Biology subjects

Sandoval-Guzman, T.

Publications and source records attributed to Sandoval-Guzman, T..

10 recordsLinked to original sources

bioRxiv2026

Tissue composition shapes differential skeletal integration strategies during axolotl limb regeneration

Limb regeneration requires rebuilding the missing structures and integrating them with stump tissues. Osteoclast-mediated tissue resorption is essential for skeletal integration during regeneration. However, it is unknown if skeletal tissue composition impacts its resorption and, if so, how it is regulated. Here, we show that osteoclast-mediated skeletal resorption is activated in amputations damaging the diaphysis, but not the epiphysis, of skeletal elements. We found that amputations in the calcified diaphysis trigger the sustained expression of RANKL and the chemokine Loc483, and that the latter is sufficient to induce osteoclast presence in non-resorbing amputations. Finally, our data suggests that the transcriptomic profile of the apical ectodermal cap is impacted by the tissues injured by the amputation. Overall, our work reveals that tissue composition at the amputation plane shapes adaptations of the regenerative program, which ultimately contribute to the near-seamless tissue integration of the regenerating axolotl limb regardless of the amputation position.

developmental biology↗

bioRxiv2025

Differential fates of vertebrate Kazald gene quartet, from ancestral roles in skeletogenesis and regeneration to putative innovations in fish and birds

Salamanders are known for their incredible regenerative abilities, but translating findings to mammals is complicated by unannotated genes and unclear orthology. An example highlighting this difficulty was a discovery in the axolotl (Ambystoma mexicanum) of a regeneration-associated gene that has been identified as either Kazald1 or Kazald2. Since orthology inference of genes across species is crucial to identifying gains and losses of gene functions, and thus if gene usage is likely to be consistent across species, we investigated the evolution of the axolotl genes using an extensive cross-species analysis. Molecular phylogeny inference conclusively identified the regeneration-associated gene as Kazald2, but also revealed an undescribed four-member Kazald gene family in jawed vertebrates. Moreover, synteny comparisons demonstrated that this family originated in the ancestral two-rounds of whole genome duplication. Additionally, we performed vertebrate-wide comparisons of Kazald gene expression profiles, employing available RNA-Seq which we validated in whole tissues of axolotl, zebrafish, and sharks. This uncovered seemingly ancestral connections conserved over jawed vertebrate evolution, such as Kazald1 with skeletogenesis and odontogenesis and Kazald2 with regeneration. It also suggested novel putative roles within specific lineages, including Kazald3 in teleost fish skeletogenesis and Kazald4 within avian brains. Our study thus demonstrates the establishment of a Kazald gene quartet in the jawed vertebrate ancestor, and elucidates the asymmetry of gene fates of its members, including deeply ancestral roles and comparably recent innovations. This provides a comprehensive report of this formerly undescribed gene family, offering a solid foundation for future studies of these genes in diverse species.

evolutionary biology↗

bioRxiv2025

Mechanical control of tissue growth during limb regeneration

The axolotl is a highly regenerative species, capable of restoring full limbs, regardless of the amputation site. However, the regeneration rate is adjusted with the plane of amputation along the proximo-distal (PD) axis, leading to equivalent regeneration times regardless of the extent of tissue removal. We hypothesized that this phenomenon could be partly explained by differences in tissue mechanical properties. In this work, we describe tissue growth mathematically and evaluate cell cycle parameters of regenerating limbs amputated at different levels along the PD axis, demonstrating a linear correlation between the cell cycle length and the amputation site during early regeneration phases. We show as well, that blastema cells require their endogenous context to retain such proliferation differences. We measured mechanical properties in regenerating limbs with in vivo optical and standard indentation-based techniques and demonstrated that distal blastema cells are stiffer than proximal ones. Accordingly, we demonstrated that axolotl cells decrease their proliferation with increased extracellular matrix stiffness in vitro. Next, we evaluated the activity of the mechanotransducers YAP/TAZ in vivo by using a GTIIC-based reporter line combined with target gene expression data, which indicated that their activity peaks during the blastema stage, with higher activity after proximal amputations. Hence, our findings strongly suggest a mechanical dependence for the position-dependent regulation of cell proliferation during axolotl limb regeneration, where YAP/TAZ likely plays a role in the mechanotransduction mechanism.

