TGF-beta signaling is required for multiple processes during Xenopus tail regeneration

Transforming growth factor-beta gene family in Labeo rohita: Genome-wide molecular characterization and phylogenetic relationship with other vertebrates

Recent advancements in animal genetics, biotechnology, and bioinformatics can potentially contribute to the required improvement in fish production and quality. Current study explored for the first-time, various genes from Transforming growth factor-beta (TGF-β) gene family which could play vital role in growth and development of Labeo rohita, an economically important freshwater fish. A number of tools and analysis like characterizing the selected genes, multiple alignment and clade-wise phylogeny, dual Synteny analysis and chromosomal distribution, characterization of proteins, secondary structure and 3D models of proteins, PROSITE scan analysis, and transcription factor binding sites (TFBSs) of selected genes were performed to explore the relationship between selected genes from Labeo rohita and referenced species (Homo sapiens, Danio rerio, Oreochromis niloticus, Chelonia mydas, and Parus major). The study evaluated 27 genes from TGF-β gene family. The results suggested that physicochemical characteristics of studied genes exhibit a basic nature with the few exceptions. Two main clades (BPM like and GDF like) were obtained by the phylogenetic analysis across six vertebrate species. Homogeneity was observed in the gene structure for all selected genes of TGF-β gene superfamily. TGF-β family and TGF-β propeptide family were dominant in domain regions of studied genes. Gene structure comparisons suggested that the TGF-β gene superfamily has arisen by gene duplications events. The study identified five pairs of duplicated gene (segmental duplications) with the Ka/Ks < 1, indicating the negative selection pressure of these genes. The length of selected TFBSs (GATA, HOXD, STAT, HNF-1A, and YY1) ranged from 5 to 9 bp, with the HOXD having maximum bp. This study explored the molecular characterization for TGF-β gene family and related proteins in L. rohita and will potentially serve as basis of development of novel strategies in improvement of fish culture.

Tail Tales: What We Have Learned About Regeneration from Xenopus Laevis Tadpoles

This review explores the regenerative capacity of Xenopus laevis, focusing on tail regeneration, as a model to uncover cellular, molecular, and developmental mechanisms underlying tissue repair. X. laevis tadpoles provide unique insights into regenerative biology due to their regeneration-competent and -incompetent stages and ability to regrow complex structures in the tail, including the spinal cord, muscle, and skin, after amputation. The review delves into the roles of key signaling pathways, such as those involving reactive oxygen species (ROS) and signaling molecules like BMPs and FGFs, in orchestrating cellular responses during regeneration. It also examines how mechanotransduction, epigenetic regulation, and metabolic shifts influence tissue restoration. Comparisons of regenerative capacity with other species shed light on the evolutionary loss of regenerative abilities and underscore X. laevis as an invaluable model for understanding the constraints of tissue repair in higher organisms. This comprehensive review synthesizes recent findings, suggesting future directions for exploring regeneration mechanisms, with potential implications for advancing regenerative medicine.

Two transcriptional cascades orchestrate cockroach leg regeneration

The mystery of appendage regeneration has fascinated humans for centuries, while the underlying regulatory mechanisms remain unclear. In this study, we establish a transcriptional landscape of regenerating leg in the American cockroach, Periplaneta americana, an ideal model in appendage regeneration studies showing remarkable regeneration capacity. Through a large-scale in vivo screening, we identify multiple signaling pathways and transcription factors controlling leg regeneration. Specifically, zfh-2 and bowl contribute to blastema cell proliferation and morphogenesis in two transcriptional cascades: bone morphogenetic protein (BMP)/JAK-STAT-zfh-2-B-H2 and Notch-drm/bowl-bab1. Notably, we find zfh-2 is working as a direct target of BMP signaling to promote cell proliferation in the blastema. These mechanisms might be conserved in the appendage regeneration of vertebrates from an evolutionary perspective. Overall, our findings reveal that two crucial transcriptional cascades orchestrate distinct cockroach leg regeneration processes, significantly advancing the comprehension of molecular mechanism in appendage regeneration.

Identification of key genes and molecular pathways associated with claw regeneration in mud crab (Scylla paramamosain)

The mud crab (Scylla paramamosain) possesses extensive regenerative abilities, enabling it to replace missing body parts, including claws, legs, and even eyes. Studying the genetic and molecular mechanisms underlying regenerative ability in diverse animal phyla has the potential to provide new insights into regenerative medicine in humans. In the present study, we performed mRNA sequencing to reveal the genetic mechanisms underlying the claw regeneration in mud crab. Several differentially expressed genes (DEGs) were expressed in biological pathways associated with cuticle synthase, collagen synthase, tissue regeneration, blastema formation, wound healing, cell cycle, cell division, and cell migration. The top GO enrichment terms were microtubule-based process, collagen trimer, cell cycle process, and extracellular matrix structural constituent. The most enriched KEGG pathways were ECM-receptor interaction and focal adhesion. The genes encoding key functional proteins, such as collagen alpha, cuticle protein, early cuticle protein, arthrodial cuticle protein, dentin sialophosphoprotein (DSPP), epidermal growth factor receptor (EGFR), kinesin family member C1 (KIFC1), and DNA replication licensing factor mcm2-like (MCM2) were the most significant and important DEGs suspected to participate in claw regeneration. The findings of this research offer a comprehensive and insightful understanding of the genetic and molecular mechanisms underlying claw regeneration in S. paramamosain. By elucidating the specific genes and molecular pathways implicated in this process, our study contributes significantly to the broader field of regenerative biology and offers potential avenues for further exploration in crustacean limb regeneration.

