Why a groundbreaking discovery about tiny RNA molecules may be helpful for humans and wildlife

The 2024 Nobel Prize in Physiology or Medicine was awarded to the scientists who uncovered the role of microRNAs. As the name suggests, microRNAs are tiny RNA molecules, and they’ve turned out to be far more important than anyone originally thought.

Discovered in the early 1990s, microRNAs were initially regarded as “junk”—small bits of RNA that seemed to serve no real purpose. But scientists were in for a surprise. First identified in the little roundworm Caenorhabditis elegans (a model organism widely used in research), it was soon found that these short RNA strands are powerful regulators. Over time, this discovery expanded beyond worms to reveal that microRNAs control key processes in virtually all living species—from growth and development to disease response.

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Small but mighty: controlling gene expression

These tiny RNA molecules—just 18 to 25 nucleotides (nt) long—control how genetic information is used to make proteins. They work by binding to much longer messenger RNAs (mRNAs), which are made up of thousands of nucleotides and carry genetic instructions from DNA to the cell’s protein-making machinery, essentially acting as a blueprint for proteins.

While microRNAs are still being explored as potential indicators of disease, they have shown promise in identifying cancers through blood tests.

You can think of mRNA as a text message with instructions for making proteins. Once the message is sent, it needs to be read and acted upon by the cell. MicroRNAs act like editors who review the message before it reaches its destination.

If a microRNA has a matching part, it ‘clings’ to the mRNA, preventing it from being read properly. In some cases, this leads to the mRNA being degraded entirely—like a message that’s never delivered. In other cases, the message is blocked or altered, stopping the protein from being made. In this way, microRNAs help control the flow of genetic information, determining which proteins should be produced and when.

MicroRNA can help control the protein-making machinery of cells by attaching to sections of mRNA, which makes proteins, and shutting down production. Graphic: Anne-Fleur Brand/NTNU SHOW MORE

Might help detect cancer

These tiny molecules have enormous implications for human health.

Over the past two decades, scientists have linked disruptions in microRNA function to a wide range of diseases, including cancer, heart disease, and neurological disorders. While microRNAs are still being explored as potential indicators of disease, they have shown promise in identifying cancers through blood tests.

Tumours often release specific microRNAs into the bloodstream, and researchers are investigating how changes in these molecules might help detect cancer or track its progression.

The discovery of microRNAs has opened up new possibilities in medicine, offering fresh approaches to diagnosing and treating diseases. For example, researchers are exploring ways to use microRNAs as therapeutic tools—either by boosting their activity to shut down harmful genes or by correcting microRNA dysfunction in certain diseases.

But what about wildlife?

As exciting as microRNA research is for human health, there’s another area where these tiny molecules are starting to make waves: wildlife research. And here’s why: thanks to their small size, microRNAs are surprisingly stable, especially for RNA.

RNA, particularly the long strands of mRNA that can be thousands of nucleotides long, is known to degrade quickly at room temperature. For instance, mRNA-based COVID vaccines had to be stored at ultra-low temperatures to prevent degradation because mRNA is highly sensitive to enzymes that break it down.

Thanks to their small size, microRNAs are much more stable than larger RNA molecules. This stability is particularly useful in wildlife research, where samples are often collected in the field under less-than-ideal conditions.

Unlike larger RNA molecules that degrade rapidly if not immediately frozen, microRNAs can survive for longer periods, even when field conditions or transportation delays prevent immediate freezing.

MicroRNA discovery in wild birds

We recently looked for microRNAs in blood samples from wild ruddy turnstones, a bird species aptly named for its habit of turning over stones to find food.

These birds are fascinating not only for their incredible globe-spanning migrations but also for their seemingly special role in influenza virus dynamics.

While it’s still not fully understood, their long-distance migrations connect distant ecosystems, and they are suspected to carry and potentially spread influenza viruses along the way.

From just 30 microliters of blood (roughly a tenth of a teaspoon!), we set out to extract and analyse the microRNAs.

