interleukin-11 induces and maintains progenitors of different cell lineages during Xenopus tadpole tail regeneration

Harnessing the regenerative potential of interleukin11 to enhance heart repair

Balancing between regenerative processes and fibrosis is crucial for heart repair, yet strategies regulating this balance remain a barrier to developing therapies. While Interleukin11 (IL11) is known as a fibrotic factor, its contribution to heart regeneration is poorly understood. We uncovered that il11a, an Il11 homolog in zebrafish, can trigger robust regenerative programs in zebrafish hearts, including cardiomyocytes proliferation and coronary expansion, even in the absence of injury. However, prolonged il11a induction in uninjured hearts causes persistent fibroblast emergence, resulting in fibrosis. While deciphering the regenerative and fibrotic effects of il11a, we found that il11-dependent fibrosis, but not regeneration, is mediated through ERK activity, suggesting to potentially uncouple il11a dual effects on regeneration and fibrosis. To harness the il11a's regenerative ability, we devised a combinatorial treatment through il11a induction with ERK inhibition. This approach enhances cardiomyocyte proliferation with mitigated fibrosis, achieving a balance between regenerative processes and fibrosis. Thus, we unveil the mechanistic insights into regenerative il11 roles, offering therapeutic avenues to foster cardiac repair without exacerbating fibrosis.

Fibroblast-derived interleukin-6 exacerbates adverse cardiac remodeling after myocardial infarction

Myocardial infarction is one of the leading causes of mortality globally. Currently, the pleiotropic inflammatory cytokine interleukin-6 (IL-6) is considered to be intimately related to the severity of myocardial injury during myocardial infarction. Interventions targeting IL-6 are a promising therapeutic option for myocardial infarction, but the underlying molecular mechanisms are not well understood. Here, we report the novel role of IL-6 in regulating adverse cardiac remodeling mediated by fibroblasts in a mouse model of myocardial infarction. It was found that the elevated expression of IL-6 in myocardium and cardiac fibroblasts was observed after myocardial infarction. Further, fibroblast-specific knockdown of Il6 significantly attenuated cardiac fibrosis and adverse cardiac remodeling and preserved cardiac function induced by myocardial infarction. Mechanistically, the role of Il6 contributing to cardiac fibrosis depends on signal transduction and activation of transcription (STAT)3 signaling activation. Additionally, Stat3 binds to the Il11 promoter region and contributes to the increased expression of Il11, which exacerbates cardiac fibrosis. In conclusion, these results suggest a novel role for IL-6 derived from fibroblasts in mediating Stat3 activation and substantially augmented Il11 expression in promoting cardiac fibrosis, highlighting its potential as a therapeutic target for cardiac fibrosis.

Genetic regulation of injury-induced heterotopic ossification in adult zebrafish

Heterotopic ossification is the inappropriate formation of bone in soft tissues of the body. It can manifest spontaneously in rare genetic conditions or as a response to injury, known as acquired heterotopic ossification. There are several experimental models for studying acquired heterotopic ossification from different sources of damage. However, their tenuous mechanistic relevance to the human condition, invasive and laborious nature and/or lack of amenability to chemical and genetic screens, limit their utility. To address these limitations, we developed a simple zebrafish injury model that manifests heterotopic ossification with high penetrance in response to clinically emulating injuries, as observed in human myositis ossificans traumatica. Using this model, we defined the transcriptional response to trauma, identifying differentially regulated genes. Mutant analyses revealed that an increase in the activity of the potassium channel Kcnk5b potentiates injury response, whereas loss of function of the interleukin 11 receptor paralogue (Il11ra) resulted in a drastically reduced ossification response. Based on these findings, we postulate that enhanced ionic signalling, specifically through Kcnk5b, regulates the intensity of the skeletogenic injury response, which, in part, requires immune response regulated by Il11ra.

Understanding interleukin 11 as a disease gene and therapeutic target

Interleukin 11 (IL11) is an elusive member of the IL6 family of cytokines. While initially thought to be a haematopoietic and cytoprotective factor, more recent data show instead that IL11 is redundant for haematopoiesis and toxic. In this review, the reasons that led to the original misunderstandings of IL11 biology, which are now understandable, are explained with particular attention on the use of recombinant human IL11 in mice and humans. Following tissue injury, as part of an evolutionary ancient homeostatic response, IL11 is secreted from damaged mammalian cells to signal via JAK/STAT3, ERK/P90RSK, LKB1/mTOR and GSK3β/SNAI1 in autocrine and paracrine. This activates a program of mesenchymal transition of epithelial, stromal, and endothelial cells to cause inflammation, fibrosis, and stalled endogenous tissue repair, leading to organ failure. The role of IL11 signalling in cell- and organ-specific pathobiology is described, the large unknowns about IL11 biology are discussed and the promise of targeting IL11 signalling as a therapeutic approach is reviewed.

