Lizard Tail Regeneration Research Articles

Observations on FGF immunoreactivity in the regenerating tail blastema, and in the limb and tail scars of lizard suggest that FGFs are required for regeneration

Tail regeneration in lizards depends on the stimulation of growth factors, including Fibroblast Growth Factors (FGFs). Light and ultrastructural immunolocalization of FGFs was compared between the rege-nerating tail blastema and the limb where no regeneration occurs. A likely epithelial-mesenchymal transition occurs following amputation in both tail and limb and FGFs are present in the wound epidermis of both organs at 7-14 days post-amputation, and at lower intensity in mesenchymal cells of the blastema. Immunoreactivity for FGFs disappears in the limb wound epidermis after 14 days post-amputation and in the epithelium covering tails induced to form scars, whereas it remains in the apical tail epithelium. These observations suggest that scarring in the limb or the induced scarring in the tail correlate with the disappearance of FGFs. Basic FGF is concen-trated in the incomplete basement membrane between the epidermis and the tail blastema where the essential signaling process that allows the continuous growth of the regenerative blastema may occur. The study suggests that the successful regeneration of lizard tail is dependent on the presence of FGFs in the wound epidermis, which are probably released into the blastema.

Effectivity of Shark Cartilage (Carcharhinus sorrah) Ointment Extract on Growth of Lizard (Mabouya multifasciata kuhl) Regenerated Tail

Shark (Carcharhinus sorrah) is a fish whose entire endoskeleton is composed of cartilage. Fish cartilage is widely used for treatment because shark cartilage (SC) contains glucosamine (GS) and chondroitin sulfate (CS) compounds. This study aims to determine the benefits of glucosamine and chondroitin sulfate derived from SC extract on lizard tail regeneration. The study was initiated by testing the characteristics of the SC extract ointment which included tests of spreadability, pH, viscosity and adhesion of the ointment. The effectiveness test of SC extract ointment was done using 36 lizards that were autotomized and divided into 4 treatment groups. The treatment in the form of SC extract ointment with concentrations of 0% (control), 5%, 10%, and 15% was applied to the autotomized tail every morning and evening. The lizards were then kept for 7; 18; and 35 days. The test data for the physicochemical character of the SC extract ointment were analyzed using one-way ANOVA with a significance level of 5% (p<0.05) and the lizard regeneration tail length data were analyzed using a two-way ANOVA with a significance level of 5%. (p<0.05). The result of the research showed that there was a significant difference in the physicochemical character of the spread of SC extract ointment, meanwhile the other physicochemical characters showed no significant difference. The SC extract ointment used in this study was not effective in the growth of lizard regenerate tails.

Protein extracts from regenerating lizard tail show an inhibitory effect on human cancer cells cultivated in-vitro

Backgroundaccumulating evidence indicates that during tail regeneration in lizards the initial stage of regenerative blastema is a tumor-like proliferative outgrowth that rapidly elongates into a new tail composed of fully differentiated tissues. Both oncogenes and tumor-suppressors are expressed during regeneration, and it has been hypothesized that an efficient control of cell proliferation avoids that the blastema is turned into a tumor outgrowth. Methodsin order to determine whether functional tumor-suppressors are present in the growing blastema we have utilized protein extracts collected from early regenerating tails of 3–5 mm that have been tested for a potential anti-tumor effect on in-vitro culture by using cancer cell lines from human mammary gland (MDA-MB-231) and prostate cancer (DU145). Resultsat specific dilutions, the extract determines a reduction of viability in cancer cells after 2–4 days of culture, as supported by statistical and morphological analyses. While control cells appear viable, treated cells result damaged and produce an intense cytoplasmic granulation and degeneration. Conclusionsthis negative effect on cell viability and proliferation is absent using tissues from the original tail supporting the hypothesis that only regenerating tissues synthesize tumor-suppressor molecules. The study suggests that the regenerating tail of lizard at the stages here selected contains some molecules that determine inhibition of cell viability on the cancer cells analyzed.

