Precise control of miR-125b levels is required to create a regeneration-permissive environment after spinal cord injury: a cross-species comparison between salamander and rat

A 72-h sedated porcine model of traumatic spinal cord injury

Introduction

There is an increasing focus on the prevention of secondary injuries following traumatic spinal cord injury (TSCI), especially through improvement of spinal cord perfusion and immunological modulation. Such therapeutic strategies require translational and controlled animal models of disease progression of the acute phases of human TSCI.

Research question

Is it possible to establish a 72-h sedated porcine model of incomplete thoracic TSCI, enabling controlled use of continuous, invasive, and non-invasive modalities during the entire sub-acute phase of TSCI?

Material and methods

A sham-controlled trial was conducted to establish the model, and 10 animals were assigned to either sham or TSCI. All animals underwent a laminectomy, and animals in the TSCI group were subjected to a weight-drop injury. Animals were then kept sedated for 72 h. The amount of injury was assessed by ex-vivo measures MRI-based fiber tractography, histology and immunohistochemistry.

Results

In all animals, we were successful in maintaining sedation for 72 h without comprising vital physiological parameters. The MRI-based fiber tractography showed that all TSCI animals revealed a break in the integrity of spinal neurons, whereas histology demonstrated no transversal sections of the spine with complete injury. Notably, some animals displayed signs of secondary ischemic tissue in the cranial and caudal sections.

Discussion and conclusions

This study succeeded in producing a porcine model of incomplete TSCI, which was physiologically stable up to 72 h. We believe that this TSCI model will constitute a potential translational model to study the pathophysiology secondary to TSCI in humans.

Upregulated miR-125b mitigates inflammation, astrocyte activation, and dysfunction of spinal cord injury by inactivating the MAPK pathway

BACKGROUND

Since the abnormal expression of miR-125b in spinal cord injury (SCI) and the regulatory effect of miR-125b on the MAPK pathway have been expounded, we attempt to investigate whether miR-125b exerts a regulatory effect on SCI by modulating the MAPK pathway.

METHOD

A SCI rat model was established. The rats were treated with miR-125b antagomir or agomir, and their motor function affected by miR-125b was further detected by Basso-Beattie-Bresnahan (BBB) scoring. The histopathological changes and neuronal loss in the spinal cord were evaluated using hematoxylin-eosin and Nissl staining. Microglia-conditioned medium (MCM) was prepared and further used to treat the astrocytes, the activation of which was evaluated via immunofluorescence staining. The expressions of miR-125b, inflammation-related factors (IL-6, IL-1β, TNF-α, and IL-10), and MAPK pathway-related proteins (p38, ERK1/2, and JNK1/2 as well as their phosphorylated (p) forms) in the spinal cord, serum, and MCM-treated astrocytes of rats were determined by reverse-transcription quantitative polymerase chain reaction (RT-qPCR), enzyme-linked immunosorbent assay, and Western blot.

RESULT

MiR-125b was lowly expressed in SCI-modeled rats. MiR-125b downregulation aggravated the impaired motor function, the disorder within the tissue, astrocyte activation, and neuron loss in the spinal cord tissues of SCI-modeled rats, while miR-125b upregulation did oppositely. MiR-125b downregulation enhanced the levels of IL-6, IL-1β, TNF-α, p38, p-p38, p-ERK1/2, and p-JNK1/2, whilst reducing that of IL-10. Contrarily, miR-125b upregulation exerted the opposite effects in SCI-modeled rats and MCM-treated astrocytes.

CONCLUSION

Up-regulation of miR-125b mitigates inflammation, astrocyte activation, and dysfunction in SCI by inactivating the MAPK pathway.

Epigenetic processes associated with neonatal spinal transection

In early development, the spinal cord in healthy or disease states displays remarkable activity-dependent changes in plasticity, which may be in part due to the increased activity of brain derived neurotrophic factor (BDNF). Indeed, BDNF delivery has been efficacious in partially ameliorating many of the neurobiological and behavioral consequences of spinal cord injury (SCI), making elucidating the role of BDNF in the normative developing and injured spinal cord a critical research focus. Recent work in our laboratory provided evidence for aberrant global and locus-specific epigenetic changes in methylation of the Bdnf gene as a consequence of SCI. In the present study, animals underwent thoracic lesions on P1, with cervical and lumbar tissue being later collected on P7, P14, and P21. Levels of Bdnf expression and methylation (exon IX and exon IV), in addition to global methylation levels were quantified at each timepoint. Results indicated locus-specific reductions of Bdnf expression that was accompanied by a parallel increase in methylation caudal to the injury site, with animals displaying increased Bdnf expression at the P14 timepoint. Together, these findings suggest that epigenetic activity of the Bdnf gene may act as biomarker in the etiology and intervention effort efficacy following SCI.

