MicroRNAs are tiny snippets of RNA that can repress activity of a gene by targeting the gene's messenger RNA (which copies DNA information and starts the process of protein production).
The first microRNA was discovered in 1993, in worms. It took seven years for the second one to be found, also in worms, but then the floodgates burst. Many microRNAs now have been found in diverse plants and animals, including hundreds in humans. Moreover, microRNAs found in mammals regulate over a third of the human genome, as shown in a 2005 study by the lab of Whitehead Member and Howard Hughes Medical Institute Investigator David Bartel and colleagues.
But given the wealth of microRNAs, and the ability of individual microRNAs to target hundreds of genes, researchers have struggled to show the biological impact of a particular microRNA on a particular target in mammals (although such connections have been shown in plants, worms and flies). Several groups have demonstrated that over-expression or under-expression of a microRNA can play a role in certain cancers, but have not clarified the genes responsible.
Looking to find a promising target for an individual microRNA, Christine Mayr, a postdoctoral researcher in the Bartel lab, picked Hmga2, a gene that is defective in a wide range of tumors.
In these tumors, the protein-producing part of the Hmga2 gene is cut short and replaced with DNA from another chromosome. Biologists have mostly focused on the shortened protein as the possible reason that the cells with this DNA swap became tumors. But this DNA swap removes not only the gene's protein-producing regions but also those areas that don't code for protein. And these non-protein-producing regions contain the elements that microRNAs rec
Source:Whitehead Institute for Biomedical Research