# The Secret Behind the Salamander That Regrows an Entire Limb > Cut off a salamander's leg, and it will grow a new one, perfectly functional, with the right bones, the right muscles, and - Author: Maxime Marquette - Publisher: MadMax (https://mad-max.co) - Section: Reportage - Published: 2026-07-07 - Canonical URL: https://mad-max.co/en/article/le-secret-de-la-salamandre-qui-fait-repousser-un-membre-entier ## Key takeaways - Retinoic acid, a vitamin A derivative, was already known to be involved in salamander limb regeneration, but the precise mechanism controlling its dosing had remained unclear. - The key finding, from a June 2025 study in Nature Communications, concerns the enzyme CYP26B1, which reduces retinoic acid at the wound site to the exact level needed for the missing part. - The Shox gene, known in humans for long-bone growth, activates after injury and works like a measuring stick that sets how far the new bone structure extends. - Humans possess the same basic ingredients, so the difference seems to lie in how these elements are activated after an adult amputation. - The researchers caution that reproducing these mechanisms safely in adult humans is far more complex, with possible applications first in wound healing and partial tissue repair. ## Introduction: the animal that refuses to stay amputated ### A power that has fascinated science for centuries Cut off a **salamander's** leg, and it will grow a new one, perfectly functional, with the right **bones**, the right **muscles**, and the right **digits**, at the right size and in the right place. This power of **regeneration**, known to naturalists for centuries, still fascinates biologists today, because it touches on a fundamental question: why can some animals rebuild an **entire limb**, while humans, equipped with the same basic **molecular ingredients**, are completely unable to do so? A study published in **June 2025** in the journal **Nature Communications** offers fresh answers to this question, precisely identifying the **molecular mechanisms** that let the **axolotl**, a species of **Mexican salamander** widely studied in laboratories, know exactly which part of the body to rebuild, at what **precise size**, and in what **exact location** on the body. ### The central role of retinoic acid At the heart of this process lies a molecule well known in biology: **retinoic acid**, a derivative of **vitamin A** also found in many cosmetic creams marketed to humans. This substance plays a central role in the **embryonic development** of a great many animal species, including our own. In salamanders, **scientists** had long known that retinoic acid was involved in **limb regeneration**, but the **precise mechanism** that allowed this molecule to be dosed with such accuracy remained largely mysterious, despite **decades of research** on the subject. This mystery was no small matter: understanding how a simple molecule can tell cells the difference between rebuilding a finger, a hand, or an entire arm represented one of the most stubborn puzzles in **developmental biology**. **Researchers** knew the answer lay somewhere in the **chemistry of the wound site**, without being able, until now, to describe the exact mechanism. *There is something almost ironic about this story: the molecule that lets a salamander regrow an entire arm also shows up, in tiny amounts, in our anti-wrinkle creams. The same ingredient, two radically different biological destinies depending on the species using it.* ## An enzyme that plays conductor ### CYP26B1, the precision dosing enzyme The major discovery of this study concerns an **enzyme** called **CYP26B1**. Contrary to what one might expect, this enzyme does not manufacture retinoic acid: it **reduces the amount** present at the wound site, with remarkable precision, down to exactly the level needed to rebuild the **missing part**. Researcher **James Monaghan**, whose work was highlighted by National Geographic among the year's standout discoveries, explains that it is the **amount of retinoic acid** present that tells cells precisely what they need to rebuild at that spot on the body. This finding **surprised the team** itself. Researchers expected to find an additional **production** mechanism for retinoic acid at the wound site, capable of raising its **concentration** as needed. Instead, they found a reversed system: a **targeted degradation enzyme**, which starts from a high initial level and gradually reduces it down to the exact required value. This subtraction-based, rather than addition-based, mechanism offers an unexpected lesson in how nature solves problems of biological precision. The higher the **residual concentration** of retinoic acid after the enzyme acts, the larger and more complex the regenerated structure will be: an **entire arm** requires more of this molecule than a simple hand, which in turn requires more than a single finger. This fine-tuned dosing system explains how the salamander manages to rebuild precisely the missing portion of the limb, neither more nor less, without ever regrowing an oversized or incomplete limb. ### A gene that determines the final size Alongside