Injury-induced cooperation of InhibinβA and JunB is essential for cell proliferation in Xenopus tadpole tail regeneration

In animal species that have the capability of regenerating tissues and limbs, cell proliferation is enhanced after wound healing and is essential for the reconstruction of injured tissue. Although the ability to induce cell proliferation is a common feature of such species, the molecular mechanisms that regulate the transition from wound healing to regenerative cell proliferation remain unclear. Here, we show that upon injury, InhibinβA and JunB cooperatively function for this transition during Xenopus tadpole tail regeneration. We found that the expression of inhibin subunit beta A (inhba) and junB proto-oncogene (junb) is induced by injury-activated TGF-β/Smad and MEK/ERK signaling in regenerating tails. Similarly to junb knockout (KO) tadpoles, inhba KO tadpoles show a delay in tail regeneration, and inhba/junb double KO (DKO) tadpoles exhibit severe impairment of tail regeneration compared with either inhba KO or junb KO tadpoles. Importantly, this impairment is associated with a significant reduction of cell proliferation in regenerating tissue. Moreover, JunB regulates tail regeneration via FGF signaling, while InhibinβA likely acts through different mechanisms. These results demonstrate that the cooperation of injury-induced InhibinβA and JunB is critical for regenerative cell proliferation, which is necessary for re-outgrowth of regenerating Xenopus tadpole tails.

Genome-wide characterization of the TGF-β gene family and their expression in different tissues during tail regeneration in the Schlegel's Japanese gecko Gekko japonicus

The transforming growth factor-β (TGF-β) gene family is unique to animals and is involved in various important processes including tissue regeneration. Here, we identified 52 TGF-β family genes based on genome sequences of the gecko (Gekko japonicus), compared TGF-β genes between G. japonicus and other four reptilian species, and evaluated the expression of 14 randomly selected genes in muscle, kidney, liver, heart, and brain during tail regeneration to investigate whether their expression was tissue-dependent. We detected 23 conserved domains, 13 in the TGF-β ligand subfamily, and 10 in the receptor subfamily. The pattern of higher genetic variation in the ligand subfamily than in the receptor subfamily in vertebrates might result from the precise localization of agonists and antagonists in the cell surface and intracellular compartment. TGF-β genes were unevenly distributed across 15 chromosomes in G. japonicus, presumably resulting from gene losses and gains during evolution. Genes in the TGF-β receptor subfamily (ACVR2A, ACVR2B, ACVR1, BMPR1A, ACVRL1, BMPR2 and TGFBR1) played a vital role in the TGF-β signal pathway. The expression of all 14 randomly selected TGF-β genes was tissue-specific. Our study supports the speculation that some TGF-β family genes are involved in the early stages of tail regeneration.

Evi5 is required for Xenopus limb and tail regeneration

Amphibians such as salamanders and the African clawed frog Xenopus are great models for regeneration studies because they can fully regenerate their lost organs. While axolotl can regenerate damaged organs throughout its lifetime, Xenopus has a limited regeneration capacity after metamorphosis. The ecotropic viral integrative factor 5 (Evi5) is of great interest because its expression is highly upregulated in the limb blastema of axolotls, but remains unchanged in the fibroblastema of post-metamorphic frogs. Yet, its role in regeneration-competent contexts in Xenopus has not been fully analyzed. Here we show that Evi5 is upregulated in Xenopus tadpoles after limb and tail amputation, as in axolotls. Down-regulation of Evi5 with morpholino antisense oligos (Mo) impairs limb development and limb blastema formation in Xenopus tadpoles. Mechanistically, we show that Evi5 knockdown significantly reduces proliferation of limb blastema cells and causes apoptosis, blocking the formation of regeneration blastema. RNA-sequencing analysis reveals that in addition to reduced PDGFα and TGFβ signaling pathways that are required for regeneration, evi5 Mo downregulates lysine demethylases Kdm6b and Kdm7a. And knockdown of Kdm6b or Kdm7a causes defective limb regeneration. Evi5 knockdown also impedes tail regeneration in Xenopus tadpoles and axolotl larvae, suggesting a conserved function of Evi5 in appendage regeneration. Thus, our results demonstrate that Evi5 plays a critical role in appendage regeneration in amphibians.

Premeiotic endoreplication is essential for obligate parthenogenesis in geckos

Obligate parthenogenesis evolved in reptiles convergently several times, mainly through interspecific hybridization. The obligate parthenogenetic complexes typically include both diploid and triploid lineages. Offspring of parthenogenetic hybrids are genetic copies of their mother; however, the cellular mechanism enabling the production of unreduced cells is largely unknown. Here, we show that oocytes go through meiosis in three widespread, or even strongly invasive, obligate parthenogenetic complexes of geckos, namely in diploid and triploid Lepidodactylus lugubris, and triploid Hemiphyllodactylus typus and Heteronotia binoei. In all four lineages, the majority of oocytes enter the pachytene at the original ploidy level, but their chromosomes cannot pair properly and instead form univalents, bivalents and multivalents. Unreduced eggs with clonally inherited genomes are formed from germ cells that had undergone premeiotic endoreplication, in which appropriate segregation is ensured by the formation of bivalents made from copies of identical chromosomes. We conclude that the induction of premeiotic endoreplication in reptiles was independently co-opted at least four times as an essential component of parthenogenetic reproduction and that this mechanism enables the emergence of fertile polyploid lineages within parthenogenetic complexes.

Acute multidrug delivery via a wearable bioreactor facilitates long-term limb regeneration and functional recovery in adult Xenopus laevis

Limb regeneration is a frontier in biomedical science. Identifying triggers of innate morphogenetic responses in vivo to induce the growth of healthy patterned tissue would address the needs of millions of patients, from diabetics to victims of trauma. Organisms such as Xenopus laevis-whose limited regenerative capacities in adulthood mirror those of humans-are important models with which to test interventions that can restore form and function. Here, we demonstrate long-term (18 months) regrowth, marked tissue repatterning, and functional restoration of an amputated X. laevis hindlimb following a 24-hour exposure to a multidrug, pro-regenerative treatment delivered by a wearable bioreactor. Regenerated tissues composed of skin, bone, vasculature, and nerves significantly exceeded the complexity and sensorimotor capacities of untreated and control animals' hypomorphic spikes. RNA sequencing of early tissue buds revealed activation of developmental pathways such as Wnt/β-catenin, TGF-β, hedgehog, and Notch. These data demonstrate the successful "kickstarting" of endogenous regenerative pathways in a vertebrate model.

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.

