Briefing Chat: An invisible tattoo that appears under UV light – and then disappears

0:00Hi, listeners. Benjamin here. It's the Friday show, The Briefing Chat, where we talk about a couple of stories that have been covered in The Nature Briefing. Joining me this week is Maren Hunsberger. Maren, how are you doing? Hello. I'm great. Happy to be here, as always. Excellent. Well, listen, why don't you go first this week? You've got an interesting story about ink. I do, and I'm going to open with a question for you, Ben. Would you get a tattoo if you could turn it on and off? Sure. I mean, yeah. I think maybe some people would, even if they hadn't considered getting a normal tattoo

0:31this kind, they might. This kind of tattoo is made out of something called a photochromic dye. And you might be familiar with this because we have photochromic materials in other places in our lives, like transition lenses. So, you know, when you go outside, you have glasses on, they darken. That's a photochromic material. It means that it responds to a certain wavelength of light by changing color. Now, what happens here is that when a certain wavelength of light hits that molecule, it changes shape so that it changes color. But what's really cool about it is that when it's exposed to a different wavelength of light, that change reverses. It goes back to

1:07its original shape and it disappears. So you can literally turn it on or off. Exactly. And so we have these materials in other places in our lives. Like I mentioned, these transition lenses is a great example. This paper that came out in the cell last week is the first evidence that we have of a photochromic material that has been injected into living human skin. Right. Now, I've seen a thing about UV tattoos, which shine when under a black light. Is this similar to that? Exactly. So anybody who's familiar with the rave scene is probably familiar with UV tattoos that,

1:38as Ben says, glow under black light. It's similar in a sense, but they're actually quite unique. So a UV tattoo is a tattoo that's been done with fluorescent dye. So its molecule is excited by a certain wavelength of photon and it only glows when a black light is shining on it. What's different about these photochromic dye tattoos is that they are activated by a certain wavelength of UV light and then they stay on. So sort of semi-permanent. Exactly. Until you can turn them off by exposing them to very strong visible light.

2:10And you say that this has been tried in a human. Was this in a warehouse with sort of pumping techno? What was the situation here? So this brings us to a great line from the paper. In the abstract, it says, in a single subject in vivo pilot, all three channels, this is the three colours of photochromic dye, remain fully photo switchable, rewritable and selectively erasable in healed human skin after more than two years. Have a guess, Ben, about who that single subject is. So I knew a tattoo artist who used to test things out on himself, right, to show customers

2:43how the inks would fade over time. And I'm getting a sense that testing tattoo stuff out on yourself is probably involved here in some case. Yes, you are correct. The person in question is the lead researcher on this story. He is a nanomaterials guy and he has founded this startup that is called HyperSkin that specializes in these more alternative nanomaterial tattoo methods. And what's interesting is that it's not only helpful for cosmetic or artistic purposes, right? So there are some great videos on our site that

3:16listeners can go check out of the researcher highlighting the tattoo or even, you know, there's an instance where you can inject basically an entire canvas of this ink. And then you have this device that looks like a pen with a UV light in the tip and you can write on your skin and the die shows up in this shape of what you've written. It's kind of amazing. But outside of, you know, maybe wanting to erase your tattoos when you're around your family, even though you're fond of them, this could be really applicable for medical applications. So when folks have to get a tattoo for radiotherapy or to indicate where they've gotten a biopsy, some folks really don't like

3:51to have that reminder. They don't like to have that staring at them all the time. So you could do them with an ink like this instead. So this is one of those neat stories where on the face of it, like, oh, that's cool and weird. But actually, yes, this could have practical and useful effects for people in the real world. I say in inverted commas. It certainly does. Well, as you say, Maren, we'll put a link in the show notes where folk can see this thing. And I'm looking at it right now. And actually, you know, this is actually pretty awesome. Let's move on to my story this week. And it couldn't be more different. Now, we love dogs here on the Nature Podcast, right? Obviously. Well, we've got a story about doggos and it's helping to answer a puzzle.