Immunolocalization of Pglyrp3 and Eps8l1 proteins in the regenerating lizard epidermis indicates they contribute to epidermal barrier formation

During tail regeneration in lizards the new corneous layer formed in the regenerating epidermis includes antimicrobial peptides, cystatin and serpins, likely forming an anti-microbial barrier. The present study aims to reveal other proteins potentially contributing to this protective barrier of the epidermis. Using immunohistochemistry we have detected a peptidoglycan-like recognition protein-3 (pglyrp3), an antimicrobial molecule, and an epidermal growth factor receptor kinase 8 l (eps8l), a receptor of EGF (Epidermal Growth Factor) that stimulates epidermal formation. The study shows that the two proteins are mostly accumulated in the forming wound epidermis and in the shedding layer of the regenerating scales. The shedding layer is the intra-epidermal layer that allows the separation of the initial corneous layer from the regenerating epidermis. While presence of pglyrp3 is likely related to the formation of the anti-microbial barrier, the function of the eps8l protein in epidermal regeneration remains unknown. Whether the latter protein is involved in keratinocyte movement within the regenerating epidermis has to be specifically determined in future studies. Together with the antimicrobial peptides cystatin and serpins, previously detected in the wound epidermis and shedding layer, the present study indicates that pglyp3, and potentially eps8l, contribute to protect the new skin and underlying regenerated tissues from the potential microbe invasion.

The regenerating tail of lizard transits through a tumour‐like stage represented by the regenerative blastema

AbstractReview. The regenerating tail of lizard transits through a tumour‐like stage represented by the regenerative blastema. Acta Zoologica (Stockolm). Molecular studies on lizard tail regeneration indicate that the blastema stage is a tumour‐like outgrowth capable of self‐regulate to produce a new tail. Various oncogenes and tumour suppressors are expressed, and their proteins are localized in specific regions of the growing blastema. SnoRNAs are exclusively overexpressed in the tail blastema suggesting changes in ribosome translation efficiency in blastema cells, like in cancer. Blastema cells secrete high levels of hyaluronate and adopt an anaerobic metabolism (Warburg effect). These studies indicate that the lizard blastema represents a unique case among terrestrial vertebrates of physiological tumour remission. Mesenchymal cells and fibroblasts forming the blastema are turned within 1–2 months into a functional organ, the tail. In vitro studies on isolated mesenchymal cells from the regenerative blastema shows that these cells do not undergo contact inhibition but continue proliferation after confluence, and contain nestin, vimentin and K17. After 2–3 weeks they stratify into 5–7 layers forming a pellicle of loose connective tissue. Future molecular studies on genes and proteins that allow the control of growth in the lizard blastema may help to determine how lizards turn a tumour into a new organ with numerous differentiated and functional tissues, providing clues on cancer growth regulation.

Immunolocalization of tumor suppressors arhgap28 and retinoblastoma in the lizard Podarcis muralis suggests that they contribute to the regulated regeneration of the tail.

Tail regeneration in lizards is an outstanding and unique postembryonic morphogenetic process. This developmental process is regulated by poorly known factors, but recent studies have suggested that it derives from a balanced activity between oncoproteins and tumor suppressors. Transcriptome and expression data have indicated that arhgap28 and retinoblastoma proteinsare among the main tumor suppressors activated during tail regeneration. However, their cellular localization is not known. Therefore, in the present immunohistochemical study, two proteins have been detected in various tissues at the beginning of their differentiation. Both proteins are present especially in the new scales, axial cartilage, and muscle bundles of the regenerating tail, the main tissues forming the new tail. Sparse or occasionally labeled cells are observed in the blastema, but intense labeling is seen in the basal layers of the wound (regenerating) epidermis and in external differentiating epidermal layers. Numerous keratinocytes also show a nuclear localization for both proteins, suggesting that the latter may activate a gene program for tissue differentiation after the inhibition of cell multiplication. Based on microscopic, molecular, experimental, and in vitro studies, a hypothesis on the "inhibition of contact" among the apical cells of the blastema and those of proximal differentiating tissues is proposed to explain the permanence of an active blastema only at the apex of the regenerating tail without tail growth can degenerate into a tumorigenic outgrowth.

