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A new study has found that genetic “dark matter” may be behind the emergence of new species.
These long, repetitive stretches of the genome can eventually prevent incompatible animals from mating by mixing up the chromosomes in their hybrid offspring. If animals from different populations are unable to mate, they will diverge over time, leading to reproduction.
For example, only 1% of the three billion letters, or nucleotides, of the human genome make proteins that determine traits such as eye color and size. Other DNA segments can tell the body how many copies of a protein to make, or turn genes on or off in different tissues, among other functions.
However, about 10% of the human genome is made up of long, repeating portions of satellite DNA, which for many years scientists did not think they were doing, study co-author Madhav Jaganathan said, currently Assistant Professor at ETH Zurich. Institute of Biochemistry in Switzerland.
“Satellite DNA replication has been extremely abundant in species and has been seen widely in eukaryotes, or life forms with cell nuclei,” Jaganathan told Live Science in an email. Despite this, it was widely dismissed as junk. It contains DNA. “
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However, in a 2018 study, Jaganathan, then at MIT, and his former postdoctoral advisor, biologist Yukiko Yamashita, also at MIT, found that some of this DNA serves a vital purpose: it regulates DNA in the body. cell nucleus. This study found that certain proteins pick up DNA molecules and organize them into dense bundles of chromosomes. They found that satellite DNA tells these proteins how to assemble and organize chromosomes.
And in the latest study, published July 24 in the journal Molecular Biology and Evolution, Jaganathan and Yamashita find another role for satellite DNA: driving species. The team was studying fertility in Drosophila melanogaster.
When researchers removed the gene for a protein called prod, which binds to satellite DNA to make chromosomes, the fly’s chromosomes spread out of the nucleus. Without the ability to properly organize chromosomes, the flies died.
It was fascinating, Jagannathan said, because the deleted protein is unique to D. melanogaster. This means that these fast-evolving satellite DNA sequences must also contain fast-evolving proteins associated with them.
To test this idea, Jaganathan bred a female D. melanogaster with males of a different species, Drosophila simulans. As expected, hybrids did not live long. When the researchers looked at the cells of the flies, they saw malformed nuclei with DNA scattered throughout the cells, just as they did when they deleted the prod protein in previous experiments.
Does this mean satellite DNA can drive a species? The team suspects that if satellite DNA evolves rapidly and two creatures make different proteins associated with satellite DNA, they will not produce healthy offspring. Since the proteins associated with the chromocenter and satellite DNA segments evolve differently in separate groups or species, this conflict can arise quite quickly.
To test this hypothesis, they mutated DNA binding satellite genes which led to incompatibility in both parents. And when they rewrote the fly genomes to match, they produced healthy hybrids.
Jaganathan suspects that such differences in satellite DNA could be an important factor in the evolution of new species. He hopes that further research will test their hybrid incompatibility model with other species.
Ultimately, this research could allow scientists to save ‘stricken’ hybrids or hybrids that do not survive long after birth. This could pave the way for the use of crossbreeding as a way to save critically endangered species, such as the northern white rhino, on which only females live.
Source: Sciences en direct
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