A detailed new map of our genome in action

DNA is a long code of instructions to build every tissue in our body. But there are little markers along the way that tell cells how to read the DNA. And those markers turn genes on and off, which could affect disease or even your personal preferences. Image by Scott Tysick/Getty Images

Each cell in your body has the same DNA, but they dont all follow the same instructions. Some become blood cells; others become brain cells or muscle tissue. But if the DNA has a mistake or the cells turn on the wrong set of genes, that can lead to disease.

So how do cells decide which genes to turn on and which to turn off in different tissues? Thats the basis of epigenomics, chemical markers on the DNA and its packaging. Epigenomics is the focus of this weeks issue of the journal Nature, which includes a collection of papers from the Roadmap Epigenomics Program, a reference map of these modifications across a variety of human cells built by an international collaboration of scientists and researchers. Eight papers from the project are featured this weeks issue of Nature, and 16 others are published this week in other Nature journals.

The genome contains all these genes, but it doesnt tell you anything about how theyre working. These maps are giving snapshots of the genome in action, said Lisa Helbling Chadwick, Roadmap Epigenomics Program team leader and program director at the National Institute of Environmental Health Sciences. Our cells all have the same instruction book, but they have very different functions. How do they take this one set of instructions and come out so different?

Think of it this way, said Manolis Kellis, professor of computer science at MIT and author of several of the papers on the issue: You start as a single cell, a zygote with a 6.5 foot-long string of DNA with billions of letters. That genetic material contains all the instructions from mom and dad that youll need throughout your lifetime. But you dont need it all at once.

Enter the epigenome. Think of the epigenome, Kellis said, as a set of color-coded Post-It notes stuck to that DNA. These Post-Its are chemical modifications that can be read by different proteins and control how the DNA is getting used.

So continuing this analogy, green Post-It notes might point to the genes that are on, and yellow notes might point to the genes that are off. Orange notes might point to the control switches that help turn these genes on and off.

All cells in our body contain a copy of the same genome, the book of life that we inherited from our parents. However, each cell is using the book in a slightly different way. Theyre all reading different chapters, bookmarking different pages, and highlighting different paragraphs and words, Kellis said. The human epigenome is this collection of marks placed on the genome in each cell type, in the form of chemical modifications on the DNA itself, and on the packaging that holds DNA together.

The journal Nature explained it in musical terms:

On the surface, about 99.9 percent of our genome is the same from person to person, Kellis said. That still leaves .1 percent, or about 3 million letters that are different, scattered throughout all our genes. But it takes nature and nurture to make us who we are, he said. If DNA is the nature part of the equation, then epigenomics straddles the line between nature and nurture. Your genome was inherited, but your epigenome is partly shaped by environment and lifestyle.

Read the original here:
A detailed new map of our genome in action