Tiny molecules control life processes - Microbiology

USA Today (Society for the Advancement of Education), June, 2003

Researchers at Oregon State University, Corvallis, have made a very important advance in the understanding of "micro-RNA" molecules, which are tiny bits of genetic material that were literally unknown 10 years ago, but now represent one of the most-exciting fields of study in biology. They reveal for the first time a new mechanism by which micro-RNA can stop the function of messenger RNA by literally cutting it in half, thus interfering with the normal function of messenger RNAs in gene expression. This "expression" of genes that code for essential proteins is ultimately what controls whether a cell turns into a lung, liver, brain, or other cell. Understanding what activates this process--or stops it--is a key to understanding the biological process of life itself, and forms the foundation for advances in medicine, agriculture, and other fields.

On this frontier of biology, experts say, the most-intriguing new component is micro-RNA, a miniscule type of regulatory molecule that once had seemed quite insignificant even in the extraordinarily tiny, microscopic world of cell biology. The first micro-RNA, in fact, was just discovered in 1993 and at the time was thought to be a biological oddity in worms. A couple of hundred have since been found in plants and animals. Yet, it has only been in the past several months that scientists working in this area have come to understand the potentially profound importance of micro-RNA.

"For a long time, people really did not know that these micro-RNAs were even there," notes James Carrington, director of the university's Center for Gene Research and Biotechnology. "They were under the radar, and observations of them were limited by our technology. But as we learn more about these regulatory molecules, we're beginning to understand the scope of their biological importance. In molecular biology, micro-RNAs are clearly one of the top two or three discoveries of the past decade."

Every normal cell in complex organisms, such as plants, flies, and humans, has a complete copy of the DNA for the entire organism--some 15,000 to 35,000 genes that collectively are thought of as the genetic blueprint for life. However, to serve as certain types of cells, such as a brain in humans or roots in plants, only a much-smaller number of genes within each cell are actually "expressed," or allowed to create the proteins that perform these separate life functions. "A key focus in biology for a long time has been what controls gene expression," Carrington explains.

It is well understood, he points out, that two of the key steps between DNA and a functional cell are the processes of transcription and translation. In transcription, single-stranded "messenger RNA" molecules that correspond to each expressed gene are produced; in other words, the messenger RNA is decoded, resulting in the production of a protein made from some combination of 20 amino acids. "This is a very complex series of biological processes that requires hundreds of proteins and other factors," Carrington says. "And we're now also learning the role of micro-RNA in controlling expression of some important genes."

Micro-RNAs are actually produced by the transcription of tiny genes, in regions of the genome that were previously thought to be vacant or useless DNA. However, unlike messenger RNAs, micro-RNAs are not translated to produce proteins. Instead, researchers are finding that they have critical functions in controlling the process of gene expression.

"It's very important that we learn how cells differentiate and grow normally," Carrington says. "Just about everything in the human body has a genetic component. Genetic abnormalities relate to birth and development defects, susceptibility to disease, misregulation of genes. And these same processes are also at work in all other life forms, including plants, and new findings could be applied to crop biotechnology or even traditional plant breeding."