Dark matter is one of the biggest mysteries of astronomy today. There’s tons of evidence that it’s there, but try as we might we haven’t been able to find it. In biology there’s a similar problem: dark DNA. When scientists were exploring the sequenced genomes of certain birds and rodents they noticed something odd. A sequenced genome means everything is laid bare, and yet certain DNA sequences were missing, which was weird because these DNA sequences were very important. They controlled the production of leptin in the birds or the secretion of insulin in the rodents, genes that the scientists knew had to be there, otherwise they’d have some mighty obese birds and dead rodents on their hands. What’s more, the scientists studying the rodents found the products of the missing DNA sequences in their cells, so they deduced that the genes weren’t missing, but were somehow hidden. They dubbed these elusive sequences “dark DNA.” Sounds spooky, but the reality is this dark DNA may be more of a blind spot in our DNA sequencing technology than anything else. A closer look at the rodent’s genome found a heavily mutated section with abnormally high amounts of guanine and cytosine, two of DNA’s four base molecules, called G and C for short.
It turns out GC rich sequences are difficult to detect, so the researchers missed this mutated pocket of DNA at first. This dark DNA raises questions about how quickly mutations occur, and what genes we may have missed when we sequenced other genomes like our own Which is crazy to think that there could be more DNA in us than we realized, especially when you consider that we only know what about 1 to 2% of the stuff we have found does. Those sections code proteins that have some function. The other 98%-ish doesn’t make anything and so we don’t know why it’s there.
This vast amount of genetic code has also been referred to as DNA’s “dark matter.” Apparently biologists love the dark matter analogy, only the kind we’re talking about now is the opposite of the first example. Instead of knowing what a gene does but not finding it, we’ve found a lot of genes but have no idea what they do. Slowly though we’re chipping away at that riddle too. It appears that a lot of this non-coding DNA is still helpful for regulating gene expression, making sure the right cells have the right hardware, like hemoglobin in blood cell precursors and ion channels in neurons. Some of these sequences are almost identical across different species like humans, mice and chickens. Considering we’ve been evolving separately for up to 200 million years, researchers concluded that these sequences must somehow be vital to our survival. When researchers deleted four of these genes in mice, they found abnormalities in the mice’s brains, and wondered if mutations in these overlooked non-coding sections of DNA could be responsible for brain diseases like alzheimer’s. So there is a lot of DNA to parse through and there could be even more we just haven’t found because of limitations in our sequencing techniques.
Our genome is still a pretty dark and mysterious place, and more research is needed. One quick thing. Seeker needs your help! Please vote for us to win a People’s Choice Webby! You’re the people you get to choose, you like us, it works! We made an awesome virtual reality doc that lets you experience what it’s like to climb Mt. Everest, and it is a finalist in the VR category for the Webby Awards. The Seeker Everest VR Expedition mixes elements of interactive documentary with the immersion of virtual reality to bring you into a first-person narrative from one of the most inaccessible places on Earth.
We are super excited about receiving this honor, and we would be even more excited if we won, so please, get out and give us a vote, and if we win, we will give you, our viewers a special surprise. Voting is open until Thursday, April 19th. Click the link in the description to vote. What are you waiting for? It’s not like climbing Mount Everest, just click that and go vote! Awesome! And then check out VR Mt. Everest, it’s super cool. Researchers believe that the rodents’ hot spots of DNA mutation could be evidence of an undiscovered and rapid mechanism of evolution. There are known cases of rapid evolution. To learn more about ways species can shift in years instead of millenia, check out Trace’s video here.
That’s it for now, I’ll see you next time on Seeker. .