Is most of your DNA junk?

Before the 1950s, people didn't know much about DNA. We weren't even sure what let animals pass down features onto their offspring. This might be a surprise to someone who lives in a world where DNA is the poster-child, and default emoji, for science - up there with the likes of gravity and electricity.

DNA can be thought of as a long list of instructions, specifically the instructions to produce proteins that go on to make everything else happen in your body. And yet only 2% of your DNA is protein 'coding'. The remaining 98% seems to serve no purpose at all, and so has been named "Junk DNA".

But maybe that's unfair, because who says DNA should encode proteins and do nothing else? Researchers at UC Berkeley and Washington University decided to focus on transposons, a component of junk DNA in mice. They found that transposons were vital in making sure a mother mouse's DNA could be reliably passed down to children, and taking them away would severely harm her ability to have healthy offspring.

This starts to make sense when you consider how similar all mammals are, and yet how different they all look. Lin He, a researcher at Berkeley, points out that "mice and humans share 99% of their protein coding genes." Transposons could be the part of a mammal's DNA that makes sure all the active sections are in the right place. As Lin He puts it, "mice and humans have the same genes, but they can be regulated differently. Transposons have the capacity to create a lot of diversity for how genes are regulated and could help us to understand species-specific differences in the world."

But stranger still, transposons don't come from evolution in the way you might expect. At least 8% of the human genome, all of it junk DNA, comes directly from 'endogenous retroviruses', ancient viruses which dug their way into our DNA over 500 million years ago. Ever since then, we have been evolving alongside them. Researchers at the Spanish National Cancer Research Centre have even found them to be vital to 'pluripotency', a key part of the process that turns a fertilised egg into an embryo.

So if we fast forward 70 years from where DNA research took off, it's getting a lot clearer that there's more to DNA than arranging proteins - and that it's not always a good idea to take out the trash.

by Louis Davies

@louis.on.air

Sources:

Sergio de la Rosa et al., Endogenous retroviruses shape pluripotency specification in mouse embryos.Sci. Adv.10,eadk9394(2024).DOI:10.1126/sciadv.adk9394

https://news.berkeley.edu/2021/10/18/so-called-junk-dna-plays-critical-role-in-mammalian-development

https://www.quantamagazine.org/the-complex-truth-about-junk-dna-20210901/