Arms!

August 30th, 2025| Topic: RaMbLeS | 0

There are about a million of these in captivity—in homes as pets, and in labs as scientific subjects: axolotls. A member of the salamander family that is “pedomorphic,” i.e., in the form of a juvenile.

Most amphibians begin their lives as aquatic animals which are unable to live on dry land, till they undergo metamorphosis to reach adulthood, losing their gills and starting to live on land. Our specimen, the axolotl, lacks some of the hormones that stimulate metamorphosis, so it retains its gills and dwells in water all its life.

And this pedomorph has even found its way into video games—Minecraft and its spinoffs. Yup, it is popular.

But this popular species is also helping researchers investigate a serious medical mystery: this thing can grow back severed limbs! And now we may have figured out how this beast accomplishes this rare feat. Reported scientists from Northeastern University and the University of Kentucky, in “Retinoic Acid Breakdown Is Required for Proximodistal Positional Identity During Axolotl Limb Regeneration,” published in Nature: Communications recently.

James Monaghan, a Northeastern University, and senior author on the paper:

This species is special. They’ve really become the champion of some extreme abilities that animals have. One of the outstanding questions that has really plagued the field is how a salamander knows what to grow back.”

Because you see, as a reporter for the Washington Post described it:

One marvel is that to enable a body part to grow back, the cells responsible for that growth need to somehow register where they are on the body. If an amputation is at the upper arm, for example, they have to re-create upper arm, then the lower arm and, finally, the hand. But if it’s at the lower arm, the cells have to know to grow back just the lower arm and hand.”

Apparently a tiny molecule called retinoic acid is responsible for this inner GPS of the axolotl. The scientists genetically engineered axolotls so that their tissue glows in the presence of retinoic acid, allowing real-time tracking. Then they severed a limb (under anesthesia and in the name of vital science) and watched what happened: plenty of the chemical accumulated at the site of regrowth.

But with a drug that blocks an enzyme involved with retinoic acid, all kinds of weirdnesses happened to the severed-limb-axolotls: upper arms growing instead of forearms, etc.

Maybe human limbs can be regenerated one day with retinoic acid?

(BTW: retinoic acid is also commonly prescribed for acne and used cosmetically. Hopefully, my acne patients don’t start growing extra limbs!)

But some arms will not be regenerated: those limbs of the enemies of the people of God.

Break the arm of the wicked and the evildoer; call him to account for his wickedness ….
Psalm 10:15

For the arms of the wicked will be broken, but the righteous are supported [by] Yahweh.
Yahweh knows the days of the blameless, and their inheritance will be forever.
Psalm 37:17–18

And that is simply because there is another whose arms are never severed, never lost, never weak.

You are the God who works wonders; You have made known among the peoples Your strength.
You have redeemed with Your arm Your people …
Psalm 77:14–15

To You [belongs] an arm with strength;
Your hand is mighty, Your right hand is exalted.
Psalm 89:13

No need for retinoic acid. Just the arm of God!

So …

Sing to Yahweh a new song, for He has done wonders;
His right hand and His holy arm have accomplished deliverance for Him.
Psalm 98:1

SOURCE: Washington Post; Nature