At 5:30 p.m. Beijing time on October 7, the first Nobel Prize of the year was announced.
The 2024 Nobel Prize in Physiology or Medicine was awarded to United States biologists Victor Ambros · Gary ·Ruvkun for their discovery of microRNAs and the role they play in the regulation of post-transcriptional genes.
MicroRNAs are a class of very small RNA molecules in cells, but they perform very important molecular biological functions.
2024 Nobel Laureates in Physiology or Medicine Victor Ambros (left) and Gary Ruvkun (right) (Image source: Royal Sweden Academy of Sciences)
Next, the author will take you to learn a little bit of background knowledge, and then explain to you why this is a very important discovery.
What is Gene Regulation?
The information stored in our chromosomes, known as DNA sequence information, is the instruction manual of all the cells in our body. Every cell contains the same DNA, but each cell is very different.
For example, at the time of writing, my brain cells are firing frantically to communicate with each other, but the cells in my stomach are frantically making digestive enzymes to digest the toast I just ate. How do they take the same instruction manual and do different things? For another example, in the process of fetal development, the circulatory system, nervous system, etc. all develop and mature in a certain chronological order, how do all the cells do different things at different times?
The answer to these questions lies in gene regulation.
Gene regulation allows each cell to carefully select certain genes from DNA to express them, resulting in the production of specific mRNAs, which are then translated into proteins to complete specific biological functions. This ensures that only the right set of genes is active in each cell type, which is the basis of the cellular division of labor.
If there is a problem with gene regulation, it can lead to various diseases, such as neurological diseases, diabetes, and cancer. As a result, people have been trying to figure out the mechanisms of gene regulation for decades.
Gene regulation allows different cells to obtain different gene expressions from the same genome (Image source: Royal Sweden Academy of Sciences)
Unusual little bugs, unusual mutants
In the late 80s of the 20th century, Ambrus and Rubken were postdoctoral researchers in Robert ·Horvitz's lab. Incidentally, Horwitz was the Nobel laureate in 2002.
The two postdocs wanted to study the mechanism of gene regulation, but the human body was too complicated, so they chose a small creature with just over 1,000 cells, Caenorhabditis elegans.
Although the structure of this insect is simple, it has all the nerves and muscles that humans have, so it is particularly suitable for use as a model organism.
In earlier studies, it was already known that there are two special mutation types in nematodes, called lin-4 and lin-14. The peculiarity of these two mutation types is that they develop almost backwards.
For example, LIN-4 is large, while LIN-14 is small; Lin-4 will accumulate many egg cells in the body, while Lin-14 will have no egg cells at all. This shows that there must be some special mutual confrontation between these two mutation types and their mutated genes.
The development of lin-4 and lin-14 mutations in nematodes showed completely opposite trends (Image source: Royal Sweden Academy of Sciences)
Evidence is emerging
After their postdoctoral studies in the Horwitz lab, Ambrus and Rufken began their own research, conducting a series of follow-up studies on the mutated genes of lin-4 and lin-14, respectively.
Further research has shown that the lin-4 gene is only a few dozen bases long, and it is impossible to encode a useful protein, which is even more puzzling.
So the two had to resort to the most primitive method. If you really want to study a certain gene, then the most direct and powerful way is to directly analyze the sequence of this gene. So they started sequencing the two mutated genes separately.
Sequencing is so easy nowadays that even high school students can operate the sequencer by pressing a button on the manual. But in the eighties and nineties of the last century, people did not have mature sequencing methods. After the unremitting efforts of Ambrus and Rufken for a long time, the sequences of these two genes were finally obtained by them.
On the evening of June 11, 1992, the two exchanged sequence data for the Lin-4 and Lin-14 genes. Almost simultaneously, the two noted a clear complementarity between the two genes. The genes in RNA are coded by the four letters of AUCG, A is always paired with U, and C is always paired with G. As can be seen in the figure below, there is a relatively long complementary pairing region between LIN-14 and LIN-4, so the duo speculated that it is this complementary pairing that allows them to resist each other.
Further experiments have verified this conjecture.
