Researchers at The Scripps Research Institute and The Genome Institute of Singapore (GIS) have shown, through a map, how the human genome is modified during embryonic development.
The study has been published in the genomics journal Genome Research on February 4, 2010.
"The cells in our bodies have the same DNA sequence," said Scripps Research Professor Jeanne Loring, who is a senior author of the paper with Chia-Lin Wei of the Genome Institute of Singapore and the National University of Singapore and Isidore Rigoutsos of IBM Thomas J. Watson Research Center. "Epigenetics is the process that determines what parts of the genome are active in different cell types, making a nerve cell, for example, different from a muscle cell."
Wei, who is senior group leader at the GIS, a biomedical research institute of the Agency for Science, Technology, and Research (A*STAR), said, "In this study, we mapped a major component of the epigenome, DNA methylation, for the entire sequence of human DNA, and went further by comparing three types of cells that represented three stages of human development: human embryonic stem cells, human embryonic stem cells that were differentiated into skin-like cells, and cells derived from skin. With these comprehensive DNA methylome maps, scientists now have a blueprint of key epigenetic signatures associated with differentiation."
DNA methylation causes specific subunits of DNA to be chemically modified, which controls which areas of the genome are active and which ones are dormant. DNA methylation is critical to the process in which embryonic cells change from "pluripotent stem cells," which have the ability to turn into hundreds of cell types, to "differentiated cells," distinct types of cells that make up different parts of the body, such as the skin, hair, nerves, etc.
In reviewing the data produced by the study-information on the methylation of three billion base pairs of DNA-the scientists were able to identify previously unknown patterns of DNA methylation. They identified cases where DNA methylation appeared to enhance, rather than repress, the activity of the surrounding DNA, and found evidence to suggest a role for DNA methylation in the regulation of mRNA splicing.
"We produced a very large amount of data," said Loring, "but it actually simplifies the picture. We identified patterns of many genes that are methylated or de-methylated during differentiation. This will allow us to better understand the exquisitely choreographed changes that cells undergo as they develop into different cell types."