The investigative team, led by former postdoctoral researcher Dr. Alice Accorsi and Stowers President Dr. Alejandro Sánchez Alvarado, has proposed the apple snail as a genetically tractable non-vertebrate model organism for eye regeneration research. Published in Nature Communications in August 2025, their work establishes a comprehensive system for studying the molecular and cellular mechanisms underlying complete camera-type eye regeneration. Crucially, the researchers developed advanced gene-editing tools, adapting CRISPR-Cas9 technology to apple snails to manipulate specific genes involved in eye development and regeneration.

Eye regeneration in the apple snail unfolds in a precisely orchestrated sequence spanning approximately 28 days and four key phases. Initially, rapid wound healing occurs, mirroring the limited regenerative response in vertebrates. Subsequently, a specialized cell mass, likely comprising progenitor or stem-like cells, forms at the site of injury, laying the foundation for new eye structures. Following this, remarkable differentiation leads to the emergence of both the lens and retina, critical components of the camera-type eye. The final stage, maturation, involves the complete functional assembly of all ocular tissues to restore visual capability.

At the core of this regenerative prowess lies the gene pax6, a master regulator universally known for its role in eye development across diverse species—from vertebrates to fruit flies. The team demonstrated for the first time that pax6 is not only present in apple snails but is absolutely essential for the formation of their eyes. Using CRISPR-Cas9 to disrupt pax6 function, they engineered gene-edited snails that developed without eyes, yet remained viable and healthy. This striking phenotype solidifies the apple snail as a powerful system for dissecting gene function related to eye development and regeneration.

This work heralds a paradigm shift because it combines two rare attributes in one model organism: the ability to fully regenerate a complex sensory organ and the capacity for precise genetic manipulation. The synergy of these features makes the apple snail a uniquely valuable platform for mechanistic studies that could illuminate how genetic networks are reactivated after injury to drive tissue regeneration. Understanding these pathways may identify therapeutic targets for treating devastating human eye conditions that currently have limited remedies.

During the investigation, transcriptomic analyses were conducted at every stage of the eye regeneration process. By profiling gene expression dynamics over time, the team compiled a curated list of candidate genes potentially critical for driving regeneration and developmental reprogramming. Future studies using targeted gene disruptions will validate the functions of these candidates, further decoding the genetic blueprint that orchestrates sensory organ restoration from the wound site to a fully functional eye.

The importance of this research resonates throughout the broader scientific community, especially among experts studying mollusk biology. As noted by Dr. Angus Davison of the University of Nottingham, this endeavor fills a significant gap by providing a genetically tractable mollusk model, thereby enabling detailed genomic and developmental analyses that were previously unattainable in this diverse animal group. Such advances not only refine our understanding of molluscan evolution but also have cross-phylum implications for regenerative biology and genetics.

From a translational perspective, this study opens new avenues for ophthalmological innovation. The apple snail’s regenerative mechanism serves as a natural template, offering clues about cellular plasticity, stem cell activation, and tissue remodeling that mammalian eyes lack. By unraveling these biological processes in a controlled experimental setting, researchers can aspire to harness or mimic similar pathways in human tissues, potentially revolutionizing how retinal degeneration, trauma-induced blindness, and other ocular disorders are managed.

Furthermore, the successful application of CRISPR-Cas9 gene editing in apple snails exemplifies a growing trend in expanding genetic toolkits to non-traditional model organisms. Overcoming technical barriers to manipulate the genome in such species not only broadens the horizon of biological research but also enhances its ecological and evolutionary relevance. The ability to induce stable gene knockouts in the apple snail accelerates functional genomics studies, teasing apart the intricate gene networks essential for regeneration.

The research team’s perseverance, innovation, and multidisciplinary approach have culminated in a robust experimental framework, allowing the scientific community to plunge deeper into the fundamental principles guiding organ regeneration. Importantly, their work underscores that with focused effort and creative methodology, organisms once considered challenging for genetic study can become accessible and illuminate fundamental biological phenomena once thought beyond reach.

