When “Junk DNA” Is Not Really “Junk”!

MicroRNAs: The Discovery That Revolutionized Our Science

For decades, scientists have thought that there are certain parts in our human genome (the DNA) that can actually do nothing! This assumption was based on the fact that these pieces of DNA do not give rise to functional proteins. In 1953, when James Watson and Francis Crick discovered the structure of DNA, Crick formulated “The Central Dogma of Life” theory, which implies that “DNA is converted to an RNA message, RNA encodes into proteins, proteins are the acting molecules that simply make us”. So, a “non-protein-coding” piece is most probably useless or, as they termed it, a “Junk DNA”.

However, since living organisms are always struggling for survival, it is somehow weird and hard to believe that they would invest so much energy on producing Junk! After all, the “Junk DNA” theory might just be “Junk”!

Thanks to the “Worm”: The Historic Discovery

In the early 1990s, a team at Harvard University, Department of Cellular and Developmental Biology was studying the life cycle of a certain worm called “C. elegans”. They found that for this worm to progress from the larval stage to the next stage in her life cycle, a certain protein needs to be shut down, otherwise the cycle will not proceed. This “shutting down” effect was found to be completely dependent on the presence of a certain small RNA molecule, that was further given the name “lin 4 microRNA”. Surprisingly, this microRNA was a part of the genome that was always referred to as “Junk DNA”! Since then, hundreds of microRNAs have been identified in humans that were shown to play a significant role in regulating many of our vital biological processes.

The myth of “Junk DNA” has been totally reconsidered after the breakthrough discovery of microRNAs, being a huge part of the non-protein-coding molecules, and indeed, we owe a lot to the worm!

Small Size, but Big Job!

Although denoted as “micro”, those tiny molecules can really control our life in both health and disease. Now, scientists believe that over two-thirds of our human genome is regulated by microRNAs. The fact that those small regulatory molecules can shut other genes down implies that they are likely involved in almost every cellular process in our body. They can affect how our cells proliferate, communicate with each other, regenerate, and how they eventually die! MicroRNAs can also shape our body structure and control how it develops and responds to the environment. The notion that microRNAs can interfere with the process of protein generation, by degrading or shutting down protein expression, implicates that their role is as paramount as the role of protein themselves. So, it does not matter how small microRNAs are, wherever you go, you will find their signature around you!

A Two-Edged Weapon, yet They Can Be Refined!

We can look at microRNAs as small magical regulatory elements, yet it is important to understand that this regulation could be either positive or negative, depending on the nature of genes that they regulate. Nonetheless, the beauty of those small molecules lies in the fact that they can always be “manipulated” to the best of our health using certain genetic techniques! It is as simple as that a “good guy” microRNA can be augmented to shut down more unhealthy genes, while a “bad guy” microRNA can instead be suppressed to stop its negative regulation on the healthy genes! Therefore, a key approach in today’s research is to identify the behavior of one microRNA in the context of a specific tissue or disease. Understanding such mechanisms is half the way to modify the expression pattern of microRNAs in our bodies and to further use them as an effective therapeutic regimen.

A New Hope for Cancer Treatment

If we agree with the fact that microRNAs are involved in every cellular process in our body, we shall also agree upon their significant role in regulating cancer, because, at the end of the day, cancer is just a miss-regulation of these normal cellular process. Being a very smart disease, cancer has many pathways to rig us and to continue developing outside the control of our bodies. Here, comes the substantial role of microRNAs being able to “invert” whatever cancer can do. This is simply by suppressing the genes that cancer favors in each certain pathway! Again, according to the specific type of cancer, biologists can selectively augment those microRNAs that can interfere with cancer functions, leading to direct suppression of cancer progression. Indeed, the preliminary positive results that were shown in almost all cancer types after modifying the expression of specific microRNAs emphasizes the efficacy of those molecules as promising cancer therapeutic agents. The thing that made several pharmaceutical companies start developing new drugs that are mainly based on interfering with endogenous microRNAs expression.

And More…

Not only cancer, but microRNAs signature has also been implicated in the pathology of several diseases such as diabetes, atherosclerosis, heart failure, fibrosis, Schizophrenia, and Alzheimer's disease. Interestingly, new doors for limb regeneration have been opened after the discovery of microRNAs that are mainly responsible for fin regeneration in zebrafish, a common aquarium fish known by its ability to regrow fins after amputation. These and other discoveries in microRNAs biology are now adding new dimensions to microRNA therapeutics and pointing us to very promising therapeutic approaches. So, by now I guess you agree with me that non-protein-coding molecules can actually mean something and that they are not so “Junk DNA”, right?!