensity toward cancer.
"One could make the argument that it will not be safe to implement therapies resulting from therapeutic cloning until these issues are addressed," Jones and Martienssen wrote in the Dec. 15 issue of Cancer Research.
Yet not all the news is bad. This month, researchers at the Salk Institute in California reported the successful introduction of human embryonic stem cells into mouse brains. Those experiments showed that stem cells really can turn into working nerve cells in live animals, not just lab dishes. The presence of working human nerve cells in mice offers a useful platform for testing drugs to treat neurological diseases. And the process provides a way to pretest stem cell lines to see if they retain their multiple-identity abilities.
So despite its drawbacks, stem cell research could prove valuable in a variety of ways. As for fraud, the best defense is more research, free from the government's stifling restrictions. Sound science always exposes fraud eventually, since nature refuses to cooperate with fraud's perpetrators. The world would be a better place if fraud could be so easily banished from government and politics as well.
E-mail: tsiegfried@nasw.org
