General demethylation:
We know and have long known that DNA is a double helix that contains pairs of bases (Chemically a base is the opposite of an acid. It took me a long time to realize that we were talking “that” kind of base.) arranged in a sequence that codes for the amino acids (Yes, an amine is a kind of base, too.) that go together in chains that get folded up somehow to make functioning proteins that are sort of the power tools of the cell.
But you have to turn a power tool on and off if it is to be useful. This was a concept so neglected for so long that any DNA found that was not coding for a gene that could make a protein was called “junk” DNA. In a way it was. It did not lend itself to writing grant proposals, and that of course is what it is all about. I sort of suspected that the junk was the control mechanism, but in line with making every possible conceptual error a human is capable of, I was wrong. At least sort of wrong.
There is another control mechanism, now much in the news. Anything that controls a gene and is not itself a gene is “epigenetic.” The most widely spoken of epigenetic mechanism is simply attaching a methyl group (That’s just a carbon atom with any loose ends plugged by hydrogen. No, I’m mixing metaphors. Loose bonds.) to the DNA in the right place.
When this came down the pike it was a long time before I had any real inkling of what it was and an even longer time before I realized that this, not mutations of DNA per se, was the most plausible mechanism for letting kindred chromosomes recognize one another.
Methylation can change rapidly. In fact it changes a lot within the lifetime of an organism. There have been recent papers on this. (Ito Shinsuke et al. Tet Proteins Can Convert 5-methylcytosine to 5-Formyl cytosine [While a methyl group is one carbon, a formyl group is has an oxygen stuck in there] and 5-Carboxylcytosine [A Carboxyl group drops the carbon but keeps the oxygen. Oh, yes, cytosine is one of those bases we were talking about.] SCIENCE vol. 333 no. 6047 September 2, 2011 page 1300 [At least I think that’s what they’re talking about.] and Jeffrey R. Shearstone et al. Global DNA Demethylation During Mouse Erythropoesis in Vivo SCIENCE vol. 334 no. 6057 November 11, 2011 page 799 [Erythropoesis means making red blood cells, which isn’t exactly what we are looking for.])
When I see such articles I do my best to get into them, knowing that somewhere in there is the secret of life the universe and everything.
But honestly all I can do is hope somebody comes up with an easy summary so I can ask him where the fertility methyl groups might be lurking.
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