Phenotype-genotype relationships in Xenopus sox9 crispants provide insights into campomelic dysplasia and vertebrate jaw evolution

Since CRISPR-based genome editing technology works effectively in the diploid frog Xenopus tropicalis, a growing number of studies have successfully modeled human genetic diseases in this species. However, most of their targets were limited to non-syndromic diseases that exhibit abnormalities in a small fraction of tissues or organs in the body. This is likely because of the complexity of interpreting the phenotypic variations resulting from somatic mosaic mutations generated in the founder animals (crispants). In this study, we attempted to model the syndromic disease campomelic dysplasia (CD) by generating sox9 crispants in X. tropicalis. The resulting crispants failed to form neural crest cells at neurula stages and exhibited various combinations of jaw, gill, ear, heart, and gut defects at tadpole stages, recapitulating part of the syndromic phenotype of CD patients. Genotyping of the crispants with a variety of allelic series of mutations suggested that the heart and gut defects depend primarily on frame-shift mutations expected to be null, whereas the jaw, gill, and ear defects could be induced not only by such mutations but also by in-frame deletion mutations expected to delete part of the jawed vertebrate-specific domain from the encoded Sox9 protein. These results demonstrate that Xenopus crispants are useful for investigating the phenotype-genotype relationships behind syndromic diseases and examining the tissue-specific role of each functional domain within a single protein, providing novel insights into vertebrate jaw evolution.

regeneration factors expressed on myeloid expression in macrophage-like cells is required for tail regeneration in Xenopus laevis tadpoles

Xenopus laevis tadpoles can regenerate whole tails after amputation. We have previously reported that interleukin 11 (il11) is required for tail regeneration. In this study, we have screened for genes that support tail regeneration under Il11 signaling in a certain cell type and have identified the previously uncharacterized genes Xetrov90002578m.L and Xetrov90002579m.S [referred to hereafter as regeneration factors expressed on myeloid.L (rfem.L) and rfem.S]. Knockdown (KD) of rfem.L and rfem.S causes defects of tail regeneration, indicating that rfem.L and/or rfem.S are required for tail regeneration. Single-cell RNA sequencing (scRNA-seq) revealed that rfem.L and rfem.S are expressed in a subset of leukocytes with a macrophage-like gene expression profile. KD of colony-stimulating factor 1 (csf1), which is essential for macrophage differentiation and survival, reduced rfem.L and rfem.S expression levels and the number of rfem.L- and rfem.S-expressing cells in the regeneration bud. Furthermore, forced expression of rfem.L under control of the mpeg1 promoter, which drives rfem.L in macrophage-like cells, rescues rfem.L and rfem.S KD-induced tail regeneration defects. Our findings suggest that rfem.L or rfem.S expression in macrophage-like cells is required for tail regeneration.

Utilization of ethanolamine phosphate phospholyase as a unique astrocytic marker

Astrocytes play diverse roles in the central nervous system (CNS) in both physiological and pathological conditions. Previous studies have identified many markers of astrocytes to analyze their complicated roles. Recently, closure of the critical period by mature astrocytes has been revealed, and the need for finding mature astrocyte-specific markers has been growing. We previously found that Ethanolamine phosphate phospholyase (Etnppl) was almost not expressed in the developing neonatal spinal cord, and its expression level slightly decreased after pyramidotomy in adult mice, which showed weak axonal sprouting, suggesting that its expression level negatively correlates with axonal elongation. Although the expression of Etnppl in astrocytes in adult is known, its utility as an astrocytic marker has not yet been investigated in detail. Here, we showed that Etnppl was selectively expressed in astrocytes in adult. Re-analyses using published RNA-sequencing datasets revealed changes in Etnppl expression in spinal cord injury, stroke, or systemic inflammation models. We produced high-quality monoclonal antibodies against ETNPPL and characterized ETNPPL localization in neonatal and adult mice. Expression of ETNPPL was very weak in neonatal mice, except in the ventricular and subventricular zones, and it was heterogeneously expressed in adult mice, with the highest expression in the cerebellum, olfactory bulb, and hypothalamus and the lowest in white matter. Subcellular localization of ETNPPL was dominant in the nuclei with weak expression in the cytosol in the minor population. Using the antibody, astrocytes in adult were selectively labeled in the cerebral cortex or spinal cord, and changes in astrocytes were detected in the spinal cord after pyramidotomy. ETNPPL is expressed in a subset of Gjb6 ⁺ astrocytes in the spinal cord. The monoclonal antibodies we created, as well as fundamental knowledge characterized in this study, will be valuable resources in the scientific community and will expand our understanding of astrocytes and their complicated responses in many pathological conditions in future analyses.

