An international team of scientists may have cracked the code of so-called “junk DNA”—the segments of our genetic code that doesn’t appear to have a valid function—discovering that it may actually be much more important than previously assumed, functioning as a set of “genetic switches” that can influence what genes are expressed without needing to rewrite the DNA itself.
“Our genome was sequenced long ago, but the function of many of its parts remain unknown,” study co-author Fumitaka Inoue, an associate professor with Kyoto University, pointed out about junk DNA. Inoue’s team’s study focused on a type of DNA sequences called transposable elements (TE), parts of our code that can reposition themselves within the genome, earning them the nickname of “jumping genes”; these TE make up about half of our DNA, with that proportion being even higher in other species.
Inoue’s research team believes that the current method of classifying genes like TEs, of which often consist of highly repetitive identical sequences, is incorrect, leading to these stretches of code being poorly studied and in turn just as poorly understood, resulting in the segments being relegated to the junk DNA bin.
While re-categorizing a group of TEs called MRE11, the researchers discovered that these genes, previously known for producing an enzyme that our bodies use to fix genetic errors called double-strand breaks, can actually act like a set of genetic switches that can influence what genes are expressed—whether they’re turned on or off—as an individual embryo develops, without the need to actually re-write the genome itself.
Curiously, MRE11 genes are a type of TE called retrotransposons, a relatively recent addition to our genome that appears to have been introduced to our genetic code by a long-extinct retrovirus that infected our simian-like ancestors about 10 million years ago. As a result, these genes exhibit retrovirus-like behavior, enabling them to re-write parts of our genome when required.
The most recent addition of the four MRE11A classifications—MRE11A_G4—is particularly adept at this, having “short stretches of DNA that serve as docking sites for transcription factors, the proteins that control when genes are turned on,” according to ScienceDaily. These docking sites, called “motifs”, “can dramatically influence how genes respond to developmental signals or environmental cues.”
Comparisons between MER11_G4 sequences in humans, chimpanzees and macaques revealed that the human and chimp versions had gathered mutations that allowed them a greater potential to regulate the genes they influence, implying that this former “junk” DNA may have also had a hand in the evolution of humans, part of what might have sent us down the unique evolutionary path we’re currently on.
Did the strange people featured in Whitley’s 2018 novel, “New”—so similar to us, and yet so unique—share these peculiar genes with their human companions? Pick up a copy of and share their adventure today!