The magic of microRNA
From regulating genes to aiding disease diagnosis, microRNAs’ outsized impact certainly belies their tiny proportions.
At the dawn of the 21st century, experts widely believed that humans had over 100,000 genes, which are parts of the DNA that encode proteins. It turns out that the actual number was much lower. After the completion of the Human Genome Project, scientists finally arrived at the figure of around 20,000 protein-coding genes, which comprise roughly 1 percent of the human genome.
The remaining 99 percent is composed of non-coding DNA. Once regarded as ‘junk,’ these stretches of DNA in fact have important biological functions. Some non-coding DNA, for instance, is transcribed into non-coding RNA (ncRNA) like transfer and ribosomal RNA—both of which are integral for protein translation. In this feature, we shine a spotlight on microRNA (miRNA), a small, but mighty type of ncRNA that powers MiRXES’ diagnostic products.
Small molecules, big impact
As hinted by its name, miRNAs are small RNA molecules around 22 nucleotides in length. By binding to and degrading RNA transcripts of protein-coding genes, miRNAs play a key role in gene regulation. This allows miRNA to silence gene expression where needed, making these molecules critical in maintaining regular biological processes. True enough, abnormal levels of miRNA have been associated with cancer and other diseases.
Though miRNA is typically found inside the cell, they’ve also been detected in bodily fluids like blood and saliva. Consequently, with a simple prick, clinicians can not only diagnose a patient, but also predict the disease’s progression and even the potential for recurrence. And that’s not all—miRNA profiles can also reveal an individual’s likelihood to develop a disease and predict drug response.
Recognizing the power of miRNA as a biomarker, MiRXES has built up its pipeline of miRNA-based diagnostic tests. In 2019, we launched GASTROclear, the world’s first blood test for the early detection of gastric cancer. Blood tests for lung, breast, colorectal, ovarian and liver cancer are also in the works.
Unlocking the mysteries of miRNA
Through the years, miRNA has proven difficult to detect due to its small size and low abundance. There are three methods commonly used in detecting and quantifying miRNA. The first relies on next-generation sequencing (NGS), which generates sequence information for all miRNAs present in a sample. While this makes NGS useful for discovering novel miRNA variants, the technique is costly and requires large amounts of input material. Furthermore, NGS cannot accurately measure miRNA levels.
Another technique is the microarray, which compares changes in miRNA expression. Microarrays rely on the binding of miRNA to fluorescent probes, with the resulting optical signal indicating the relative quantity of DNA. The brighter the signal, the more there is of a specific miRNA. Like NGS, however, microarrays are not quantitative, making them sometimes unable to detect very low levels of miRNA.
Unlike the two previous methods, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) has the ability to quantify the amount of miRNA in a given sample. MiRXES’ miRNA-based diagnostic products rely on RT-qPCR, albeit with a unique twist that makes our technology far more sensitive than the rest.
As easy as one, two, three (primers)
MiRXES’ patented RT-qPCR technology relies on the three-primer approach. The first kind of primer comes into play during the initial step of RT-qPCR, called reverse transcription. In this step, the enzyme reverse transcriptase converts miRNA into complementary sequences of DNA. This is made possible by using conformation-restricted primers designed specifically for each miRNA. These primers are distinguished by their stem loop structures, which prevent the primers from detaching easily once it binds to the miRNA.
After reverse transcription, the resulting DNA is amplified with the help of forward and reverse primers that attach on either side of the sequence, further ensuring specificity. With each cycle of PCR, the amount of DNA in the sample exponentially multiplies until it reaches a detectable level.
Finally, to quantify the DNA (and by extension, the target miRNA), PCR progress is tracked by the machine in real-time using dyes that nestle in between the DNA bases. As each dye corresponds to a distinct sequence, multiple miRNA can be detected and quantified even in a single set-up. Collectively, these three primers guarantee the sensitive, specific and robust detection of miRNA in biological samples.
Adopted globally for discovery and diagnostics
To facilitate the adoption of our game-changing technology by researchers in academia, the National University of Singapore (NUS) ncRNA core facility was set up in partnership with the NUS Yong Loo Lin School of Medicine. Now in its second year, the facility is an early-phase discovery center that encourages industry-academic collaboration. We have since established similar partner ncRNA core facilities at Beth Israel Deaconess Medical Center (BIDMC) and other top academic institutes worldwide.
Once considered as genetic junk, miRNA has since transformed into a diagnostic mainstay thanks to MiRXES. Now, that is the magic of miRNA.