Summary: In a monumental cross-species collaboration, scientists have identified a “universal genetic program” that drives limb regeneration. By studying axolotls, zebrafish, and mice, researchers discovered that a specific family of genes, the SP genes, is the common denominator for regrowing lost tissue.
The study demonstrates that a novel viral gene therapy can partially restore regenerative powers in mammals, offering a foundational blueprint for one day regrowing human limbs.
Key Findings
- Universal Blueprint: Regeneration isn’t a collection of different tricks; it is a shared genetic program that is “active” in salamanders but “silent” or limited in humans.
- A New Pillar of Treatment: While bioengineered scaffolds and stem cells are currently the focus of limb replacement, this gene-therapy approach offers a way to trigger the body’s own internal repair mechanisms.
- Global Impact: With over 1 million amputations occurring annually due to diabetes and trauma, this research provides a biological target to move beyond mechanical prosthetics toward true limb restoration.
Source: Wake Forest University
Investigating a common gene in three very different species – axolotls, mice and zebrafish – scientists have discovered the potential for a novel gene therapy aimed at eventually regrowing limbs in humans, according to new research published this week.
“This significant research brought together three labs, working across three organisms to compare regeneration,” said Wake Forest Assistant Professor of Biology Josh Currie, whose lab studies the Mexican axolotl salamander.
“It showed us that there are universal, unifying genetic programs that are driving regeneration in very different types of organisms, salamanders, zebrafish and mice.”
The research, with results appearing in the Proceedings of the National Academy of Sciences, included David A. Brown, a plastic surgeon who studies digit regeneration in mice at Duke University, and Kenneth D. Poss, who studies fin regeneration in zebrafish at the University of Wisconsin-Madison.
Each year, around the world, more than 1 million limb amputations occur because of vascular diseases such as diabetes, traumatic injuries, cancer or infections, according to annual Global Burden of Disease statistics. The number is expected to rise with the aging population and the increase in diabetes diagnoses.
That looming challenge has inspired Brown, Currie and Poss to search for a treatment beyond prosthetics, for something that could replace the complex senses and motor skills of an actual limb.
They might have found the start of a solution in something called SP genes, which the scientists discovered are vital for limb regeneration and shared by the mouse, zebrafish and axolotl.
Therapy makes up for missing gene
The scientists chose to study these three animals for specific reasons:
- The axolotl excels at regeneration, with the ability to regrow complete limbs; tails, including the spinal cord; parts of the heart, brain, liver, lungs and jaw.
- Zebrafish offer one of the best models for appendage regeneration because their tail fins regrow rapidly and have unlimited capacity for regrowth. The zebrafish also can regenerate its heart, spinal cord, brain, retinas, kidneys and pancreas.
- Mice represent mammals like humans, and they already can regenerate the tips of their digits. Humans, too, can regrow their fingertips when an injury preserves the nailbed. That allows regrowth of flesh, skin and bone.
Currie said that once the scientists determined the regenerating epidermis, or skin, of all three species expressed the SP genes SP6 and SP8, they set out to test what the genes do and how they work.
Biology Ph.D. student Tim Curtis Jr. contributed to the research in the Currie lab, with assistance from undergraduate Elena Singer-Freeman, a Goldwater Scholar and 2025 Wake Forest biochemistry and molecular biology graduate.
Emulating the abilities of salamander genes
In salamanders, SP8 does the work in regenerating limbs. Using CRISPR gene-editing technology, Currie’s lab removed SP8 from the axolotl genome. Without SP8, the axolotl could not properly regenerate the limb bones; a similar result occurred with the mouse digits missing SP6 and SP8.
With that information in hand, Brown’s lab used a btissue regeneration enhancer found in zebrafish to develop a viral gene therapy.
That therapy delivered a secreted molecule called FGF8, a gene that is usually turned on by SP8, to encourage digit bone regrowth and partially restore the regenerative effects of the missing SP genes in mice.
