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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.
More Information
Reactivation of mammalian regeneration by turning on an evolutionarily disabled genetic switch
The ability to regenerate damaged organs can be reactivated in nonregenerative mammals. For example, rabbits, but not mice and rats, can fully regenerate damaged ear pinna (the outer ear). Lin et al. performed comparative single-cell sequencing and spatial transcriptomic analyses of pinna regeneration in rabbits, rats, and mice. They found that insufficient production of retinoic acid caused the failure of mouse and rat ear pinna regeneration.
ScienceAdviser: Scientists flip the switch on tissue regeneration in mammals
It’s no big deal for a starfish or octopus to lose an arm—after all, it’ll just grow back. Axolotls are even more impressive, able to regenerate not only severed limbs, but also their spinal cord and even parts of the brain. At some point, however, we mammals lost this remarkable superpower.