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A “hairpin” helps with identification

As mentioned earlier, in wildlife research, it’s often impossible to freeze samples immediately due to logistical challenges. In this case, the blood samples were kept in a fridge for up to 10 days. By then, most of the longer mRNA had likely broken down into smaller fragments. So, how do we distinguish true microRNAs from these fragmented pieces of mRNA?

Thankfully, microRNAs have some unique characteristics that help us tell them apart from the broken fragments of mRNA. One key feature is how they are made. Like mRNA, microRNAs are created from DNA, but the process is different.

The precursors to microRNAs don’t just form long, straight strands; instead, they fold into shapes called “hairpins” – strands of RNA that fold back onto themselves. However, not all RNA can fold this way. For the RNA to form a hairpin, the building blocks (nucleotides) need to fit together in a specific way, much like a lock and key.

The precursors to microRNAs don’t just form long, straight strands; instead, they fold into shapes called “hairpins” – strands of RNA that fold back onto themselves. To make the mature microRNA, the hairpin gets cut, producing three parts: the mature microRNA, the part of the hairpin that folded onto it, and the loop that connects the two arms of the hairpin. This characteristic helps researchers figure out if the little fragments they find in blood samples is from microRNA, not from fragmented mRNA. Illustration: Anne-Fleur Brand/NTNU SHOW MORE

This special folding helps us identify real microRNAs. When we find a small piece of RNA in blood samples, we first figure out where it came from in the DNA. Then, we look nearby in the DNA to see if there’s a match that would allow the RNA to fold into a hairpin shape.

If it can form that loop, it’s a good first sign that we may be looking at a true microRNA, rather than a broken-off piece of mRNA. To make the mature microRNA, the hairpin gets cut, producing three parts: the mature microRNA, the part of the hairpin that folded onto it, and the loop that connects the two arms of the hairpin.

If we can find the two other parts produced when the hairpin is cut, besides the mature microRNA, in the blood, it’s an even stronger indicator that we’re dealing with a true microRNA.

Some microRNA unique to birds

Using this approach, we discovered 163 different microRNAs in ruddy turnstone blood. Many microRNAs are very similar across different species, meaning the same microRNA sequence found in a ruddy turnstone might also be found in our own blood, or in simpler organisms such as a little roundworm.

This similarity shows how important microRNAs are for basic biological functions. However, some microRNAs are unique to certain groups of animals or even specific species. We discovered two new microRNAs in the blood of ruddy turnstones that seem to be unique to birds. These microRNAs weren’t found in the genomes of other animals, like mammals or reptiles.

Ruddy turnstones. Photo: Louis Westgeest/NTNU SHOW MORE

It has been suggested that microRNAs could revolutionize species identification, offering several advantages over traditional methods like DNA barcoding. Since many microRNAs are conserved across closely related species, they allow for identification even when little is known about a species. This is particularly useful when studying rare or newly discovered species, where traditional genetic markers may not be available.

Beyond identification, microRNAs also play a key role in regulating immune responses and disease susceptibility. This could help explain the special role ruddy turnstones may have in influenza dynamics, as microRNAs influence how species interact with pathogens like the flu virus.

In our study, we found that male and female birds, as well as birds of different ages, show different microRNA profiles in their blood when infected with influenza. This suggests that sex and age affect how birds respond to the virus, and these differences could offer valuable insights into how wild birds’ immune systems react to infection.

There are many fascinating possibilities on the horizon, but further research is needed to fully understand how these microRNA profiles influence disease dynamics and to explore their potential as tools for monitoring wildlife health—stay tuned!

Reference: Brand, A.-F., Waugh, C.A., Fernandes, J.M.O., Klaassen, M., Wille, M., Jaspers, V.L.B. and Andreassen, R., 2024. Circulating miRNAome of avian influenza-infected ruddy turnstones (Arenaria interpres). Journal of Avian Biology, e03404