this chemical dosing mechanism sits a second genetic player: the **Shox** gene, already known in humans for its role in the **growth of long bones**. In salamanders, this same gene activates after an injury to orchestrate the reconstruction of the **bone structures** of the forming limb. **Researchers** believe that access to these precise **genetic programs** after an injury is what allows the animal to literally switch back on the **instructions** that were used to build the arm the first time, during its initial **embryonic development**. This gene acts a bit like an invisible measuring stick, determining how far the new bone structure should extend before stopping. Without this precise regulation, the salamander could theoretically produce a limb that is too long, too short, or poorly proportioned. The fact that nature selected a **rigorous system**, combining both a chemical signal and a **genetic signal**, speaks to the **sophistication** of the regeneration process, long underestimated by science. The combination of these two elements, the precise dosing of retinoic acid by the CYP26B1 enzyme and the targeted activation of the Shox gene, forms a kind of molecular blueprint that the salamander appears able to reread at will, unlike most other vertebrates. *What stuns me about this mechanism is its almost mathematical elegance. A simple shift in a molecule's concentration is enough to distinguish, in cellular language, a finger from an entire arm. Nature did not need to invent a complex system: it simply learned how to dose.* ## Why humans cannot do the same thing ### The same ingredients, but a different recipe The most troubling part of this discovery is probably this: **humans also possess** **retinoic acid**, the CYP26B1 enzyme, and the Shox gene. We therefore have, in theory, the same basic molecular building blocks as the salamander. And yet, when a human loses a limb, these elements do not organize themselves the same way to rebuild the missing part. The difference does not lie in the presence or absence of these ingredients, then, but in how our bodies activate them, or rather fail to properly reactivate them after an amputation in adulthood. This distinction is **crucial** for **medical research**: it means the goal is not to import exotic genes into the human genome, but to understand how to wake up **biological capabilities** that are already present, yet silenced over the course of evolution. A far more realistic prospect, even though it remains extraordinarily complex to put into practice. ### The gap between theory and the clinic Despite the enthusiasm sparked by these results, the researchers themselves stress the need for caution. Identifying the molecular mechanisms in salamanders is one thing; managing to reproduce them safely and in a controlled way in an adult human organism is another matter entirely, far more complex. The **human body**, with its far more sophisticated physiology, its distinct **immune response**, and its different healing processes, poses **considerable obstacles** to any attempt at directly transposing these mechanisms. Nevertheless, this research opens up a serious theoretical avenue toward longer-term medical applications, notably for improving **wound healing** after severe trauma, or for exploring partial regeneration of damaged tissue, well before considering the complete regeneration of a human limb. *I find it reassuring that the researchers themselves refuse to oversell the dream prematurely. Honestly saying "we have the same ingredients, but not yet the recipe" is infinitely more useful to science than promising regenerated limbs within a decade without solid proof.* ## A discovery among the most notable of the year ### Recognition beyond the academic circle This **research** on regeneration in salamanders was highlighted by **National Geographic** among the **major medical discoveries** of 2025. This recognition illustrates the importance the scientific community and the general public place on this work, which touches on a universal question: how the body repairs itself after severe injury, a major medical concern for millions of amputees and severe trauma victims worldwide. The choice of the **axolotl** as a study model is no accident. This species of salamander, native to **Mexico** and now **threatened in the wild**, has become a go-to laboratory animal for studying regeneration, thanks to its **exceptional ability** to rebuild not just its limbs but also certain internal organs, its **spinal cord**, and even parts of its heart or brain. ### The next steps for research Research teams, including the one led by Monaghan, now plan to deepen their understanding of the interactions between retinoic acid, the CYP26B1 enzyme, and the Shox gene, in order to determine whether targeted interventions could one day modulate these same pathways in mammals, initially for experimental purposes. This work fits into a broader research field devoted to **regenerative medicine**, which explores multiple parallel avenues for restoring damaged tissues and organs. This convergence between fundamental biology and therapeutic prospects illustrates well why studying a creature as unusual as the axolotl continues to attract top-tier funding and researchers, decades after nineteenth-century naturalists first observed its regenerative abilities. *Every time I think about the axolotl, I am reminded that it perfectly embodies the idea that answers to human medicine's biggest questions sometimes hide in the most unlikely creatures, quietly swimming in a laboratory tank.