Genome complexity: histones control epigenetics (Introduction)

by David Turell , Thursday, July 20, 2017, 18:07 (2469 days ago) @ David Turell

In C. elegans nematode worms histones maintain warmth experience over 14 generations:

http://www.the-scientist.com/?articles.view/articleNo/49848/title/Epigenetic-Inheritanc...

"When genomicist Ben Lehner and his colleagues at the Centre for Genomic Regulation in Barcelona engineered nematode worms to express a fluorescent reporter, they were hoping to learn about the control of gene expression. Fluorescence indicated activation of the promoter for the gene daf-21, which encodes an essential C. elegans heat-shock protein. Glowing worms meant high expression levels; dull worms, low expression. But during the project, the team stumbled across something else.

“'Working with this strain, we noticed that if you had individuals that were brighter, their progeny tended to be brighter,” says Lehner. With lab worms that are genetically identical, “this is something you don’t normally see. There seemed to be inheritance.”

"Suspecting they had an epigenetic phenomenon on their hands, and knowing that daf-21 is temperature-sensitive, the researchers decided to grow worms at different temperatures to see if it would affect gene-expression levels through the generations. Sure enough, worms grown at 25 degrees Celsius had offspring that were brighter at normal temperature (20 degrees) than the offspring of worms that had always been kept at 20 degrees.

"In worms engineered with multiple copies of the fluorescence transgene, this effect persisted for seven generations after the temperature spike, and even longer when the scientists raised multiple generations at 25 degrees. In one nematode line, the worms’ glow persisted for 14 generations after the temperature had been dialed back to normal.

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"Looking more closely, the team found that offspring of worms grown in warmer temperatures showed reduced modification of histone proteins around the transgenes from an early stage of embryonic development. Over generations kept at normal temperature, this histone modification gradually returned to normal, suggesting epigenetic readjustment. These findings, says Rechavi, are “the most surprising and interesting part.'”

Comment: Epigenetics usually works with methylation, but in this case it is histone modulation. More than likely other mechanisms will be found. Too complex for chance development.