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How The hedgehog Got Its Name

This week’s episode of It’s Okay To Be Smart (below) focuses on a very special chunk of DNA and the things that it does, part of a family of genes that help sculpt complex body shapes across the animal kingdom, from fruit flies to fish to humans to hedgehogs. Sonic hedgehogs, to be exact.

Sonic hedgehog is a gene that every vertebrate carries that, working in beautiful concert with dozens of other developmental genes, helps guide and shape everything from your spinal cord to your face (as Emily showed us in the recent Two-Faced Calf episodes on The Brain Scoop). It helps the developing embryo determine which is the front side of the hand and which is the rear. And coolest of all, it helps precisely five fingers sprout, not four, not six, and determines which will be the thumb and which will be the pinky. 

It also has something to do with the evolutionary biology of The Simpsons, but we’ll have to save that for another post. 

Sonic hedgehog isn’t the only hedgehog gene we carry. We also carry inside our DNA an indian hedgehog and desert hedgehog. So what’s up with the names? Our array of hedgehogs (that’s the official term for a group of hedgehogs, as it happens) are all related to a gene from fruit flies.

In the late 1970’s Christiane Nüsslein-Volhard and Eric Wieschaus randomly mutated fruit flies and (quite literally) combed through them by the tens of thousands looking for interestingly deformed mutant embryos. Pretty macabre stuff, if it wasn’t flies, eh? Based on this screen (which won them the Nobel Prize), they discovered a swarm of genes that affect how the fly’s body decodes its form (read their original paper). And they gave those genes funny names based on funny patterns or phenotypes in the mutant embryos.

Why? Well, it’s possible that Germans have some hidden sense of humor that they aren’t telling the rest of the world about, but it’s more likely that they named the genes this way because that’s how Thomas Hunt Morgan, master of mutant flies, did it.

How do you get a hedgehog from a fruit fly? Let’s start with a normal fly embryo. Usually these tiny worm-beasts display an elegant, banded pattern of “denticles”:

Well, one of the random mutations that Christiane and Eric identified resulted in a scrunched up embryo with completely bunched denticles. The reasons for that scrunchiness are complex, but if you want to know more, read up on the treasures that lie within pair-rule genes and gap genes. Anyway, since fruit fly folks name genes based on what the mutant looks like (e.g. wingless, yellow, curly) they named it hedgehog!!

Relatives of that gene in other animals were discovered in the following years in many other species, and thanks to the finely tuned comedic skills (and long nights at the pub) that biologists are known for, we ended up with Indian, Desert, Sonic, and in fish, even Tiggywinkle hedgehogs. And that hedgehog lives in every cell, brought out of its burrow with careful genetic choreography to make you the thumbed wonder you are today. Ain’t biology adorable? 

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