Biology 101: An explanation of stem cells and cloning

[CarolynS]

October 13, 2006

Biology 101: An explanation of stem cells and cloning

http://www.stlouisreview.com/article.php?id=11643

The following are commonly asked questions about stem-cell research and human cloning. Answers have been provided by Dr. Richard A. Chole of Washington University School of Medicine and Barbara Quigley, executive director of the St. Louis Center for Bioethics and Culture. Both also serve on the board of directors of Missourians Against Human Cloning.

Why all the fuss about stem cells?

The human body is made of millions of cells. When some cells are injured, missing or not working properly, individuals experience problems or diseases. Scientists have found that one way to treat some diseases is to substitute healthy cells for those that are unable to work properly. Stem cells have the ability to transform into other cells and can sometimes serve as these replacements.

What are stem cells?

Stem cells are cells that do not have specific functions but can develop into other cells that have specific roles in the body, that is, any type of body cell. Some stem cells are "totipotent" — they can develop into any type of cell. Other stem cells are "unipotent" or "multipotent" and can develop into only one type of cell or a limited number of other types of cells.

Are all stem cells the same?

No. There are many types of stem cells but they can be classified into two basic groups: "adult" stem cells, also known as "somatic" cells (cells taken from body tissues) and "embryonic" stem cells, which are taken from an embryo.

What is wrong with taking stem cells from an embryo?

In order for stem cells to be harvested from an embryo the embryo is destroyed. A human embryo is the earliest stage of human life.

What is an embryo?

After fertilization of the egg, a zygote is formed. The zygote is the earliest form of the embryo. Over time the zygote grows as it continues to develop by cell division. In about five days the embryo has about 200 cells and is called a blastocyst.

Where do the embryonic stem cells come from?

Embryonic stem cells (ES cells) come from the inner cell mass of the blastocyst. These are the cells that will develop into all of the different tissues of the body.

What is so special about embryonic stem cells?

ES cells can develop into any type of cell depending on the conditions in which they are cultivated: nerve cells, muscle cells, etc. Furthermore, when cultivated in the laboratory, they continue to divide and reproduce themselves indefinitely.

Why haven’t embryonic cells been used to treat chronic diseases in people?

The only reported use of human ES cells to treat human disease was an attempt to cure Parkinson’s disease. This study showed some promise but many of the patients developed abnormal movements that could not be controlled with medicines. Some patients actually became worse. These studies were stopped and no further human uses of ES cells have been reported. Although scientists believe that embryonic stem cells may someday be useful in medical treatments, knowledge of the behavior of ES cells is incomplete. When implanted in experimental animals, ES cells continue to replicate and often develop into tumors called teratomas.

Are there ethical concerns in the use of adult (or somatic) stem cells?

No. Somatic stem cells are obtained from body tissues such as bone marrow, umbilical cord blood, fat cells, etc. Adult (somatic) stem cells can be obtained without damaging the donor and they cannot develop into an embryo.

Can adult stem cells be used for treatment of medical diseases?

Yes. Although adult stem cells may not be as flexible as embryonic stem cells, adult stem cells have been used for years to treat and cure human diseases. Every week scientists discover new ways to use adult stem cells to treat chronic diseases. Examples are sickle cell anemia and leukemia. Studies in animals have shown that there are possible cures for diabetes, heart disease and neurological diseases with adult stem cells

What is cloning?

In cloning, an egg (ovum) from a woman is surgically removed from her body and taken to the laboratory where the nucleus is removed. A body cell (somatic cell) is removed from any part of the body, commonly skin cells, and its nucleus is taken to the laboratory where it is inserted into the "empty" egg. The cell that is formed is a cloned zygote which then develops spontaneously into a cloned blastocyst, or cloned embryo.

What is SCNT?

SCNT (Somatic Cell Nuclear Transfer) is the scientific term for cloning. The term SCNT is sometimes confusing because it sounds like "somatic stem cell," but actually refers to the transfer of the nucleus from the somatic cell to the ovum (egg). SCNT results in a cloned embryo.

Are there concerns about removing eggs from healthy women?

Yes. Even women’s groups that support ES research have concerns about SCNT. Judy Norsigian wrote in the Boston Globe on February 25, 2005: "There is a disturbing lack of attention to the risks to women’s health posed by the advent of embryo cloning ... Omitted from the polarized debate is any discussion of the thousands of women who will need to undergo egg extraction procedures for such embryo cloning. A primary concern is the substantial risks to women’s health posed by the extraction procedure and the inability to obtain true informed consent from egg donors given the current lack of adequate safety data." Since women are paid to donate their eggs, some people believe that this process would exploit poor young women.

Can a cloned embryo continue to develop?

We know that cloned embryos of mice, cats, sheep and cattle have been allowed to develop into adult animals. As far as we know, no human cloned embryo has ever been allowed to develop beyond a blastocyst, but one could assume that what has been successful in other mammals could also work in humans. Further development would require implantation into a uterus and this has never been attempted, as far as we know.

Are cloned embryos genetically identical to the donor of the somatic cell?

Actually, no. While the nucleus of the donor somatic cell contains most of the genes, there are some genes outside the nucleus (mitochondrial genes) which are carried along with the transplanted nucleus (blue dots below). The egg with its nucleus removed also carries some mitochondrial genes (green dots below). The resulting cloned zygote contains nuclear genes from the donor somatic cell and mitochondrial genes from both the donor somatic cell and the egg. This combination of mitochondrial DNA from two individuals does not occur in nature.

Is it appropriate to regulate scientific research in the United States?

