MicroRNA may have fail-safe role in limb development

December 01, 2005

GAINESVILLE, Fla. - A tiny strand of molecules plays a role in how our arms and legs develop and grow - a finding that sheds light on perplexing bits of material once dismissed as genetic "junk," say scientists at the University of Florida and Harvard University.

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 as a protective mechanism in the hindlimbs in the event normal gene transcription goes awry.

"A large body of evidence indicates this new class of regulators is not something to turn things off in the first place, but a fail-safe," said Clifford Tabin, Ph.D., a professor of genetics at Harvard Medical School and senior author of the research. "You don't want cells in a hindlimb seeing cells that should only be in a forelimb - it would create a defective limb. So you not only want to shut the faucet tight on the wrong cells, you want to shove a towel into it, too, to really make sure the wrong thing doesn't leak out. One way of doing that is with microRNA."

Researchers looked at gene activity in chicken embryos and in mice, finding miR-196 silences a chemical important for transferring information from DNA to RNA within a cell - a transcription factor.

"It's turning off a transcription factor in the hindlimb that is important for forelimb development," Harfe said. "But it still doesn't explain why a hindlimb is a hindlimb and a forelimb is a forelimb."

The next step in the research is to observe limb development in mice engineered to not express miR 196.

"The authors have shown a role for miR 196 in limb development," said John Fallon, the University of Wisconsin's Harland Winfield Mossman professor of anatomy. "People talked about ways microRNA may have a role in embryonic development, and this work is a solid contribution that supports that idea. Researchers have also been looking for differences between gene expression in forelimbs and hindlimbs, with little success. This paper suggests there is a new mechanism to control the fidelity of protein expression in the limbs through microRNA expression. That is a hypothesis that people in the field will have to test, but it is strongly supported by their research."
-end-


University of Florida

Related DNA Articles from Brightsurf:

A new twist on DNA origami
A team* of scientists from ASU and Shanghai Jiao Tong University (SJTU) led by Hao Yan, ASU's Milton Glick Professor in the School of Molecular Sciences, and director of the ASU Biodesign Institute's Center for Molecular Design and Biomimetics, has just announced the creation of a new type of meta-DNA structures that will open up the fields of optoelectronics (including information storage and encryption) as well as synthetic biology.

Solving a DNA mystery
''A watched pot never boils,'' as the saying goes, but that was not the case for UC Santa Barbara researchers watching a ''pot'' of liquids formed from DNA.

Junk DNA might be really, really useful for biocomputing
When you don't understand how things work, it's not unusual to think of them as just plain old junk.

Designing DNA from scratch: Engineering the functions of micrometer-sized DNA droplets
Scientists at Tokyo Institute of Technology (Tokyo Tech) have constructed ''DNA droplets'' comprising designed DNA nanostructures.

Does DNA in the water tell us how many fish are there?
Researchers have developed a new non-invasive method to count individual fish by measuring the concentration of environmental DNA in the water, which could be applied for quantitative monitoring of aquatic ecosystems.

Zigzag DNA
How the cell organizes DNA into tightly packed chromosomes. Nature publication by Delft University of Technology and EMBL Heidelberg.

Scientists now know what DNA's chaperone looks like
Researchers have discovered the structure of the FACT protein -- a mysterious protein central to the functioning of DNA.

DNA is like everything else: it's not what you have, but how you use it
A new paradigm for reading out genetic information in DNA is described by Dr.

A new spin on DNA
For decades, researchers have chased ways to study biological machines.

From face to DNA: New method aims to improve match between DNA sample and face database
Predicting what someone's face looks like based on a DNA sample remains a hard nut to crack for science.

Read More: DNA News and DNA Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.