Bacterial lipopolysaccharides can initiate regeneration of the Xenopus tadpole tail

Protocol for tail vein injection in Xenopus tropicalis tadpoles

Functional studies in post-embryonic Xenopus tadpoles are challenging because embryonic perturbations often lead to developmental consequences, such as lethality. Here, we describe a high-throughput protocol for tail vein injection to introduce fluorescent tracers into tadpoles, which we have previously used to effectively inject morpholinos and molecular antagonists. We describe steps for safely positioning tadpoles onto agarose double-coated plates, draining media, injecting into the ventral tail vein, rehydrating plates, and sorting tadpoles by fluorescence with minimal injury for high-throughput experiments. For complete details on the use and execution of this protocol, please refer to Kakebeen et al.,1 Patel et al.,2 and Patel et al.3.

An overview of the traditional use, phytochemistry, and biological activity of the genus Homalanthus

Homalanthus species are native to tropical Asia and the Pacific region. This genus, comprising 23 accepted species, received less scientific attention compared to other genera of the Euphorbiaceae family. Seven Homalanthus species, such as H. giganteus, H. macradenius, H. nutans, H. nervosus, N. novoguineensis, H. populneus, and H. populifolius, have been reported to treat various health problems in traditional medicine. Only a few Homalanthus species have been investigated for their biological activities, including antibacterial, anti-HIV, anti-protozoal, estrogenic, and wound-healing activities. From a phytochemical point of view ent-atisane, ent-kaurane, and tigliane diterpenoids, triterpenoids, coumarins, and flavonol glycosides were found to be characteristic metabolites of the genus. The most promising compound is prostratin, isolated from H. nutans, with anti-HIV activity and the ability to eradicate the HIV reservoir in infected patients by mechanism of protein kinase C (PKC) agonist. This review provides information on traditional usage, phytochemistry, and biological activity of the genus Homalanthus with the aim to delineate future research directions.

Gradual specialization of phagocytic ameboid cells may have impaired regenerative capacities in metazoan lineages

Animal regeneration is a fascinating field of research that has captured the attention of many generations of scientists. Among the cellular mechanisms underlying tissue and organ regeneration, we highlight the role of phagocytic ameboid cells (PACs). Beyond their ability to engulf nutritional particles, microbes, and apoptotic cells, their involvement in regeneration has been widely documented. It has been extensively described that, at least in part, animal regenerative mechanisms rely on PACs that serve as a hub for a range of critical physiological functions, both in health and disease. Considering the phylogenetics of PAC evolution, and the loss and gain of nutritional, immunological, and regenerative potential across Metazoa, we aim to discuss when and how phagocytic activity was first co-opted to regenerative tissue repair. We propose that the gradual specialization of PACs during metazoan derivation may have contributed to the loss of regenerative potential in animals, with critical impacts on potential translational strategies for regenerative medicine.

Thyroid hormone receptor knockout prevents the loss of Xenopus tail regeneration capacity at metamorphic climax

BACKGROUND

Animal regeneration is the natural process of replacing or restoring damaged or missing cells, tissues, organs, and even entire body to full function. Studies in mammals have revealed that many organs lose regenerative ability soon after birth when thyroid hormone (T3) level is high. This suggests that T3 play an important role in organ regeneration. Intriguingly, plasma T3 level peaks during amphibian metamorphosis, which is very similar to postembryonic development in humans. In addition, many organs, such as heart and tail, also lose their regenerative ability during metamorphosis. These make frogs as a good model to address how the organs gradually lose their regenerative ability during development and what roles T3 may play in this. Early tail regeneration studies have been done mainly in the tetraploid Xenopus laevis (X. laevis), which is difficult for gene knockout studies. Here we use the highly related but diploid anuran X. tropicalis to investigate the role of T3 signaling in tail regeneration with gene knockout approaches.

RESULTS

We discovered that X. tropicalis tadpoles could regenerate their tail from premetamorphic stages up to the climax stage 59 then lose regenerative capacity as tail resorption begins, just like what observed for X. laevis. To test the hypothesis that T3-induced metamorphic program inhibits tail regeneration, we used TR double knockout (TRDKO) tadpoles lacking both TRα and TRβ, the only two receptor genes in vertebrates, for tail regeneration studies. Our results showed that TRs were not necessary for tail regeneration at all stages. However, unlike wild type tadpoles, TRDKO tadpoles retained regenerative capacity at the climax stages 60/61, likely in part by increasing apoptosis at the early regenerative period and enhancing subsequent cell proliferation. In addition, TRDKO animals had higher levels of amputation-induced expression of many genes implicated to be important for tail regeneration, compared to the non-regenerative wild type tadpoles at stage 61. Finally, the high level of apoptosis in the remaining uncut portion of the tail as wild type tadpoles undergo tail resorption after stage 61 appeared to also contribute to the loss of regenerative ability.

