APR 12, 2018 11:02 AM PDT

An Important Role for 'Junk' DNA

WRITTEN BY: Carmen Leitch

Researchers have long wondered about the possible roles of junk DNA, long strings of genetic material we carry in our genomes that serve no readily apparent purpose when compared with the rest of our genome, which contains genes that code for protein and their associated regulatory regions. Now scientists at the University of Michigan Life Sciences Institute and the Howard Hughes Medical Institute have found that one kind of non-coding DNA, satellite DNA, has an essential function in keeping the genome together. This work has been reported in the journal eLife, and shows that satellite regions are not throwaway sequences, but are required to bundle chromosomes properly inside of the cell, which helps keep it alive.

When studying genes, scientists often look at a feature called conservation, which indicates how similar that gene is across different species. Usually, it’s assumed that genes that have a high degree of conservation have important biological roles. It has been found that many junk regions are in fact highly conserved, which was also shown in this study. The work is briefly described in the video.

The sequences under study, pericentromeric satellite DNA, are very repetitive sequences, accounting for a vast portion of the genome. It does not code for any proteins and had been thought of as an unstable and useless area, susceptible to disease or damage. 

"But we were not quite convinced by the idea that this is just genomic junk," noted lead author Yukiko Yamashita, a professor of cell and developmental biology at the U-M Medical School. "If we don't actively need it, and if not having it would give us an advantage, then evolution probably would have gotten rid of it. But that hasn't happened."

To investigate the role of this DNA, Yamashita’s team wanted to remove it from cells and see how they reacted. But these sequences are really long and could not be simply cut or edited out of the genome entirely. To overcome that hurdle, they turned to a protein called D1, which binds to satellite DNA. D1 was deleted from the cells of one of genetics’ favorite model organisms, the fruit fly Drosophila melanogaster. The researchers observed that when they did that, the cells that develop into sperm or eggs, the germ cells of Drosophila, started to die.

Non-coding regions, which have been called junk DNA, make up the vast majority of our genome. / Image credit: Maxpixel

Additional experiments showed that in the dying cells, micronuclei, tiny buds outside of the nucleus that contain pieces of the genome, were forming. Since the whole genome was no longer present in the nuclei of those cells, they died.

The scientists hypothesized that D1 binds to the satellite DNA, pulling all of it together in the nucleus. When D1 is unable to do so, the cell’s nucleus carries a genome with missing pieces, killing the cell.

"It's like forming a bouquet," explained Yamashita, who is also an HHMI investigator. "The protein has multiple binding sites, so it can bind onto multiple chromosomes and package them together in one place, preventing individual chromosomes from floating out of the nucleus."

Additional work replicated the findings. In mouse cells, a protein that binds satellite DNA was deleted, and those altered cells created micronuclei and died.

The researchers suggested that satellite DNA is therefore critical for the survival of cells across species.


Sources: AAAS/Eurekalert! via University of Michigan, Wikipedia, eLife 

About the Author
  • Experienced research scientist and technical expert with authorships on 28 peer-reviewed publications, traveler to over 60 countries, published photographer and internationally-exhibited painter, volunteer trained in disaster-response, CPR and DV counseling.
You May Also Like
DEC 15, 2018
Videos
DEC 15, 2018
Using Genomics to Study Bacterial Evolution and More
Learn more about how genetics and bioinformatics techniques are helping researchers to understand how microbes adapt, survive and spread in the world....
DEC 15, 2018
Genetics & Genomics
DEC 15, 2018
Neanderthal Genes Provide Insight Into Human Brain Evolution
Neanderthal heads are almost football-shaped, while modern humans have much rounder brains and skulls....
DEC 21, 2018
Microbiology
DEC 21, 2018
How the Gut Microbiome Controls the Intestinal Immune System
The gut microbiome has many important functions, including helping us digest food. But it has to protect itself from the immune system....
DEC 24, 2018
Genetics & Genomics
DEC 24, 2018
Insight Into the Cause of Huntington's Disease, and a Potential Treatment
There is no treatment for Huntington's disease at this time, and the scientists hope that this work will lead to one....
DEC 28, 2018
Genetics & Genomics
DEC 28, 2018
The Epigenetic Profile of Sperm is Altered by Cannabis
There has been considerable debate about the safety of marijuana, which has only increased since the drug has been legalized in some states....
JAN 06, 2019
Genetics & Genomics
JAN 06, 2019
Exploring the Impact of Extensive Newborn Screening
While the exact number now varies by state, newborns are screened for several diseases. Should we be doing more?...
Loading Comments...