De Novo Transcriptome Sequencing and Analysis of Differential Gene Expression among Various Stages of Tail Regeneration in Hemidactylus flaviviridis.

Across the animal kingdom, lizards are the only amniotes capable of regenerating their lost tail through epimorphosis. Of the many reptiles, the northern house gecko, Hemidactylus flaviviridis, is an excellent model system that is used for understanding the mechanism of epimorphic regeneration. A stage-specific transcriptome profile was generated in the current study following an autotomized tail with the HiSeq2500 platform. The reads obtained from de novo sequencing were filtered and high-quality reads were considered for gene ontology (GO) annotation and pathway analysis. Millions of reads were recorded for each stage upon de novo assembly. Up and down-regulated transcripts were categorized for early blastema (EBL), blastema (BL) and differentiation (DF) stages compared to the normal tail (NT) by differential gene expression analysis. The transcripts from developmentally significant pathways such as FGF, Wnt, Shh and TGF-β/BMP were present during tail regeneration. Additionally, differential expression of transcripts was recorded from biological processes, namely inflammation, cell proliferation, apoptosis and cell migration. Overall, the study reveals the stage-wise transcriptome analysis in conjunction with cellular processes as well as molecular signaling pathways during lizard tail regeneration. The knowledge obtained from the data can be extrapolated to configure regenerative responses in other amniotes, including humans, upon loss of a complex organ.

Immunolocalization of adenomatous polyposis coli protein (apc) in the regenerating lizard tail suggests involvement in tissue differentiation and regulation of growth

Lizard tail regeneration is likely regulated by the balanced activity of oncogenes and tumor suppressors that control cell proliferation avoiding tumorigenic degeneration. One of the main tumor suppressor genes present in the regenerating tail is the "adenomatous polyposis coli (apc)" but the localization of its coded protein (apc) is not known. This protein may be involved in regulation of apical-basal tail regeneration in lizards. The present immunohistochemical study shows that apc is localized in apical wound epidermis and regenerating ependyme, two tissues that proliferate and also express onco-genes. Apc is not present in blastema cells but localizes in differentiating cells of regenerating scales, muscles and less intensely in the non-apical ependymal epithelium and cartilage. This suggests that apc is involved in the induction of their differentiation. The apc immunolabeling is mainly nuclear in the basal epidermal layer of the apical wound epidermis where it may be involved in modulating keratinocytes proliferation, like in the forming scales. In regenerating muscle and cartilage apc is mainly cytoplasmic while sparse labeled nuclei are seen in proliferative areas of these tissues. In the regenerating spinal cord, the nuclear and cytoplasmic apc labeling is present in ependymal cells of the distal-most ependymal ampulla but the labeling fades in more proximal regions and mainly remains in the cytoplasm facing the central canal and in sparse nuclei. It is suggested that the pattern of immunolabeling for apc indicates that this tumor suppressor may contribute to tissue differentiation within the regenerating tail.

Lizard Blastema Organoid Model Recapitulates Regenerated Tail Chondrogenesis.

(1) Background: Lizard tail regeneration provides a unique model of blastema-based tissue regeneration for large-scale appendage replacement in amniotes. Green anole lizard (Anolis carolinensis) blastemas contain fibroblastic connective tissue cells (FCTCs), which respond to hedgehog signaling to create cartilage in vivo. However, an in vitro model of the blastema has not previously been achieved in culture. (2) Methods: By testing two adapted tissue dissociation protocols and two optimized media formulations, lizard tail FCTCs were pelleted in vitro and grown in a micromass blastema organoid culture. Pellets were analyzed by histology and in situ hybridization for FCTC and cartilage markers alongside staged original and regenerating lizard tails. (3) Results: Using an optimized serum-free media and a trypsin- and collagenase II-based dissociation protocol, micromass blastema organoids were formed. Organoid cultures expressed FCTC marker CDH11 and produced cartilage in response to hedgehog signaling in vitro, mimicking in vivo blastema and tail regeneration. (4) Conclusions: Lizard tail blastema regeneration can be modeled in vitro using micromass organoid culture, recapitulating in vivo FCTC marker expression patterns and chondrogenic potential.

