How 'junk' DNA could control how species evolve

Our non-coding DNA could dictate an organism's ability to speciate. Speciation is the term that described the ability to evolve into a new species, and it could be heavily influenced by so-called ‘satellite dna’. This is DNA that encompasses our coding DNA, and gives it structure. The 3 dimensional structure of a gene can heavily influence how it expresses itself, so how the satellite DNA acts around it surely has some say in how those genes behave, and even the rate at which they mutate, the backbone of speciation. MIT's Yukiko Yamashita explains more...

Yukiko - So if you think about coding DNA, you can imagine the contents information of a book. Those words that you enjoy in the book, that is a coding part. On the contrary, we barely pay attention to the binding margin of the book, because it doesn't give us any information. However, the binding margins are critically important because if we don't have it, all those pages are completely jumbled up. After you read page one, you don't know where page two is and then you end up jumping to page 527 and then you know, the next thing you see might be page 18, that kind of thing. So one function the satellite DNA might be playing is to function as a glue or a binding margin of the pages of the book to bring all pages or in another's chromosome in this case together into one place so that you know, it doesn't get separated from each other.

Will - So if you had two organisms with different satellite DNA, how could that affect their speciation?

Yukiko - So you could imagine, the exact same story. Two publishers can publish those two stories and then one publisher might decide to bundle those pages on the side. And then on the other hand, the other publisher might decide to print a book in a way that everything is bundled on the top of the pages. The story is exactly the same, but if you mix up those pages before bundling and then how can you decide how to bundle them into pages in the right kind of order. But then just because formatting the information is not the same, you cannot just form the correct functional book. That might contribute to some sort of dysfunctionality of the hybrid cells.

Will - Yes. I suppose if you had half of the pages from one book, which had binding on the side and half the pages was binding on the top, they wouldn't be able to fit together. There'd be basically two different books.

Yukiko - Exactly. Yeah. So that could actually explain that even when protein coding genes are extremely similar to each other, the two kinds of chromosome from two species might not necessarily function very well.

Will - So do we think the changes in satellite DNA could come about due to random mutation, same as regular speciation?

Yukiko - I think probably satellite DNA mutates even faster because coding sequences are so much of a constraint so that there's a selection against the changes, right? So that means if you are talking about the book, if you change just one character in the word, the whole meaning could change. Zoom versus zoo would be very different. And then also probably Zoom would be very different from boom and then the next change like bloom is going to be completely different. But then if it's just formatting information, the satellite DNA is just formatting information. And then for example, satellite DNA can be just A-A-T-A-T repeating so many times only to signal out 'put the glue here' or that kind of thing. Let's say you have 10,000 copies of A-A-T-A-T still probably it's going to work completely okay, but 1000 copies mutated to A-A-T-A-C. I think that there is minimal impact to the species. So that allows satellite DNA to change much more than individual words as a content information. So I think that's why the satellite DNA or those kinds of non-coding junk DNA tend to change a lot. And then by the time you realise your formatting information, like binding margin information, might be very different from your cousin species or cousin populations.

Will - If that is the case then, albeit completely inadvertently, perhaps unfairly, do we think then that certain organisms with certain structures of satellite DNA may be able to adapt quicker than others?

Yukiko - Oh, that's an interesting possibility <laugh>. it's possible. I feel some species might get lucky to get an adaptable kind of satellite DNA. I don't know if species or any organisms would have that foresight <laugh>. So let's go that direction because that is going to make us better and then more adaptable in the face of changes. For that, you know, I want to be very neutral. But with that said, yes, you know, in hindsight the sudden changes that happen to your satellite DNA structure, junk DNA structure, might make a particular species a little more faster evolving. That's possible.