Bacterial lipopolysaccharides can initiate regeneration of the Xenopus tadpole tail

Tadpoles of the frog Xenopus laevis can regenerate tails except for a short "refractory" period in which they heal rather than regenerate. Rapid and sustained production of ROS by NADPH oxidase (Nox) is critical for regeneration. Here, we show that tail amputation results in rapid, transient activation of the ROS-activated transcription factor NF-κB and expression of its direct target cox2 in the wound epithelium. Activation of NF-κB is also sufficient to rescue refractory tail regeneration. We propose that bacteria on the tadpole's skin could influence tail regenerative outcomes, possibly via LPS-TLR4-NF-κB signaling. When raised in antibiotics, fewer tadpoles in the refractory stage attempted regeneration, whereas addition of LPS rescued regeneration. Short-term activation of NF-κB using small molecules enhanced regeneration of tadpole hindlimbs, but not froglet forelimbs. We propose a model in which host microbiome contributes to creating optimal conditions for regeneration, via regulation of NF-κB by the innate immune system.

Cell transplantation and secretome based approaches in spinal cord injury regenerative medicine

The axonal growth-restrictive character of traumatic spinal cord injury (SCI) makes finding a therapeutic strategy a very demanding task, due to the postinjury events impeditive to spontaneous axonal outgrowth and regeneration. Considering SCI pathophysiology complexity, it has been suggested that an effective therapy should tackle all the SCI-related aspects and provide sensory and motor improvement to SCI patients. Thus, the current aim of any therapeutic approach for SCI relies in providing neuroprotection and support neuroregeneration. Acknowledging the current SCI treatment paradigm, cell transplantation is one of the most explored approaches for SCI with mesenchymal stem cells (MSCs) being in the forefront of many of these. Studies showing the beneficial effects of MSC transplantation after SCI have been proposing a paracrine action of these cells on the injured tissues, through the secretion of protective and trophic factors, rather than attributing it to the action of cells itself. This manuscript provides detailed information on the most recent data regarding the neuroregenerative effect of the secretome of MSCs as a cell-free based therapy for SCI. The main challenge of any strategy proposed for SCI treatment relies in obtaining robust preclinical evidence from in vitro and in vivo models, before moving to the clinics, so we have specifically focused on the available vertebrate and mammal models of SCI currently used in research and how can SCI field benefit from them.

The Warburg effect is necessary to promote glycosylation in the blastema during zebrafish tail regeneration

Throughout their lifetime, fish maintain a high capacity for regenerating complex tissues after injury. We utilized a larval tail regeneration assay in the zebrafish Danio rerio, which serves as an ideal model of appendage regeneration due to its easy manipulation, relatively simple mixture of cell types, and superior imaging properties. Regeneration of the embryonic zebrafish tail requires development of a blastema, a mass of dedifferentiated cells capable of replacing lost tissue, a crucial step in all known examples of appendage regeneration. Using this model, we show that tail amputation triggers an obligate metabolic shift to promote glucose metabolism during early regeneration similar to the Warburg effect observed in tumor forming cells. Inhibition of glucose metabolism did not affect the overall health of the embryo but completely blocked the tail from regenerating after amputation due to the failure to form a functional blastema. We performed a time series of single-cell RNA sequencing on regenerating tails with and without inhibition of glucose metabolism. We demonstrated that metabolic reprogramming is required for sustained TGF-β signaling and blocking glucose metabolism largely mimicked inhibition of TGF-β receptors, both resulting in an aberrant blastema. Finally, we showed using genetic ablation of three possible metabolic pathways for glucose, that metabolic reprogramming is required to provide glucose specifically to the hexosamine biosynthetic pathway while neither glycolysis nor the pentose phosphate pathway were necessary for regeneration.

Future Tail Tales: A Forward-Looking, Integrative Perspective on Tail Research

Synopsis Tails are a defining characteristic of chordates and show enormous diversity in function and shape. Although chordate tails share a common evolutionary and genetic-developmental origin, tails are extremely versatile in morphology and function. For example, tails can be short or long, thin or thick, and feathered or spiked, and they can be used for propulsion, communication, or balancing, and they mediate in predator-prey outcomes. Depending on the species of animal the tail is attached to, it can have extraordinarily multi-functional purposes. Despite its morphological diversity and broad functional roles, tails have not received similar scientific attention as, for example, the paired appendages such as legs or fins. This forward-looking review article is a first step toward interdisciplinary scientific synthesis in tail research. We discuss the importance of tail research in relation to five topics: (1) evolution and development, (2) regeneration, (3) functional morphology, (4) sensorimotor control, and (5) computational and physical models. Within each of these areas, we highlight areas of research and combinations of long-standing and new experimental approaches to move the field of tail research forward. To best advance a holistic understanding of tail evolution and function, it is imperative to embrace an interdisciplinary approach, re-integrating traditionally siloed fields around discussions on tail-related research.

Finding Solutions for Fibrosis: Understanding the Innate Mechanisms Used by Super-Regenerator Vertebrates to Combat Scarring

Soft tissue fibrosis and cutaneous scarring represent massive clinical burdens to millions of patients per year and the therapeutic options available are currently quite limited. Despite what is known about the process of fibrosis in mammals, novel approaches for combating fibrosis and scarring are necessary. It is hypothesized that scarring has evolved as a solution to maximize healing speed to reduce fluid loss and infection. This hypothesis, however, is complicated by regenerative animals, which have arguably the most remarkable healing abilities and are capable of scar-free healing. This review explores the differences observed between adult mammalian healing that typically results in fibrosis versus healing in regenerative animals that heal scarlessly. Each stage of wound healing is surveyed in depth from the perspective of many regenerative and fibrotic healers so as to identify the most important molecular and physiological variances along the way to disparate injury repair outcomes. Understanding how these powerful model systems accomplish the feat of scar-free healing may provide critical therapeutic approaches to the treatment or prevention of fibrosis.

Tgf-β superfamily and limb regeneration: Tgf-β to start and Bmp to end

Axolotls represent a popular model to study how nature solved the problem of regenerating lost appendages in tetrapods. Our work over many years focused on trying to understand how these animals can achieve such a feat and not end up with a scarred up stump. The Tgf-β superfamily represents an interesting family to target since they are involved in wound healing in adults and pattern formation during development. This family is large and comprises Tgf-β, Bmps, activins and GDFs. In this review, we present work from us and others on Tgf-β & Bmps and highlight interesting observations between these two sub-families. Tgf-β is important for the preparation phase of regeneration and Bmps for the redevelopment phase and they do not overlap with one another. We present novel data showing that the Tgf-β non-canonical pathway is also not active during redevelopment. Finally, we propose a molecular model to explain how Tgf-β and Bmps maintain distinct windows of expression during regeneration in axolotls.

