How does the body know what cells to make from basic genetic material contained in our DNA? For example, why are nerve cells what they are, powerhouses of electrical impulses that can send messages at lightning speed all over our bodies, allowing us to do everything from breathing to talking, eating, walking, and thinking? Why are they so distinct from say, heart cells, liver cells, kidney cells or the light-sensing cells in our retinas and so on? How does the body regulate the production of the right diversity of cells needed to sustain life?

The answer is gene expression. Every cell in the human body contains the same raw genetic material, locked in our DNA. Gene expression refers to whether a particular gene is making too much, too little or the normal amount of its protein at a particular time. Why proteins? Because they are the active players in most cell processes. They implement the myriad tasks that are directed by the information encoded in genomic DNA. The ultimate goal of gene expression therefore is to regulate protein synthesis and by extension, all the specialized cells needed by the body to function normally. Put differently, without the body’s ability to control gene expression, every cell would be identical. That, clearly, won’t do.

The natural question then is, what regulates gene expression? Until recently, scientists had no clue. Things changed in 1993 when a scientific paper announced the discovery of microRNAs – a class of tiny RNA molecules that are effectively the regulator of gene expression. The scientists did their experiment on roundworms but in the decade since their seminal work, more studies have revealed that microRNAs are not just confined to worms; they are present in all multicellular organisms including us. For their pioneering discovery of microRNA, two American geneticists – Victor Ambros and Gary Ruvkun – were awarded this year’s Nobel Prize in Physiology or Medicine. Professor Ambros, 70, works at the University of Massachusetts Medical School, and Professor Ruvkun, 72, is a professor at Harvard Medical School.

How MicroRNA Regulates Gene Expression

MicroRNA controls gene expression mainly by binding with messenger RNA (mRNA) in the cell cytoplasm. Instead of being translated quickly into a protein, the marked mRNA will be either destroyed and its components recycled, or it will be preserved and translated later. Here are the key steps:

1. A gene or genetic instruction is contained within our DNA.
2. Our cells make a copy called messenger RNA or simply mRNA.
3. Sometimes, microRNAs get in the way by binding to the mRNA. By doing so, the microRNA prevents the gene from being expressed in the cell.
4. At other times, the mRNA is “allowed” to his travel out of the cell’s nucleus impeded. There it instructs the cell’s protein-making factories to start making the specific protein.

In short, MicroRNAs act as a gateway to either prevent or facilitate gene expression, protein synthesis and ultimately cell production. If this process works normally, the body will produce the right level of proteins for healthy cell and tissue formation. On the other hand, abnormal regulation by microRNAs (i.e., too little or too much gene expression) can lead to cancers and other problems such as epilepsy and bone disorders. The discovery of microRNA not only sheds light on how our body produces the right kind and amount of cells but also paves the way for novel therapies for a range of devastating diseases.