Retinoids Can Make Limbs Grow

by
Julie Froehlig
Scientist

Hormones Tell Limbs to Grow

How does a tadpole know when and where to grow its legs? This is a very complex process involving many chemical signals. We call these signals HORMONES , which are chemical messengers sent through the blood.

Scientists don't completely understand how the all the hormones work to form the limb at the right place and time. They do know that one type of hormone known as RETINOIDS plays a very important role.

The Salamander Limb Experiment

Scientists have performed experiments that show that retinoids are involved in limb development. They have been able to get a limb to regrow after it had been cut off, by treating the stub with retinoids. One experiment used a salamander similar to this one:

PICTURE COURTESY OF THE OHIO DEPARTMENT OF NATURAL RESOURCES

The picture below shows what happened in the experiment. The dotted line marks where scientists cut off the limb of a salamander. The second picture shows that a whole new limb reformed after being treated with RETINOIDS.

PICTURE COURTESY OF DR. STAN SESSIONS

What Does This Have To Do With Frogs?

Scientists have also applied retinoids to the limb buds of tadpoles as they begin to develop into frogs. They have been able to produce extra limbs or limbs that grow in the wrong place: the same types of limb deformities seen in nature.

Scientists have not been able to produce these deformities with methoprene. But because methoprene is a chemical that is very similar to a retinoid, it is possible that methoprene is related to deformities.