When biologists first examined the landscape of human genes they were perplexed by the, seemingly useless pieces of DNA that floated in the structure. It was labelled ‘junk DNA’ and the name stuck.
However, new research suggests it may not be junk at all. In fact the DNA, which is now called satellite DNA, plays a crucial role in holding the genome together and, by extension, the survival of much of life on Earth.
The study, which has been published in the journal eLife, outlines that the “junk” is actually essential for the cell’s survival because it performs the vital function of ensuring that chromosomes bundle correctly inside the cell’s nucleus.
“We were not quite convinced by the idea that this is just genomic junk,” lead author on the study, Yukiko Yamashita, said. “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.”
Yamashita and her colleagues decided to see what would happen if cells could not use the satellite DNA.
Because it exists in long, repetitive sequences, the researchers could not simply mutate or cut the entire satellite DNA out of the genome so they removed a small part of the DNA from fruit fly cells.
They quickly found that the germ cells, which ultimately develop into sperm or eggs, were losing their ability to form a complete nucleus and were dying.
“It’s like forming a bouquet,” explains Yamashita, who is also a research professor at the University of Michigan. “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.”
The researchers carried out similar experiments using mouse cells and got the same findings, again the cells began to die off.
The results lead Yamashita and her colleagues to conclude that so-called Junk DNA is essential for cellular survival, not just in model organisms, but for any species that embeds DNA into the nucleus – even humans.
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