Microscopical observations on the regenerating tail of tsinling dwarf skink (Scincella tsinlingensis)

Although the key steps of tail regeneration in lizards are well understood, further investigations involving skinks can provide the field of regeneration research with additional information. In order to characterize the cytoarchitecture of tail regeneration in Scincella tsinlingensis, an endemic species in China, its histological events and growth trends are investigated. The rate of tail regeneration varies with the season: it proceeds faster in summer and autumn than it does in winter and spring. Tail regeneration of S. tsinlingensis is summarized as wound healing, blastema formation, cell differentiation and tail growth, which can be subdivided into seven stages. Wound healing following tail loss, begins with an obvious outgrowth undergoing re-epithelialization. Numerous proliferating mesenchymal-like cells aggregate near the distal end of the severed spinal cord to form the blastema. The expanding blastema is invaded by blood vessels, nerves and ependyma. A cartilaginous skeleton is formed around the ependymal tube and the muscle starts to differentiate. The keratinization of epidermis coincides with scale formation. Pigmentation eventually occurs in the regenerated tail. Tail regeneration in S. tsinlingensis is an epimorphic kind of regeneration that is also known as blastema-mediated. Structure and composition of the regenerated tail, including its cytoarchitecture, represent a conserved pattern of regeneration also known from other lizards.

Microscopy suggests that glutathione S‐transferase is stored in large granules of myeloid cells in bone marrow and sparse granulocytes of the regenerating tail of lizard

AbstractMicroscopy suggests that glutathione S‐transferase is stored in large granules of myeloid cells in bone marrow and sparse granulocytes of the regenerating tail of lizard. Acta Zoologica (Stockolm). Tail regeneration in lizards occurs after an immune‐privileged blastema and is formed where various immunosuppressive cells and biomolecules keep inflammation low. Molecules that limit inflammation may include glutathione and glutathione S‐transferase (GST). These molecules reduce reactive oxidative species (ROS) and detoxify extraneous molecules. In the present study, the presence of GST has been analysed in the early phases of tail regeneration in the lizard Podarcis muralis. Using a rabbit polyclonal antibody directed against epitopes present in GST of P. muralis, a light and electron microscopy immunohistochemical and Western blotting study has been done. The study detected proteins of 25 and 32 kDa in pale‐medium electron‐dense and large granules present in promyelocytes and myelocytes of likely basophilic or eosinophilic fate that is present in the bone marrow of tail vertebrae. These cells are still proliferating and give rise to basophilic or eosinophilic granulocytes that also migrate into the regenerating tail. The enzyme stored in granules of promyelocytes and myelocytes is also localized in the cytoplasm of granulocytes present in the regenerating blastema‐cone, basophilic or/and eosinophilic. It is suggested that these granulocytes in the blastema reduce ROS and detoxify potentially inflammatory metabolites, contributing with other molecules to limit inflammation and favour regeneration.

At What Cost? Trade-Offs and Influences on Energetic Investment in Tail Regeneration in Lizards Following Autotomy.

Caudal autotomy, the ability to shed a portion of the tail, is a widespread defence strategy among lizards. Following caudal autotomy, and during regeneration, lizards face both short- and long-term costs associated with the physical loss of the tail and the energy required for regeneration. As such, the speed at which the individual regenerates its tail (regeneration rate) should reflect the fitness priorities of the individual. However, multiple factors influence the regeneration rate in lizards, making inter-specific comparisons difficult and hindering broader scale investigations. We review regeneration rates for lizards and tuatara from the published literature, discuss how species’ fitness priorities and regeneration rates are influenced by specific, life history and environmental factors, and provide recommendations for future research. Regeneration rates varied extensively (0–4.3 mm/day) across the 56 species from 14 family groups. Species-specific factors, influencing regeneration rates, varied based on the type of fracture plane, age, sex, reproductive season, and longevity. Environmental factors including temperature, photoperiod, nutrition, and stress also affected regeneration rates, as did the method of autotomy induction, and the position of the tail also influenced regeneration rates for lizards. Additionally, regeneration could alter an individual’s behaviour, growth, and reproductive output, but this varied depending on the species.

