More than 10% of our genome is made up of repetitive, thought-to-be-nonsense genetic sequences.
In a series of works over several years, a member of the instituteWhitehead Yukiko Yamashita and his colleagues have proven that so-called junk DNA is not as useless as it seems at first glance. In fact, it plays an important role in the cell: this DNA works with cellular proteins to keep all of the cell's individual chromosomes together in one nucleus.
During their work, the authors studied how thispart of the DNA affects the fertility and survival of species, then scientists had the first hint that these repetitive sequences could play a role in speciation.
To test this, the researchers removed the proteincalled Prod, which binds to a specific sequence of junk DNA in the fruit fly Drosophila melanogaster, causing their chromosomes to scatter outside the nucleus into tiny balls of cellular material and the insects die.
If this piece of "junk" DNA wasnecessary for the survival of one species, but was absent in the other, this could mean that the two species of flies over time developed different sequences for the same role. And since junk DNA played a role in keeping all chromosomes together, researchers wondered if these evolutionary differences could be one of the reasons different species are reproductively incompatible.
To understand how the differences in satellite DNAcould lead to reproductive incompatibility, the researchers decided to focus on two branches of the fruit fly family tree: the classic laboratory model of Drosophila melanogaster and its closest relative, Drosophila simulans. These two species diverged from each other about 2-3 million years ago.
Researchers can breed a female Drosophila melanogaster with a male Drosophila simulans, but as a result, the offspring are either sterile or die.
The authors bred flies and then studied the tissuesoffspring to understand why this is happening. When the authors looked at the hybrid tissues, they found that their phenotype was exactly the same as if someone had violated the "junk" DNA of a pure species. The chromosomes were scattered around rather than encapsulated in a single nucleus.
As a result, the authors concluded that “junk” DNA regularly mutates and literally sets the crossing strategy for different species.
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