biophysics↗

bioRxiv2025

Static morphogen scaling enables proportional growth in tissue growth model inspired by axolotl limb regeneration

Axolotls can regenerate lost limbs throughout life, while they continue to grow. This poses the question of how the size and pattern of a regenerating limb is matched to a widely varying animal size. Two interacting signaling molecules, SHH and FGF8, are produced at opposite sides of the regenerating limb and sustain tissue growth through a pair of oppositely-oriented signaling gradients. As the size of the regrowing tissue can vary more than three-fold depending on the size of the animal, it is unclear how the activities of these mutually dependent morphogens are maintained and subsequently terminated to determine appropriate growth. Scaling of limb regeneration suggests a size-dependent adaptation of morphogen gradient parameters. Inspired by this biological example, we theoretically investigate general mechanisms of morphogen-controlled growth arrest and proportional growth. In the proposed mechanism, tissue growth increases the spatial distance between the two morphogen gradients, which eventually arrests morphogen activity and growth. We put forward two distinct scaling scenarios of morphogen gradients: either dynamic scaling with blastema size, where morphogen gradient parameters change dynamically with the growing tissue, or static scaling with animal size, where morphogen gradient parameters stay constant during blastema growth and only depend on animal size. We show that static scaling ensures proportional growth, but dynamic scaling does not. We compare theory predictions to experimental quantification of SHH and FGF8 morphogen gradient parameters at different time-points of regeneration in different-sized animals, indicating static scaling for some morphogen parameters, which is sufficient to ensure proportional growth in our model.

biophysics↗

bioRxiv2024

Axolotl mandible regeneration occurs through mechanical gap closure and a shared regenerative program with the limb

The mandible plays an essential part in human life and, thus, defects in this structure can dramatically impair the quality of life in patients. Axolotls, unlike humans, are capable of regenerating their lower jaws; however, the underlying mechanisms and their similarity to those in limb regeneration are unknown. In this work, we used morphological, histological, and transcriptomic approaches to analyze the regeneration of lateral resection defects in the axolotl mandible. We found that this structure can regenerate all missing tissues in 90 days through gap minimization, blastema formation, and finally tissue growth, differentiation, and integration. Moreover, transcriptomic comparisons of regenerating mandibles and limbs showed that they share molecular phases of regeneration, that these similarities peak during blastema stages, and that mandible regeneration occurs at a slower pacing. Altogether, our study demonstrates the existence of a shared regenerative program used in two different regenerating body structures with different embryonic origins in the axolotl, and contributes to our understanding of the minimum requirements for a successful regeneration in vertebrates, bringing us closer to understand similar lesions in human mandibles.

developmental biology↗

bioRxiv2023

Multi-species atlas resolves an axolotl limb development and regeneration paradox

Humans and other tetrapods are considered to require apical-ectodermal-ridge, AER, cells for limb development, and AER-like cells are suggested to be re-formed to initiate limb regeneration. Paradoxically, the presence of AER in the axolotl, the primary regeneration model organism, remains controversial. Here, by leveraging a single-cell transcriptomics-based multi-species atlas, composed of axolotl, human, mouse, chicken, and frog cells, we first established that axolotls contain cells with AER characteristics. Surprisingly, further analyses and spatial transcriptomics revealed that axolotl limbs do not fully re-form AER cells during regeneration. Moreover, the axolotl mesoderm displays part of the AER machinery, revealing a novel program for limb (re)growth. These results clarify the debate about the axolotl AER and the extent to which the limb developmental program is recapitulated during regeneration.

developmental biology↗

bioRxiv2022

Osteoclast-mediated resorption primes the skeleton for successful integration during axolotl limb regeneration

