October 15, 2009

Scientists Reveal Map Of Human Genome Chemical Switches

Despite the fact that the human genome sequence lists nearly every single DNA base of the roughly 3 billion bases that make up a human genome, it has remained a biological mystery as to how its function is regulated.

Now, scientists from the Salk Institute have revealed the first detailed map of the human epigenome, which is the network of chemical switches that regulates activation of human genes.

The human genome was decoded almost 10 years ago, which plainly showed the building blocks of life and raised expectations that science would be able to quickly find the connection between disease and genes.

However, this proved to be far more complicated than anyone had anticipated.

Scientists discovered in their research that there is a whole other layer of genetic signaling, called epigenetics, which literally means "on top of" genes , that is still not understood very well.

What also surprised scientists is when they found that environmentally-induced alterations in these chemical triggers could be passed genetically from one generation to another.

The things we consume and the toxins we are exposed to can actually lead to heritable modifications in how and when genes are silenced or activated.

Joseph Ecker of the Salk Institute in La Jolla, California led U.S. scientists in using powerful computers and new technologies to compare the epigenomes of two types of human cells: embryonic stem cells and cells from the lung called fibroblasts.

"In the past we've been limited to viewing small snippets of the epigenome," Ecker said in a press release.

"Being able to study the epigenome in its entirety will lead to a better understanding of how genome function is regulated in health and disease, but also how gene expression is influenced by the environment," he added.

The study, published in the British journal Nature, showed a sub-cellular landscape of chemical signals.

The researchers hope that the information could help decipher how stem cells have the ability to transform into any kind of tissue in the body.

The study said that epigenetic signals can code genetic information in at least two ways.

One aims for "˜histones"˜, or spool-like structures in the cells around which strands of DNA are wound. For the genes to be acted upon, the spools must be "unwound".

Another way it can be done is through a process known as DNA methylation, which is the chemical modification of cytosine, one of the four molecular parts that make up the "rungs" in the double-helix ladder of DNA.


Image 2: Joseph Ecker, Ryan Lister and Mattia Pelizzola are in the lab at the Salk Institute. Credit: Image: Courtesy of the Salk Institute for Biological Studies


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