Self-Control of Inflammation during Tail Regeneration of Lizards.

Lizards can spontaneously regenerate their lost tail without evoking excessive inflammation at the damaged site. In contrast, tissue/organ injury of its mammalian counterparts results in wound healing with a formation of a fibrotic scar due to uncontrolled activation of inflammatory responses. Unveiling the mechanism of self-limited inflammation occurring in the regeneration of a lizard tail will provide clues for a therapeutic alternative to tissue injury. The present review provides an overview of aspects of rapid wound healing and roles of antibacterial peptides, effects of leukocytes on the tail regeneration, self-blocking of the inflammatory activation in leukocytes, as well as inflammatory resistance of blastemal cells or immature somatic cells during lizard tail regeneration. These mechanistic insights of self-control of inflammation during lizard tail regeneration may lead in the future to the development of therapeutic strategies to fight injury-induced inflammation.

The vascularization, innervation and myogenesis of early regenerated tail in Gekko japonicus.

Many species of lizards are capable of tail regeneration. There has been increased interest in the study of lizard tail regeneration in recent years as it is an amenable regeneration model for amniotes. In this study, Gekko japonicus was used as a model to investigate the initiation of vascularization, innervation and myogenesis during tail regeneration. We found that angiogenesis and axon regeneration occurred almost simultaneously within 4days post amputation. The results showed that the endothelial cells of the original vasculature proliferated and extended into the blastema as capillary vessels, which inter-connected to form a capillary network. The nerve fibers innervated the regenerated tissue from the original spinal cord and dorsal root ganglia, and the fiber bundles increased during 14days. Regenerating muscle tissues emerged 2weeks after amputation. PAX3 and PAX7 expression were detected during myogenesis, with PAX7 showing a continuous increase in expression from day 3 until the day 14, whereas PAX3 reached a peak level on day 10day post amputation, and then declined quickly to level as normal control on day 14. PCNA and PAX3 double-positive satellite cells were observed in the original rostral tissues, indicating the involvement of satellite cell proliferation during tail regeneration. Taken together, these data suggest that tail regeneration in Gekko japonicus involved rapid angiogenesis from the beginning to the day 10 and followed by capillary remodeling. The innervation of regenerated tail was significant on day 4 and increased gradually during regeneration, while the regenerated muscle tissues was obvious on day 14 after amputation.

Immunoreactivity for Dab2 and Foxp3 suggests that immune‐suppressive cells are present in the regenerating tail blastema of lizard

AbstractImmunoreactivity for Dab2 and Foxp3 suggests that immune‐suppressive cells are present in the regenerating tail blastema of lizard. Acta Zoologica (Stockolm). Tail regeneration in lizards likely occurs in immune‐evasive conditions. In order to strengthen this hypothesis, the presence of the tumour suppressor and macrophage marker Dab2 and the lymphocyte regulatory marker, Foxp3, are evaluated by immunofluorescence in lizard regenerating blastema. The observations reveal sparse Dab2 and Foxp3 cells among blastema cells, identified, respectively, as healing M2‐macrophages and Tregs‐lymphocytes. Dab2 is also detected in basal/suprabasal layers of the apical wound epidermis, suggesting that this protein may participate in controlling cell proliferation of the growing tail by regulating Epidermal Mesenchymal Transition. Tregs marker, Foxp3, is localized in sparse cells among blastema mesenchymal cells and in the regenerating apical ependyma, suggesting the presence of immune cells that stimulate healing and sustain blastema growth. However, due to a similar 14 amino acid‐long epitope between Foxp3 and Foxj1, the employed antibody might also recognize the latter protein, known to be involved in ciliogenesis of ependymal cells in fish and amphibians. It is, therefore, possible that Foxj1 may also be produced in the regenerating ependyma of lizards during ciliogenesis. The study further supports the hypothesis that lizard tail regeneration occurs in immune‐tolerant conditions and that organ regeneration in vertebrates can only occur in an immune‐suppressed or immune‐evasive environment.

