Using Gene Editing To Repaint Butterfly Wings

published on July 17, 2020

Thanks to The Great Courses Plus for supporting PBS Digital Studios How… to paint…a butterfly wing Hey smart people, Joe here CRISPR: it’s a DNA-editing technology that you’ve probably heard about in terms of disease, medicine, maybe making genetically modified organisms But scientists are using it for some really interesting questions, like why do butterflies have such awesome looking wing patterns, and how do they form?

So I’m here at George Washington University And I’m gonna go CRISPR some butterflies Now, there’s been a lot of hype around CRISPR CRISPR RRRRRRRRRRRRR But what is it actually? CRISPR is a DNA hacking system with two parts

One part is a piece of RNA that carries a set of coordinates matching a specific spot in the genome’s DNA The other part is a protein that chews through DNA, which creates a small mutation And we can program CRISPR with a specific set of coordinates so it cuts exactly what we want AM: You see this red stuff here?

JH: Mhmm AM: This is CRISPR (wink) JH: A tube full of CRISPR AM: CRISPRRRRR JH: Ahhhhhh JH: So, everytime you hear someone say CRISPR, now you know what it looks like That’s Dr Arnaud Martin Dr Martin and his team are using CRISPR to understand how butterfly genes make so many

Crazy patterns and colors There’s more than 200,000 species of butterfly and moth – all with their own unique wing patterns We know they use those patterns to attract mates, hide from predators, and send warning signals, but how and why these colors get painted is still a mystery But this is about more than just studying butterfly patterns

These scientists are trying to answer an important question about our own biology and even life itself: How do the instructions in DNA build bodies? I mean, genes–the letters of DNA–are just codes How do we go from those letters and codes to the many beautiful shapes and colors we see in nature? This is a question CRISPR can help us answer

AM: Those fundamental basic questions of how genes make shapes, this is relevant to us I mean, what I want to understand is how DNA makes, you know, people The first step to figuring out the mystery is easy: collect some butterfly eggs This is Joe This is also Joe He’s a researcher in the lab

So, we’re on the roof of a building in downtown Washington DC, in a greenhouse JH: That’s why I feel so tropical OJ: Yeah, it’s maybe 72 fahrenheit in here Maybe a little warmer And about 85% humidity We keep Gulf fritillary butterflies here

If the team is lucky, they can collect around 40 eggs a day from these butterflies to modify with CRISPR JH: These are one of my favorite butterflies They’re super pretty They have these lovely silver patches on the underside of their wings, which I just think are really, really beautiful

JH: So you wait for the butterflies to lay enough of the eggs, and you collect them so you can do the work you’re going to do? Exactly! What we do with CRISPR, rather than being super precise we're sort of going in with a hammer and smashing the gene and then seeing what happens It’s like if you wanted to understand how a car worked, so you open the hood and just

Started smashing pieces And then found the way in which the car stopped working If the car just completely stops, then maybe that doesn't tell you anything But if the car still works, except the radiator is now broken, then you understand that the bit you smashed has something to do with the radiator So that’s the version of this that we’re doing

Very broad strokes, breaking bits and seeing what breaks The next step is we take those eggs down to the lab to inject them with CRISPR And by we, I mean me I’m going to do it Alright, your turn! Here we have a Gulf fritillary egg from the top

You move the needle back, you approach gently, you get in, and you press the pedal There it is! I did it! Oh you can see the little red burst inside CRISPRRR The eggs will develop and hatch like usual, only the DNA inside has been altered by the

CRISPR that we injected The caterpillars, look, well, like normal caterpillars You’d never know the difference Unless you look inside their bodies Okay, let’s talk metamorphosis You’ve maybe heard that when a caterpillar morphs into its final form, inside the chrysalis,

It completely liquifies into soup, and that liquid rearranges to form a butterfly This misconception has been repeated so often it’s replaced the truth And what actually happens is way cooler Caterpillars mature from the inside out The larvae move through stages of growth, called instars When an instar gets big enough, it crawls out of its skin and the next stage of growth

Emerges from inside And when the caterpillar is just about big enough to form a chrysalis, it already has some pieces of the adult butterfly inside it… What you’re about to see absolutely blew my mind: So, you see this and you’re thinking no way this thing has wings, it’s a larva, it’s not even flying!

