Genome complexity: gene controls (Introduction)

by David Turell , Friday, December 16, 2016, 01:37 (2900 days ago) @ David Turell

Activation or repression of genes is a tug of war between two processes:

http://medicalxpress.com/news/2016-12-reveals-gene.html

"New research from Stowers Institute for Medical Research suggests the process may be more like a battle between two opposing genetic forces rather than a step-wise assembly of ingredients.

"In their report, published online in Genome Research, Stowers researchers examined regions of fruit fly DNA, called enhancers, which increase the likelihood of gene expression. Gene expression is the process of turning genes on or off, and is crucial for creating specific cells in the body such as nerve cells or cells that make up skin and bone.

"But a duel comes first. Stowers Associate Investigator Julia Zeitlinger, Ph.D., and Postdoctoral Research Associate Nina Koenecke, Ph.D., discovered that DNA enhancers engage in an ongoing contest between activation and repression, which results in a different epigenetic state of the histone proteins around which DNA is wrapped.

"Activation sparks the addition of acetyl groups to histones, which in turn loosen their grip on DNA enhancers, allowing them to be switched on. Repression, on the other hand, removes this acetylation mark and prevents the switch from ever being flipped.

"'Through this balance between forces you can shift an enhancer more easily from inactivity to activity," Zeitlinger says.

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"The finding therefore clarifies the often misunderstood role of repression in DNA enhancers, and underscores its importance as an action, and not just an inaction. Typically, activation gets the most credit for its role in gene expression. For example, enhancers that are epigenetically modified but still inactive have been thought to be "poised" for future action. However, this new evidence suggests that "poised" enhancers - rather than lacking a key ingredient for activation - may be repressed.

"'When there is an opposition between the two enzymes responsible for acetylation state, it creates an ultra-sensitivity under some conditions," Zeitlinger says. "With just a little more activation, this can create a very dramatic switch in the enhancer's activity. This mechanism could allow a gene being turned on in some cells, while turned off in other cells of the body.'"

Comment: This type of exact knife-edge control is what is needed for precise manufacture of new cells in embryology or replacement cells in adult animals. This mechanism had to be developed at one time since it is a balanced go or no go. It cannot be stepwise or trial and error which is the Darwin approach. It requires precise planning only a mind can bring to the working design