In summary, the establishment of the apple snail as a genetically manipulable system for complete eye regeneration represents a monumental stride in developmental biology and regenerative medicine. This model offers an unprecedented window into the genetic and cellular orchestration of complex organ regeneration, holding immense promise for understanding the limitations of human eye repair and guiding future therapeutic strategies. As this field matures, the apple snail may well become emblematic of nature’s intrinsic regenerative potential, inspiring scientists and clinicians alike to rethink the possibilities of healing in sensory organs and beyond.

Subject of Research: Animals

Article Title: A genetically tractable non-vertebrate system to study complete camera-type eye regeneration

News Publication Date: 6-Aug-2025

Web References:

• Stowers Institute for Medical Research: www.stowers.org
• Study DOI: 10.1038/s41467-025-61681-6

References:

• Accorsi, A., Sánchez Alvarado, A., et al. (2025). A genetically tractable non-vertebrate system to study complete camera-type eye regeneration. Nature Communications. DOI: 10.1038/s41467-025-61681-6

Image Credits: Stowers Institute for Medical Research

Keywords: Regeneration, Developmental biology, Genetic engineering, CRISPR-Cas9, Eye regeneration, Pomacea canaliculata, pax6 gene, Sensory organ regeneration, Molecular biology, Stem cell differentiation, Evolutionary biology, Molecular genetics

The study, led by researchers Johanna Ritter and Elke Grönniger at Beiersdorf AG’s Research and Development center in Hamburg, employs a sophisticated microphysiological co-culture system designed to simulate human tissue environments with remarkable fidelity. This system connects a three-dimensional (3D) skin equivalent with a 3D bone marrow (BM) model under dynamic conditions intended to mimic in vivo circulation. By introducing human serum samples from young and old donors into these co-cultures, the team dissected how age-associated systemic factors modulate skin biology through interactions with the bone marrow niche.

One of the most striking findings was that young human serum, when applied alone to skin models, failed to produce significant rejuvenation. However, when skin was co-cultured alongside bone marrow cells, aged skin models exhibited markedly enhanced regenerative markers in the presence of young serum. This was evidenced by a significant increase in Ki67-positive cells, a hallmark indicating heightened proliferative activity and tissue regeneration. The result underscores the pivotal role of bone marrow as a cellular intermediary, translating systemic rejuvenation cues into functional effects on distal organs such as the skin.

To delve deeper mechanistically, the researchers used tandem liquid chromatography-ion mobility spectrometry-mass spectrometry (LC-IMS-MS/MS) proteomics to catalog proteins secreted by bone marrow cells exposed to either young or old human serum over a five-week culture period. This high-resolution proteomic analysis identified 55 proteins whose abundance was significantly modulated by the youthful serum environment. Among these proteins, seven were linked to key biological processes including cell renewal, extracellular matrix synthesis, and mitochondrial energy metabolism—processes intimately tied to cellular youthfulness and tissue homeostasis.

This proteomic signature not only revealed a repertoire of secreted factors potentially responsible for skin rejuvenation but also offered insight into the cellular origins of these molecules within the bone marrow compartment. By integrating protein expression data from distinct bone marrow cell populations—such as granulocytes, progenitor cells, and monocytes—the study mapped these secreted factors’ cellular sources. This cellular mapping suggests that specific bone marrow subsets act as critical responders to systemic signals, orchestrating downstream regenerative effects in peripheral tissues.

The findings provide a crucial mechanistic underpinning to longstanding observations from heterochronic parabiosis experiments in rodents—studies in which the circulatory systems of young and old animals are surgically joined, resulting in rejuvenation of aged tissues. While those experiments demonstrated remarkable cross-tissue rejuvenation, the molecular and cellular conduits remained elusive. This new human cell-based model clarifies that bone marrow cells serve as vital intermediaries, capable of sensing young systemic factors and secreting bioactive proteins that promote tissue renewal, particularly in the skin.

Beyond the basic science implications, the research carries significant translational potential. It identifies a panel of secreted proteins that could serve as therapeutic targets or biomarkers for developing interventions to mitigate skin aging. By harnessing the crosstalk between bone marrow and skin cells, future therapies might leverage these molecular mediators to restore youthful skin characteristics, including enhanced collagen production, increased cellular proliferation, and improved mitochondrial function.