What the heck… I’m going to make an incision between the two nostrils, between the diaphragms Check that out This is incredible That… is… That’s a larval wing

That’s a baby wing! Here we go! You can see the veins and everything, it looks like a tiny, clear butterfly wing Wow! That’s right This is the stage where not only the shape of the wings is defined, but also the position

Of patterns That’s right, caterpillars have baby butterfly wings inside them And even at this early stage, the butterfly’s wing pattern is being painted The team can label which genetic instructions are turned on in that baby wing And what’s crazy is where we see certain genes turned on lines up perfectly with where the patterns will be on the adult butterfly

And when CRISPR messes up that DNA instruction? We can also see how the pattern is disrupted So the different genes that you study here in the lab lay down different parts of this pattern? Exactly, so during larval development you have a canvas of cells that are communicating, and the wings need to decide where to make, maybe, reflective scales, or dark scales

And it’s really, a little bit, – if I can make an analogy – of sketching process, where the outlines of each patterns are determined super early It’s during metamorphosis in the pupa or chrysalis that really the scales are emerging, and the colors happen It’s like a paint by numbers The genes they’ve identified draw in the boundaries and say “paint here”

Later on, inside the chrysalis different genes paint in the colors based on those early instructions But the basic shapes, the organization, the concentric rings, stripes – the position of all the system is established super early in the larva Which is mind blowing So now you know caterpillars don’t turn into total mush as they mature, and they have some adult body parts hidden inside them

BUT! There’s still a ton we don’t know about how wings form inside the chrysalis If only we could see inside Well some scientists have figured out a way to do that, like our old friend Aaron Pomerantz a PhD candidate at UC Berkeley: What my lab tries to understand is how butterflies form their wings and their scales, which occurs

In the pupal stage Now If you’ve ever stared a pupa for long enough, you may have been a bit underwhelmed It doesn’t look like they’re doing a whole lot They don't really move They don't often look that flashy But just below the surface there’s an incredible amount of change happening Caterpillars do contain the precursors to their adult wings: a small cluster of cells

Known as an imaginal disc And these cells have all the information necessary to transform into an adult wing when the time is right A couple of scientists- Julian Kamura and Ryan Null–figured out on accident that if you remove this imaginal disc, now you would have a window into the pupa So now we can set up a time lapse under a microscope to watch this entire process happen

And what we see is *incredible* The cells in the immature wing start to specialize, or differentiate into elaborate shapes and colors Those gene instructions, laid down in the baby butterfly wing, tucked inside the caterpillar, tell the wing where to paint in these colors It’s both fascinating to me, and important to science, that we can watch the wings as they develop, and see how colors are filled in

The adult butterfly wing is covered in thousands and thousands of scales, and this is where the color comes from, because each one of those scales produces a specific color – either through the architecture of the scale that creates a certain wavelength, known as structural color, or from pigments that become deposited inside those scales …in the CRISPR mutants, some of those cells are broken, like the car’s radiator, so we can see how that changes the wing pattern

When metamorphosis is complete, the butterfly that emerges is called a mosaic mutant It has a change in some part of its body Here is the butterflies we had in the cage over there, Agraulis, where you have these lovely precisely placed silver spots all over the wing surfaces And then we knock out one gene – a gene called WntA We literally just go in and smash it with a hammer so it’s not there anymore, and

What we get is this There are still silver spots, but the arrangement of those silver spots is completely different In other butterfly species, switching off that gene had totally different results: it can make patterns fade, or even disappear WntA seems to be the master sketching pencil for butterfly wing patterns And they’ve identified another gene, called optix, that’s more of a master paintbrush

Messing with it can turn some butterflies black, and make others iridescent blue These genes are part of the master set of instructions to build a body, and we have similar genes in our bodies We can’t go in and break those genes in humans to understand how they work, but we can learn something about them by decoding how these beautiful insect patterns are painted When people talk about CRISPR they like to think of creating mutant creatures or superhumans,

But here in real life, CRISPR has given scientists more power than ever to study how genetic instructions give us all life’s diversity of shapes and forms CRISPR has made this kind of gene tweaking cheaper, faster, and more accurate than ever This really makes me wonder, if you have this ability to tweak how butterfly patterns end up coming out can we get more control and actually design butterfly artwork of our own? Make butterflies look the way we want to?

I think we will be able to, so yes, we can but should we? It’s a new power, a new tool to harness nature, so we’re responsible, we need to do things that are relatively ethical, I would say

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