Now that We Got There, What Next?

As seen in the protocols in this book, the opportunities to pursue work at the cellular and molecular work in salamanders have considerably broadened over the last years. The availability of genomic information and genome editing, and the possibility to image tissues live and other methods enhance the spectrum of biological questions accessible to all researchers. Here I provide a personal perspective on what I consider exciting future questions open for investigation.

IL11 stimulates ERK/P90RSK to inhibit LKB1/AMPK and activate mTOR initiating a mesenchymal program in stromal, epithelial, and cancer cells

IL11 initiates fibroblast activation but also causes epithelial cell dysfunction. The mechanisms underlying these processes are not known. We report that IL11-stimulated ERK/P90RSK activity causes the phosphorylation of LKB1 at S325 and S428, leading to its inactivation. This inhibits AMPK and activates mTOR across cell types. In stromal cells, IL11-stimulated ERK activity inhibits LKB1/AMPK which is associated with mTOR activation, ⍺SMA expression, and myofibroblast transformation. In hepatocytes and epithelial cells, IL11/ERK activity inhibits LKB1/AMPK leading to mTOR activation, SNAI1 expression, and cell dysfunction. Across cells, IL11-induced phenotypes were inhibited by metformin stimulated AMPK activation. In mice, genetic or pharmacologic manipulation of IL11 activity revealed a critical role of IL11/ERK signaling for LKB1/AMPK inhibition and mTOR activation in fatty liver disease. These data identify the IL11/mTOR axis as a signaling commonality in stromal, epithelial, and cancer cells and reveal a shared IL11-driven mesenchymal program across cell types.

Effective enrichment of stem cells in the regenerating Xenopus laevis tadpole tails using the side population method

Xenopus laevis tadpoles have high regenerative ability and can regenerate their whole tails after tail amputation. Lineage-restricted tissue stem cells are thought to provide sources for the regenerating tissues by producing undifferentiated progenitor cells in response to tail amputation. However, elucidating the behavioral dynamics of tissue stem cells during tail regeneration is difficult because of their rarity, and there are few established methods of isolating these cells in amphibians. Here, to detect and analyze rare tissue stem cells, we attempted to enrich tissue stem cells from tail regeneration buds. High Hoechst dye efflux capacity is thought to be a common characteristic of several types of mammalian tissue stem cells; these stem cells designated as the "side population (SP)" may be enriched by flow cytometry (SP method). To evaluate the effectiveness of stem cell enrichment using the SP method in regenerating X. laevis tadpole tails, we performed single-cell RNA sequencing (scRNA-seq) of SP cells from regeneration buds and analyzed the frequency of satellite cells, which are muscle stem/progenitor cells expressing pax7. The pax7-expressing cells were enriched in the SP compared with whole normal tails and regeneration buds. Furthermore, hes1-expressing cells assumed to be neural stem/progenitor cells were also enriched in the SP. Our findings suggest that the SP method was efficient for successfully enriching tissue stem cells in the regenerating X. laevis tadpole tails, indicating that the combination of the SP method and scRNA-seq was useful for studying tissue stem cells that contribute to tail regeneration.

Glass-patternable notch-shaped microwave architecture for on-chip spin detection in biological samples

We report a notch-shaped coplanar microwave waveguide antenna on a glass plate designed for on-chip detection of optically detected magnetic resonance (ODMR) of fluorescent nanodiamonds (NDs). A lithographically patterned thin wire at the center of the notch area in the coplanar waveguide realizes a millimeter-scale ODMR detection area (1.5 × 2.0 mm²) and gigahertz-broadband characteristics with low reflection (∼8%). The ODMR signal intensity in the detection area is quantitatively predictable by numerical simulation. Using this chip device, we demonstrate a uniform ODMR signal intensity over the detection area for cells, tissue, and worms. The present demonstration of a chip-based microwave architecture will enable scalable chip integration of ODMR-based quantum sensing technology into various bioassay platforms.