TGF-β1 signaling is essential for tissue regeneration in the Xenopus tadpole tail

Amphibians such as Xenopus tropicalis exhibit a remarkable capacity for tissue regeneration after traumatic injury. Although transforming growth factor-β (TGF-β) receptor signaling is known to be essential for tissue regeneration in fish and amphibians, the role of TGF-β ligands in this process is not well understood. Here, we show that inhibition of TGF-β1 function prevents tail regeneration in Xenopus tropicalis tadpoles. We found that expression of tgfb1 is present before tail amputation and is sustained throughout the regeneration process. CRISPR-mediated knock-out (KO) of tgfb1 retards tail regeneration; the phenotype of tgfb1 KO tadpoles can be rescued by injection of tgfb1 mRNA. Cell proliferation, a critical event for the success of tissue regeneration, is downregulated in tgfb1 KO tadpoles. In addition, tgfb1 KO reduces the expression of phosphorylated Smad2/3 (pSmad2/3) which is important for TGF-β signal-mediated cell proliferation. Collectively, our results show that TGF-β1 regulates cell proliferation through the activation of Smad2/3. We therefore propose that TGF-β1 plays a critical role in TGF-β receptor-dependent tadpole tail regeneration in Xenopus.

The Potential of Nail Mini-Organ Stem Cells in Skin, Nail and Digit Tips Regeneration

Nails are highly keratinized skin appendages that exhibit continuous growth under physiological conditions and full regeneration upon removal. These mini-organs are maintained by two autonomous populations of skin stem cells. The fast-cycling, highly proliferative stem cells of the nail matrix (nail stem cells (NSCs)) predominantly replenish the nail plate. Furthermore, the slow-cycling population of the nail proximal fold (nail proximal fold stem cells (NPFSCs)) displays bifunctional properties by contributing to the peri-nail epidermis under the normal homeostasis and the nail structure upon injury. Here, we discuss nail mini-organ stem cells’ location and their role in skin and nail homeostasis and regeneration, emphasizing their importance to orchestrate the whole digit tip regeneration. Such endogenous regeneration capabilities are observed in rodents and primates. However, they are limited to the region adjacent to the nail’s proximal area, indicating the crucial role of nail mini-organ stem cells in digit restoration. Further, we explore the molecular characteristics of nail mini-organ stem cells and the critical role of the bone morphogenetic protein (BMP) and Wnt signaling pathways in homeostatic nail growth and digit restoration. Finally, we investigate the latest accomplishments in stimulating regenerative responses in regeneration-incompetent injuries. These pioneer results might open up new opportunities to overcome amputated mammalian digits and limbs’ regenerative failures in the future.

The complexity of TGFβ/activin signaling in regeneration

The role of transforming growth factor β TGFβ/activin signaling in wound repair and regeneration is highly conserved in the animal kingdom. Various studies have shown that TGF-β/activin signaling can either promote or inhibit different aspects of the regeneration process (i.e., proliferation, differentiation, and re-epithelialization). It has been demonstrated in several biological systems that some of the different cellular responses promoted by TGFβ/activin signaling depend on the activation of Smad-dependent or Smad-independent signal transduction pathways. In the context of regeneration and wound healing, it has been shown that the type of R-Smad stimulated determines the different effects that can be obtained. However, neither the possible roles of Smad-independent pathways nor the interaction of the TGFβ/activin pathway with other complex signaling networks involved in the regenerative process has been studied extensively. Here, we review the important aspects concerning the TGFβ/activin signaling pathway in the regeneration process. We discuss data regarding the role of TGF-β/activin in the most common animal regenerative models to demonstrate how this signaling promotes or inhibits regeneration, depending on the cellular context.

Epigenetic control of myeloid cells behavior by Histone Deacetylase activity (HDAC) during tissue and organ regeneration in Xenopus laevis

In the present work we have focused on the Histone Deacetylase (HDAC) control of myeloid cells behavior during Xenopus tail regeneration. Here we show that myeloid differentiation is crucial to modulate the regenerative ability of Xenopus tadpoles in a HDAC activity-dependent fashion. HDAC activity inhibition during the first wave of myeloid differentiation disrupted myeloid cells dynamics in the regenerative bud as well the mRNA expression pattern of myeloid markers, such as LURP, MPOX, Spib and mmp7. We also functionally bridge the spatial and temporal dynamics of lipid droplets, the main platform of lipid mediators synthesis in myeloid cells during the inflammatory response, and the regenerative ability of Xenopus tadpoles. In addition, we showed that 15-LOX activity is necessary during tail regeneration. Taken together our results support a role for the epigenetic control of myeloid behavior during tissue and organ regeneration, which may positively impact translational approaches for regenerative medicine.

Genome-Wide Association Study of Body Shape-Related Traits in Large Yellow Croaker (Larimichthys crocea)

Large yellow croaker (Larimichthys crocea) is one of the most important cultured marine fish on the southeast coast of China. Its body shape is important for the aquaculture industry since it affects the behavior such as swimming, ingesting, and evading, as well as customer preference. Due to the greater consumer demand of small head, slender body large yellow croaker, selecting and breeding of slender individuals with the assistance of genetic markers will benefit the industry quickly. In this study, several traits were employed to represent body shape, including body depth/body length (BD/BL), body thickness/body length (BT/BL), caudal peduncle depth/caudal peduncle length (CPDLR), tail length/body length (TL/BL), and body area/head area (BA/HA). Genome-wide association study was conducted with a panmictic population of 280 individuals to identify SNP and genes potentially associated with body shape. A set of 20 SNPs on 12 chromosomes were identified to be significantly associated with body shape-related traits. Besides, 5 SNPs were identified to be suggestive associated with CPDLR and BT/BL. Surrounding these SNPs, we found some body shape-related candidate genes, including fabp1, acrv1, bcor, mstn, bambi, and neo1, which involved in lipid metabolism, TGF-β signaling, and BMP pathway and other important regulatory pathways. These results will be useful for the understanding of the genetic basis of body shape formation and helpful for body shape controlling of large yellow croaker by using marker-assisted selection.