Human limbs don’t have that kind of regenerative power – but might someday, with a therapy that emulates the abilities of SP genes.
“We can use this as a kind of proof of principle that we might be able to deliver therapies to substitute for this regenerative style of epidermis in regrowing tissue in humans,” Currie explained.
Building the foundation for human therapies
Although it will require much more research to take the findings from mouse digits to human limbs, Currie called this study foundational in the search for therapies to regrow limbs after injury or disease.
“Scientists are pursuing many solutions for replacing limbs, including bioengineered scaffolds and stem cell therapies,” Currie explained. “The gene-therapy approach in this study is a new avenue that can complement and potentially augment what will surely be a multi-disciplinary solution to one day regenerate human limbs.”
He said the decision to collaborate among scientists studying such different animals made all the difference in this research.
“Many times, scientists work in their silos: we’re just working in axolotl, or we’re just working in mouse, or just working in fish,” Currie said. “A real standout feature of this research is that we work across all these different organisms. That is really powerful, and it’s something that I hope we’ll see more of in the field.”
Key Questions Answered:
A: Humans have the “hardware” (the SP genes), but our “software” turns them off shortly after birth (except in our fingertips). This research shows we might be able to use gene therapy to “re-install” the active version of the software used by salamanders.
A: This is “foundational” research. It proves the concept works in mouse digits, but regrowing a full human arm, with its complex nerves, muscles, and blood vessels, is a much larger challenge that will require combining this gene therapy with other tech like bio-scaffolds.
A: Zebrafish have incredibly powerful “enhancer” sequences in their DNA, essentially high-voltage switches that turn on regeneration genes. The researchers used one of these zebrafish switches to make their gene therapy effective in mice.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this genetics and limb regeneration research news
Author: Alicia Roberts
Source: Wake Forest University
Contact: Alicia Roberts – Wake Forest University
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Enhancer-directed gene delivery for digit regeneration based on conserved epidermal factors” by David A. Brown, Katja K. Koll, Erin Brush, Grant Darner, Timothy Curtis Jr., Thomas Dvergsten, Melissa Tran, Colleen Milligan, David W. Wolfson, Trevor J. Gonzalez, Sydney Jeffs, Alyssa Ehrhardt, Rochelle Bitolas, Madeleine Landau, Kendall Reitz, David S. Salven, Leslie A. Slota-Burtt, Isabel Snee, Elena Singer-Freeman, Sayuri Bhatia, Jianhong Ou, Aravind Asokan, Joshua D. Currie, and Kenneth D. Possg. PNAS
DOI:10.1073/pnas.2532804123
Abstract
Enhancer-directed gene delivery for digit regeneration based on conserved epidermal factors
Limb loss remains a significant clinical challenge, but regenerative medicine approaches such as gene therapy offer a promising strategy to trigger endogenous regeneration programs. Optimal vector configurations and molecular targets for appendicular skeletal repair are not well defined.
Here, we leveraged insights from species with a high endogenous capacity for appendage regeneration to design an enhancer-directed gene delivery platform that functions during mouse digit regeneration, a well-characterized model for partial limb regeneration in mammals.
Single-cell RNA sequencing of zebrafish caudal fin regeneration, combined with expression data in regenerating salamander limbs and mouse digit tips, implicated the SP family of transcription factors as conserved, epidermally expressed mediators of appendage regrowth.
Null mutants of Sp8 demonstrated impaired limb regeneration in salamanders, while conditional knockout of Sp6 and/or Sp8 in the mouse basal epidermis resulted in defective bony digit tip regeneration, involving an IL-17-mediated osteoclastogenic program.
Spatiotemporally focused expression of FGF8, a known target of SP factors, using a zebrafish-derived tissue regeneration enhancer element via adeno-associated viral vectors, could partially rescue digit tip regeneration in SP knockout mice and accelerate digit regeneration in wild-type mice.
Our results demonstrate a contextual gene therapy approach to address limb loss based on genes like SP transcription factors conserved across multiple contexts of appendage regeneration.