Optimization of CRISPR/Cas9-mediated gene disruption in Xenopus laevis using a phenotypic image analysis technique

The CRISPR/Cas9 method has become popular for gene disruption experiments in Xenopus laevis. However, the experimental conditions that influence the efficiency of CRISPR/Cas9 remain unclear. To that end, we developed an image analysis technique for the semi-quantitative evaluation of the pigment phenotype resulting from the disruption of tyrosinase genes in X. laevis using a CRISPR/Cas9 approach, and then examined the effects of varying five experimental parameters (timing of the CRISPR reagent injection into developing embryos; amount of Cas9 mRNA in the injection reagent; total injection volume per embryo; number of injection sites per embryo; and the culture temperature of the injected embryos) on the gene disruption efficiency. The results of this systematic analysis suggest that the highest possible efficiency of target gene disruption can be achieved by injecting a total of 20 nL of the CRISPR reagent containing 1500 pg of Cas9 mRNA or 4 ng of Cas9 protein into two separate locations (10 nL each) of one-cell stage embryos cultured at 22°C. This study also highlights the importance of balancing the experimental parameters for increasing gene disruption efficiency and provides valuable insights into the optimal conditions for applying the CRISPR/Cas9 system to new experimental organisms.

Toll signalling promotes blastema cell proliferation during cricket leg regeneration via insect macrophages

Hemimetabolous insects, such as the two-spotted cricket Gryllus bimaculatus, can recover lost tissues, in contrast to the limited regenerative abilities of human tissues. Following cricket leg amputation, the wound surface is covered by the wound epidermis, and plasmatocytes, which are insect macrophages, accumulate in the wound region. Here, we studied the function of Toll-related molecules identified by comparative RNA sequencing during leg regeneration. Of the 11 Toll genes in the Gryllus genome, expression of Toll2-1, Toll2-2 and Toll2-5 was upregulated during regeneration. RNA interference (RNAi) of Toll, Toll2-1, Toll2-2, Toll2-3 or Toll2-4 produced regeneration defects in more than 50% of crickets. RNAi of Toll2-2 led to a decrease in the ratio of S- and M-phase cells, reduced expression of JAK/STAT signalling genes, and reduced accumulation of plasmatocytes in the blastema. Depletion of plasmatocytes in crickets using clodronate also produced regeneration defects, as well as fewer proliferating cells in the regenerating legs. Plasmatocyte depletion also downregulated the expression of Toll and JAK/STAT signalling genes in the regenerating legs. These results suggest that Spz-Toll-related signalling in plasmatocytes promotes leg regeneration through blastema cell proliferation by regulating the Upd-JAK/STAT signalling pathway.

Single-cell transcriptome analysis reveals three sequential phases of gene expression during zebrafish sensory hair cell regeneration

Loss of sensory hair cells (HCs) in the mammalian inner ear leads to permanent hearing and vestibular defects, whereas loss of HCs in zebrafish results in their regeneration. We used single-cell RNA sequencing (scRNA-seq) to characterize the transcriptional dynamics of HC regeneration in zebrafish at unprecedented spatiotemporal resolution. We uncovered three sequentially activated modules: first, an injury/inflammatory response and downregulation of progenitor cell maintenance genes within minutes after HC loss; second, the transient activation of regeneration-specific genes; and third, a robust re-activation of developmental gene programs, including HC specification, cell-cycle activation, ribosome biogenesis, and a metabolic switch to oxidative phosphorylation. The results are relevant not only for our understanding of HC regeneration and how we might be able to trigger it in mammals but also for regenerative processes in general. The data are searchable and publicly accessible via a web-based interface.

