Leptin gives frogs legs
The hormone leptin, known for its role as an appetite suppressant, triggers the formation of legs in young tadpoles, thereby initiating the metamorphosis into frogs. This is reported by researchers led by Robert Denver from the University of Michigan after experiments with clawed frogs (Xenopus laevis).
The scientists had identified the gene for leptin in the frog's genome and introduced it into bacteria to produce the frog-typical leptin. Denver and his colleagues explain that while the sequence differs greatly between humans and frogs, the proteins are very similar. They then injected the frog leptin into different stages of clawed frogs, from young tadpoles to almost adult animals.
In the older specimens, as in humans and mice, leptin acted as an appetite suppressant: the animals ate significantly less. However, young tadpoles did not change their eating behavior, but very quickly developed the first rudiments of their legs.
Denver suspects a safety mechanism behind this: Young tadpoles have to grow as quickly as possible in order not to end up as prey, which is why the hormone cannot develop its usual effect. In frogs, therefore, leptin may have the effect of signaling that the body now has enough supplies to initiate metamorphosis.