Early events during axolotl limb regeneration include an immune response and the formation of a wound epithelium. These events are linked to a clearance of damaged tissue prior to blastema formation and regeneration of the missing structures. Here, we report the resorption of calcified skeletal tissue as an active, cell-driven and highly regulated event. This process, carried out by osteoclasts, is essential for a successful integration of the newly formed skeleton. Indeed, the extent of resorption is directly correlated with the integration efficiency. Moreover, we identified the wound epithelium as a major regulator of skeletal resorption, likely creating a zone of influence in which signals involved in recruitment/differentiation of osteoclasts are released. Finally, we reported a correlation between resorption and blastema formation, particularly, a coordination of resorption with cartilage condensation. In sum, our results identify resorption as a major event upon amputation, playing a critical role in the overall process of skeletal regeneration.

developmental biology↗

bioRxiv2022

In vivo assessment of mechanical properties during axolotl development and regeneration using confocal Brillouin microscopy

In processes such as development and regeneration, where large cellular and tissue rearrangements occur, cell fate and behavior are strongly influenced by tissue mechanics. While most well-established tools probing mechanical properties require an invasive sample preparation, confocal Brillouin microscopy captures mechanical parameters optically with high resolution in a contact-free and label-free fashion. In this work, we took advantage of this tool and the transparency of the highly regenerative axolotl to probe its mechanical properties in vivo for the first time. We mapped the Brillouin frequency shift with high resolution in developing limbs and regenerating digits, the most studied structures in the axolotl. We detected a gradual increase in the cartilage Brillouin frequency shift, suggesting decreasing tissue compressibility during both development and regeneration. Moreover, we were able to correlate such increase with the regeneration stage, which was undetected with fluorescence microscopy imaging. The present work evidences the potential of Brillouin microscopy to unravel the mechanical changes occurring in vivo in axolotls, setting the basis to apply this technique in the growing field of epimorphic regeneration.

developmental biology↗

bioRxiv2021

Post-embryonic development and aging of the appendicular skeleton in Ambystoma mexicanum

BackgroundThe axolotl is a key model to study appendicular regeneration. The limb complexity resembles that of humans in structure and tissue components; however, axolotl limbs develop post-embryonically. In this work, we evaluated the post-embryonic development of the appendicular skeleton and its changes with aging. ResultsThe juvenile limb skeleton is formed mostly by Sox9/Col1a2 cartilage cells. Ossification of the appendicular skeleton starts when animals reach a length of 10 cm, and cartilage cells are replaced by a primary ossification center, consisting of cortical bone and an adipocyte-filled marrow cavity. Vascularization is associated with the ossification center and the marrow cavity formation. We identified the contribution of Col1a2-descendants to bone and adipocytes. Moreover, ossification progresses with age towards the epiphyses of long bones. Axolotls are neotenic salamanders, and still ossification remains responsive to L-thyroxine, increasing the rate of bone formation. ConclusionsIn axolotls, bone maturation is a continuous process that extends throughout their life. Ossification of the appendicular bones is slow and continues until the complete element is ossified. The cellular components of the appendicular skeleton change accordingly during ossification, creating a heterogenous landscape in each element. The continuous maturation of the bone is accompanied by a continuous body growth.

developmental biology↗

bioRxiv2019

The Prrx1 limb enhancer marks an adult population of injury-responsive, multipotent dermal fibroblasts

The heterogeneity of adult tissues has been posited to contribute toward the loss of regenerative potential in mammals. Here we characterize an adult population of dermal fibroblasts that maintain expression of a Prrx1 enhancer which originally marked mesenchymal limb progenitors. Prrx1 enhancer-positive cells (Prrx1enh+) make up a small subset of adult dermal cells (~0.2%) and reside mainly within specific dermal perivascular and hair follicle niches. Upon injury, however, Prrx1enh+ cells readily migrate into the wound bed and amplify on average 16-fold beyond their uninjured numbers. Additionally, Prrx1enh+ cells emigrate out of their dermal niches following wounding and contribute to subcutaneous tissue. Prrx1enh+ cells are uniquely injury-responsive and do not contribute to tissue homeostasis or enriched by neonatal-like Wnt signaling. Prrx1enh+ cells represent a potent regenerative cell population that, despite being a meager minority in adult skin, demonstrate the potential to tip the balance of mammalian wound healing toward scar-free healing.

developmental biology↗