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Hank: Sea urchins? Fruit flies? Why do scientists learn about people by studying creatures that none of us could ever be mistaken for? And why sea urchins rather than, like, sea horses? What makes some animals more useful in the lab than others?
A model organism is any living thing that we can use to mimic some feature of human physiology. In other words, an animal whose body functions somewhat like our own, especially when it comes to diseases. Choosing a model organism is a balancing act between finding something that's similar to us and finding one that's simple to understand and take care of. The simpler an organism is, the easier it is for us to manipulate its genetics and development. But the more similar it is to us, the more confident we can be that it makes sense for studying human illnesses.
To find these proxies for human health, we've had to scour our evolutionary family tree, and we've found some pretty strange but useful choices.
The fruit fly Drosophila Melanogaster is a humble, vaguely annoying creature that you might see buzzing around your bananas, but in the field of genetics, it's been king for more than a century. It's so easy to care for that you can just keep it in a bottle, it produces hundreds of offspring in a matter of weeks, so genetic changes become obvious really quickly. It also has giant chromosomes that are easy to map and, best of all, it has many of the same genes we do. (1:27)
75% of human genes that are affected by hereditary diseases also show up in fruit flies, and they even have some of the same regulatory genes, called hox genes, that basically determine what parts of our bodies go where when our embryos are developing. N' I know. You'd never guess by looking at a fruit fly, would you? (1:43)
Sometimes a model organism proves useful just because of its simplicity, like the nematode worm Caenorhabditis Elegans. An adult worm has just nine hundred and fifty nine cells, and scientists can trace the development of every single one. C. Elegans is so simple that it was the first multicellular organism to have its genome sequenced. Now, it's not very similar to humans, as you might expect, but in a strange coincidence, C. Elegans is weirdly amenable to a technology called RNA interference. This is the technique biologists use to effectively silence, or turn off, certain genes in an organism by introducing a specialized RNA molecule into its system. (2:21)
By selectively turning genes on and off in C. Elegans, scientists can see how the worm responds. And the worms can take in this interfering RNA really easily, soaking it up through their skin or even eating it in their food. In this way, we can probe the function of every gene in their genome, in the process better understanding how genes affect our own health. (2:42)
Now sometimes, you just want the closest organisms to humans that you can still grow in a bowl on your lab bench. Enter: the purple sea urchin. This might seem like a super arbitrary choice, but in terms of the very,very earliest phases of animal development -- like, when we're just a tiny little cluster of cells -- urchins and us have a lot in common. (3:00)
Some animals, like nematodes and insects, develop from that wad of cells by forming a mouth first. These are called protostomes. But others, called deuterostomes, start out life by forming an anus first, and the rest of the animal takes shape from there. And guess what. You and sea urchins are both butt-first deuterostomes. (3:19)
This makes urchins a great model for studying early development. After all, it's hard to study mammal embryos because they're safely encased in the mother's body. But these sea urchins develop the same way we do, and their embryos are free-floating and tiny and nearly transparent. So: big thanks to sea urchins from everyone here on Team Deuterostome.
Finally, you probably know that the common mouse is the organism of choice for studying many human diseases. But it's hard to study respiratory disease in them, for one simple reason: mice can't sneeze. Which is a tragedy, because it would be super cute. (3:50)
If a mouse doesn't act like it has the flue, it's hard to study what affect the flu is having on it. The solution to this problem turns out to be... the domestic ferret. Ferrets make fantastic immunological models because they get sick with flu and other respiratory diseases like cystic fibrosis practically the same way we do. And if a ferret gets sick the same way we do, then the same treatments that help it get better should work on us. This allows us to test things like vaccines and stay one step ahead of the latest influenza virus and other pathogens. There's always a reason that studies about human diseases are done with weird creatures like these, whether they're buzzy or fuzzy or poky or squirmy. And to all of them, I say thank you. (4:27)
And thank you, for joining me for this SciShow Dose. To learn how you can keep exploring the world and the universe and the insides of you, just go to Subbable.com/SciShow, and don't forget to go to YouTube.com/SciShow and subscribe.
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