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A pair of twin brothers, one stayed on Earth and one lived on the International Space Station for 340 days. In the process, the scientists tested a number of physiological indicators of the brothers, hoping to understand how long space flight will affect people.
Last Friday, NASA’s long-known “space twins” experiment finally published its results in the journal Science. A new round of the title party followed: “New discovery! NASA astronauts stayed in space for 340 days, and the DNA was permanently mutated.”
In these eye-catching reports, the most striking sentence is that after astronaut Scott Kelly has experienced nearly a year of space life and returned to Earth for 6 months, his “8.7% change in the gene is still present Not restored”.
According to this sentence, either 8.7% of Scott’s genes have undergone unrecovered changes (if so, he may be expelled from the population, knowing that humans and chimpanzees have the same genetic code of 98.8% ), or there have been many changes in the genes, of which 8.7% did not recover. But no matter what kind, this is the conclusion that the original paper does not support.
The 8.7% data cannot be directly found in the original paper. Moreover, only the results of RNA sequencing and DNA methylation sequencing are reported in the paper. Through these results, it should be impossible to know what proportion of genes in the entire genome have been mutated. Although the paper mentions analysis of DNA damage, chromosomal abnormalities, DNA methylation, and telomere length in peripheral blood cells, these results have nothing to do with “genetic changes of 8.7%.”
In fact, the term “gene has changed by 8.7%” is probably from a misunderstanding of the “gene expression” part of the paper. In this study, the researchers analyzed changes in gene expression of astronauts’ peripheral blood cells. They found that there are indeed many genes whose expressions have become different in space. 91.3% of these changes were restored within 6 months of Scott’s return to Earth-the rest of them have not been restored. Is 8.7%.
In other words, some reports made the same mistake as they did a year ago: confusing changes in gene expression with changes in the gene itself.
In 2018, there had been media misreading NASA press releases, describing Scott Kelly’s “gene expression change” as a “gene change” problem. The following is a description of the interpretation of the article:
Humans have about 20,000 genes distributed among 23 pairs of chromosomes. Every cell in your body has a full set of these genes. Nevertheless, our cells are different-for example, nerve cells are not similar to gastric parietal cells. Their functions are also quite different: one transmits electrical and chemical signals in the nervous system, and the other releases stomach acid to help humans digest food.
These functional differences are not due to differences in DNA, but because of their different expressions. Complex chemical pathways and feedback loops can turn certain genes on or off. Each gene encodes a protein (a building block in the human body), and according to the open and closed state of the gene, different structures are constructed and different reactions are generated.
Subtle changes in gene expression will not turn your neurons into blood cells, but it can change the working state of the cells. Changes in gene expression can lead to cancerous cells, or lead to a series of events leading to increased prevalence of heart disease.
There are several different ways to determine changes in gene expression. One is to look at the level of RNA. This signaling molecule helps the gene execute and create the protein it encodes. Another method is to check the methylation level. Methylation means that the DNA molecule is labeled with a chemical substance. As Nature explains, this chemical can prevent a part of the gene from being turned on.
The results of the study did show a series of changes in the gene expression of astronaut cells. These gene expressions affect physiological processes such as immunity and metabolism.
What does this mean? In fact, researchers are still not very clear. In a related report in the Atlantic Monthly, the geneticist Christopher Mason, who participated in the study, said: “We don’t yet know whether these changes are good or bad. This may just be a response from the body, but these genes Was disturbed, so we wanted to see why, and follow them to see how long it will last.”
In fact, the whole paper is in this style: it describes a wealth of detailed information, but it is not enough to draw any firm conclusions. The “Twin Experiment” is more like the beginning of an exploration, and the impact of a long space flight on people still needs follow-up research to determine.
Author: Window knock rain
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