All human cells, from skin cells to nerve cells, contain the same DNA. However, they are all highly specialized cells, able to perform drastically different functions. Although all cells carry the same genetic material, they “specialize” through gene regulation. This process ensures that only the necessary genes are active in a cell, enabling it to express specific proteins. These proteins are produced via transcription, a process in which genetic information from DNA is carried by messenger RNA (mRNA) to ribosomes within the cell. The mRNA is then translated into the correct code to produce proteins - proteins originally coded for by the DNA. These proteins dictate the function of the cell. Yet these instructions can only be transcripted when the correct genes are “turned on” by gene regulation processes; if these processes go wrong, the cell will code for the wrong proteins, which can potentially lead to diseases like cancer and diabetes.

Ambros and Ruvkun made their groundbreaking discovery while researching the genes that control the timing of the activation of genetic processes. These genes determine whether cell types will develop along the proper timeline. In the 1980s, they were studying C. elegans, tiny roundworms approximately a millimeter in length, at the laboratory of 2002 Nobel Laureate Robert Horvitz; these tiny worms contained many of the specialized cell types found in larger, more complex organisms, making them the ideal test subjects for experiments studying how tissues developed in multicellular organisms. While studying two C. elegans worms with mutated forms of lin-4 and lin-14, two genes critical to timing gene activation, Ambros and Ruvkun found that unknown molecules were inhibiting the development of worms by delaying the activation of genetic programs. 

At first, this discovery did not gain any traction, as the lin-4 and lin-14 genes from the C. elegans did not have homologues (corresponding genes) in other organisms, including humans. However, in 2000, the second microRNA, let-7, was discovered, and this one was found in humans along with several other organisms. Let-7, similar to lin-4 and lin-14, also blocked the activity of its targeted gene. This subsequent finding led to the discovery of 100 more microRNA variations. It has since been determined that humans contain over 1,000 microRNAs that are responsible for many protein-producing genes. MicroRNAs can be used to identify types of tumors; they have also been linked to heart disease, neural disease, and other disorders. Trials have begun to investigate microRNA as a possible therapy for heart disease.