The axolotl can regrow lost limbs, parts of its heart and even its brain.
The axolotl, a Mexican salamander that never really grows up, keeps its feathery gills and lives in water all its life. Lose a leg and it grows a complete new one over a few months, without a scar. Yet this champion of regeneration is nearly extinct in the wild.
Most amphibians start life as aquatic larvae and then metamorphose into land-living adults. The axolotl skips that step. It lacks the hormone signal that triggers metamorphosis, so it becomes sexually mature while still in larval form, with external gills and a finned tail, a trait called neoteny. Given thyroid hormones in the lab, it can be pushed to transform into a land salamander. In Paris in the 1860s, the zoologist Auguste Duméril was startled to find what looked like a new species of salamander in his axolotl tank; it was the first clue to neoteny.
Its fame, though, comes from regeneration. Where we form scar tissue, an axolotl rebuilds. Lost limbs and tails regrow over months, and it can restore tissues of the eye and heart and even non-vital parts of its brain. First skin seals the wound; then cells gather into a mass called a blastema, which grows and patterns itself into the new limb, with nerve signals essential to the process. The ability declines with age and is much reduced in animals made to metamorphose. The axolotl's genome, published in 2018, is about ten times the size of ours, and researchers study it in the hope of improving human healing.
In the wild, axolotls live only in what remains of an ancient lake system in the Valley of Mexico, now largely covered by Mexico City. Lake Xochimilco survives mainly as canals. Surveys found about 6,000 axolotls per square kilometre in 1998, 1,000 in 2003 and 100 in 2008; a four-month search in 2013 found none at all, until two turned up a month later. Polluted water and invasive tilapia and carp, which eat the young, are major threats, and the species is critically endangered.
In captivity the story is reversed: large captive populations are bred for research and the pet trade, and many descend from 34 animals shipped to Paris in 1863. The axolotl is named after the Aztec god Xolotl, who in legend became one to escape sacrifice, and it now appears on Mexico's 50-peso note. Conservationists are testing whether captive-bred animals can survive being released.
Source: Wikipedia — Axolotl · Text summarised from Wikipedia (CC BY-SA 4.0)
