On May 30, we learned in the journal Nature that a longstanding mystery about a very important human gene has finally been cleared up, over 100 years after the gene’s effects were first observed. All it took was some biochemistry experiments and the willingness to look beyond groupthink.
The gene’s name is nocturnin, and it’s been of keen interest because of the effects it can have on the metabolism of mammals. Twelve years ago, it was found that a certain mutation in mice keeps them thin, even when they are fed a high-fat diet:
Mice that are missing nocturnin are quite interesting indeed:
- They stay thin on high-fat diets
- They don’t develop fatty livers
- They don’t exercise more than regular mice
- They don’t eat less than regular mice
In other words, a mutation in nocturnin acts like a magic bullet for preventing obesity. It changes something fundamental about metabolism, enabling a mouse to eat lots of fat, but behave normally and yet not gain weight. Trouble is, up to now, no one knew what nocturnin actually did.
Nocturnin got its name because it was discovered in the retina of the nocturnal African clawed frog, and its levels get quite elevated at night as the frog wakes up. In humans, it is also at a very high level as we wake up, but we’re not nocturnal, so that happens in the morning.
A cool side note is that these frogs are used to study retinal disorders. You can add genes to the frog and get those genes to turn on specifically in the retina to study their effects, and you can use a marker gene like the one that encodes green fluorescent protein from jellyfish to help you track them:
Nocturnin, as it turns out, goes back way further than this:
In the 1910s, Thomas Hunt Morgan was busy laying the foundations of genetics by discovering that chromosomes contain genes that confer inherited traits (for which he’d go on to win the 1933 Nobel Prize). He found several mutations in the fruit fly that gave visible differences, such as white eyes. This made it easier to study inheritance in higher organisms like the fly. Another mutation he found was one he called curled:
A modern still photo of such a fly:
Once the fly emerges from being a pupa, its wings get pumped up like inflatable rafts in a few minutes. It’s pretty wild! There’s a video of that here; just click on “File S1” when you get there for the curled version.
Why are we talking about fruit flies with curled wings, though? Because the curled mutation is a mutation in none other than the gene that encodes nocturnin. This match between curled and nocturnin was discovered in 2009, but at that time, of course, nobody knew exactly what nocturnin did. Why does it straighten a fly’s wings? What does it do for an animal who’s waking up? Why does it make mice gain weight? What’s going on?
Flies with the curled mutation, by the way, have been known for awhile to not only have curled wings, but also to have altered metabolism. Interesting.
Up to now, everyone (and I mean everyone) had assumed that nocturnin is a deadenylase, responsible for chewing the tail ends off of RNA molecules in order to destabilize them. After all, it looks a lot like other proteins that are known to do that. If that’s what nocturnin actually did, it would be pretty hard to figure out exactly what its role is. You’d have to track which RNAs it attacks and then figure out what the roles of all those RNAs in concert might be.
For years and years people have been writing in their papers that nocturnin is a deadenylase, and nobody really thought to challenge that. Until now, that is.
These people were trying to get nocturnin to chew up some RNA so they could start unraveling what it does. But despite everyone saying it would, it wouldn’t. So they had to back up and do some biochemistry.
These days, biochemistry is a bit of a lost art because everyone wants to use genome sequences and computers and “big data”. There’s nothing wrong with that, but when you don’t understand what some of the components you’re dealing with actually DO, you hit some snags.
I have to say, these people pulled off a pretty slick way to do a bajillion experiments at once. Instead of testing nocturnin on one kind of molecule at a time, they let it loose on a whole biological extract with thousands of kinds of molecules in it. Then they looked for any changes. That’s expensive to do, because you have to separate all the molecules by chromatography and then blast them apart and weigh all the teeny fragments so that you can identify them. But it is doable.
Fortunately, when they got the data, it was as clear as day what had happened:
The big cluster of dots is all the chemicals whose levels stayed the same in all 3 experiments they did — that is, almost all of them. But two dots fall way outside the cluster, meaning those two chemicals got depleted bigly by nocturnin. Their names are NADPH and NADP+, and they’re both actually the same chemical.
NADPH has one job: to carry 2 electrons. When it loses those electrons, it’s called NADP+.
