In Xenopus smooth (Xenopus laevis), a species native to southern Africa, only individuals who are still larvae or tadpoles — they do not yet have legs, but a tail they use to swim — can see their tail repel. Adults cannot. A team American scientists therefore tried to find out if it would be possible to stimulate this ability in adults: 100 frogs whose legs had been amputated received a cocktail of five drugs for 24 hours. Results, do they report January 26 in the magazine Science Advances: there has indeed been regrowth after 18 months.
But the downsides to this research are numerous: we are talking about incomplete and not fully functional members. Moreover, this frog differs from the salamander, which is often the biological model when we talk about “regrowing” a limb, since the salamander does indeed have this ability to regrow a complete limb.
The adult frog in question can normally only regrow what’s called a point of flesh — the equivalent of a heel rather than a leg — and this is the reason why it was targeted: the objective was to see if it was at least possible to stimulate this already existing capacity, rather than “inventing” one in a living being that does not possess one. And on this plane, so we went from a simple piece of flesh to a limb which, although incomplete, has bones, muscles, nerves and even the beginnings of toes.
It is far from one hope for human amputees, but it is a major breakthrough, after decades of trying to figure out the “regenerative” secret of salamanders.