Role of microRNAs in the control of mRNA translation

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This project studies the function of a recently discovered class of ribonucleic acid (RNA) molecules termed microRNAs (miRNAs). They appear to have very important functions in all multicellular organisms, since many of them have undergone little change over hundreds of millions of years. At present we know that miRNAs probably work by regulating the efficiency with which messenger RNAs (mRNAs) are translated into protein molecules. However we do not know how they accomplish this, or which mRNAs are regulated by miRNAs. Our work to date has suggested to us that miRNAs may act in combination with one another on mRNAs, so that the effect on a given mRNA depends on just which miRNAs are present, and how abundant they are. We propose to construct a system in which the function of miRNAs can be studied in vitro, using crude cell extracts that are known to perform mRNA translation and related functions. This will, for the first time, make it possible to test miRNAs in carefully controlled conditions, and ask which steps in translation they affect. We will be able to investigate just how the pairing of miRNA and mRNA sequences determines the ability of a miRNA to act on a specific mRNA, and to confirm that a given miRNA actually does regulate a specific mRNA. To facilitate this goal, we will use three methods to isolate mRNAs that are targets of miRNA regulation. Each of these methods relies on the physical interaction of miRNA and mRNAs in cell extracts. In one method, we will attach a tag to a miRNA, and use the tag to pull out associated mRNAs. In another method, we will use an antibody to a protein that is thought to associate with all miRNAs. The antibody should pull out any mRNAs associated with the miRNA-protein complex. Finally, we will identify mRNAs that have responded to the presence of a miRNA by changing the efficiency with which they are translated. These experiments will provide essential knowledge about an extremely important biological system.