4:25Why do small dogs live longer than big dogs? And this is based on some research published in Science and a story that I read about in Nature. Ah, this is a very well-known phenomenon. Yeah, everybody that I know who has had a little dog has had that dog live well into the teens. Right. So some of the largest dogs, things like Irish wolfhounds, they live for an average of, what, 10 years or less, which is in marked contrast to smaller breeds. Now, when I was a kid, I had a dog. He was a good boy. He was a West Highland white terrier, quite a small thing. He lived for, I think, like almost 20 years. A long-lived Westie. Yeah, absolutely. And this study

5:00encompasses nearly 900 dogs representing 120 breeds. And this is part of the dog aging project. Okay. Wow. And I mean, it sounds like it's relatively obvious, but what exactly are they looking at? So this is a genetic study and the team found that canine aging is accompanied by changes in specific chemical groups. Now, they're called methyl groups, right? You and I know them. They're very small chemical groups that are added to DNA. Now, these marks are part of this thing called the epigenome, this kind of overarching layer of control of how genes are switched on

5:35and off, but that is kind of separate to the genome itself. Yeah, sort of like little handles and levers, right, that are pulled to open doors or switch things on and off. And it can change throughout your life based on different things that are happening to you or happening in your body, right? Absolutely right. And the loss or gain of these groups is sometimes used as a biological marker of aging. Now, what the researchers have done here is they've looked at this and they've shown that big dogs tend to accumulate epigenetic changes at a faster rate than small dogs do. And also,

6:05male dogs seem to amass alterations faster than female dogs do, even if the male dogs have been neutered. Now, this seems to be down to the fact that some of these changes are related to the X chromosome. The male dogs only have one of these, so it could be that having two X chromosomes helps alleviate that. So that might explain why male dogs don't live as long necessarily. And what the researchers have done is they've used this information to develop a molecular clock. And this is based on the correlation between the methylation patterns and the chronological age,

6:37because all the dogs who are part of this study, the birth date of these dogs is known, right? So we know exactly how old they are. And in this case, this clock can be used to predict a dog's age within a year based on just its epigenome. You can tell just by looking at its DNA. That is wild. You know, that's funny. I've heard of some companies that are trying to do this for human ageing as well, right? They're trying to sell you this idea of molecular age, if you will. And jury's out on how valid any of that testing is, but it's an interesting methodology across species, it seems.

7:09And ageing is a phenomenally complicated thing. We've covered it on the podcast here before. And this is one aspect of it. And what's interesting here is that dogs whose epigenetic age was older than their chronological age had a higher risk of dying in the next couple of years. So it is almost like a marker to know, which is actually kind of sad on the face of it. And kind of an interesting ethical question of would you want to know? But that's not really the thrust of this research. It's just what's going on. And it seems that some of these age-related changes in this methylation, this pattern of methylation, occurred in what are known as jumping genes.

7:39Now, all animal genomes have these genes, and they were, in many cases, ancient viruses that were just kind of incorporated into the genome. But they can move about, right? They can hop from one location to another and disrupt the genes where they land, right? So they can land in the middle of a gene, for example, and upset what it does. Now, the methyl groups help to tether these jumping genes in place, preventing them from interfering with other parts of the genome. And so loss of the methyl groups has been linked to inflammation and ageing in humans and other

8:14animals. And the team found that big dogs tend to lose this methylation more rapidly than the small dogs. Their genes are jumping around more often. Potentially. And it's super complicated, right? So although these methylation patterns are correlated with longevity, it's not known whether they directly cause ageing or whether they just make the jumping genes more active, what role those jumping genes are playing. As I say, ageing is a phenomenally complicated thing that loads of researchers are trying to figure out. But the researchers here hope that this data will be a starting point to learn more about how DNA

8:47methylation is related to ageing in dogs. And that then could potentially be used to figure out a bit more about human aging and maybe lead to treatments for elderly canines, which I think we can both get on board with. Helping us care for dogs and understand human aging, potentially, sounds like a positive story to me, Ben. Very good. We absolutely don't want those dogs feeling rough now, do we? We want them around forever. God, we've got to stop. We have to stop now. Right. Listeners, we'll put links to both of those stories in the show notes and where you can sign up

9:20for the nature briefing to get even more of them delivered directly to your inbox. But for the time being, Maren Hunsberger, thanks so much for being here. Oh, thank you for having me. It's the leash I could do. Doggone it.