We have another very similar electron carrier inside us called NADH. It’s the same as NADPH, except it lacks the phosphate (“P”) tag that NADPH has. That phosphate tag is super-important, though. It’s like a first-class ticket, because it allows those electrons to go places they otherwise couldn’t. Think of NADPH as first class and NADH as coach.
A few more experiments with nocturnin showed that its function turns out to be very simple: rip off that phosphate tag. Turn NADPH into NADH. Downgrade those electrons to coach!
NADPH gets to go around the cell and donate its electrons to lots of fun things like building new molecules, sending out little signals, helping antioxidants keep the cell safe, and all that jazz. NADH for the most part just gets the grunt work: dumping its electrons off to oxygen. But that’s highly crucial grunt work. That’s respiration.
NADPH and NADH are your solar battery pack. Plants use sunlight to rip electrons away from water, and they store that energy as sugar. You eat the sugar, those electrons get released, and NADPH and NADH carry them to where they need to go. When you breathe in oxygen, NADH hands off its electrons to oxygen, and you get water.
If NADH simply handed electrons over to oxygen directly, the result would be this:
Combustion. Lightning. A short circuit. Luckily, your body is a lot smarter than that. You’ve got lots of teeny motors and pumps set up to harness this energy. It’s how you move!
You can get by for a short time without respiration, like when you work a muscle really hard. NADH might be forced to dump its electrons elsewhere when the oxygen runs out, but then you get waste products like lactic acid, and that can’t go on for very long. That’s when you feel the Bern — er, the burn.
There’s one other thing NADH is really good for:
Yeast are quite comfortable with no oxygen. They eat sugar and then use NADH to dump electrons to a new carrier: ethyl alcohol. I am showing On Fleek by Stillwater Brewing (Baltimore, MD) here because it has 13% alcohol, yet manages to be most tasty. I’m just saying.
But let’s get back to nocturnin. Remember that it rises overnight in order to peak when you wake up. Reason? You need to wake up and go hunt woolly mammoths, caveman, and that takes energy! Your blood sugar peaks in the morning, too, and nocturnin makes sure you are primed and ready by directing lots of electrons to NADH and therefore to respiration! This is starting to make sense now!
But what about the fat thing?
Well …. remember I mentioned that NADPH sends out nice little signals in the cell as part of its privileged activities, and one of those signals goes to fat cells, telling them to chill out and stop proliferating. But if those phosphate tags get ripped off…
...then we don’t have much NADPH left, and we can’t send that chill-out signal to fat cells anymore. Nocturnin made that NADH at the expense of NADPH, and so it took a lot of that signal away. It’s all good, though, caveman, because you need that energy to go hunt, and storing fat is a smart thing for you anyway. You never know when you’ll have to go a few days without food.
Are you — 2019 you — tempted to eat a late-night snack? Remember your nocturnin is rising, and when the NADPH is away, the fat cells will play.
Seven years ago, a different mutation was found that does the opposite of the nocturnin mutation; it CAUSES mice to become much more obese on a high-fat diet. Mice missing a gene called NOX4 balloon out to huge weights when fed a high-fat diet for just 12 weeks.
You know what NOX4 is? It’s what converts NADPH’s electrons to the chill-out signal for fat cells. This ties it all back together. Nocturnin steals NADPH, so fat cells don’t get the chill-out signal from NOX4, and you pack on a little extra fat. Especially if you’re still metabolizing, midnight snacker.
«Hides potato chip bag»
As for the flies with curled wings: entomologists, you’ve got your big clue. I know this only came out a couple of days ago, but that will give you something to chew on. I’m pretty sure you all are going to figure this out.
In conclusion, I’ll step back for a second and let the lead author sum this up:
“The realization that Nocturnin works in this manner will guide our thinking about sleep, oxidative stress and metabolism, and eventually may serve as a step toward finding better treatments for metabolic diseases,” said Alexei Korennykh, an associate professor of molecular biology at Princeton, who led the work.
You bet your sweet bippy it will. If I’m in charge of R&D at a pharmaceutical company (I’m not), I’m not being as measured as Professor Korennykh. I’m realizing that weight control — a huge market — could boil down to two simple molecules that I already know a lot about, and … I already have 3 or 4 ideas about what we could do, and … me and that other VP have talked about getting the hell out of here and starting our own company one day if only we had an idea, and … this sounds like something we could sell to the VC guys and … the … I … uh … I think I have to go now….