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| An epigenomic signature can be made on the genome in two ways.--Courtesy of John Stamatoyannopoulos and Rae Senarighi (Click to see larger version) |
Researchers supported by the National Institutes of Health Common Fund's Roadmap Epigenomics Program have successfully mapped the epigenomes of 127 types of human cells and tissues. This bridges the basic charting of the human genome by filling in the specificities on which parts of it are involved in making a particular kind of cell.
Epigenomics is the study of the layering of chemical signatures that makes up the epigenome of each cell, thereby turning genes on or off. An epigenetic signature can be created in two ways on the genome: by the attachment of chemical tags called methyl groups directly to a DNA molecule or through the attachment of these chemical tags to the tails of histone proteins that package DNA.
"This represents a major advance in the ongoing effort to understand how the 3 billion letters of an individual's DNA instruction book are able to instruct vastly different molecular activities, depending on the cellular context," NIH Director Dr. Francis Collins said in a statement. "This outpouring of data-rich publications, produced by a remarkable team of creative scientists, provides powerful momentum for the rapidly growing field of epigenomics."
The NIH Common Fund's Roadmap Epigenomics Program researchers have published epigenomic maps describing this work in the journal Nature. The tissue studies are both adult and embryonic and are broken down by cell type or region.
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| Reference epigenomes are available for more than 100 cell and tissue types.--Image courtesy of Nature and Roadmap Epigenomics Consortium |
For example, blood was broken into several types of immune cell and the brain was studied as specific regions including the hippocampus and dorsolateral prefrontal cortex. Embryonic cells were taken at the blastocyst stage of pregnancy. They were subjected to a range of epigenomic analysis along with genome sequencing and genome-wide association studies.
"Soon after the human genome sequence had been completed, it became clear that an epigenome--a map of the genome-wide modifications made to DNA and the protein scaffold that supports it--would also be required. The task at hand was, as researchers like to say, not trivial. Every cell in the body carries the same genome (with a few exceptions), but the epigenome changes with cell and tissue type," summed up Nature on the importance of the epigenomic research in an editorial accompanying the data.
But all this is just the tip of the iceberg. The International Human Epigenomic Consortium aims to research the epigenomes of every cell type in the human body, which is estimated to number several hundred to 1,000.
In addition, individual-level studies need to be conducted to understand the genetic variation within cell-type-specific epigenomes. And testing also needs to be done to further understand epigenomic changes due to ageing or environmental factors such as nutrients and metabolites.
- here is the NIH release
- and the Nature epigenomics package