( University of Florida researchers have ...)Micro-molecule plays big role in birth defects

The finding, which will be reported this week in the online Proceedings of the National Academy of Sciences, deals with tiny strands of genetic material called microRNAs.

Once thought to be little more than cellular debris, these short strands of RNA may perform a vital role in healthy development by strategically turning off gene activity.

By genetically modifying mice, scientists with the UF Genetics Institute were able to get the first-ever picture of how limbs would develop in a vertebrate without the help of microRNAs. When microRNAs were not available to turn off certain genes, the mice grew malformed, nonfunctional limbs.

The finding may provide insight into human birth defects, but scientists say its greater value will be as a new technique to study the function and malfunction of microRNAs, more than 200 types of which are thought to exist in the human body.

"We looked at limb development because it's a great place to demonstrate the technique," said Brian Harfe, Ph.D., an assistant professor of molecular genetics and microbiology in the College of Medicine and lead author of the report. "We were able to show it's feasible to eliminate the activity of microRNAs from a specific tissue while the rest of the tissue remains normal."

Had researchers inhibited microRNAs in every single cell, Harfe said the mouse embryos would survive little more than seven days after fertilization.

"That isn't enough time to study development," Harfe said. "Most structures, such as the heart, the gut and the lungs, haven't even formed yet. Now we can bypass the problem of early mortality and study the structures as they develop. It's a new tool for the genetic researcher's toolbox."