Xenopus laevis il11ra.L is an experimentally proven interleukin-11 receptor component that is required for tadpole tail regeneration

Xenopus laevis tadpoles possess high regenerative ability and can regenerate functional tails after amputation. An early event in regeneration is the induction of undifferentiated cells that form the regenerated tail. We previously reported that interleukin-11 (il11) is upregulated immediately after tail amputation to induce undifferentiated cells of different cell lineages, indicating a key role of il11 in initiating tail regeneration. As Il11 is a secretory factor, Il11 receptor-expressing cells are thought to mediate its function. X. laevis has a gene annotated as interleukin 11 receptor subunit alpha on chromosome 1L (il11ra.L), a putative subunit of the Il11 receptor complex, but its function has not been investigated. Here, we show that nuclear localization of phosphorylated Stat3 induced by Il11 is abolished in il11ra.L knocked-out culture cells, strongly suggesting that il11ra.L encodes an Il11 receptor component. Moreover, knockdown of il11ra.L impaired tadpole tail regeneration, suggesting its indispensable role in tail regeneration. We also provide a model showing that Il11 functions via il11ra.L-expressing cells in a non-cell autonomous manner. These results highlight the importance of il11ra.L-expressing cells in tail regeneration.

Single Cell Genomics Identifies Unique Cardioprotective Phenotype of Stem Cells derived from Epicardial Adipose Tissue under Ischemia

The conventional management strategies of myocardial infarction (MI) are effective to sustain life; however, myocardial regeneration has not been achieved owing to the inherently poor regenerative capacity of the native myocardium. Stem cell-based therapies are promising; however, lineage specificity and undesired differentiation profile are challenging. Herein, we focused on the epicardial fat (EF) as an ideal source for mesenchymal stem cells (MSCs) owing to the proximity and same microvasculature with cardiac muscle. Unfortunately, the epicardial adipose tissue derived stem cells (EATDS) remain understudied regarding their phenotype heterogeneity and cardiac regeneration potential. As EF closely reflects the cardiac pathology during ischemia, the present study aims to determine the EATDS subpopulations under simulated ischemic and reperfused conditions employing single cell RNA sequencing (scRNAseq). EATDS were isolated from three hyperlipidemic Yucatan microswine and were divided into Control, Ischemia (ISC), and Ischemia/reperfusion (ISC/R). The scRNAseq analysis was performed using 10 genomics platform which revealed 18 unique cell clusters suggesting the existence of heterogeneous phenotypes. The upregulated genes were taken into consideration and subsequent functional assessment revealed the cardioprotective phenotypes with diverse mechanisms including epigenetic regulation (Cluster 1), myocardial homeostasis (Cluster 1), cell integrity and cell cycle (Clusters 2 and 3), prevention of fibroblast differentiation (Cluster 4), differentiation to myocardial lineage (Cluster 6), anti-inflammatory responses (Clusters 5, 8, and 11), prevention of ER-stress (Cluster 9), and increasing the energy metabolism (Cluster 10). These unique phenotypes of heterogeneous EATDS population open significant translational opportunities for myocardial regeneration and cardiac management.

Interleukin-11 signaling promotes cellular reprogramming and limits fibrotic scarring during tissue regeneration

Damage-induced fibrotic scarring limits tissue regeneration in mammals and is a leading cause of morbidity. In contrast, species like zebrafish can regenerate damaged tissues without excessive fibrosis. However, whether specific signaling pathways can both limit fibrosis and promote regeneration is unclear. Here, we show that interleukin-11 (Il-11)/Stat3 signaling has such a dual function. Zebrafish lacking Il-11 receptor function display severely compromised heart, fin, and scale regeneration. Deep phenotyping and transcriptional analysis of adult hearts and fins show that Il-11 signaling drives cellular reprogramming to orchestrate global and tissue-specific regenerative programs and broadly antagonizes hallmarks of adult mammalian scarring. Mechanistically, our data indicate that IL-11 signaling in endothelial cells antagonizes profibrotic transforming growth factor–β signaling and endothelial-to-mesenchymal transition, limiting scarring and promoting cardiomyocyte repopulation, after injury. Overall, our findings position damage-induced Il-11/Stat3 signaling in a key role limiting fibrosis and promoting regeneration, revealing novel targets for regenerative therapies.

Form and function of the caudal fin throughout the phylogeny of fishes

Fishes are the longest persisting living vertebrates and as such, display an incredible array of diversity. Variation in the tail, or caudal fin, is often a reflection of a fish's environment, and affects movement, predation, defense, and reproduction. Previous literature has discussed many aspects of caudal fin form and function in particular taxonomic groups; however, no previous work has synthesized these studies in order to detail how the caudal fin is structured, and what purpose this structure serves, throughout the phylogeny of fishes. This review examines the caudal fin throughout the main lineages of fish evolution, and highlights where changes in shape and usage have occurred. Such novelties in form and function tend to have far-reaching evolutionary consequences. Through integration of past and present work, this review creates a coherent picture of caudal fin evolution. Patterns and outliers that demonstrate how form and function of this appendage are intertwined can further inform hypotheses that fill critical gaps in knowledge concerning the caudal fin.