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.

Xvent-2 expression in regenerating Xenopus tails

The tail of Xenopus tadpole is an excellent model for appendage regeneration studies. We analyzed the distribution pattern of the transcription factor Xvent-2 mRNA and protein in the beginning of the regeneration of Xenopus tadpole tail stumps after amputation. We revealed the emergence of Xvent-2 mRNA and protein in regeneration bud during the first day after amputation. The data obtained confirm that soon after amputation of the part of the Xenopus tadpole tail, there occurs the emergence of a structure, to some extend, resembling the early embryonic tail bud.

Regeneration enhancers: A clue to reactivation of developmental genes

During tissue and organ regeneration, cells initially detect damage and then alter nuclear transcription in favor of tissue/organ reconstruction. Until recently, studies of tissue regeneration have focused on the identification of relevant genes. These studies show that many developmental genes are reused during regeneration. Concurrently, comparative genomics studies have shown that the total number of genes does not vastly differ among vertebrate taxa. Moreover, functional analyses of developmental genes using various knockout/knockdown techniques demonstrated that the functions of these genes are conserved among vertebrates. Despite these data, the ability to regenerate damaged body parts varies widely between animals. Thus, it is important to determine how regenerative transcriptional programs are triggered and why animals with low regenerative potential fail to express developmental genes after injury. Recently, we discovered relevant enhancers and named them regeneration signal-response enhancers (RSREs) after identifying their activation mechanisms in a Xenopus laevis transgenic system. In this review, we summarize recent studies of injury/regeneration-associated enhancers and then discuss their mechanisms of activation.

Chromatin accessibility dynamics and single cell RNA-Seq reveal new regulators of regeneration in neural progenitors

Vertebrate appendage regeneration requires precisely coordinated remodeling of the transcriptional landscape to enable the growth and differentiation of new tissue, a process executed over multiple days and across dozens of cell types. The heterogeneity of tissues and temporally-sensitive fate decisions involved has made it difficult to articulate the gene regulatory programs enabling regeneration of individual cell types. To better understand how a regenerative program is fulfilled by neural progenitor cells (NPCs) of the spinal cord, we analyzed pax6-expressing NPCs isolated from regenerating Xenopus tropicalis tails. By intersecting chromatin accessibility data with single-cell transcriptomics, we find that NPCs place an early priority on neuronal differentiation. Late in regeneration, the priority returns to proliferation. Our analyses identify Pbx3 and Meis1 as critical regulators of tail regeneration and axon organization. Overall, we use transcriptional regulatory dynamics to present a new model for cell fate decisions and their regulators in NPCs during regeneration.

Model systems for regeneration: Xenopus

Understanding how to promote organ and appendage regeneration is a key goal of regenerative medicine. The frog, Xenopus, can achieve both scar-free healing and tissue regeneration during its larval stages, although it predominantly loses these abilities during metamorphosis and adulthood. This transient regenerative capacity, alongside their close evolutionary relationship with humans, makes Xenopus an attractive model to uncover the mechanisms underlying functional regeneration. Here, we present an overview of Xenopus as a key model organism for regeneration research and highlight how studies of Xenopus have led to new insights into the mechanisms governing regeneration.

The vertebrate tail: a gene playground for evolution

The tail of all vertebrates, regardless of size and anatomical detail, derive from a post-anal extension of the embryo known as the tail bud. Formation, growth and differentiation of this structure are closely associated with the activity of a group of cells that derive from the axial progenitors that build the spinal cord and the muscle-skeletal case of the trunk. Gdf11 activity switches the development of these progenitors from a trunk to a tail bud mode by changing the regulatory network that controls their growth and differentiation potential. Recent work in the mouse indicates that the tail bud regulatory network relies on the interconnected activities of the Lin28/let-7 axis and the Hox13 genes. As this network is likely to be conserved in other mammals, it is possible that the final length and anatomical composition of the adult tail result from the balance between the progenitor-promoting and -repressing activities provided by those genes. This balance might also determine the functional characteristics of the adult tail. Particularly relevant is its regeneration potential, intimately linked to the spinal cord. In mammals, known for their complete inability to regenerate the tail, the spinal cord is removed from the embryonic tail at late stages of development through a Hox13-dependent mechanism. In contrast, the tail of salamanders and lizards keep a functional spinal cord that actively guides the tail's regeneration process. I will argue that the distinct molecular networks controlling tail bud development provided a collection of readily accessible gene networks that were co-opted and combined during evolution either to end the active life of those progenitors or to make them generate the wide diversity of tail shapes and sizes observed among vertebrates.

Role of TGF-β in Skin Chronic Wounds: A Keratinocyte Perspective

Chronic wounds are characterized for their incapacity to heal within an expected time frame. Potential mechanisms driving this impairment are poorly understood and current hypotheses point to the development of an unbalanced milieu of growth factor and cytokines. Among them, TGF-β is considered to promote the broadest spectrum of effects. Although it is known to contribute to healthy skin homeostasis, the highly context-dependent nature of TGF-β signaling restricts the understanding of its roles in healing and wound chronification. Historically, low TGF-β levels have been suggested as a pattern in chronic wounds. However, a revision of the available evidence in humans indicates that this could constitute a questionable argument. Thus, in chronic wounds, divergences regarding skin tissue compartments seem to be characterized by elevated TGF-β levels only in the epidermis. Understanding how this aspect affects keratinocyte activities and their capacity to re-epithelialize might offer an opportunity to gain comprehensive knowledge of the involvement of TGF-β in chronic wounds. In this review, we compile existing evidence on the roles played by TGF-β during skin wound healing, with special emphasis on keratinocyte responses. Current limitations and future perspectives of TGF-β research in chronic wounds are discussed.

