February 1, 2023

So-Called “Junk” DNA Is Essential, Plays a Key Role in Speciation

” Seven or 8 years back when we chose we desired to study satellite DNA, we had no plans to study development,” said Yamashita, who is likewise a teacher of biology at the Massachusetts Institute of Technology and a private investigator with the Howard Hughes Medical Institute. “This is one very enjoyable part of doing science: when you do not have a preconceived concept, and you just follow the lead till you bump into something totally unanticipated.”
The origin of species: DNA edition.
Scientists have actually known for many years that satellite DNA is highly variable in between types. “If you take a look at the chimpanzee genome and the human genome, the protein coding areas are, like, 98 percent, 99 percent similar,” she states. “But the scrap DNA part is really, really different.”.
” These are about the most quickly evolving sequences in the genome, however the previous viewpoint has been, Well, these are junk series, who cares if your scrap is different from mine?” stated Jagannathan.
However as they were investigating the value of satellite DNA for fertility and survival in pure types, Yamashita and Jagannathan had their very first tip that these repeated series may contribute in speciation.
When the scientists erased a protein called Prod that binds to a particular satellite DNA series in the fruit fly Drosophila melanogaster, the flies chromosomes scattered beyond the nucleus into small globs of cellular product called micronuclei, and the flies died. “But we understood at this point that this [piece of] satellite DNA that was bound by the Prod protein was entirely missing out on in the nearest family members of Drosophila melanogaster,” Jagannathan stated. “It totally doesnt exist. So thats an intriguing little problem.”.
If that piece of satellite DNA was necessary for survival in one species but missing from another, it might suggest that the two types of flies had evolved different satellite DNA series for the same role over time. And given that satellite DNA contributed in keeping all the chromosomes together, Yamashita and Jagannathan wondered whether these developed differences could be one reason various types are reproductively incompatible.
, the reality that satellite DNA is quite different in between species really hit like lightning,” Yamashita stated. “All of an unexpected, it ended up being a completely various investigation.”.
A tale of two fruit fly species.
To study how satellite DNA distinctions might underlie reproductive incompatibility, the researchers chose to concentrate on two branches of the fruit fly family tree: the timeless lab model Drosophila melanogaster, and its closest relative, Drosophila simulans. These 2 species diverged from each other 2 to 3 million years back.
Researchers can reproduce a Drosophila melanogaster female to a Drosophila simulans male, “but [the cross] produces extremely unhappy offspring,” Yamashita said. “Either theyre sterilized or they die.”.
Yamashita and Jagannathan reproduced the flies together, then studied the tissues of the offspring to see what was leading these “dissatisfied” hybrids to drop like flies. “The chromosomes were spread, and not encapsulated in a single nucleus.”.
Additionally, the researchers might develop a healthy hybrid fly by altering certain genes in the parent flies called “hybrid incompatibility genes,” which have been shown to localize to satellite DNA in the cells of pure species. Via these experiments, the researchers had the ability to show how these genes affect chromosomal packaging in hybrids, and determine the cellular phenotypes associated with them for the very first time. “I believe for me, that is probably the most vital part of this paper,” Jagannathan stated.
Taken together, these findings suggest that since satellite DNA alters fairly frequently, the proteins that bind the satellite DNA and keep chromosomes together need to progress to maintain, leading each types to establish their own “strategy” for working with the satellite DNA. When two organisms with different techniques interbreed, a clash happens, leading the chromosomes to spread beyond the nucleus.
In future studies, Yamashita and Jagannathan hope to put their model to the supreme test: if they can develop a protein that can bind the satellite DNA of two different species and hold the chromosomes together, they could in theory rescue a doomed hybrid, enabling it to endure and produce feasible offspring.
This feat of bioengineering is likely years off. “Right now its just a pure conceptual thing,” Yamashita said. “In doing this tinkering, theres probably a lot of specifics that will have to be solved.”.
For now, the researchers prepare to continue investigating the roles of satellite DNA in the cell, equipped with their brand-new understanding of the part it plays in speciation. “To me, the unexpected part of this paper is that our hypothesis was right,” Jagannathan said. “I mean, in retrospection, there are many ways things might have been irregular with what we hypothesized, so its type of incredible that weve sort of had the ability to chart a clear path from start to finish.”.
Reference:” Defective Satellite DNA Clustering into Chromocenters Underlies Hybrid Incompatibility in Drosophila” by Madhav Jagannathan and Yukiko M Yamashita, 24 July 2021, Molecular Biology and Evolution.DOI: 10.1093/ molbev/msab221.

Researchers have understood for years that satellite DNA is extremely variable in between types. When the scientists erased a protein called Prod that binds to a specific satellite DNA sequence in the fruit fly Drosophila melanogaster, the flies chromosomes scattered outside of the nucleus into small globs of cellular material called micronuclei, and the flies passed away., the reality that satellite DNA is rather different in between species truly hit like lightning,” Yamashita said. The researchers could create a healthy hybrid fly by altering particular genes in the moms and dad flies called “hybrid incompatibility genes,” which have been shown to localize to satellite DNA in the cells of pure species. For now, the researchers prepare to continue examining the functions of satellite DNA in the cell, equipped with their new understanding of the part it plays in speciation.

Credit: MIT
More than 10 percent of our genome is comprised of repeated, relatively ridiculous stretches of genetic product called satellite DNA that do not code for any proteins. In the past, some scientists have described this DNA as “genomic junk.”
Over a series of documents spanning a number of years, nevertheless, Whitehead Institute Member Yukiko Yamashita and coworkers have made the case that satellite DNA is not scrap, however rather has a necessary function in the cell: it works with cellular proteins to keep all of a cells specific chromosomes together in a single nucleus.
Now, in the most current installation of their work, released online July 24 in the journal Molecular Biology and Evolution, Yamashita and previous postdoctoral fellow Madhav Jagannathan, presently an assistant teacher at ETH Zurich, Switzerland, take these research studies a step further, proposing that the system of chromosomal company made possible by satellite DNA is one reason that organisms from different species can not produce feasible offspring.

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