( A tiny strand of molecules plays a role...)MicroRNA may have fail-safe role in limb development

The research, available today in the online edition of Nature, may help scientists understand whether bits of RNA called microRNAs act as protective mechanisms in healthy development not just by strategically turning off gene activity, but by making sure it stays turned off.

More specifically, researchers report linking a specific microRNA - miR 196 - to limb development, a finding that may be useful in understanding birth defects.

Until about five years ago, genetic researchers focused on DNA, which contains all the genetic instructions for the human body, and RNA, which translates DNA's message into proteins - the building blocks of cells, organs and all of the various systems of the body.

Unnoticed next to the main ingredients, microRNAs were considered to be "junk" DNA, leftovers from millions of years of evolution. More recently, this genetic material is suspected to be part of an intricate mechanism that helps repress about one-third of our 25,000 genes. It has been linked to diabetes, hepatitis C, leukemia, lymphoma and breast cancer.

But only now have microRNAs been connected to actual growth processes.

"We found miR 196 expressed only in the hindlimbs of mice, not the forelimbs - in other words, the feet but not the hands," said Brian Harfe, Ph.D., an assistant professor of molecular genetics and microbiology in the College of Medicine and a member of the UF Genetics Institute. "In developmental biology, there has always been debate about why forelimbs are different from hindlimbs. We now think this microRNA is regulating something important in the hindlimbs but not in the forelimbs."

Scientists do not know exactly what is happening, but they think miR 196 acts a
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Source:University of Florida