Cellular response to spinal cord injury in regenerative and non-regenerative stages in Xenopus laevis

BACKGROUND

The efficient regenerative abilities at larvae stages followed by a non-regenerative response after metamorphosis in froglets makes Xenopus an ideal model organism to understand the cellular responses leading to spinal cord regeneration.

METHODS

We compared the cellular response to spinal cord injury between the regenerative and non-regenerative stages of Xenopus laevis. For this analysis, we used electron microscopy, immunofluorescence and histological staining of the extracellular matrix. We generated two transgenic lines: i) the reporter line with the zebrafish GFAP regulatory regions driving the expression of EGFP, and ii) a cell specific inducible ablation line with the same GFAP regulatory regions. In addition, we used FACS to isolate EGFP⁺ cells for RNAseq analysis.

RESULTS

In regenerative stage animals, spinal cord regeneration triggers a rapid sealing of the injured stumps, followed by proliferation of cells lining the central canal, and formation of rosette-like structures in the ablation gap. In addition, the central canal is filled by cells with similar morphology to the cells lining the central canal, neurons, axons, and even synaptic structures. Regeneration is almost completed after 20 days post injury. In non-regenerative stage animals, mostly damaged tissue was observed, without clear closure of the stumps. The ablation gap was filled with fibroblast-like cells, and deposition of extracellular matrix components. No reconstruction of the spinal cord was observed even after 40 days post injury. Cellular markers analysis confirmed these histological differences, a transient increase of vimentin, fibronectin and collagen was detected in regenerative stages, contrary to a sustained accumulation of most of these markers, including chondroitin sulfate proteoglycans in the NR-stage. The zebrafish GFAP transgenic line was validated, and we have demonstrated that is a very reliable and new tool to study the role of neural stem progenitor cells (NSPCs). RNASeq of GFAP::EGFP cells has allowed us to clearly demonstrate that indeed these cells are NSPCs. On the contrary, the GFAP::EGFP transgene is mainly expressed in astrocytes in non-regenerative stages. During regenerative stages, spinal cord injury activates proliferation of NSPCs, and we found that are mainly differentiated into neurons and glial cells. Specific ablation of these cells abolished proper regeneration, confirming that NSPCs cells are necessary for functional regeneration of the spinal cord.

CONCLUSIONS

The cellular response to spinal cord injury in regenerative and non-regenerative stages is profoundly different between both stages. A key hallmark of the regenerative response is the activation of NSPCs, which massively proliferate, and are differentiated into neurons to reconstruct the spinal cord. Also very notably, no glial scar formation is observed in regenerative stages, but a transient, glial scar-like structure is formed in non-regenerative stage animals.

Low-temperature incubation improves both knock-in and knock-down efficiencies by the CRISPR/Cas9 system in Xenopus laevis as revealed by quantitative analysis

The recent development of the CRISPR/Cas9-mediated gene editing technique has provided various gene knock-down and knock-in methods for Xenopus laevis. Gene-edited F0 individuals created by these methods, however, are mosaics with both mutated/knocked-in and unedited wild-type cells, and therefore precise determination and higher efficiency of knock-down and knock-in methods are desirable, especially for analyses of F0 individuals. To clarify the ratio of cells that are gene-edited by CRISPR/Cas9 methods to the whole cells in F0 individuals, we subjected Inference of CRISPR Edits analysis for knock-down experiments and flow cytometry for knock-in experiments to the F0 individuals. With these quantitative methods, we showed that low-temperature incubation of X. laevis embryos after microinjection improved the mutation rate in the individuals. Moreover, we applied low-temperature incubation when using a knock-in method with long single-strand DNA and found improved knock-in efficiency. Our results provide a simple and useful way to evaluate and improve the efficiency of gene editing in X. laevis.

