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The Science Of Stem Cells

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They’re on the cutting edge of science and the sharp tongues of politicians.

They are the builders of life. And they are one of the most divisive topics of discussion in the United States: stem cells.

They’re on the cutting edge of science and the sharp tongues of politicians.

They are the builders of life. And they are one of the most divisive topics of discussion in the United States: stem cells.

Debates often center on a certain type of stem cell, the embryonic stem cell.

An embryonic stem cell is a non-specialized cell that can divide indefinitely into identical copies of itself.

“Basically it’s an immortal cell,” said Dr. John Kessler, director of the Northwestern University Stem Cell Institute and the Feinberg Clinical Neuroscience Institute.

“The only other cell in the body that has the same trait is a cancer cell,” said Kessler, who spoke at the symposium. “More recently it’s been recognized that many, if not most, cancers seem to arise in stem cells that are present in the body.”

So how should teachers approach the topic of stem cells in the classroom?

Scientists and educators tackled that question at the Chicagoland Stem Cell Symposium hosted by Northwestern University in February.

The symposium kicked off the first of four that the Biotechnology Institute of Arlington, Va., plans to hold in academic institutions across the country this year.

The Biotechnology Center at Northwestern University's Kellogg School of Management partnered with the Biotechnology Institute, the national biotechnology education organization, to organize the Chicagoland Stem Cell Education Symposium. The goal of the symposium was to give teachers the tools to offer the next generation of students abroad-based education so they can make informed decisions about the use of new technologies. Most biology textbooks provide little or no coverage of stem cell biology, making it difficult for science teachers to prepare students for understanding the fundamental science and ethical landscape critical for developing future medical innovations in this complex area.

Kessler and other speakers covered the ethics of stem cell research, its medical potential and its alternatives in order to give science teachers the background to approach the topic in their classes.

Embryonic stem cells

Researchers collect embryonic stem cells during the blastocyst stage, when a fertilized egg has developed after a few days into a mass of cells that will become the placenta and the embryo.

Embryonic stem cells eventually differentiate into all the different types of cells that make up the body. That’s how a cluster of indistinct cells can develop into a baby.

But even when the body is fully formed, some stem cells are still at work. They continue to grow hair, to repair skin, to form new blood cells and even to form new brain cells.

Researchers are now trying to use different types of stem cells to aid patients with anything from multiple sclerosis to heart disease.

Types of stem cells

There are three different types of stem cells: totipotent cells, pluripotent cells and multipotent cells.

More powerful than the embryonic stem cell is the fertilized egg. It is a totipotent cell that can develop into an entire embryo.

Embryonic stem cells are pluripotent cells, which can give rise to all the cell types in the body but cannot create the substance in which embryonic cells must live.

Multipotent cells have the potential to differentiate into different types of cells, but they are much more limited.

For example, multipotent cells regenerate our skin cells, Kessler said.

“If you think about my skin, I would’ve eroded it away a long time ago if I didn’t have stem cells constantly replacing it,” he said.

Multipotent stem cells are often called “adult” stem cells, which, according to Dr. Kessler, “is a bit of a misnomer” because embryos have them as well.

One of the best known examples of this type of cell is found in the bone marrow. This cell creates the family of blood cells: red blood cells, white blood cells and platelets.

One can also find adult stem cells in the nervous system, heart and many, if not all, organs of the body.

Embryonic stem cell lines

Anatomy professor James Thomson created the first embryonic stem cell line in 1998 at the University of Wisconsin in Madison.

To develop an embryonic stem cell line, a researcher must use the inner cell mass of a blastocyst. The researcher separates these cells, puts them in a culture dish and tries to keep them growing without differentiating into specific types of cells.

“It sounds easy,” Kessler said. “It’s not.”

Researchers obtain the blastocysts used in creating embryonic stem cell lines mainly from fertility clinics that conduct in vitro fertilization for women who have trouble becoming pregnant.

The in vitro fertilization procedure involves removing the eggs from a woman’s ovaries and fertilizing them outside of the womb.

The fertilized eggs are then allowed to develop in a Petri dish, usually for three to five days. Doctors check the development of the embryos and transfer one or more to the uterus.

Not every embryo is used in the procedure. Doctors often choose only the best-developed embryos and transfer as few as possible to avoid the risk of a more dangerous multiple-birth pregnancy.

Embryos that aren’t used are either discarded or stored. The stored embryos are cryopreserved, or frozen.

In 2002, about 400,000 embryos were frozen in storage in the United States, according to a study by the Society for Artificial Reproductive Technology.

Of the embryos in the 2002 study, about 11,000 – 3 percent – were set aside for research.

But unused embryos are often of poorer quality and some lose viability in the freeze-thaw process. Researchers estimated that in the unlikely event they were all dedicated to stem cell research, those 11,000 embryos could create at most 275 stem cell lines.

Stem cell lines cannot develop by themselves at the bottom of a Petri dish. They need to be cultured in something.

The first embryonic stem cell lines created in the United States were cultured on a layer of feeder cells. Back then, researchers typically used skin cells from mice for this.

Today scientists have discovered how to develop stem cell lines without the use of mouse cells.

But researchers used animal feeder cells in all the embryonic stem cell lines created before Aug. 9, 2001 – the only embryonic lines that may be used for federally funded research.

Scientists continue to create new stem cell lines in the United States, but they are prohibited from using federal funding to pay for the research.

Designer cells

The stem cells lines being used for research now cannot be used to treat patients, Kessler said.

Embryonic stem cells can become any type of cell in the body, but no one can change their genetic makeup.

New cells created by these lines would be like donated organs. They would not match the DNA of the recipient and would be rejected by the immune system.

One way to get around this problem is to create cells that perfectly match the recipient’s DNA.

This can be done through somatic cell nuclear transfer, also known as therapeutic cloning.

It’s called “cloning” because the process involves taking DNA from an adult cell and creating exact copies of it.

To create embryonic stem cells that match a patient’s DNA, a scientist must take the nucleus, the part of the cell that contains all of its genetic information, from one of that patient’s cells.

In recent experiments, researchers have used the nuclei of adult skin cells.

The scientist then places that nucleus into an egg cell. The egg cell begins to divide and eventually forms a blastocyst with DNA identical to that of the patient.

That blastocyst contains embryonic stem cells that can recreate any cell in the patient’s body.

Using adult cells

Investigators in Japan have discovered a way to use adult cells to create cells that act like embryonic stem cells.

Researchers used a virus to insert four genes into a skin cell. With that bit of manipulation, they can convert the adult cell into one that can be differentiated into other types of cells. This is called an induced pluripotent stem cell.

“A lot of people are hopeful that this technique will get around a lot of the ethical issues having to do with somatic cell nuclear transfer,” Kessler said.

But the technology of creating these cells is not perfect, Kessler said.

“There’s a concept of plasticity,” Kessler said. “For example, you could take a fat stem cell and use that to create cells for the brain. I wish that were true because we’d have no trouble getting donors for it.”

Until alternatives become as versatile as embryonic stem cell lines, scientists should not limit their research to only one type of stem cell, Kessler said.

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