Yes. Modern society has appropriately restricted research in many ways. Since the atrocities in Nazi Germany, society has adopted rules about research on humans (the Nuremberg Code). Scientists left to their own discretion have not always done the right thing. In Tuskegee, Ala., black men were infected with syphilis and left untreated to see what happened. In Willowbrook, N.Y., retarded children were infected with hepatitis to see how the disease spread. In Germany, Jews were tortured and killed in medical experiments to test the limits of human physiology. By "dehumanizing" these groups of people (black men, retarded children, Jews) scientists of the time saw no ethical problem in doing these experiments.

Moreover, the promise of future benefit from the research was used to help justify the experiments. If a scientist does not consider the human embryo to be human, destroying it poses no moral or ethical problems. It is the right and responsibility of society to limit or regulate scientific research that is morally or ethically unacceptable.

[GRAPHIC #1 found at the URL provided above.]

A quick summary: Stem cells offer the potential for significant medical treatment. The use of adult stem cells has led to many medical breakthroughs and poses no ethical problem. However the production and destruction of human embryos required for embryonic stem cell research is a significant ethical and moral problem. Human beings, even the tiniest developing human beings, should not be used in experiments which result in their death.

[GRAPHIC #2found at the URL provided above.]

[Chicory]

Great article! Thank you Carolyn.

[CarolynS]

I posted this as a piece of "in the news"...not as an opinion.

[pegleg]

This is a pretty good scaled down explanation. I am to present later this year to a women's group about stem cells, and this will be very helpful.

Peggy

[Howardh]

expressed from a Catholic point of view is well know. They come down hard on Embryonic Stem Cell Research in any form. The catholic view is not necessarily the view held by the wider community with a good 60 percent of Americans in favour of research using discarded embryos thrown out from the thousands of abortions that occur globally every day.

Some of the questions are loaded and reek of Frankenstein technology, when we know science today is not still stuck in the stone ages as religion would have us believe. Science today is accountable and transparent and cannot afford to be anything else but honest and open in everything they achieve. The recent exposure of the Korean scientist Hwang attests to that. Attention to detail, constant testing and measuring, will advance science into the stratosphere of success.

As with the Democrats, England, Israel, Korea, Singapore, and others, the need to carry on valued research in Embryonic Stem Cell Research is gathering momentum. Public opinion has swung clearly in favour of research using discarded embryos, just what form that takes remains to be seen. Keep valued research in the hands of science and not in the hands of religious or political commentators.

GO HARD SCIENCE

[olsen]

recent news of utility of embryonic stem cells in ALS knockout rats--if new nerons and their connections can be coaxed to grow in the spinal column--why not the substantia nigra. problem in studying PD is that there exists no great mouse/rat model for study, as in ALS...
http://tinyurl.com/yab9wy

Human stem cells delay start of Lou Gehrig's disease in rats
Researchers at Johns Hopkins have shown that transplanting human stem cells into spinal cords of rats bred to duplicate Lou Gehrig's disease delays the start of nerve cell damage typical of the disease and slightly prolongs life. The grafted stem cells develop into nerve cells that make substantial connections with existing nerves and do not themselves succumb to Lou Gehrig's, also known as amyotrophic lateral sclerosis (ALS). The study is published in this week's issue of Transplantation.

"We were extremely surprised to see that the grafted stem cells were not negatively affected by the degenerating cells around them, as many feared introducing healthy cells into a diseased environment would only kill them," says Vassilis Koliatsos, M.D., an associate professor of pathology and neuroscience at Hopkins.

Although all the rats eventually died of ALS, Koliatsos believes his experiments offer "proof of principle" for stem cell grafts and that a more complete transplant of cells - already being planned -- along the full length of the spine to affect upper body nerves and muscles as well might lead to longer survival in the same rats.

"We only injected cells in the lower spine, affecting only the nerves and muscles below the waist," he noted. "The nerves and muscles above the waist, especially those in the chest responsible for breathing, were not helped by these transplanted stem cells."

The research team used so-called SOD-1 rats, animals engineered to carry a mutated human gene for an inherited form of ALS. As in human ALS, the rats experience slow nerve cell death where all the muscles in the body eventually become paralyzed. The particular SOD-1 rats in the study developed an "especially aggressive" form of the disease.

Adult rats not yet showing symptoms were injected in the lower spine with human neural stem cells - cells that can in theory become any type found in the nervous system. As a comparison, the researchers injected rats with dead human stem cells, which would not affect disease progression. Both groups of rats were treated with drugs to prevent transplant rejection.

The rats were weighed and tested for strength twice a week for 15 weeks. Weight loss, according to Koliatsos, indicates disease onset. On average, rats injected with live stem cells started losing weight at 59 days and lived for 86 days after injection, whereas control rats injected with dead stem cells started losing weight at 52 days and lived for 75 days after injection.

The rats were coaxed to crawl uphill on an angled plank, and their overall strength was calculated by considering the highest angle they could cling to for five seconds without sliding backwards. While all the rats grew progressively weaker, those injected with live cells did so much more slowly than those injected with dead cells.

Close examination of the transplanted cells also revealed that more than 70 percent of them developed into nerve cells, and many of those grew new endings connecting to other cells in the rat's spinal cord.

"These stem cells differentiate massively into neurons," says Koliatsos, "a pleasant surprise given that the spinal cord has long been considered an environment unfavorable to this type of transformation."

Another important feature of the transplanted cells is their ability to make nerve-cell-specific proteins and growth factors. The researchers measured five-times more of one particular factor, known as GNDF (short for glial cell derived neurotrophic factor) in spinal cord fluid. The transformation of the transplanted cells also may allow them to deliver these growth factors to other cells in the spinal cord through physical connections.

Cautioning that clinical applications are still far from possible, Koliatsos hopes to take further advantage of his rodents with ALS to learn as much as possible about how human stem cells behave when transplanted.