Although lin-4 encodes only a small RNA, it complements the RNA of lin-14 (Image source: Royal Sweden Academy of Sciences)
A surprising discovery that was given a cold shoulder
lin-4 does not encode a piece of mRNA and then translate into a protein to perform biological functions, as normal genes do. It only encodes a small, 22-letter piece of RNA, so it is also called microRNA (called small RNA in Chinese).
The only function of this microRNA is to identify an mRNA that looks very similar to it in the cell, and this mRNA comes from the lin-14 gene.
Once the mRNA is found through complementary pairing, the microRNA produced by lin-4 will call a group of brothers to directly kill the mRNA from the lin-14 gene, thus achieving the purpose of inhibiting the lin-14 gene.
The results of this experiment overturned the textbook dogma that all genes must eventually be translated into proteins in order to function, and when it was published, it was met with a "deafening silence" in the scientific community.
No one is interested in this study, thinking that this is just an adaptive adjustment made by a small creature such as a nematode in order to adapt to the living environment, and today it is at most just a Weibo joke, and it can't even be on the Home, let alone on the hot search.
But Ambrus and Rufken insist that their findings are enough to shake up the scientific community. So the two continued to study the microRNAs they had discovered.
In 2000, Rufken's team reported another microRNA, called let-7. Unlike lin-4, let-7 is present in almost all animals, suggesting that the microRNA mechanism is not unique to nematodes, but a regulatory mechanism that is common to all animals.
Later, it was discovered that microRNAs were also found in plants. Later, with the development of sequencing technology, it was discovered that many organisms have thousands of microRNAs in their genomes.
In this way, it is well deserved to be awarded the Nobel Prize for discovering a law that applies almost everywhere in the biological world.
Rufken discovered that there is a microRNA called let-7 in almost all animals (Image source: Royal Sweden Academy of Sciences)
Leading the way
Research on microRNAs has flourished in the scientific community, and it has been discovered that many important gene regulation is mediated by it.
For example, we found from genetic studies that human cells and tissues cannot develop properly without microRNAs. Aberrant regulation of microRNAs can lead to cancer. In addition, mutations in the microRNA gene have been found in humans, leading to diseases such as congenital hearing loss, eye and bone diseases, etc.
The expression of many genes must be maintained at a precise magnitude, in a state of "more is stronger, less is weak". The regulation of genes by microRNA can achieve this precise regulation, avoiding the extensive regulation of "adding water to more surfaces, and adding more water to surfaces".
In this sense, it is precisely because of the precise and delicate regulation of gene expression by microRNAs that the complication of biological genes and the further complication of organisms are possible. For example, if you don't master the various precise methods of dough mixing, the mainland will not produce thousands of different kinds of pasta.
Assertive persistence in experimental phenomena, diligence in the scientific process, and a positive attitude in the face of skepticism are the three cornerstones of Ambrus and Rufken's achievement. This is not only a good quality that every researcher should maintain, but also a successful method that should be remembered by each of us.
Next, the author will also write another article to provide readers with an in-depth interpretation of the research status of microRNA and its application in biology and medicine, so stay tuned!
Author: Mu Xin
bibliography
[1] Rosalind C. Lee, Rhonda L. Feinbaum and Victor Ambros (1993) “The C. elegans heterochronic gene lin-4 encodes small RNAs with antisense complementarity to lin-14”. Cell, 75(5), pp. 843–854.
[2] Bruce Wightman, Ilho Ha, and Gary Ruvkun (1993) “Posttranscriptional regulation of the heterochronic gene lin-14 by lin-4 mediates temporal pattern formation in C. elegans”. Cell, 75(5), pp. 855–862.
[3] Amy E. Pasquinelli, Brenda J. Reinhart, Frank Slack, Mark Q. Martindale, Mitzi I. Kurodak, Betsy Maller, David C. Hayward, Eldon E. Ball, Bernard Degnan, Peter Müller, Jürg Spring, Ashok Srinivasan, Mark Fishman, John Finnerty, Joseph Corbo, Michael Levine, Patrick Leahy, Eric Davidson & Gary Ruvkun (2000) “Conservation of the sequence and temporal expression of let-7 heterochronic regulatory RNA”. Nature, 408(6808), pp. 86–89.