Importantly, the research emphasizes that the systemic milieu alone—represented by young serum—is insufficient to drive skin rejuvenation without bone marrow participation. This highlights the necessity of multicellular, organ-level interactions in mediating complex biological phenomena like aging. The in vitro co-culture approach adopted in the study sets a new standard for investigating human tissue communication and could be extended to other organ systems where bone marrow- or blood-derived cells modulate tissue regeneration.

The authors are cautious to note that these findings are currently preclinical and derived from in vitro human tissue models. Although highly informative, translating these results into viable human therapies will require extensive further research, including rigorous validation in clinical contexts. Safety, delivery mechanisms, and sustained efficacy over time remain critical hurdles to address before the promise of systemic factor-driven rejuvenation can be realized.

Nonetheless, this study provides a sophisticated proof-of-concept that systemic factors from young individuals wield rejuvenating potential on skin via bone marrow mediation. It sparks a paradigm shift—moving away from direct application of young blood factors towards recognizing the indispensable role of bone marrow-derived cellular networks in translating systemic cues into targeted tissue renewal.

With aging populations worldwide facing increasing skin-related morbidities and cosmetic concerns, such foundational insights into the interplay of systemic biology and tissue-specific responses mark an exciting frontier. They offer hope for innovative treatments that may preserve skin integrity, improve wound healing, and potentially delay or reverse visible signs of aging in the near future.

In sum, this research represents a significant advancement in the quest to decode aging’s biological complexity. By integrating human serum proteomics, microphysiological modeling, and cellular biology, the study provides a nuanced understanding of how youthful systemic factors can contact and activate bone marrow cells to secrete regenerative mediators essential for skin rejuvenation. It opens new avenues for regenerative medicine and highlights the indispensable role of bone marrow in maintaining skin health and combating aging.

The full paper, titled “Systemic factors in young human serum influence in vitro responses of human skin and bone marrow-derived blood cells in a microphysiological co-culture system,” was published on July 25, 2025, and is available via DOI: 10.18632/aging.206288. Correspondence regarding the study can be directed to Elke Grönniger at Beiersdorf AG.

Subject of Research: Cells
Article Title: Systemic factors in young human serum influence in vitro responses of human skin and bone marrow-derived blood cells in a microphysiological co-culture system
News Publication Date: July 25, 2025
Image Credits: Copyright: © 2025 Ritter et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0).
Keywords: aging, skin rejuvenation, microphysiological systems, systemic factors, bone marrow model, human serum

A major breakthrough in unraveling this enigma has now been achieved by Elly Tanaka and her research group at the Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA). Published in the prestigious journal Nature, their study elucidates the molecular framework underpinning the axolotl’s positional memory during limb regeneration. The work reveals how specific gene expression patterns provide a stable yet dynamic map of cellular identity, enabling the limb to be rebuilt with astonishing fidelity after injury. Upon damage, a positional memory signal is reactivated and broadcasts from one side of the limb, directing cells to regenerate structures appropriate for their spatial domain.

Central to this regenerative choreography are two signaling molecules: Fibroblast Growth Factor 8 (FGF8) and Sonic Hedgehog (Shh). During the regeneration process, FGF8 is expressed by stem cells on the anterior or thumb side of the limb, while Shh expression is confined to the posterior or pinky side. These two factors create a mutually reinforcing loop, which stimulates growth and orchestrates the spatial patterning necessary for correct limb formation. Previously, the Tanaka lab had identified this interaction, but the question remained: what guides the initial asymmetric activation of these signaling centers? In other words, which cues determine why FGF8 is switched on exclusively on one side and Shh on the other during regeneration?

Addressing this question posed significant challenges because axolotls possess large and complex genomes, hindering the rapid use of genetic tools that are routinely applied in other model organisms like mice or zebrafish. Only recently have molecular tools become sophisticated enough to enable a systematic search for positional cues active in the limb. Using these advanced genetic manipulation and cell tracing techniques, Tanaka’s team undertook exhaustive analyses to uncover the key molecular players that demarcate the anterior from the posterior side of the axolotl limb.