The AP-1 transcription factor JunB functions in Xenopus tail regeneration by positively regulating cell proliferation

Xenopus tropicalis tadpoles can regenerate an amputated tail, including spinal cord, muscle and notochord, through cell proliferation and differentiation. However, the molecular mechanisms that regulate cell proliferation during tail regeneration are largely unknown. Here we show that JunB plays an important role in tail regeneration by regulating cell proliferation. The expression of junb is rapidly activated and sustained during tail regeneration. Knockout (KO) of junb causes a delay in tail regeneration and tissue differentiation. In junb KO tadpoles, cell proliferation is prevented before tissue differentiation. Furthermore, TGF-β signaling, which is activated just after tail amputation, regulates the induction and maintenance of junb expression. These findings demonstrate that JunB, a downstream component of TGF-β signaling, works as a positive regulator of cell proliferation during Xenopus tail regeneration.

Cell type-specific transcriptome analysis unveils secreted signaling molecule genes expressed in apical epithelial cap during appendage regeneration

Wound epidermis (WE) and the apical epithelial cap (AEC) are believed to trigger regeneration of amputated appendages such as limb and tail in amphibians by producing certain secreted signaling molecules. To date, however, only limited information about the molecular signatures of these epidermal structures is available. Here we used a transgenic Xenopus laevis line harboring the enhanced green fluorescent protein (egfp) gene under control of an es1 gene regulatory sequence to isolate WE/AEC cells by performing fluorescence-activated cell sorting during the time course of tail regeneration (day 1, day 2, day 3 and day 4 after amputation). Time-course transcriptome analysis of these isolated WE/AEC cells revealed that more than 8,000 genes, including genes involved in signaling pathways such as those of reactive oxygen species, fibroblast growth factor (FGF), canonical and non-canonical Wnt, transforming growth factor β (TGF β) and Notch, displayed dynamic changes of their expression during tail regeneration. Notably, this approach enabled us to newly identify seven secreted signaling molecule genes (mdk, fstl, slit1, tgfβ1, bmp7.1, angptl2 and egfl6) that are highly expressed in tail AEC cells. Among these genes, five (mdk, fstl, slit1, tgfβ1 and bmp7.1) were also highly expressed in limb AEC cells but the other two (angptl2 and egfl6) are specifically expressed in tail AEC cells. Interestingly, there was no expression of fgf8 in tail WE/AEC cells, whose expression and pivotal role in limb AEC cells have been reported previously. Thus, we identified common and different properties between tail and limb AEC cells.

Identification of a regeneration-organizing cell in the Xenopus tail

Unlike mammals, Xenopus laevis tadpoles have a high regenerative potential. To characterize this regenerative response, we performed single-cell RNA sequencing after tail amputation. By comparing naturally occurring regeneration-competent and -incompetent tadpoles, we identified a previously unrecognized cell type, which we term the regeneration-organizing cell (ROC). ROCs are present in the epidermis during normal tail development and specifically relocalize to the amputation plane of regeneration-competent tadpoles, forming the wound epidermis. Genetic ablation or manual removal of ROCs blocks regeneration, whereas transplantation of ROC-containing grafts induces ectopic outgrowths in early embryos. Transcriptional profiling revealed that ROCs secrete ligands associated with key regenerative pathways, signaling to progenitors to reconstitute lost tissue. These findings reveal the cellular mechanism through which ROCs form the wound epidermis and ensure successful regeneration.

HDAC Regulates Transcription at the Outset of Axolotl Tail Regeneration

Tissue regeneration is associated with complex changes in gene expression and post-translational modifications of proteins, including transcription factors and histones that comprise chromatin. We tested 172 compounds designed to target epigenetic mechanisms in an axolotl (Ambystoma mexicanum) embryo tail regeneration assay. A relatively large number of compounds (N = 55) inhibited tail regeneration, including 18 histone deacetylase inhibitors (HDACi). In particular, romidepsin, an FDA-approved anticancer drug, potently inhibited tail regeneration when embryos were treated continuously for 7 days. Additional experiments revealed that romidepsin acted within a very narrow, post-injury window. Romidepsin treatment for only 1-minute post amputation inhibited regeneration through the first 7 days, however after this time, regeneration commenced with variable outgrowth of tailfin tissue and abnormal patterning. Microarray analysis showed that romidepsin altered early, transcriptional responses at 3 and 6-hour post-amputation, especially targeting genes that are implicated in tumor cell death, as well as genes that function in the regulation of transcription, cell differentiation, cell proliferation, pattern specification, and tissue morphogenesis. Our results show that HDAC activity is required at the time of tail amputation to regulate the initial transcriptional response to injury and regeneration.

Peripheral Macrophages Promote Tissue Regeneration in Zebrafish by Fine-Tuning the Inflammatory Response

The role of macrophages during regeneration in zebrafish has been well-documented. Nevertheless, new evidence indicates that zebrafish macrophages are a heterogeneous population of cells, and that they can play different roles during immune responses and in tissue restoration after damage and infection. In this work, we first aimed to classify zebrafish macrophages according to their distribution in the larva during homeostasis and after tissue damage, distinguishing peripheral, and hematopoietic tissue resident macrophages. We discovered differences between the migratory behavior of these two macrophage populations both before and after tissue damage, triggered by the amputation of the tail fin. Further, we found a specific role for peripheral tissue-resident macrophages, and we propose that these cells contribute to tail fin regeneration by down-regulating inflammatory mediators such as interleukin-1b (il1b) and by diminishing reactive oxygen species (ROS) in the damage site. Our work suggests that specific macrophage populations recruited after tissue damage in zebrafish larvae can display different functions during both inflammation and tissue regeneration.

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.

Epithelial to mesenchymal transition is mediated by both TGF-β canonical and non-canonical signaling during axolotl limb regeneration

Axolotls have the amazing ability to regenerate. When compared to humans, axolotls display a very fast wound closure, no scarring and are capable to replace lost appendages perfectly. Understanding the signaling mechanism leading to this perfect healing is a key step to help develop regenerative treatments for humans. In this paper, we studied cellular pathways leading to axolotl limb regeneration. We focus on the wound closure phase where keratinocytes migrate to close the lesion site and how epithelial to mesenchymal transitions are involved in this process. We observe a correlation between wound closure and EMT marker expression. Functional analyses using pharmacological inhibitors showed that the TGF-β/SMAD (canonical) and the TGF-β/p38/JNK (non-canonical) pathways play a role in the rate to which the keratinocytes can migrate. When we treat the animals with a combination of inhibitors blocking both canonical and non-canonical TGF-β pathways, it greatly reduced the rate of wound closure and had significant effects on certain known EMT genes.