CONCLUSIONS

Our findings for the first time revealed an evolutionary conservation in the loss of tail regeneration capacity at metamorphic climax between X. laevis and X. tropicalis. Our studies with molecular and genetic approaches demonstrated that TR-mediated, T3-induced gene regulation program is responsible not only for tail resorption but also for the loss of tail regeneration capacity. Further studies by using the model should uncover how T3 modulates the regenerative outcome and offer potential new avenues for regenerative medicines toward human patients.

Local problems need global solutions - the metabolic needs of regenerating organisms

The vast majority of species that belong to the plant or animal kingdom evolved with two main strategies to counter tissue damage - scar formation and regeneration. Whereas scar formation provides a fast and cost-effective repair to exit life-threatening conditions, complete tissue regeneration is time-consuming and requires vast resources to reinstall functionality of affected organs or structures. Local environments in wound healing are widely studied and findings have provided important biomedical applications. Less well understood are organismic physiological parameters and signaling circuits essential to maintain effective tissue repair. Here, we review accumulated evidence that positions the interplay of local and systemic changes in metabolism as essential variables modulating the injury response. We particularly emphasize the role of lipids and lipid-like molecules as significant components long overlooked. This article is protected by copyright. All rights reserved.

Manipulating the microbiome alters regenerative outcomes in Xenopus laevis tadpoles via lipopolysaccharide signalling

Xenopus laevis tadpoles can regenerate functional tails, containing the spinal cord, notochord, muscle, fin, blood vessels and nerves, except for a brief refractory period at around 1 week of age. At this stage, amputation of the tadpole's tail may either result in scarless wound healing or the activation of a regeneration programme, which replaces the lost tissues. We recently demonstrated a link between bacterial lipopolysaccharides and successful tail regeneration in refractory stage tadpoles and proposed that this could result from lipopolysaccharides binding to Toll-like receptor 4 (TLR4). Here, we have used 16S rRNA sequencing to show that the tadpole skin microbiome is highly variable between sibships and that the community can be altered by raising embryos in the antibiotic gentamicin. Six Gram-negative genera, including Delftia and Chryseobacterium, were over-represented in tadpoles that underwent tail regeneration. Lipopolysaccharides purified from a commensal Chryseobacterium spp. XDS4, an exogenous Delftia spp. or Escherichia coli, could significantly increase the number of antibiotic-raised tadpoles that attempted regeneration. Conversely, the quality of regeneration was impaired in native-raised tadpoles exposed to the antagonistic lipopolysaccharide of Rhodobacter sphaeroides. Editing TLR4 using CRISPR/Cas9 also reduced regeneration quality, but not quantity, at the level of the cohort. However, we found that the editing level of individual tadpoles was a poor predictor of regenerative outcome. In conclusion, our results suggest that variable regeneration in refractory stage tadpoles depends at least in part on the skin microbiome and lipopolysaccharide signalling, but that signalling via TLR4 cannot account for all of this effect.

To regenerate or not to regenerate: Vertebrate model organisms of regeneration-competency and -incompetency

Why only certain species can regenerate their appendages (e.g. tails and limbs) remains one of the biggest mysteries of nature. Unlike anuran tadpoles and salamanders, humans and other mammals cannot regenerate their limbs, but can only regrow lost digit tips under specific circumstances. Numerous hypotheses have been postulated to explain regeneration-incompetency in mammals. By studying model organisms that show varying regenerative abilities, we now have more opportunities to uncover what contributes to regeneration-incompetency and functionally test which perturbations restore appendage regrowth. Particularly, Xenopus laevis tail and limb, and mouse digit tip model systems exhibit naturally occurring variations in regenerative capacities. Here, we discuss major hypotheses that are suggested to contribute to regeneration-incompetency, and how species with varying regenerative abilities reflect on these hypotheses.

Complete Genome Sequences of Kinneretia sp. Strain XES5, Shinella sp. Strain XGS7, and Vogesella sp. Strain XCS3, Isolated from Xenopus laevis Skin

Here, we report the genome sequences of three bacterial isolates, Kinneretia sp. strain XES5, Shinella sp. strain XGS7, and Vogesella sp. strain XCS3, which were cultured from skin of adult female laboratory-bred Xenopus laevis.