The Amazing Spider-Man 2 is about to swing into theaters, revealing the long-awaited fate of Lizard, the scientist-turned-monster who’s obsessed with reptilian regeneration (video). Regrowing body parts isn’t only the stuff of movies, though—many animals regenerate for various reasons.
Many lizards, such as anoles, have a slick defense called autotomy, which occurs “when the animal severs a body part itself in order to distract the predator and allow the animal to get away,” Bely said.An anole missing its tail in Puerto Rico’s Black Bull Forest Reserve. Photograph by Robert Fried, Alamy
When a lizard is threatened, it can sever its own tail using a muscular contraction. The reptiles have weak points in their tail that allow the appendage to easily break off.
That’s not the end of the tail—another one grows in its place. But a 2012 study by researchers at Arizona State and the University of Arizona found that the regenerated anole tail is not an exact replica of the original. The new tail is less flexible partly because it’s structured as a long tube of cartilage, rather than being made of interlocking vertebrae.
That’s because the physical makeup of the new appendage is “much less important than just having a tail,” Bely says—especially when losing the old one can mean saving your life.
This humble little amphibian is an astonishing regeneration multitasker, able to regrow limbs and also parts of its eyes, spine, brain, and other parts. (Related: “Newt Healing Factors Unaffected by Age, Injury.”)
Their regenerating ability has been under scientific scrutiny for centuries, and in 2013 the University of Dayton in Ohio and the Max Planck Institutes gave us new insight into how it actually happens: They made the first map of the RNA molecules expressed in regeneration, called the transcriptome. RNA is responsible for controlling the activity of cells.
These marine invertebrates have eyestalks that can’t be withdrawn into their shells. But if a predator grabs them, they have a backup plan: regrowing their eyes.
Ivan R. Schwab of the University of California, Davis, wrote in a 2007 paper in the British Journal of Opthalmology that within a few weeks new eyes regenerate to their full size.
A number of gastropods—the group that includes snails, slugs, and conch—are underrated regenerators, Bely says: Some can even regenerate their whole head.
They’ve been largely ignored, Bely said, because researchers tend to focus on what she calls “regeneration superstars,” like newts or flatworms. (Related: “An Entire Flatworm Regenerated From a Single Cell.”)
Zebrafish, mentioned in the first Amazing Spiderman movie, are also regeneration aces, able to regrow numerous parts including fins, spinal cords, and heart muscle, a process you can see in this video animation from the Howard Hughes Medical Institute.
A 2010 study, done by researchers at the Salk Institute for Biological Studies in California and the Center of Regenerative Medicine in Barcelona, found that the two-chambered zebrafish heart can regenerate after up to 20 percent of the ventricle is amputated.
Does that mean good things for the troubled human heart?
“The challenge is finding common patterns in the regeneration process that then can be used to translate to humans, but I think there are very good reasons to be optimistic,” Bely says.
Figuring out how animals regenerate—and how to emulate it in people—will likely have to do with how an embryo develops. “The information is in the genome,” Bely says. “The trick is finding a way to start that process again.”
African Spiny Mice
In 2012, Ashely Seifert, now of the University of Kentucky in Lexington, and colleagues published a paper showing that the African spiny mouse leaves pieces of skin behind to escape predators. (Related: “Spiny Mice Defend Themselves With Self-Flaying Skin and Fast Healing Factors.”)
That study “overturned the dogma that mammals are uniformly pathetic regenerators,” Bely says.
Even more reason to be optimistic about our regenerating future.