Salamander-like tail regeneration in the West African lungfish.

Salamanders, frog tadpoles and diverse lizards have the remarkable ability to regenerate tails. Palaeontological data suggest that this capacity is plesiomorphic, yet when the developmental and genetic architecture of tail regeneration arose is poorly understood. Here, we show morphological and molecular hallmarks of tetrapod tail regeneration in the West African lungfish Protopterus annectens, a living representative of the sister group of tetrapods. As in salamanders, lungfish tail regeneration occurs via the formation of a proliferative blastema and restores original structures, including muscle, skeleton and spinal cord. In contrast with lizards and similar to salamanders and frogs, lungfish regenerate spinal cord neurons and reconstitute dorsoventral patterning of the tail. Similar to salamander and frog tadpoles, Shh is required for lungfish tail regeneration. Through RNA-seq analysis of uninjured and regenerating tail blastema, we show that the genetic programme deployed during lungfish tail regeneration maintains extensive overlap with that of tetrapods, with the upregulation of genes and signalling pathways previously implicated in amphibian and lizard tail regeneration. Furthermore, the lungfish tail blastema showed marked upregulation of genes encoding post-transcriptional RNA processing components and transposon-derived genes. Our results show that the developmental processes and genetic programme of tetrapod tail regeneration were present at least near the base of the sarcopterygian clade and establish the lungfish as a valuable research system for regenerative biology.

Appendage regeneration in anamniotes utilizes genes active during larval-metamorphic stages that have been lost or altered in amniotes: The case for studying lizard tail regeneration.

This review elaborates the idea that organ regeneration derives from specific evolutionary histories of vertebrates. Regenerative ability depends on genomic regulation of genes specific to the life-cycles that have differentially evolved in anamniotes and amniotes. In aquatic environments, where fish and amphibians live, one or multiple metamorphic transitions occur before the adult stage is reached. Each transition involves the destruction and remodeling of larval organs that are replaced with adult organs. After organ injury or loss in adult anamniotes, regeneration uses similar genes and developmental process than those operating during larval growth and metamorphosis. Therefore, the broad presence of regenerative capability across anamniotes is possible because generating new organs is included in their life history at metamorphic stages. Soft hyaluronate-rich regenerative blastemas grow in submersed or in hydrated environments, that is, essential conditions for regeneration, like during development. In adult anamniotes, the ability to regenerate different organs decreases in comparison to larval stages and becomes limited during aging. Comparisons of genes activated during metamorphosis and regeneration in anamniotes identify key genes unique to these processes, and include thyroid, wnt and non-coding RNAs developmental pathways. In the terrestrial environment, some genes or developmental pathways for metamorphic transitions were lost during amniote evolution, determining loss of regeneration. Among amniotes, the formation of soft and hydrated blastemas only occurs in lizards, a morphogenetic process that evolved favoring their survival through tail autotomy, leading to a massive although imperfect regeneration of the tail. Deciphering genes activity during lizard tail regeneration would address future attempts to recreate in other amniotes regenerative blastemas that grow into variably completed organs.

Gene expression in regenerating and scarring tails of lizard evidences three main key genes (wnt2b, egfl6, and arhgap28) activated during the regulated process of tail regeneration.

