Spinal Confusion

...an attempt to clarify confusing and innacurate information in science articles

Saturday, March 04, 2006

Altered Nuclear Transfer - Not So Ethical?

Altered Nuclear Transfer (ANT) is one of the procedures Congressman Roscoe Bartlett spoke of when addressing methods of funding research into "ethical methods of deriving embryonic stem cells." But, for those who oppose SCNT, is it really ethical?

Let's take a closer look.

ANT describes a general concept for performing an altered form of somatic cell nuclear transfer (SCNT); thus the name. As we know, SCNT involves replacing the nucleus of an egg cell with one from an adult cell and stimulating it with electricity, tricking the cell into believing it is fertilized.

The NT-product, or clone, then attempts to do ... something. Essentially, whatever the instructions in the cytoplasm tell it to do. Scientists hope that they can use SCNT to make a cell that functions as a zygote, developing into a morula and eventually a blastocyst. It is at this point that scientists will attempt to extract the embryonic stem cells, destroying the blastocyst in the process.

ANT is SCNT, with a small difference: a modification is made to either the egg's cytoplasm or the donor cell's nucleus to prevent an embryo from developing. (Some would say, ANT is SCNT with the aim of creating a "developmentally disabled" embryo. The difference in terminology is philisophical, so please choose the definition you prefer and continue. I am not saying which is right or wrong.)

The most prominent proponent of ANT is Stanford Bioethicist William Hurlbut. The best known proposed implementation of ANT is through silencing the expression of a gene known as Cdx2. In mice, this gene contributes to the formation of the trophectoderm, or outer "shell" of the blastocyst. Silencing this gene does not interfere with the formation of the blastocyst's inner cell mass (ICM), which is what scientists extract to obtain embryonic stem cells.

So far, this all sounds like it could be pretty kosher. If you prevent the formation of the trophectoderm, you interfere with the integrity of the embryo. If you disrupt the embryo's integrity, it's not really an embryo. Right?

Well, the trophectoderm later forms the placenta. The placenta, of course, is necessary for the embryo to implant into the uterus. The placenta is, effectively, the feeding tube that allows nutrients and oxygen to pass from the mother to the embryo (and later to the fetus). Silencing Cdx2, basically, starves the embryo of the nourishment it needs to further develop into a fetus.

If a person believes a zygote is a life, I see no reason why they should support this method.

Fortunately, the vast majority of those who support this method only support it conditionally. They specify that they only support such research in animal models, in an attempt to see if it works.

Interestingly, William Hurlburt himself does not believe that silencing Cdx2 is necessarily the "holy grail". Writing in Wired, Clive Thompson reported:
For his part, Hurlbut is particularly incensed that his detractors keep oversimplifying his proposal. They maintain that the experiment on mice - knocking out CDX2 - wouldn't work in humans. Hurlbut insists he's never claimed it would. He says he cited CDX2 only as an example of what's possible; in humans, he suspects, you'd need to knock out some other gene, and only experiments will figure out which one.
This paragraph, particularly the last sentence, should raise major concerns for Catholics. In order to validate the technique in humans, experimentation on embryos would be required. Pope Benedict XVI recently indicated that such research should never be performed (the understood exception being that it can be conducted if the aim of the research is to save the life of the embryo), which throws up a significant hurdle.

Now, all this doesn't mean ANT is a bad idea. One implementation of ANT could propose to alter the egg's cytoplasm so that it directly reprograms the donor nucleus so that the cell becomes an embryonic stem cell.

This version would still face one ethical drawback: it would still rely on women to donate their eggs. Could women be pressured to undergo ovarian hyperstimulation to donate eggs? You bet. Would they? In some instances, it's hard to say they wouldn't be.

Is forcing women to donate eggs really that big of a deal, when the potential benefits are so great? Aside from the potential side effects, I guess it's a personal decision. Personally? I say it is.

Well, I guess that's it for tonight. Thanks for reading!