Digit Tip Injuries: Current Treatment and Future Regenerative Paradigms

Over the past several decades there has been a profound increase in the understanding of tissue regeneration, driven largely by the observance of the tremendous regenerative capacity in lower order life forms, such as hydra and urodeles. However, it is known that humans and other mammals retain the ability to regenerate the distal phalanges of the digits after amputation. Despite the increased knowledge base on model organisms regarding regenerative paradigms, there is a lack of application of regenerative medicine techniques in clinical practice in regard to digit tip injury. Here, we review the current understanding of digit tip regeneration and discuss gaps that remain in translating regenerative medicine into clinical treatment of digit amputation.

Cellular and Molecular Mechanisms of Hydra Regeneration

Regeneration of lost body parts is essential to regain the fitness of the organism for successful living. In the animal kingdom, organisms from different clades exhibit varied regeneration abilities. Hydra is one of the few organisms that possess tremendous regeneration potential, capable of regenerating complete organism from small tissue fragments or even from dissociated cells. This peculiar property has made this genus one of the most invaluable model organisms for understanding the process of regeneration. Multiple studies in Hydra led to the current understanding of gross morphological changes, basic cellular dynamics, and the role of molecular signalling such as the Wnt signalling pathway. However, cell-to-cell communication by cell adhesion, role of extracellular components such as extracellular matrix (ECM), and nature of cell types that contribute to the regeneration process need to be explored in depth. Additionally, roles of developmental signalling pathways need to be elucidated to enable more comprehensive understanding of regeneration in Hydra. Further research on cross communication among extracellular, cellular, and molecular signalling in Hydra will advance the field of regeneration biology. Here, we present a review of the existing literature on Hydra regeneration biology and outline the future perspectives.

Dissecting BMP signaling input into the gene regulatory networks driving specification of the blood stem cell lineage

Hematopoietic stem cells (HSCs) that sustain lifelong blood production are created during embryogenesis. They emerge from a specialized endothelial population, termed hemogenic endothelium (HE), located in the ventral wall of the dorsal aorta (DA). In Xenopus, we have been studying the gene regulatory networks (GRNs) required for the formation of HSCs, and critically found that the hemogenic potential is defined at an earlier time point when precursors to the DA express hematopoietic as well as endothelial genes, in the definitive hemangioblasts (DHs). The GRN for DH programming has been constructed and, here, we show that bone morphogenetic protein (BMP) signaling is essential for the initiation of this GRN. BMP2, -4, and -7 are the principal ligands expressed in the lineage forming the HE. To investigate the requirement and timing of all BMP signaling in HSC ontogeny, we have used a transgenic line, which inducibly expresses an inhibitor of BMP signaling, Noggin, as well as a chemical inhibitor of BMP receptors, DMH1, and described the inputs from BMP signaling into the DH GRN and the HE, as well as into primitive hematopoiesis. BMP signaling is required in at least three points in DH programming: first to initiate the DH GRN through gata2 expression, then for kdr expression to enable the DH to respond to vascular endothelial growth factor A (VEGFA) ligand from the somites, and finally for gata2 expression in the DA, but is dispensable for HE specification after hemangioblasts have been formed.

Bioelectric signaling in regeneration: Mechanisms of ionic controls of growth and form

The ability to control pattern formation is critical for the both the embryonic development of complex structures as well as for the regeneration/repair of damaged or missing tissues and organs. In addition to chemical gradients and gene regulatory networks, endogenous ion flows are key regulators of cell behavior. Not only do bioelectric cues provide information needed for the initial development of structures, they also enable the robust restoration of normal pattern after injury. In order to expand our basic understanding of morphogenetic processes responsible for the repair of complex anatomy, we need to identify the roles of endogenous voltage gradients, ion flows, and electric fields. In complement to the current focus on molecular genetics, decoding the information transduced by bioelectric cues enhances our knowledge of the dynamic control of growth and pattern formation. Recent advances in science and technology place us in an exciting time to elucidate the interplay between molecular-genetic inputs and important biophysical cues that direct the creation of tissues and organs. Moving forward, these new insights enable additional approaches to direct cell behavior and may result in profound advances in augmentation of regenerative capacity.

A transgenic reporter under control of an es1 promoter/enhancer marks wound epidermis and apical epithelial cap during tail regeneration in Xenopus laevis tadpole

Rapid wound healing and subsequent formation of the apical epithelial cap (AEC) are believed to be required for successful appendage regeneration in amphibians. Despite the significant role of AEC in limb regeneration, its role in tail regeneration and the mechanisms that regulate the wound healing and AEC formation are not well understood. We previously identified Xenopus laevis es1, which is preferentially expressed in wounded regions, including the AEC after tail regeneration. In this study we established and characterized transgenic Xenopus laevis lines harboring the enhanced green fluorescent protein (EGFP) gene under control of an es1 gene regulatory sequence (es1:egfp). The EGFP reporter expression was clearly seen in several regions of the embryo and then declined to an undetectable level in larvae, recapitulating the endogenous es1 expression. After amputation of the tadpole tail, EGFP expression was re-activated at the edge of the stump epidermis and then increased in the wound epidermis (WE) covering the amputation surface. As the stump started to regenerate, the EGFP expression became restricted to the most distal epidermal region, including the AEC. EGFP was preferentially expressed in the basal or deep cells but not in the superficial cells of the WE and AEC. We performed a small-scale pharmacological screening for chemicals that affected the expression of EGFP in the stump epidermis after tail amputation. The EGFP expression was attenuated by treatment with an inhibitor for ERK, TGF-β or reactive oxygen species (ROS) signaling. These treatments also impaired wound closure of the amputation surface, suggesting that the three signaling activities are required for es1 expression in the WE and successful wound healing after tail amputation. These findings showed that es1:egfp Xenopus laevis should be a useful tool to analyze molecular mechanisms regulating wound healing and appendage regeneration.

