字幕表 動画を再生する 英語字幕をプリント AHHHH haha just kidding Hey everyone, Julia here for DNews Losing a limb is never something to laugh at. While humans can build awesome robotic arms, other animals have their handy own way of dealing with the problem. Like the moon jellyfish. If this ocean invertebrate loses a limb it simply moves around the other remaining limbs. In a recent study published in the Proceedings of the National Academy of Sciences found that the jellyfish restore functionality in a process the researchers call symmetrization. The jellyfish have to be perfectly symmetrical in order to swim properly. If they can’t swim to find food or swim away from a predator, well they’ll be swimming with the fishes. Or… they’ll you know get eaten or something. The researchers found that the jellyfish pull off this game of musical arms by using their muscles to push apart the arms as widely as possible. And the whole process is fast, like anywhere from 12 hours to 4 days. While the moon jellyfish use symmetrization to compensate for losing a limb or two, other animals simply regrow their missing body parts. Most of us know that the starfish, excuse me sea stars, can regrow their arms and in some species, they can regrow entire bodies out of limbs. But there’s tons of other animals out there who can regrow limbs too. Like Salamanders, Zebrafish and even some insects like cockroaches. But sometimes limbs aren’t always perfect copies of the original. Like regrown tadpole tails are missing a few nerves. But some animals go one step further, some animals can perfectly regrow their heads. One small animal, Hydractinia, is a head above the rest. Commonly called “snail fur” because it grows on the shells of snails and crabs, this tiny animal can regrow its entire head if it gets bitten off by a hungry predator. But they aren’t alone in this remarkable ability. Planaria also have amazing abilities to regrow themselves. Literally, they can reproduce asexually and just make more copies of themselves. And these guys can also regrow their heads. But what’s weird is, in one study published in the Journal of Experimental Biology, researchers found that worms with regrown heads had the same memories as before. How? Well the researchers aren’t so sure, but think that maybe their memories get stored in other cells in the body and then get imprinted into the new brain when it grows. But what makes these animal’s powers of regeneration so good? In short, stem cells. Stem cells are undifferentiated cells which have the ability to grow into any type of cell or tissue. All animals have these, I mean we grow body parts from scratch as an embryo. But most mammals lose their pluripotent stem cells, or stem cells that are general but can grow into more specific cells later. Some animals like Hydractinia and Planaria use pluripotent stem cells to regenerate themselves. Hydractinia keep their embryonic stem cells for their whole lives. Whenever their heads get eaten up, stem cells flood the neck area and start to build a new head. But other animals have different cellular mechanisms. In salamanders, their limbs regenerate from adult tissue cells. Basically the cells dedifferentiate and form a mass called a blastema. And from this structure, the cells differentiate again and can regrow an arm or a leg. This whole process can take anywhere from a month to three months depending on how old the animal is. But what’s interesting is that some researchers like David M. Gardiner, a professor of developmental and cell biology at the University of California-Irvine, think that all animals might have the ability to grow body parts of pluripotent cells. That some common ancestor that even we share with something like the snail fur was able to keep its stem cells well into adulthood. For some reason ours is just turned off, but he thinks one day we’ll find the on switch. Speaking of animals remarkable ability to regenerate, there might an animal that can live forever!! Check out this short and sweet video from our new show TestTube 101!