* ## Conclusion: between wonder and scientific caution ### What this discovery really changes The study on limb regeneration in **salamanders** provides a precise answer to a question asked for generations: how does an organism know exactly what to rebuild after an amputation? The answer combines fine chemical dosing of **retinoic acid**, orchestrated by the enzyme **CYP26B1**, and activation of the **Shox** gene, which together dictate the size and nature of the structure to be regenerated. This mechanistic understanding is a significant advance in fundamental biology, regardless of any immediate medical application. It enriches our knowledge of living organisms and of how certain species have, over the course of evolution, preserved repair capabilities that others, such as mammals, have largely lost. ### A human application still distant, but not impossible While the complete regeneration of a human limb remains, at this stage, a very distant theoretical horizon, this research nonetheless provides a solid foundation for future work on wound healing and tissue repair in humans. The road between the laboratory salamander and a possible clinical application remains long, but every step of molecular understanding, like this one, brings regenerative medicine a little closer to its boldest ambitions. **By Maxime Marquette, columnist** ## Columnist's transparency note ### Editorial stance I am not a journalist but a **columnist and analyst**. My expertise lies in observing and analysing the geopolitical, economic and strategic dynamics that shape our world. My work is to take political strategies apart, to understand global economic movements, to put the decisions of international actors in context and to offer analytical perspectives on the changes that are redefining our societies. I do not claim the cold objectivity of traditional journalism, which stops at reporting facts. **I claim analytical clarity**, rigorous interpretation and a deep understanding of the complex issues that concern us all. My role is to give meaning to the facts, to place them in their historical and strategic context, and to offer a critical reading of events. ### Method and sources This text keeps the basic distinction between **verified facts and interpretive analysis**. The rule never changes: a factual claim is published only when a verifiable source supports it, and the sources this article actually used are listed under **Sources**, never here. **Primary source families** used by the publication, when the story has them: official statements from governments and international institutions, public statements by political leaders, reports from intergovernmental organisations, dispatches from recognised international news agencies. **Secondary source families**: specialised publications, internationally recognised news media, analyses from established research institutions, reports from industry organisations. When an article cites statistical, economic or geopolitical data, it comes from the institutions that produce it (intergovernmental organisations, central banks, national statistics offices), and the exact institution is named under **Sources**. ### Nature of the analysis The analyses, interpretations and perspectives in the analytical sections of this article are a **critical, contextual synthesis** based on the information available, the trends observed and the expert comments cited in the sources consulted. My role is to interpret these facts, to set them in the context of today's geopolitical and economic dynamics, and to give them a coherent meaning within the larger story of the changes shaping our time. These analyses reflect expertise built through continuous observation of international affairs and an understanding of the strategic mechanisms that drive global actors. This article describes a documented state of affairs on its publication date, not a prediction: later developments may shift its outlook. No update is promised in advance; when an article is corrected or completed, the change is dated in the text. ## Sources ### Primary sources - National Geographic France — Nine medical discoveries that marked 2025, including salamander regeneration — 2025 - Nature — Regeneration: scientific publications on animal regeneration mechanisms — 2025 - Cell Press — Research on regeneration biology and retinoic acid — 2025 ### Secondary sources - Futura Sciences — Accessible analysis of limb regeneration in amphibians — 2025 - Sciences et Avenir — Coverage of discoveries on the axolotl and regenerative medicine — 2025 - Science et Vie — Reports on animal regenerative capabilities and their medical implications — 2025 --- Source: Maxime Marquette, MadMax. 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