The Ultimate in Grow Your Own (Ears)

Evolution generally means we get stronger and smarter, but not always. Humans, for example, can’t regrow limbs once we’ve lost them, while some animals can.

Salamanders can regenerate limbs and even their brains and spinal cord. Starfish and octopuses can regrow lost arms. Some mammals have retained this ability. Rabbits and goats can regrow pieces of their ears damaged from injury, while rats can no longer. So, scientists hoped that by comparing genes in those animals, they could figure out which is responsible.   

They made “punch holes” in rabbit and mouse ears and looked for gene changes at the injury site.  When they used a technique called comparative single-cell sequencing, they found differences in the activity of a gene called Aldh1a2. This gene controls the production of a chemical called retinoic acid, related to Vitamin A. It’s long known to support tissue repair in mammals.  It is also involved in embryo growth, male fertility, bone growth and immunity. 

To prove this is the gene, researchers enhanced retinoic acid levels in the injured mouse by transplanting a gene enhancer from a rabbit into the mouse tissue to increase production of retinoic acid.   

In other experiments, they also applied “pure” retinoic acid on the injured tissue. Both sets of animals regrew ear tissue that closed the “punch holes” in their ears, which means this single chemical can stimulate the regrowth of the natural tissue. 

Is this a switch that can prompt other tissues to regrow? Only time and more science will tell.