The Womb's Strange Epigenome

An impossibly long string of DNA letters floats inside each of our trillions of cells. Somehow, incredibly, that one string produces a huge variety of tiny biological machines, from red blood cells that carry oxygen, to brown fat cells that generate heat, to neurons that fire electrical messages. How does one* fixed code manage all that?The answer is, it’s not fixed. There’s epigenetics: In response to changes in the environment, stuff (chemicals and proteins) interacts with the DNA and affects how the code is interpreted. For example, a methyl group (one carbon and three hydrogen atoms) can latch on to the genome and help switch on or off the expression of the genes below. So in fat cells, say, some suite of genes is methylated, but in brain cells, it’s a different group of genes.Until fairly recently, research on this so-called DNA methylation focused on places in the DNA code where a G immediately follows a C — CpG sites — which are known hotspots of methylation. When hundreds or thousands of CpG sites appear in a row, it’s called a CpG island, and this intense methylation usually silences the underlying gene. But in the past few years, DNA sequencing technology has allowed researchers to look at methylation patterns not just at the glittering islands, but across the entire genome.It turns out that at least 70 percent of the genome is covered by methyl groups. And the pattern of methylation across the genome, known as the epigenetic landscape, is more varied than ever expected. But as researchers create more and more elaborate epigenetic maps, they still don’t know much about where they’ll take us.Read more at...Only Human, March 2013.