FOXG1 fish - and their glowing brains

20 February 2020

Interview with 

Hannah Bruce, King's College London

Zebrafish_brain.jpg

Green inhibitory and red excitatory cells glowing in a live zebrafish brain.

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On the spectrum of important genes for development, FOXG1 is high. In fact, it used to be called Brain factor-1; that’s how big a role it plays in your brain. Phil Sansom spoke to Hannah Bruce, one of the people studying that role...

Hannah - In science, it's not always feasible or ethical to use humans in studies. Instead we like to use models, model systems, to try and understand more about diseases. So when I say a model, I'm using the zebrafish to model FOXG1 syndrome. Because I'm not able to do experiments on the children with FOXG1 syndrome, of course, that would be terrible.

Phil - What's a zebrafish?

Hannah - A zebrafish is this tiny little fish. It's maybe about an inch long.

Phil - Are they cute?

Hannah - They are quite cute. Yeah. They have little stripes just like zebras. Clue's in the name!

Phil - And do they have brains that are similar to human ones?

Hannah - They do have the same brain areas as we do.

Phil - So how do you test the FOXG1 in the zebra fish brain?

Hannah - I have these sort of families of zebra fish and one family, or line, as we call them, has had its genome edited so that it doesn't have any FOXG1 genes.

Phil - What does that do to them?

Hannah - The fish that don't have any FOXG1 die. They die about seven to 10 days after they're born.

Phil - Wow.

Hannah - Yeah, I know. But we can take them before they die and have a look at their brains. So one really cool thing about the zebrafish is that we can make them see-through. We add like a special chemical that stops them from developing any pigment in their skin. So I can then look down the microscope and look at the zebrafish brain while it's still alive. When I do this, the zebrafish that doesn't have any FOXG1, first of all, it has a much smaller brain, but it also has an increased number of cells that are important for excitation.

Phil - We're talking nerve cells, right, neurons, in your brain?

Hannah - That's right, brain cells. And when I say excitation in your brain, cells connect to each other. An excitatory cell will make its neighbours or connecting cells active, whereas an inhibitory cell will prevent the cells it's connected to from being active. And it's really important the number of each of those cells, or what we call the excitation inhibition balance, because if the number of those cells is skewed towards either direction, it can result in disease. So the most obvious example is probably epilepsy. The excitement of the brain is increased causing your brain to be hyper excitable, resulting in things like seizures.

Phil - Does that mean a seizure is too many nerves firing going off all at once and nothing's damping them down?

Hannah - Yes, exactly yes.

Phil - How does that relate to your poor, transparent zebrafish that die after seven days?

Hannah - What we think one of the main jobs of FOXG1 is to sort of set up the developmental boundaries where each of these cells, the excitatory and inhibitory cells, are produced. So we think it's pro-inhibitory, but it also coordinates the boundary for the production of the excitatory cells.

Phil - Oh. So if it doesn't work, then you don't get the inhibitory cells 'cause that's where it seems to be working the most strongly.

Hannah - Exactly. So the zebra fish that doesn't have any FOXG1 doesn't produce any of these inhibitory cells.

Phil - Okay. Here's my big question. Kids that have FOXG1 don't die after seven days, a lot of them live many years.

Hannah - Yes.

Phil - Are they the same as these transparent week long Zebrafish?

Hannah - That is a really good point. The answer is no. The children with FOXG1 syndrome, they still have one copy of FOXG1; so one of the main aims of my research is to take another zebrafish line, which only has one copy of FOXG1, to try and make it a more reliable and accurate model of the disease that we see in humans. One of the main ways that I'm trying to do this is use special zebrafish that have fluorescent proteins and their brain. Basically this means that I can have a fish that as well as only having one copy of FOXG1 is engineered in such a way that the excitatory cells glow red and the inhibitory cells glow green.

Phil - What? Like physically glow?

Hannah - Yes. Like, I can see them glowing. You should, I wish I could show you, it is beautiful.

Phil - Like Christmas lights in the fishes' brain!

Hannah - Exactly. Some people say red and green should never be seen, but I disagree.

Phil - That's amazing!

Hannah - Yeah. And one of the things that I know from preliminary research is that these zebra fish with only one copy of the FOXG1 have a decrease in the number of inhibitory cells.

Phil - And you can tell that because their brains are glowing more..?

Hannah - They're glowing, less green and more red.

Phil - Wow.

Hannah - And the really cool thing about this particular zebrafish light that I'm really excited about, is that we can use it as a fast, efficient way to read out a library of small molecule drugs. And these drugs have already been tested for safety in humans. They're completely safe to use, but the original purpose that they were to be used for, they weren't effective. And so they were basically abandoned. So what we're hoping to do is take these zebra fish that glow red and green, and pop them into single wells of a 96 well plate. So I can have 96 fish on a plate and put a different drug into each well and then readout the ratio of red to green, glowing to see if the therapy has been effective. And it's a really nice, fast, efficient way of being able to translate back from the lab bench to the bed site. Because if anything is effective, it doesn't have to go through these decades of clinical trial failures because we know they're already safe in humans and there is an effect in fish.

Phil - I'm also excited about these red, green glowing options. Have you ever turned out all the lights in your lab and had a party?

Hannah - The Christmas party? Why not? Yeah!

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