Methylated spirits
Oct 15th 2009
From The Economist print edition
The human genome gets more and more complicated
Illustration by Claudio Munoz
IT WAS, James Watson claimed, something even a monkey could do. Sequencing the human genome, that is. In truth, Dr Watson, co-discoverer of the double-helical structure of DNA back in the 1950s, had a point. Though a technical tour-de-force, the Human Genome Project was actually the sum of millions of small, repetitive actions by cleverly programmed robots. When it was complete, so the story went, humanity’s genes—the DNA code for all human proteins—would be laid bare and all would be light.
It didn’t quite work out like that. Knowing the protein-coding genes has been useful. It has provided a lexicon of proteins, including many previously unknown ones. What is needed, though, is a proper dictionary—an explanation of what the proteins mean as well as what they are. For that, you need to know how the genes’ activities are regulated in the 220 or so different types of cell a human body is made from. And that is the purpose of the American government’s Roadmap Epigenome Programme, results from which are published this week in Nature by Ryan Lister and Mattia Pelizzola of the Salk Institute in California, and their colleagues.
Epigenomics studies the distribution over the genome’s DNA of control molecules called methyl groups. These can attach themselves to cytosine, one of the four chemical bases that form the “letters” of the genetic code. In so doing, they help control a process called transcription, in which a copy of a gene is made in the form of a molecule called RNA, the first stage in the translation of a gene into a protein. The presumption is that the pattern of methylation, by controlling which proteins are manufactured, helps determine what type of cell is produced. A cell with its haemoglobin genes switched on to overdrive, for example, will become a red blood cell. One that churns out actin and myosin, which link up to form units that can expand and contract, will become a muscle cell. And so on. Dr Lister and Dr Pelizzola have tested this idea by describing the first two reasonably complete human epigenomes.
...
Read more here/Leia mais aqui.
