Birds such as orioles, canaries, willow warblers, and larks all belong to the passerine order, and this family was once inconspicuous in the large family of birds. 22.4 million years ago, a mysterious force led to the explosion of the bird family, and today there are more than 6,600 species of passerinees, accounting for about 60% of the total number of bird species.
On April 12, Beijing time, mainland scientists published a study on the impact of ancient viruses on the evolution of bird species in the international academic journal Nature Communications -- ancient viruses were once inserted into bird DNA and proliferated in bird hosts with the outbreak of passerines, and birds can not only efficiently remove these proliferating viral DNA, but also may use the residual virus source sequence to regulate their own gene expression.
Ancient viruses may help diversify bird species
In the long process of evolution, the virus and the host are both confrontational and cooperative, which has a profound impact on the host. RNA viral sequences that can be integrated into the host genome and have transcriptional activity and expand in the host genome are called endogenous retroviruses (ERVs). When retrovirus-infected host cells are germ cells, endogenous retroviruses can spread vertically between generations. For example, in the human genome, the self-protein coding sequence accounts for only about 2%, but the endogenous retroviral sequence (ERVs) accounts for as much as 8%, and recent studies have found that ERVs play an important regulatory role in cancer, aging, cell differentiation and other important biological processes, and have a profound impact on human disease and health.
On April 12, 2024, Feng Shaohong's team from the Center for Life Evolution Research of Zhejiang University and the Liangzhu Laboratory published research results related to the evolution of transposable elements derived from ancient viruses in the bird genome. Based on the data of the second phase of the "10,000 Bird Genome Project", this study systematically studied the endogenous virus sequences in the bird genome, analyzed the potential reasons why the bird genome as a whole has fewer endogenous virus sequences than other vertebrates, and found that birds have a higher level of evolutionary pressure to clear the expanding virus sequence.
Chen Guangji, the first author of the paper and a doctoral student at the University of Chinese Academy of Sciences, told Modern Express: "Passerine birds underwent a rapid radiation evolution event about 22.4 million years ago, which laid the pattern of contemporary species diversity. We found that ancient endogenous retroviruses may be involved in the formation of species diversity in passerine birds. ”
Ancient viral sequences may still contribute to the diversity of birds today
"In the long evolutionary process, there is a class of endogenous retrovirus K sequence elements that are widely present in the genome of passerine birds, and the more recently produced species, the more copies of such sequences," Feng Shaohong, corresponding author of the paper, further explained by researcher Feng Shaohong of the Liangzhu Laboratory of the Center for Life Evolution Research of Zhejiang University. They are inserted at different locations in the genome of passerine birds, and a large number of them are presented as interspecies commonalities and some species-specific phenomena, which means that they continue to affect the genome pattern of the host during the species differentiation events of these birds. ”
In the long evolutionary history, the explosive invasion of the host genome by endogenous retrovirus K (ERVK) occurred not only in passerine birds, but also in mammals rodents and primates. The co-outbreak of ERVK in multiple taxa may suggest that the ancient virus sequences of ERVK may have been widely distributed across the paleocontinent and frequently integrated into these host genomes during the Paleogene-Neogene boundary (about 22.4 million years ago).
Despite experiencing similar explosive expansion events, ERVK has taken very different evolutionary paths in the genomes of mammals and birds. In mammals, especially humans, HERV-K still retains the ability to encode viral proteins and form viral particles. These granules are involved in several cellular processes during host embryonic development and are associated with cellular senescence.
In the evolutionary process of birds, they may face the pressure of selection to eliminate endogenous retroviruses, and most of them no longer have complete viral gene functions in the bird genome, but they bring genetic raw materials for the regulatory function of the bird genome. For example, the research team found that ITGA2, which is potentially regulated by ERVK Solo-LTRs of an ancient virus, was more expressed in brain regions upstream of songsong control by songbirds.
The results show that retrovirus K derived from ancient viral sequences is still active in the genome of passerine birds, and these sequences continue to change the genome structure of passerine birds and affect the composition of genetic diversity of birds. Feng Shaohong said, "This discovery not only enriches people's understanding of the role of ancient virus sequences in the evolution of bird species, but also provides an example of how ancient virus sequences regulate host gene function and thus affect host evolution." ”
Modern Express/Hyundai+ reporter is Zhong Yin