Opposite effects of Activin type 2 receptor ligands on cardiomyocyte proliferation during development and repair

Zebrafish regenerate damaged myocardial tissue very effectively. Hence, insights into the molecular networks underlying zebrafish heart regeneration might help develop alternative strategies to restore human cardiac performance. While TGF-β signaling has been implicated in zebrafish cardiac regeneration, the role of its individual ligands remains unclear. Here, we report the opposing expression response during zebrafish heart regeneration of two genes, mstnb and inhbaa, which encode TGF-β family ligands. Using gain-of-function (GOF) and loss-of-function (LOF) approaches, we show that these ligands mediate inverse effects on cardiac regeneration and specifically on cardiomyocyte (CM) proliferation. Notably, we find that Inhbaa functions as a CM mitogen and that its overexpression leads to accelerated cardiac recovery and scar clearance after injury. In contrast, mstnb GOF and inhbaa LOF both lead to unresolved scarring after cardiac injury. We further show that Mstnb and Inhbaa inversely control Smad2 and Smad3 transcription factor activities through alternate Activin type 2 receptors.

Spinal cord self-repair during tail regeneration in Polypedates maculatus and putative role of FGF1 as a neurotrophic factor

Spinal cord injury could be fatal in man and often results in irreversible medical conditions affecting mobility. However, anuran amphibians win over such pathological condition by the virtue of regeneration abilities. The tail of anuran tadpoles therefore allures researchers to study spinal cord injury and self- repair process. In the present study, we inflicted injury to the spinal cord by means of surgical transection of the tail and investigated the self-repair activity in the tadpoles of the Indian tree frog Polypedates maculatus. We also demonstrate for the first time by immunofluorescence localization the expression pattern of Fibroblast Growth Factor1 (FGF1) during spinal cord regeneration which has not been documented earlier in anurans. FGF1, bearer of the mitogenic and neurotrophic properties seems to be expressed by progenitor cells that facilitate regeneration. Spinal cord during tail regeneration in P. maculatus attains functional recovery within a span of 2 weeks thus enabling the organism to survive in an aquatic medium till metamorphosis. Moreover, during the course of spinal cord regeneration in the regenerating tail, melanocytes showed an interesting behaviour as these neural crest derivatives were missing near the early regenerates until their reappearance where they were positioned in close proximity with the regenerated spinal cord as in the normal tail.

Methylisothiazolinone toxicity and inhibition of wound healing and regeneration in planaria

Methylisothiazolinone (MIT) is a common biocide used in cosmetic and industrial settings. Studies have demonstrated that MIT is a human sensitizer, to the extent that in 2013 MIT was named allergen of the year. Recently, we showed that MIT exposure in Xenopus laevis (the African clawed frog) inhibits wound healing and tail regeneration. However, it is unknown whether MIT affects these processes in other animals. Here, we investigated the effects of MIT exposure in planaria-non-parasitic freshwater flatworms able to regenerate all tissues after injury. Using a common research strain of Dugesia japonica, we determined that intact planarians exposed to 15μM MIT displayed both neuromuscular and epithelial-integrity defects. Furthermore, regenerating (head and tail) fragments exposed to 15μM MIT failed to close wounds or had significantly delayed wound healing. Planarian wounds normally close within 1h after injury. However, most MIT-exposed animals retained open wounds at 24h and subsequently died, and those few animals that were able to undergo delayed wound healing without dying exhibited abnormal regeneration. For instance, head regeneration was severely delayed or inhibited, with anterior structures such as eyes failing to form in newly produced tissues. These data suggest that MIT directly affects both wound healing and regeneration in planarians. Next, we investigated the ability of thiol-containing antioxidants to rescue planarian wound closure during MIT exposure. The data reveal both n-acetyl cysteine and glutathione were each able to fully rescue MIT inhibition of wound healing. Lastly, we established MIT toxicity levels by determining the LC₅₀ of 5 different planarian species: D. japonica, Schmidtea mediterranea, Girardia tigrina, Girardia dorotocephala, and Phagocata gracilis. Our LC₅₀ data revealed that concentrations as low as 39μM (4.5ppm) are lethal to planarians, with concentrations of just 5μM inhibiting wound healing, and suggest that phylogeny is predictive of species toxicity levels. Together these results indicate MIT may have broad wound healing effects on aquatic species in general and are not limited to X. laevis alone. Future studies should investigate the impact of MIT on wound healing in other organisms, including non-aquatic organisms and mammals.

A microRNA-mRNA expression network during oral siphon regeneration in Ciona

Here we present a parallel study of mRNA and microRNA expression during oral siphon (OS) regeneration in Ciona robusta, and the derived network of their interactions. In the process of identifying 248 mRNAs and 15 microRNAs as differentially expressed, we also identified 57 novel microRNAs, several of which are among the most highly differentially expressed. Analysis of functional categories identified enriched transcripts related to stress responses and apoptosis at the wound healing stage, signaling pathways including Wnt and TGFβ during early regrowth, and negative regulation of extracellular proteases in late stage regeneration. Consistent with the expression results, we found that inhibition of TGFβ signaling blocked OS regeneration. A correlation network was subsequently inferred for all predicted microRNA-mRNA target pairs expressed during regeneration. Network-based clustering associated transcripts into 22 non-overlapping groups, the functional analysis of which showed enrichment of stress response, signaling pathway and extracellular protease categories that could be related to specific microRNAs. Predicted targets of the miR-9 cluster suggest a role in regulating differentiation and the proliferative state of neural progenitors through regulation of the cytoskeleton and cell cycle.

CNS repair and axon regeneration: Using genetic variation to determine mechanisms

The importance of genetic diversity in biological investigation has been recognized since the pioneering studies of Gregor Johann Mendel and Charles Darwin. Research in this area has been greatly informed recently by the publication of genomes from multiple species. Genes regulate and create every part and process in a living organism, react with the environment to create each living form and morph and mutate to determine the history and future of each species. The regenerative capacity of neurons differs profoundly between animal lineages and within the mammalian central and peripheral nervous systems. Here, we discuss research that suggests that genetic background contributes to the ability of injured axons to regenerate in the mammalian central nervous system (CNS), by controlling the regulation of specific signaling cascades. We detail the methods used to identify these pathways, which include among others Activin signaling and other TGF-β superfamily members. We discuss the potential of altering these pathways in patients with CNS damage and outline strategies to promote regeneration and repair by combinatorial manipulation of neuron-intrinsic and extrinsic determinants.