Our DNA may encode all the instructions needed to build the human body and keep it running, but each of our cells must follow just a subset of those instructions in order for the body to work properly.
Thanks to the $300 million, National Institutes of Health Roadmap Epigenomics Project, researchers have now identified most of the chemical tags on DNA and its associated proteins that influence gene function and help define more than 100 different kinds of human cells.
These chemical tags include so-called methyl or acetyl groups; they don’t change the DNA sequence itself, but they can make the DNA nearby fold or unfold, blocking access to a gene so it can’t turn on, or exposing a gene so it can be activated.
The epigenome helps determine the genes a cell can use, turning it, for example, into a liver cell or neuron.
Those cells don’t necessarily accurately reflect what’s happening in normal cells, Glass says, so the Roadmap project instead examined samples taken from the body directly, such as cells from the heart, liver, kidney, muscle, intestines, skin, fat, and brain, as well as fetal tissue.
Some of the project’s investigators tested several kinds of stem cells and even sampled stem cells as they differentiated into nerve cells or other tissues.
When the teams were done mapping and comparing the epigenomes of these 111 tissues and cells, they were able to define active and inactive regions of each cell type’s genome.