Making Embryonic Stem Cells Gets Even Easier

Scientists Have Created an Embryonic Stem Cell by Adding Two Genes to an Adult Stem Cell

by Dr. Barry Starr, Stanford University

In mid 2007, scientists showed us how to turn a mouse skin cell into an embryonic stem (ES) cell by adding four genes. Then in November 2007, they showed us that the same thing works with human skin cells and fibroblasts (a different kind of adult cell).

Now a new study has found an even simpler way to make these cells. Instead of using skin cells, they used a neural stem cell. These cells are responsible for making new nerve cells in the body.

The researchers were able to turn these cells into ES cells by adding just two new genes. Not only is this easier, but it may prove to be safer too.

One of the four genes used in the experiments with skin cells often causes a cell to turn cancerous. This gene wasn't needed with this new procedure.

Even better, the researchers may be able to mimic the effects of the added genes with chemicals. It is much easier to add chemicals to the outside of a cell than it is to add genes to the inside. If the chemicals work (a big IF), then getting ES cells will get a lot easier in the future.

ES Cells Might Cure many Ailments

Embryonic stem cells
can become any type
of cell.

Of course the reason to get ES cells is because they have the potential to cure so many illnesses. This is because they have the ability to turn into any other kind of cell. So they might cure anything where cells are damaged or destroyed and the body can't replace them.

The list of ways to potentially use ES cells is very long. Theoretically, they could be used for diabetes, severed spines, Parkinson's, multiple sclerosis, heart damage and many other diseases and injuries. No medical condition has yet been successfully treated with ES cells though.

Part of the reason is that scientists haven't yet worked out the conditions to turn ES cells into the cells they want. They also haven't worked out how to deliver the new cells to the patient.

Another big problem is that scientists don't have a good, stable source of ES cells to do their research with. This new study might help with this last problem.

Induced Pluripotent Stem (iPS) Cells

Everyone starts off as a small cluster of embryonic stem (ES) cells. Over time, these cells go on to become muscle, skin, nerve, and all of the other types of cells that make up an organism.

On the way to becoming these different kinds of cells, ES cells first change to "adult" or somatic stem cells. There are many different types of adult stem cells in the body. Their job is to replace worn out cells with new ones.

Adult stem cells are really at a point halfway between ES cells and the final cell types. This means that adult stem cells can become some kinds of cells but not all cells.

So a blood stem cell can become red or white blood cells, platelets, or any other kind of blood cell. But they can't become a nerve cell. The opposite is true of neural stem cells.

The researchers reasoned that it should be easier to turn an adult stem cell into an ES cell than it would be to turn a skin cell into an ES cell. The researchers were right. It took only two genes instead of four to make induced pluripotent stem (iPS) cells (as created ES cells are called).

More Information

Personalized Stem Cells Treat Sickle Cell Anemia in Mice

Turning a Neural Stem Cell into an iPS Cell

Neural stem cells from
the nose might cure
many diseases one day.

Four genes, Oct4, Sox2, c-Myc, and Klf4, were needed to turn a skin cell into an iPS cell. Researchers could get away without c-Myc if they used fibroblasts instead. Fibroblasts already make lots of the c-Myc protein.

What does a gene have to do with a protein? Each gene has the instructions for a particular protein. The Oct4 gene makes the Oct4 protein, the Sox2 gene the Sox2 protein, etc.

Every cell has a full complement of all 21,000 or so human genes. What makes each cell different is how much of each protein gets made from each gene.

ES cells naturally have a lot of Oct4, Sox2, c-Myc, and Klf4 proteins. Skin cells do not. The skin cells will make more of these four proteins if the genes for the proteins are added to the skin cells.

The researchers reasoned that if fibroblasts don't need c-Myc, maybe they could find a cell type that wouldn't need one or two of the other genes. They wanted to do this because adding one or two genes is much easier than adding four.

When the researchers looked at neural stem cells, they found that these cells had about twice as much Sox2 protein as an ES cell. And ten times as much c-Myc. And eight times as much Klf4. This seemed like a promising cell type to start with.

The researchers added the four genes in fifteen possible combinations. Of these fifteen possibilities, six caused neural stem cells to act like ES cells. These six combinations were:

Oct4, Sox2, c-Myc, Klf4
Oct4, Sox2, c-Myc,
Oct4, Sox2, Klf4
Oct4, c-Myc, Klf4
Oct4, c-Myc,
Oct4, Klf4

Some of these combinations took longer to work than others, but they all worked. The most exciting combination was the Oct4, Klf4 one.

First off, this combination has only two genes. Two genes are much easier to add to a cell than are four genes. Also, the researchers didn't need c-Myc. This is useful because c-Myc is the gene that can cause a cell to turn cancerous.

The final reason this is such an exciting combination is that there are chemicals that can increase the amount of Oct4 and Klf4 in a cell. In other words, researchers may be able to add chemicals to the cells instead of genes.

Adding chemicals to the outside of a cell is trivial. In fact, this is one way scientists make ES cells turn into other kinds of cells! If these chemicals can safely increase the amount of Oct4 and Klf4 proteins without adding genes, then the process of making iPS cells will become relatively simple.

Before calling your doctor about a cure using iPS cells, it is important to mention that neural stem cells are not that easy to get. There are some in the nose that might be used but researchers don't know if these stem cells are the same as the neural stem cells they used.

Even if neural stem cells aren't useful, this research opens up the possibility that another adult stem cell will be. Using what they learned here, researchers may be able to quickly screen through other adult stem cells and find one that works and is more common.

More Information

How to tell a cell is an ES cell

Researchers can study a
cell's genes using arrays
like these to tell cells apart.

It isn't easy to tell if a cell is an ES cell. The researchers showed the cells they created looked and acted like ES cells in three ways.

First they looked to see which genes were turned on in their newly created cells. And how much product each gene was making.

Remember, each cell type has a distinct set of genes turned on to a particular level. This is called a gene expression profile.

The researchers used microarrays to compare the gene expression pattern of their new cells to real embryonic stem cells and to the neural stem cells they came from. The researchers found that the pattern of gene expression matched an ES profile and was different from a neural stem cell.

The next step was to see if the cells could do things that ES cells can. ES cells can become a variety of cell types when grown under certain conditions in the lab. So could their iPS cells.

The big test for a cell, though, is whether or not it can grow into a new animal. ES cells by definition can. And so could their iPS cells.

The cells the researchers used had the GFP gene in it. GFP is a protein that makes a cell glow green. What this means is that researchers can easily trace the cells that came from their iPS cells in a whole mouse.

The researchers put one of their iPS cells into a mouse blastocyst. (A blastocyst is a clump of ES cells that will grow into an animal.)

They found that the mice that grew from this blastocyst had cells with GFP. So the cells could become any kind of cell. In fact, in some mice they became part of the eggs or sperm and were successfully passed on to create a whole GFP mouse.

Content provided by the Department of Genetics, Stanford University.