Why do humans have so few genes?

When leading biologists around the world are trying to explain the human genome in the late 1990s, they try to estimate the number of genes contained in the 3 billion base pairs that make up our genome. And so many predictions appear. According to the classical speculation that existed about a decade ago, humans have about 100,000 genes that conduct countless reactions in the cell that make up the biological function of the body. But now it actually turns out that we have only about 25,000 genes, nearly equal to the number of genes of the species, which are smaller than Arabidopsis and only slightly larger than the round worm Caenorhabditis elegans.

This surprise reinforces a new perception that is forming among geneticists: our genome and some other mammals are more flexible and complex than previously thought. Even the most basic doctrine in the genetics of a gene / protein has to make way for a more accurate and universal theory: many genes that each gene can produce more than one protein. Even when looking at the problems of how, where and when genes are expressed, it is found that the process of controlling gene expression is not only encapsulated in foreign elements such as proteins. conditioning, even the genome itself controls it through non-coding DNA regions or structural and chemical changes of the genome itself. So one of the biggest challenges of modern biologists today is to show how all these factors work together to create a play called 'gene expression'.

Graph of relative number of genes in humans (Photo: sciencemag)

To explain why the human genome is able to achieve amazing levels of complexity with a small number of genes, it is thought that the 'differential coupling' phenomenon plays the most important role. The human genome contains both regions: the encoded DNA region - called exon - and the non-coding DNA region . In many different genes, the combination of different exons can take place at different times and each combination produces different proteins. In fact, at the beginning of the discovery of the different pairing process, biologists thought this was an 'anomalous phenomenon' during the transcription process, but until now researchers have agreed. conclude that this phenomenon occurs in the feces half - some even claim that in most - our genes. Finding a different pairing mechanism helps explain how only a modest number of genes can produce hundreds of thousands of different proteins. However, what is considered a mystery is still waiting for the answer to how the transcription machine determines which part of the gene will be read at a certain point in time?

In addition to the different coupling mechanism that researchers use to explain the phenomenon of one gene / multiple proteins, several other mechanisms are also concerned. Accordingly, the researchers noted an interesting point that in order for the gene to function well at a point in time, some space it needs hundreds of assistants to support the assigned task. . Participating assistants include proteins that switch off or open a gene indirectly by, for example, adding methyl or acetyl groups to DNA. Other protein groups interact with genes more directly as a group of transcription factors: they land and occupy positions near the genes that they will participate in. As with different coupling mechanisms, different transcriptional regulatory factors can be attached

RNA molecule (Photo: psc.edu)

Different gathering points to control gene expression in a subtle way. Here another challenge is that biologists have to show how proteins involved in regulation, whether directly or indirectly, can coordinate smoothly in a complex system and similarity. Interrelated between regulatory proteins with the differential coupling mechanism mentioned above .

In another approach, in the past decade, researchers have been really fascinated by the key role of sperm and RNA proteins in regulating gene expression. Sperm proteins are the basic component for packaging and compressing DNA in the cell nucleus as well as helping chromosomes to remain rigid. In fact, just a slight change in configuration in a certain region, the sperm can open the door to allow one or more genes in that region to be transcribed.

Gene, in addition to coding for proteins, also creates RNA. Small-sized RNA molecules, sometimes below 30 bases, can now be confirmed to have a similar role to other gene regulators. Many biologists, who previously focused on tracking information RNA molecules and large-sized RNA molecules, have now turned their attention to their smaller siblings, including microRNAs, RNAs. small in the core. At least now, it has been discovered that small-size RNAs play a key role in determining the fate of cells during the development of organisms , but the mechanism is not well understood.

By the beginning of the 21st century, researchers actually took great strides in understanding the above mentioned biological mechanisms. In addition to the traditional methods still in effect, biologists also use information from the genomes of organisms that are located on different branches on the evolutionary tree to conduct comparisons and analyzes. extensive. From those analyzes, researchers gradually revealed how these mechanisms, such as the different pairing mechanisms, can evolve, as well as what areas of the genome they show acts as a conditioning area. From there, returning can help us understand how these areas perform their functions. In addition to experimenting on classical research subjects such as mice, such as adding or reducing areas of regulating and modifying RNA, it is possible to say that computer models have been helping researchers a lot. However, the central question that has not been answered so far: How did all the biological properties of the genetic apparatus blend together to create a miraculous product ie the whole body? Can we?

Tran Hoang Dung