June 7, 1999
Layman's Explanation
By DawnC

In February 1997, the month of my birthday (not that that had anything to do with it), Dr. Wilmut, an American scientist in Scotland, wrote a rather short article that stunned the world. For me, it was one of those, "I remember what I was doing when..." moments. I was walking from the medical sciences library at Texas A&M University back to my lab. I picked up the school newspaper on my way and did a double-take when I saw the "Adult Mammal Cloned!" headline. Figures. There I was in the field of biochemistry and genetics and I first get the news from the school newspaper (which published it the day after it came out in Nature). I did have an excuse, though: I was so busy on my own research project and classes that I was behind on my general journal reading. *grin* However, I did immediately go find myself a copy of Nature to read the actual article.

I was ecstatic. You see, before then, the scientific dogma was that one could not clone from an adult mammal, and I love it when scientific dogma gets thrown out. People had tried with frogs/tadpoles, but the tadpoles never developed into frogs. Something just didn't go right and they never got any further than that. However, we have been able to clone from embryos for many years. In fact, a few years before Dr. Wilmut made his announcement, the New York Times carried a front page headline announcing the first "cloning" of a human embryo. That was no big deal to the scientific community. We'd been able to do that for years, and had done it for other organisms. No one had ever done it with a human before because of the ethical implications. The procedure, however, is relatively simple. You take an early embryo and basically just split it into two. Each half will start to develop again and you'll have two identical wholes as the finished product. The main difference is that embryonic cells are not differentiated and adult cells are differentiated. Differentiation is when certain genes in a cell type are active, and others inactive, so that that cell has developed as a certain "type" of cell: a liver cell, or a muscle cell, or a neuron, for example.

What Dr. Wilmut did was much different, and totally unexpected. He took a mammary epithelial cell (an adult cell) from a sheep and an egg cell from another sheep. He removed the nucleus from the egg cell, and then arrested the donor nucleus of the adult cell in a cell state called G0. In this stage, the cell is "starved" of nutrients and becomes quiescent, or inactive. One of the main reasons why scientists had not been able to successfully clone from adult cells prior to Dr. Wilmut's experiment was because they had not induced the adult cell to become inactive.

Once the adult cell was "sleeping," Dr. Wilmut fused the adult cell nucleus with the egg cell (that had its nucleus removed). From this fusion, Dolly, the first sheep cloned from an adult cell, was born. However, the process wasn't very efficient. Out of 277 tries, only one was successful.

But could this be done with other species? Yes! In July of 1998, another team of scientists announced that they had cloned mice from differentiated adult mouse cells. Can this be done with humans? Almost certainly. Should this be done with humans? Most scientists and philosophers say, "no."

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