Neural circuit repair after central nervous system injury

Central nervous system injury often causes lifelong impairment of neural function, because the regenerative ability of axons is limited, making a sharp contrast to the successful regeneration that is seen in the peripheral nervous system. Nevertheless, partial functional recovery is observed, because axonal branches of damaged or undamaged neurons sprout and form novel relaying circuits. Using a lot of animal models such as the spinal cord injury model or the optic nerve injury model, previous studies have identified many factors that promote or inhibit axonal regeneration or sprouting. Molecules in the myelin such as myelin-associated glycoprotein, Nogo-A or oligodendrocyte-myelin glycoprotein, or molecules found in the glial scar such as chondroitin sulfate proteoglycans, activate Ras homolog A (RhoA) signaling, which leads to the collapse of the growth cone and inhibit axonal regeneration. By contrast, axonal regeneration programs can be activated by many molecules such as regeneration-associated transcription factors, cyclic AMP, neurotrophic factors, growth factors, mechanistic target of rapamycin or immune-related molecules. Axonal sprouting and axonal regeneration largely share these mechanisms. For functional recovery, appropriate pruning or suppressing of aberrant sprouting are also important. In contrast to adults, neonates show much higher sprouting ability. Specific cell types, various mouse strains and different species show higher regenerative ability. Studies focusing on these models also identified a lot of molecules that affect the regenerative ability. A deeper understanding of the mechanisms of neural circuit repair will lead to the development of better therapeutic approaches for central nervous system injury.

Comparative Transcriptome Analysis of the Regenerating Zebrafish Telencephalon Unravels a Resource With Key Pathways During Two Early Stages and Activation of Wnt/β-Catenin Signaling at the Early Wound Healing Stage

Owing to its pronounced regenerative capacity in many tissues and organs, the zebrafish brain represents an ideal platform to understand the endogenous regeneration mechanisms that restore tissue integrity and function upon injury or disease. Although radial glial and neuronal cell populations have been characterized with respect to specific marker genes, comprehensive transcriptomic profiling of the regenerating telencephalon has not been conducted so far. Here, by processing the lesioned and unlesioned hemispheres of the telencephalon separately, we reveal the differentially expressed genes (DEGs) at the early wound healing and early proliferative stages of regeneration, i.e., 20 h post-lesion (hpl) and 3 days post-lesion (dpl), respectively. At 20 hpl, we detect a far higher number of DEGs in the lesioned hemisphere than in the unlesioned half and only 7% of all DEGs in both halves. However, this difference disappears at 3 dpl, where the lesioned and unlesioned hemispheres share 40% of all DEGs. By performing an extensive comparison of the gene expression profiles in these stages, we unravel that the lesioned hemispheres at 20 hpl and 3 dpl exhibit distinct transcriptional profiles. We further unveil a prominent activation of Wnt/β-catenin signaling at 20 hpl, returning to control level in the lesioned site at 3 dpl. Wnt/β-catenin signaling indeed appears to control a large number of genes associated primarily with the p53, apoptosis, forkhead box O (FoxO), mitogen-activated protein kinase (MAPK), and mammalian target of rapamycin (mTOR) signaling pathways specifically at 20 hpl. Based on these results, we propose that the lesioned and unlesioned hemispheres react to injury dynamically during telencephalon regeneration and that the activation of Wnt/β-catenin signaling at the early wound healing stage plays a key role in the regulation of cellular and molecular events.

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.

Dysregulated interleukin 11 in primary Sjögren's syndrome contributes to apoptosis of glandular epithelial cells

The purpose of this study was to explore the potential function of interleukin-11 (IL-11) in the pathogenesis of primary Sjögren's syndrome (pSS) patients. Real-time polymerase chain reaction was performed to examine IL-11 expression in the labial glands of 30 pSS patients and 30 healthy controls. Immunohistochemistry was conducted to assess the distribution of IL-ll-positive cells in labial glands. The human salivary gland (HSG) cell line was used to study the effects of IL-11 on gland epithelial cells in vitro. Cell viability and cell proliferation were examined by CCK-8 kit and EdU assay, respectively. The population of apoptotic cells was detected in flow cytometry followed by Annexin V/PI and Hoechst staining. We found that the expression levels of IL-11 were remarkably decreased in pSS labial glands and were positively correlated with C-reactive protein levels and negatively correlated with rheumatoid factor levels. Fewer numbers of glandular epithelial cells were observed to be positively stained with IL-11 antibody in labial glands from pSS patients than those in healthy control patients. After IL-11 treatment, the viability and proliferation of HSG cells were significantly higher than those in the control group. The total apoptotic and necrotic rates of HSG cells in the group after IL-11 treatment were significantly lower. In conclusion, the results indicated that IL-11 promoted viability and proliferation and inhibited apoptotic and necrotic rates of glandular epithelial cells. In pSS, downregulated IL-11 might contribute to the apoptosis of salivary gland epithelial cells. However, it might be a potential target to alleviate the pathological atrophy of glandular epithelial cells in pSS patients.

