Thursday, March 10, 2005

Dermoid cysts and teratoma

Columbus Botanic Gardens
Nature has a commentary this week called Eggs alone. It argues that it may be possible to circumvent some ethical quandaries about embryonic stem cell research by using parthenogenetically created cells, cell created by inducing an unfertilized egg to begin dividing.

The authors point out that eggs are capable of dividing into specialized cells. I know someone who had a dermoid cyst removed from her ovary. During a normal exam, the doctor found a grapefruit sized growth in this person's abdomen. Ultrasound and other excitement ensued, and in the end, surgery was recommended. The growth came out, and was identified as a non-cancerous dermoid cyst.
What happened was, an egg got stuck in her ovary, and after a while started dividing on its own. When eggs divide, they specialize, and pretty soon, her cyst had its first tooth, skin cells, nerves, and hair at least 6 inches long. Given time, it could have developed eye-like structures, and there was talk of fingernail. All this on a grapefruit sized hollow ball.
The cyst is sitting in alcohol in my friend's office. I look at it now and then, and I think about life as a haploid. What would be different if people only had one copy of each chromosome?

Plants have alternation of generations, a pattern in which independent, multicellular haploid plants produce sperm and eggs, which fuse and form an independent, multicellular diploid plant. The diploid form is almost always the more robust of the two, though liverworts and mosses have a haploid phase which is larger than their diploid forms.

The switch from a dominant gametophyte (haploid) to a dominant sporophyte (diploid) is one of the great evolutionary transitions in plants. One common form of speciation in plants is polyploidy, where a plant has more than two copies of some chromosomes. Polyploid plants tend to be larger and more robust than their ancestors, so agricultural researchers like to induce polyploidy.

Extra copies of a chromosome mean a few things. You can transcribe RNA in greater volume, so you can produce protein faster (potentially). Mutations in one gene will be even less likely to matter, since instead of one backup, you could have 5 or even more.

People have derived a line of embryonic stem cells from a monkey's unfertilized egg, and early work is being done on human eggs. How long before heart attack damage can be treated with stem cells derived from a woman's own eggs? How long before sick people are made whole with half cells?

Half a World Away” by R.E.M. from the album
Out of Time
(1991, 3:27).