To their surprise, the researchers identified hundreds of genes differentially expressed between the thumb and pinky sides of the limb, even before any injury occurred. However, one gene, Hand2, stood out distinctly. Its expression was strictly localized to the posterior half of the limb, with no detectable presence in the anterior side. This highly spatially restricted expression pattern positioned Hand2 as a prime candidate for a master regulator of positional identity. Experimental manipulation confirmed Hand2’s essential role: after limb injury, Hand2 activates Shh expression in cells on the posterior side, establishing the vital signaling gradient needed for precise limb patterning.

Building on these insights, the team proposed a compelling ‘radio broadcast’ model of limb regeneration. In this model, cells in a fully developed limb maintain a low level of Hand2 expression on the posterior side, serving as a stable positional memory marker signaling “pinky side.” Upon injury, these same cells ramp up Hand2 expression, which triggers the induction of Shh within a subset of Hand2-positive cells. The Shh signal then emanates outward like a broadcast: cells in close proximity to the Shh source adopt posterior identities suitable for pinky-side structures, while those further away interpret lower levels of the signal, regenerating more anterior-like structures. Once regeneration completes, Hand2 expression reverts to its low baseline, readying the limb for potential future injuries and regenerative cycles. This model elegantly explains how a preexisting positional code is preserved, reactivated, and dynamically harnessed to direct accurate tissue reconstruction.

Perhaps even more striking is the discovery that this signaling network is remarkably flexible. The study demonstrated that cells from the anterior thumb side, when transplanted onto the posterior pinky side, can be reprogrammed by the Shh broadcast to adopt posterior identities. This transition underscores the plasticity of cell fates during regeneration and provides a powerful proof-of-concept for intentionally altering cellular positional identity. Such capability has profound implications for tissue engineering and regenerative medicine, where reprogramming cells to acquire new identities could revolutionize therapeutic strategies.

The ability to manipulate cell identity post-injury addresses a critical barrier in regenerative therapy: the limited regenerative capacity of human tissues. If cells in damaged human limbs similarly harbor positional memory mechanisms, it might become possible to coax them into generating complex structures by activating or modulating key factors like Hand2 and Shh. This capacity would vastly improve outcomes following traumatic injuries or degenerative diseases by guiding cells back into a developmental program that restores tissue integrity and function, rather than merely forming a scar.

Significantly, the molecular players identified in axolotls are evolutionarily conserved. Human homologs of Hand2 and Shh exist and function in limb development, raising tantalizing possibilities for translating the axolotl’s regenerative abilities to humans. Elly Tanaka emphasizes that understanding whether human limbs possess comparable positional memory circuits is a crucial next step. If such pathways can be activated or mimicked therapeutically, they might unlock previously inaccessible regenerative potentials in human tissues.

In a visionary perspective, Tanaka and colleagues speculate that expressing Hand2 ectopically—such as in the anterior half of the limb where it is normally inactive—could initiate limb formation de novo. This approach is profoundly exciting because it suggests the potential to induce limb regeneration from scratch, a feat long dreamed of in regenerative biology. By combining Hand2 manipulation with other molecular insights derived from axolotl studies, researchers aspire toward regenerating complex mammalian limbs, marking a transformative advance for regenerative medicine.

In conclusion, the unraveling of the axolotl’s positional memory through the Hand2-Shh molecular circuit represents a landmark achievement. This discovery not only clarifies fundamental biological principles governing tissue regeneration but also opens avenues for innovative therapies capable of reprogramming cellular identities. The research exemplifies how model organisms with extraordinary biological capabilities can illuminate pathways for human medical breakthroughs. As the field progresses, the prospect of harnessing these regenerative blueprints to restore lost limbs or engineer tissues in humans moves closer to reality, carrying profound implications for medicine and human health.

Subject of Research: Animals

Article Title: Molecular basis of positional memory in limb regeneration.

Web References: DOI: 10.1038/s41586-025-09036-5

References: Tanaka et al., Nature, 21 May 2025.

Keywords: Regeneration, Tissue regeneration, Developmental biology

A groundbreaking study conducted at the Marine Biological Laboratory (MBL) in Woods Hole, Massachusetts, unveils a pivotal role for a distinct group of neurons in the axolotl brain in promoting tail regeneration. The research illuminates how activation of these neurons triggers downstream molecular pathways essential for successful regrowth, offering unprecedented insight into brain-to-body communication during regeneration. Such findings raise the intriguing possibility that similar neuronal populations exist in mammals and may modulate regenerative responses, heralding new avenues for therapeutic strategies in human medicine.