We have analyzed the expression of key genes orchestrating tail regeneration in lizard under normal and scarring conditions after cauterization. At 1-day post-cauterization (1dpc), the injured blastema contains degenerating epithelial and mesenchymal cells, numerous mast cells, and immune cells. At 3 and 7dpc, a stratified wound epidermis is forming while fibrocytes give rise to a scarring connective tissue. Oncogenes such as wnt2b, egfl6, wnt6, and mycn and the tumor suppressor arhgap28 are much more expressed than other oncogenes (hmga2, rhov, fgf8, fgfr4, tert, shh) and tumor suppressors (apcdd1, p63, rb, fat2, bcl11b) in the normal blastema and at 7dpc. Blastemas at 3dpc feature the lowest upregulation of most genes, likely derived from damage after cauterization. Immunomodulator genes nfatc4 and lef1 are more expressed at 7dpc than in normal blastema and 3dpc suggesting the induction of immune response favoring scarring. Balanced over-expression of oncogenes, tumor suppressor genes, and immune modulator genes determines regulation of cell proliferation (anti-oncogenic), of movement (anti-metastatic), and immunosuppression in the normal blastema. Significant higher expression of oncogenes wnt2b and egfl6 in normal blastema and higher expression of the tumor suppressor arhgap28 in the 7dpc blastema indicate that they are among the key/master genes that determine the regulated regeneration of the tail.

Single cell sequencing analysis of lizard phagocytic cell populations and their role in tail regeneration

Lizards are the closest relatives of mammals capable of tail regeneration, but the specific determinants of amniote regenerative capabilities are currently unknown. Macrophages are phagocytic immune cells that play a critical role in wound healing and tissue regeneration in a wide range of species. We hypothesize that macrophages regulate the process of lizard tail regeneration, and that comparisons with mammalian cell populations will yield insight into the role phagocytes play in determining an organism's regenerative potential. Single cell RNA sequencing (scRNAseq) was used to profile lizard immune cells and compare with mouse counterparts to contrast cell types between the two species. Treatment with clodronate liposomes effectively inhibited lizard tail stump tissue ablation and subsequent regeneration, and scRNAseq was used to profile changes in lizard immune cell populations resulting from tail amputation as well as identifying specific cell types affected by clodronate treatment. ScRNAseq analysis of lizard bone marrow, peripheral blood, and tissue-resident phagocyte cell populations was used to trace marker progression during macrophage differentiation and activation. These results indicated that lizard macrophages are recruited to tail amputation injuries faster than mouse populations and express high levels of matrix metalloproteinases (MMPs). In turn, treatment with MMP inhibitors inhibited lizard tail regeneration. These results provide single cell sequencing data sets for evaluating and comparing lizard and mammalian immune cell populations, and identifying macrophage populations that are critical regulators of lizard tail regrowth.

Fibroblast growth factor-2 signaling modulates matrix reorganization and cell cycle turnover rate in the regenerating tail of Hemidactylus flaviviridis

Lizards restore their lost tail by the recruitment of multipotent cells which are selectively differentiated into varied cell types so as to sculpt a new tail. The precise coordination of the events involved in this complex process requires crosstalk between many signaling molecules and differential regulation of several mediators that facilitate the achievements of various milestones of regeneration. Fibroblast growth factor-2 is one such signaling molecule which activates a number of intracellular signaling pathways. Herein, the regulatory role of FGF2 during tail regeneration in Hemidactylus flaviviridis was investigated. Upon inhibition of FGFR using SU5402, the FGF2 levels were found to be significantly reduced at both transcript and protein level. Further, the compromised levels of the gelatinases, namely MMP2 and MMP9 in the tail tissues of treated lizards indicate that FGF2 regulates the activity of these enzymes perhaps to facilitate the recruitment of multipotent mesenchymal cells (blastema). The in vivo 5BrdU incorporation assay showed a lower cell proliferation rate in FGF2 signal inhibited animals during all the proliferative stages of regeneration studied. This observation was substantiated by decreased levels of PCNA in treated group. Moreover, from the combined results of Caspase-3 localization and its expression levels in the regenerates of control and SU5402 treated lizards it can be deduced that FGF2 signal regulates apoptosis as well during early stages of regeneration. Overall, the current study indicates beyond doubt that FGF2 signaling plays a pivotal role in orchestrating the matrix reorganization and cell cycle turnover during lizard tail regeneration.