Self-Control of Inflammation during Tail Regeneration of Lizards

Loss of the ability to regenerate body appendages in vertebrates: from side effects of evolutionary innovations to gene loss

The ability to regenerate large body appendages is an ancestral trait of vertebrates, which varies across different animal groups. While anamniotes (fish and amphibians) commonly possess this ability, it is notably restricted in amniotes (reptiles, birds, and mammals). In this review, we explore the factors contributing to the loss of regenerative capabilities in amniotes. First, we analyse the potential negative impacts on appendage regeneration caused by four evolutionary innovations: advanced immunity, skin keratinization, whole-body endothermy, and increased body size. These innovations emerged as amniotes transitioned to terrestrial habitats and were correlated with a decline in regeneration capability. Second, we examine the role played by the loss of regeneration-related enhancers and genes initiated by these innovations in the fixation of an inability to regenerate body appendages at the genomic level. We propose that following the cessation of regenerative capacity, the loss of highly specific regeneration enhancers could represent an evolutionarily neutral event. Consequently, the loss of such enhancers might promptly follow the suppression of regeneration as a side effect of evolutionary innovations. By contrast, the loss of regeneration-related genes, due to their pleiotropic functions, would only take place if such loss was accompanied by additional evolutionary innovations that compensated for the loss of pleiotropic functions unrelated to regeneration, which would remain even after participation of these genes in regeneration was lost. Through a review of the literature, we provide evidence that, in many cases, the loss in amniotes of genes associated with body appendage regeneration in anamniotes was significantly delayed relative to the time when regenerative capability was lost. We hypothesise that this delay may be attributed to the necessity for evolutionary restructuring of developmental mechanisms to create conditions where the loss of these genes was a beneficial innovation for the organism. Experimental investigation of the downregulation of genes involved in the regeneration of body appendages in anamniotes but absent in amniotes offers a promising avenue to uncover evolutionary innovations that emerged from the loss of these genes. We propose that the vast majority of regeneration-related genes lost in amniotes (about 150 in humans) may be involved in regulating the early stages of limb and tail regeneration in anamniotes. Disruption of this stage, rather than the late stage, may not interfere with the mechanisms of limb and tail bud development during embryogenesis, as these mechanisms share similarities with those operating in the late stage of regeneration. Consequently, the most promising approach to restoring regeneration in humans may involve creating analogs of embryonic limb buds using stem cell-based tissue-engineering methods, followed by their transfer to the amputation stump. Due to the loss of many genes required specifically during the early stage of regeneration, this approach may be more effective than attempting to induce both early and late stages of regeneration directly in the stump itself.

Comparative proteomic analysis of tail regeneration in the green anole lizard, Anolis carolinensis

As amniote vertebrates, lizards are the most closely related organisms to humans capable of appendage regeneration. Lizards can autotomize, or release their tails as a means of predator evasion, and subsequently regenerate a functional replacement. Green anoles (Anolis carolinensis) can regenerate their tails through a process that involves differential expression of hundreds of genes, which has previously been analyzed by transcriptomic and microRNA analysis. To investigate protein expression in regenerating tissue, we performed whole proteomic analysis of regenerating tail tip and base. This is the first proteomic data set available for any anole lizard. We identified a total of 2,646 proteins - 976 proteins only in the regenerating tail base, 796 only in the tail tip, and 874 in both tip and base. For over 90% of these proteins in these tissues, we were able to assign a clear orthology to gene models in either the Ensembl or NCBI databases. For 13 proteins in the tail base, 9 proteins in the tail tip, and 10 proteins in both regions, the gene model in Ensembl and NCBI matched an uncharacterized protein, confirming that these predictions are present in the proteome. Ontology and pathways analysis of proteins expressed in the regenerating tail base identified categories including actin filament-based process, ncRNA metabolism, regulation of phosphatase activity, small GTPase mediated signal transduction, and cellular component organization or biogenesis. Analysis of proteins expressed in the tail tip identified categories including regulation of organelle organization, regulation of protein localization, ubiquitin-dependent protein catabolism, small GTPase mediated signal transduction, morphogenesis of epithelium, and regulation of biological quality. These proteomic findings confirm pathways and gene families activated in tail regeneration in the green anole as well as identify uncharacterized proteins whose role in regrowth remains to be revealed. This study demonstrates the insights that are possible from the integration of proteomic and transcriptomic data in tail regrowth in the green anole, with potentially broader application to studies in other regenerative models.

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

BACKGROUND

accumulating 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.

METHODS

in 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).

RESULTS

at 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.

CONCLUSIONS

this 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.

Immunohistochemistry Indicates That Persistent Inflammation Determines Failure of Tail, Limb and Finger Regeneration in the Lizard Podarcis muralis

BACKGROUND

The presence of white blood inflammatory cells in injured tissues and their effect on the process of organ regeneration in lizards has been assessed on tail, limb and digits.

METHODS

The present immunohistochemical survey analyzes the occurrence of CD68-labeled cells in lizard organs uncapable of regenerating tissues that exhibit strong inflammatory activity.

RESULTS

This marker mainly identifies macrophages and mast cells present in large number within tissues of injured limbs and digits. Also a high inflammation is associated with amputated tails that do not regenerate, derived from cauterization or infection of tissues of the tail stump. In the healing limbs and fingers at 12-20 days post-amputation, numerous CD68-labeled cells, most likely macrophages, are seen among superficial connective tissues and injured muscles and bones. These cells likely stimulate and give rise to scarring tissues and no regeneration of limb and fingers occurs. In the cauterized or in the infected tail stump a strong accumulation of CD68-positive mast cells and macrophages is observed, where they likely evoke epidermal coagulation, formation of scarring connective tissue, and loss of regeneration.

CONCLUSIONS

The present observations provide further cytological evidence that support the notion that a strong and lasting inflammatory condition impedes organ regeneration in specifically lizards and, more generally other vertebrates as well.

Introduction to the Study on Regeneration in Lizards as an Amniote Model of Organ Regeneration

Initial observations on the regeneration of the tail in lizards were recorded in brief notes by Aristotle over 2000 years ago, as reported in his book, History of Animals (cited from [...].