Wednesday, October 5, 2011

First embryonic stem cells created in the lab

With a new cloning technique, it is now possible to create embryonic stem cells (ES) in the lab from unfertilized eggs, instead of obtaining them from embryos. When the scientists artificially fertilized the eggs with the genetic material of an adult skin cell, a fibroblast, the resulting embryo was able to reach a stage that is called a blastocyst. In this stage, the embryo has an outer layer, and an inner layer of cells, that are true stem cells. In this early stage, none of the cells have differentiated into a specific cellular lineage, which means they can be used to make all kinds of tissues. This is the hallmark of stem cell research: being able to grow cells without limits to differentiation, to create tissues that we can use to repair damaged bodies.

There is a drawback to the method that the scientists used. Because they combined the genome of the egg and the fibroblast, the resulting embryonic cells have more genetic material than normal, which renders them unsuitable for therapeutic purposes. They have tried to remove the genetic material of the egg when fusing the cells, but this ceased development of the embryo. The researchers think they can find a way to eliminate the extra genetic material, but until they do, their therapeutic potential can not be investigated.

One of the most important things of this study is that, when the technique can be used by everyone to create the stem cells, there is no longer a need to use already existing embryos to isolate ES. Using embryos to obtain the cells, for example by leftovers from IVF treatments, stirred up a lot of controversy and debates about ethics. With the new technique, the use of embryos is circumvented, though researchers still have to destroy a blastocyst when harvesting the cells. This can, however, hardly be called a real human embryo, as it typically consists of only 70 to 100 cells: a clump of cells with hardly any specialization.

An other way to get around using embryos from stem cells is to reprogram adult cells into stem cells. A technique to create these so-called induced pluripotent stem cells (iPS) has been created over ten years ago, and sparked a lot of research with stem cells. These cells, however effective, are more artificial, and seem to retain some sort of memory of the cell they used to be, which makes their potential as a true stem cell lower than ES. iPS do seem to form less tumours when injected in the body than ES, though. A second possibility is to isolate adult stem cells from the patient itself. Almost all cell types have their own stem cell that causes renewal of organs. These adult stem cells have the capability of self-renewal, but are limited in their differentiating capacity, as they have already commited to a cell lineage. A downside of using adult stem cells in patients that need repair of a certain organ is, that the stem cells we need are often damaged: they might very well be the cause of the lack of repair by the body itself.

Normally, during fertilization, a sperm cell enters the egg, causing them to fuse together. Sperm and egg cells are specialized in the respect that they only have half the genetic material an ordinary (somatic) cell has. So, when they fuse together, the total amount of genetic material is equal to that of somatic cells. When in the lab a skin cell, with ordinary amounts of genetic material, is fused with an egg cell, their total amount of DNA comes to 1.5 times the normal count.

Each somatic cell has two copies of a chromosome, which contain the DNA. Sperm and egg cells have only one. So, the ES that were created have a total of three copies of each chromosome. This will cause a lot of abnormalities in the development of the embryo in a later stage, and makes it unlikely that it will continue to grow for a long time. But at least it grows long enough for us to harvest the promising ES cells from the blastocyst.

If we find a way to remove the extra genetic material from the ES, and are able to tune them the way we want, our possibilities of creating tissues are endless. While this field of research is promising, much more is needed to make it actually happen. But being able to create the cells without having to answer to lots of difficult ethical questions is a big step forward. The only hard thing to do right now is to find women that are willing to donate their eggs to science.

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