Comparison of gene expression profile of the spinal cord of sprouting-capable neonatal and sprouting-incapable adult mice

Background

The regenerative ability of severed axons in the central nervous system is limited in mammals. However, after central nervous system injury, neural function is partially recovered by the formation of a compensatory neural circuit. In a mouse pyramidotomy model, axonal sprouting of the intact side of the corticospinal tract is observed in the spinal cord, and the axons make new synapses with the denervated side of propriospinal neurons. Moreover, this sprouting ability is enhanced in neonatal mice compared to that in adult mice. Myelin-associated molecules in the spinal cord or intrinsic factors in corticospinal neurons have been investigated in previous studies, but the factors that determine elevated sprouting ability in neonatal mice are not fully understood. Further, in the early phase after pyramidotomy, glial responses are observed in the spinal cord. To elucidate the basal difference in the spinal cord, we compared gene expression profiles of entire C4–7 cervical cord tissues between neonatal (injured at postnatal day 7) and adult (injured at 8 weeks of age) mice by RNA-sequencing. We also tried to identify discordant gene expression changes that might inhibit axonal sprouting in adult mice at the early phase (3 days) after pyramidotomy.

Results

A comparison of neonatal and adult sham groups revealed remarkable basal differences in the spinal cord, such as active neural circuit formation, cell proliferation, the development of myelination, and an immature immune system in neonatal mice compared to that observed in adult mice. Some inflammation-related genes were selectively expressed in adult mice after pyramidotomy, implying the possibility that these genes might be related to the low sprouting ability in adult mice.

Conclusions

This study provides useful information regarding the basal difference between neonatal and adult spinal cords and the possible differential response after pyramidotomy, both of which are necessary to understand why sprouting ability is increased in neonatal mice compared to that in adult mice.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5974-9) contains supplementary material, which is available to authorized users.

Spinal Cord Regeneration in Amphibians: A Historical Perspective

In some vertebrates, a grave injury to the central nervous system (CNS) results in functional restoration, rather than in permanent incapacitation. Understanding how these animals mount a regenerative response by activating resident CNS stem cell populations is of critical importance in regenerative biology. Amphibians are of a particular interest in the field because the regenerative ability is present throughout life in urodele species, but in anuran species it is lost during development. Studying amphibians, who transition from a regenerative to a nonregenerative state, could give insight into the loss of ability to recover from CNS damage in mammals. Here, we highlight the current knowledge of spinal cord regeneration across vertebrates and identify commonalities and differences in spinal cord regeneration between amphibians.

More Than Just a Bandage: Closing the Gap Between Injury and Appendage Regeneration

The remarkable regenerative capabilities of amphibians have captured the attention of biologists for centuries. The frogs Xenopus laevis and Xenopus tropicalis undergo temporally restricted regenerative healing of appendage amputations and spinal cord truncations, injuries that are both devastating and relatively common in human patients. Rapidly expanding technological innovations have led to a resurgence of interest in defining the factors that enable regenerative healing, and in coupling these factors to human therapeutic interventions. It is well-established that early embryonic signaling pathways are critical for growth and patterning of new tissue during regeneration. A growing body of research now indicates that early physiological injury responses are also required to initiate a regenerative program, and that these differ in regenerative and non-regenerative contexts. Here we review recent insights into the biophysical, biochemical, and epigenetic processes that underlie regenerative healing in amphibians, focusing particularly on tail and limb regeneration in Xenopus. We also discuss the more elusive potential mechanisms that link wounding to tissue growth and patterning.

JAK/STAT signaling in stem cells and regeneration: from Drosophila to vertebrates

The JAK/STAT pathway is a conserved metazoan signaling system that transduces cues from extracellular cytokines into transcriptional changes in the nucleus. JAK/STAT signaling is best known for its roles in immunity. However, recent work has demonstrated that it also regulates critical homeostatic processes in germline and somatic stem cells, as well as regenerative processes in several tissues, including the gonad, intestine and appendages. Here, we provide an overview of JAK/STAT signaling in stem cells and regeneration, focusing on Drosophila and highlighting JAK/STAT pathway functions in proliferation, survival and cell competition that are conserved between Drosophila and vertebrates.