Enlarge / It’s so cute! Let’s chop off its leg in the name of science.
It’ll grow back. (credit: IMP Vienna)
Some human tissues, like the liver and muscles, retain the ability to regrow after damage.

But most of our bodies do not—if you lose a limb, the limb’s gone.

But elsewhere in the animal kingdom, regeneration is much more widespread. Many reptiles can regrow tails, and some salamanders can replace entire limbs. More distantly related worms called planaria can be cut into multiple pieces and see each piece regrow an entirely new body.
There are a couple of organisms that have been extensively studied due to their ability to regenerate: the planarian Schmidtea mediterranea and a type of salamander called an axolotl (Ambystoma mexicanum).

But those studies have been limited by the fact that we don’t have a complete catalog of genes for these organisms.

Attempts to correct that were bogged down by the fact that the genomes appeared to be littered with duplicate copies of virus-like DNA—in the case of the axolotl, enough to balloon its genome up to 10 times the size of our own.
Now, researchers have figured out a way to overcome that hurdle, and they have gotten high-quality copies of both the planarian’s and the axolotl’s genomes. Unfortunately, the copies don’t shed much light on the animals’ regeneration abilities.

And all that extra DNA carried by the axolotl doesn’t seem to be doing anything useful in particular.
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