Led by Associate Scientist Dr. Karen Echeverri, the investigators focused on neurons extending from the telencephalon—a brain region situated at the anterior part of the axolotl brain—toward the hypothalamus, which lies near its base. These neurons act as crucial messengers, conveying signals that orchestrate regenerative processes following injury. The study demonstrates that upon injury, these neurons exhibit increased activity of the extracellular signal-regulated kinase (Erk) pathway, a critical signaling cascade known to influence gene expression and cellular behavior.

The Erk pathway’s engagement within this neuronal subset appears to be integral to initiating and sustaining regeneration. When researchers experimentally inhibited Erk activation in these brain neurons, the axolotls exhibited markedly truncated tail regrowth, underscoring the essential nature of this pathway’s function in neuronal signaling during regeneration. Concurrently, these neurons ramped up production of neurotensin, a neuropeptide implicated in cellular growth and repair, further enhancing the regenerative milieu.

This discovery builds upon prior findings where Erk signaling was noted in glial cells of the spinal cord after injury, expanding the role of Erk from peripheral nervous system components to specific centers in the brain. The syntropic interplay between these neuronal populations and peripheral injury sites suggests an integrated systemic response rather than a purely localized regenerative mechanism.

Remarkably, this area of neurons responds to diverse types of injury—including both tail amputations and limb loss—by increasing Erk activity, implying a generalized brain-mediated response to bodily trauma. The study’s authors emphasize the need to dissect this response further, aiming to decipher whether distinct subpopulations within these neurons differentially respond to unique injury types or severities, particularly differentiating limb wounds from tail injuries.

The research journey began during Dr. Echeverri’s tenure at the University of Minnesota, where student researcher Keith Sabin first identified Erk-positive neurons in the telencephalon. With postdoctoral fellow Sarah Walker leading experimental investigations at MBL, the team employed sophisticated molecular and imaging techniques to map activation patterns and evaluate functional consequences of pathway blockade. Their precise elucidation of neural signaling pathways involved in axolotl regeneration represents a significant leap forward in regenerative neuroscience.

From a translational perspective, elucidating whether comparable neuronal circuits exist and function similarly in mammalian brains could revolutionize approaches to injury recovery. Unlike axolotls, mammals—including humans—demonstrate limited regenerative capacity, often resorting to scarring rather than true regrowth of lost tissues. Understanding the mechanisms that allow axolotls to coordinate brain signals and regenerate complex structures may unlock therapeutic targets aimed at enhancing or reawakening latent regenerative programs in humans.

Despite humans possessing some regenerative potential limited to tissues like skin, muscle, and liver, the scale and speed of regeneration are drastically lower than in axolotls. Factors such as larger body size, longer timeframes required for tissue regrowth, and heightened risk of infection or injury during prolonged recovery periods may have driven evolutionary trade-offs favoring scar formation over regeneration in mammals.

Still, the study raises optimism about the possibility of harnessing and accelerating intrinsic regenerative capabilities. By deciphering the molecular dialog between injury sites and brain neurons, researchers hope to stimulate faster and more complete tissue regeneration, mitigating long-term disabilities resulting from spinal cord and limb injuries.

The MBL study also exemplifies collaborative interdisciplinary science, involving partnerships with the National Human Genome Research Institute and the National Institutes of Health, to blend genetic, molecular, and neurobiological methods aimed at comprehending complex regenerative phenomena.

As this research progresses, further exploration into the specificity and plasticity of neuronal responses in the brain, the identification of key signaling molecules mediating brain-injury site communication, and cross-species comparative studies will be critical to advancing regenerative medicine. Decoding the brain’s command over regeneration paves the way for therapeutic innovations that could transform human healing in the future.

Subject of Research: Animals

Article Title: Neuronal activation in the axolotl brain promotes tail regeneration

News Publication Date: 8-May-2025

Web References:
https://doi.org/10.1038/s41536-025-00413-2

Image Credits: Christian Selden, Marine Biological Laboratory

Keywords: Regeneration, Tissue regeneration, Limb regeneration, Neuroscience