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What are retrotransposons, segments of DNA?
I retrotransposons they are segments of DNA that are approximately 7,000 letters long. These are copied and pasted in different parts of the genome of plants and animals.
In terms of their activity and function, retrotransposons not only play a role in rewriting DNA, but also in regulating how the cell uses its genes.
How Retrotransposons use the cellular machine
Similar to retroviruses (such as the HIV virus), researchers have discovered that retrotransposons can literally borrow the cell’s machinery to achieve their developmental goals.
In a new work published online in the magazine Naturea Duke University team has determined that retrotransposons hijack a poorly understood part of the function of DNA repair of the cell. Then, they tend to close into a ring-like shape and then create a corresponding double strand.
The discovery overturns previous knowledge that these rings were just a useless by-product of bad gene copying. While instead the new discoveries could also provide new information on cancer, viral infections e immune responses.
The study was supported and funded by the National Cancer Institute, the National Institutes of Health and the Pew Biomedical Scholars Program.
Retrotransposons and cancer: a possible connection?
There is much research suggesting that these DNA loops outside the chromosomes are somehow involved in the development and progression of cancer. This finding is also supported by the fact that they are known to harbor oncogenes within their DNA sequences and these influence tumor development.
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Retrotransposons and HIV: a common link
Even the retrovirus HIVwhich causes theAIDSform Circular DNA. And again like retroviruses, it has been seen that retrotransposons can use the cellular machine.
Zhao Zhang is an assistant professor of pharmacology and cancer biology and a Duke Science & Technology scholar. He consulted a thick textbook on retroviruses for this study. And the books say that the loop sequences are “created by recombining the two ends of linear DNA, and are just a dead end, a byproduct of failed replication.”
Duke University Research: A New Perspective
In previous work with fruit fly eggs, Zhang’s team had established that inherited retrotransposons use the cells that support the egg as factories to produce many copies of themselves. Copies that are then distributed throughout the genome in the fly’s developing egg. This model system has allowed researchers to expand knowledge and learn more about retrotransposons.
In the latest work, the researchers found that most of the newly added retrotransposons were in this circular shape, rather than being integrated into the host genome. Then, they ran others and knocked out the cell’s DNA repair machinery one by one to figure out how and where these loops formed.
Thus, it has been seen that there is a little-studied DNA repair mechanism. It is a process of alternative DNA repair, also called all-EJ, which repairs double-strand breaks. The retrotransposon sequences were using this part of the host’s repair machinery to stitch the ends of their single-stranded DNA and its DNA synthase together to create a matching double-strand.
The researchers confirmed that this is also the process inside human cells.
Thus, retrotransposons do not exist by chance. They actually use and hijack the cell’s machinery a bit to develop, just like viruses do.
The role of retrotransposons in evolution
Based on what is known so far, retrotransposons are thought to also regulate the expression of genes and how a cell uses them. It is these genome segments that are thought to underlie much of the variation and innovation in the genes that driveevolution. Furthermore, both parents pass on these portions of DNA to their children.
Conclusions: the future of retrotransposon research
The finding actually upends the textbook model, says scholar Zhang. The recombination event proposed by the textbook is not important for forming rings, as this process is driven by the alt-EJ path.
Zhang’s lab is currently trying to test whether circular DNA could be an intermediate for making new insertions into the genome. She also investigates whether circular DNA can be sensed by our immune system to trigger an immune response.
As for retroviruses and retrotransposons, circular DNA is thought to be only a minor occurrence, but this study instead emphasizes that more attention should be paid to circular DNA.
Source: DNA element with a murky past is borrowing cell’s repair machinery
Photo on Mahmoud Ahmed and Pixabay
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