The Phoenix Gene: Axolotl, Mouse, and Zebrafish Secrets to Human Regeneration

An extensive investigation into a ubiquitous gene across three distinct species—axolotls, mice, and zebrafish—has unveiled promising potential for a groundbreaking gene therapy designed to eventually facilitate limb regeneration in humans, according to contemporary research published this week.

“This pivotal research united three distinct laboratories, each examining regeneration across three different organisms,” stated Wake Forest Assistant Professor of Biology, Josh Currie, whose laboratory focuses on the Mexican axolotl salamander. “It demonstrated that universal and unifying genetic pathways govern regeneration across vastly dissimilar life forms, including salamanders, zebrafish, and mice.”

This research endeavor, with its findings documented in the Proceedings of the National Academy of Sciences, involved David A. Brown, a plastic surgeon at Duke University specializing in digit regeneration in mice, and Kenneth D. Poss, who conducts research on fin regeneration in zebrafish at the University of Wisconsin-Madison.

Globally, upwards of one million limb amputations occur annually, primarily attributed to vascular conditions such as diabetes, severe injuries, malignancies, or infections, as indicated by the annual Global Burden of Disease statistics. Projections suggest this figure will escalate due to demographic aging and the rising prevalence of diabetes diagnoses.

This impending challenge has motivated Brown, Currie, and Poss to seek a remedial approach that transcends prosthetic solutions, aiming for a method that could potentially restore the intricate sensory and motor functionalities of an original limb.

A potential genesis for such a solution may lie within what are termed SP genes. Scientists have identified these genes as critical for limb regeneration and common to mice, zebrafish, and axolotls.

Restoration Through Gene Therapy for Deficiencies

The selection of these three species for study was deliberate and founded on their specific regenerative capabilities:

• The axolotl exhibits unparalleled regenerative proficiency, capable of regrowing entire limbs; tails, complete with the spinal cord; and segments of the heart, brain, liver, lungs, and jaw.
• Zebrafish provide an exceptional model for appendage regeneration, characterized by the rapid regrowth of their tail fins and an indefinite capacity for renewal. Furthermore, zebrafish can regenerate their hearts, spinal cords, brains, retinas, kidneys, and pancreases.
• Mice serve as a mammalian analogue to humans, and they possess an inherent ability to regenerate the very tips of their digits. Humans similarly exhibit the capacity to regrow fingertips when an injury occurs in a manner that preserves the nailbed, thereby enabling the regeneration of flesh, skin, and bone.

Currie elaborated that once the research team ascertained that the regenerating epidermis, or skin, of all three studied species expressed the SP genes, specifically SP6 and SP8, their subsequent objective was to rigorously examine the functions and mechanisms of these genes.

Tim Curtis Jr., a doctoral candidate in Biology, contributed to the research efforts within the Currie laboratory, with valuable assistance provided by Elena Singer-Freeman, an undergraduate student and Goldwater Scholar slated to graduate from Wake Forest in 2025 with a degree in biochemistry and molecular biology.

Mimicking Salamander Gene Capabilities

In salamanders, the SP8 gene plays a crucial role in limb regeneration. Employing CRISPR gene-editing technology, Currie’s laboratory successfully deactivated SP8 within the axolotl genome. The absence of SP8 impeded the proper regeneration of limb bones in the axolotl. A comparable outcome was observed in mouse digits when SP6 and SP8 were rendered non-functional.

Leveraging this acquired knowledge, Brown’s laboratory developed a viral gene therapy utilizing a tissue regeneration enhancer identified in zebrafish.

This therapeutic intervention delivered a secreted molecule known as FGF8, a gene typically activated by SP8, thereby stimulating the regrowth of bone in digits and partially reinstating the regenerative functions lost due to the absence of the SP genes in mice.

While human limbs currently lack this intrinsic regenerative capacity, future possibilities may emerge through therapies capable of emulating the regenerative prowess of SP genes.

This can serve as a demonstration of principle, suggesting that we might be able to administer therapies that substitute for this regenerative epidermal style to promote tissue regrowth in humans.

Josh Currie, Wake Forest Assistant Professor of Biology

Establishing a Foundation for Human-Specific Therapies

Despite the considerable further investigation required to translate findings from mouse digits to human limb regeneration, Currie characterized this study as foundational for the ongoing pursuit of therapies aimed at regrowing limbs following injury or disease.

“Researchers are actively exploring numerous strategies for limb replacement, including bioengineered scaffolds and stem cell therapies,” Currie explained. “The gene therapy approach elucidated in this study represents a novel pathway that can complement, and potentially enhance, what will undoubtedly be a multidisciplinary endeavor aimed at one day achieving human limb regeneration.”

He emphasized that the decision to foster interdisciplinary collaboration among scientists studying such disparate organisms proved instrumental to the success of this research.

“Frequently, scientific inquiry operates in isolation: researchers might focus exclusively on axolotls, mice, or fish,” Currie remarked. “A truly exceptional aspect of this research is our collaborative engagement across these diverse organisms. This cross-species approach is immensely potent and is something I hope to see gain greater traction within the scientific community.”