A Reproducible Spinal Cord Crush Injury in the Regeneration-Permissive Axolotl

Following injury, axolotls are able to functionally regenerate their spinal cord, regaining both motor and sensory control. In contrast, humans respond to severe spinal cord injury by forming a glial scar, which prevents further damage but also inhibits any regenerative growth, resulting in loss of function caudal to the injury site. The axolotl has become a popular system to elucidate the underlying cellular and molecular events that contribute to successful CNS regeneration. However, the experimental injuries (tail amputation and transection) that are utilized in axolotls do not mimic the blunt trauma that is often sustained in humans. Here, we report a more clinically relevant model for spinal cord injuries in the axolotl using a weight-drop technique. This reproducible model allows precise control over the severity of the injury by regulating the drop height, weight, compression, and position of the injury.

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.

Axolotl: A resourceful vertebrate model for regeneration and beyond

The regenerative capacity varies significantly among the animal kingdom. Successful regeneration program in some animals results in the functional restoration of tissues and lost structures. Among the highly regenerative animals, axolotl provides multiple experimental advantages with its many extraordinary characteristics. It has been positioned as a regeneration model organism due to its exceptional renewal capacity, including the internal organs, central nervous system, and appendages, in a scar-free manner. In addition to this unique regeneration ability, the observed low cancer incidence, its resistance to carcinogens, and the reversing effect of its cell extract on neoplasms strongly suggest its usability in cancer research. Axolotl's longevity and efficient utilization of several anti-aging mechanisms underline its potential to be employed in aging studies.

Regulation of stem cell identity by miR-200a during spinal cord regeneration

Axolotls are an important model organism for multiple types of regeneration, including functional spinal cord regeneration. Remarkably, axolotls can repair their spinal cord after a small lesion injury and can also regenerate their entire tail following amputation. Several classical signaling pathways that are used during development are reactivated during regeneration, but how this is regulated remains a mystery. We have previously identified miR-200a as a key factor that promotes successful spinal cord regeneration. Here, using RNA-seq analysis, we discovered that the inhibition of miR-200a results in an upregulation of the classical mesodermal marker brachyury in spinal cord cells after injury. However, these cells still express the neural stem cell marker sox2. In vivo cell tracking allowed us to determine that these cells can give rise to cells of both the neural and mesoderm lineage. Additionally, we found that miR-200a can directly regulate brachyury via a seed sequence in the 3′UTR of the gene. Our data indicate that miR-200a represses mesodermal cell fate after a small lesion injury in the spinal cord when only glial cells and neurons need to be replaced.

Summary: Axolotl spinal cord cells have the potential to form cells of the ectoderm and mesoderm depending on the extent of the injury they are responding to.

The MAPK Signaling Pathway Presents Novel Molecular Targets for Therapeutic Intervention after Traumatic Spinal Cord Injury: A Comparative Cross-Species Transcriptional Analysis

Despite the debilitating consequences following traumatic spinal cord injury (SCI), there is a lack of safe and effective therapeutics in the clinic. The species-specific responses to SCI present major challenges and opportunities for the clinical translation of biomolecular and pharmacological interventions. Recent transcriptional analyses in preclinical SCI studies have provided a snapshot of the local SCI-induced molecular responses in different animal models. However, the variation in the pathogenesis of traumatic SCI across species is yet to be explored. This study aims to identify and characterize the common and inconsistent SCI-induced differentially expressed genes across species to identify potential therapeutic targets of translational relevance. A comprehensive search of open-source transcriptome datasets identified four cross-compatible microarray experiments in rats, mice, and salamanders. We observed consistent expressional changes in extracellular matrix components across the species. Conversely, salamanders showed downregulation of intracellular MAPK signaling compared to rodents. Additionally, sequence conservation and interactome analyses highlighted the well-preserved sequences of Fn1 and Jun with extensive protein-protein interaction networks. Lastly, in vivo immunohistochemical staining for fibronectin was used to validate the observed expressional pattern. These transcriptional changes in extracellular and MAPK pathways present potential therapeutic targets for traumatic SCI with promising translational relevance.

Genetic, Epigenetic, and Post-Transcriptional Basis of Divergent Tissue Regenerative Capacities Among Vertebrates

Regeneration is widespread across the animal kingdom but varies vastly across phylogeny and even ontogeny. Adult mammalian regeneration in most organs and appendages is limited, while vertebrates such as zebrafish and salamanders are able to regenerate various organs and body parts. Here, we focus on the regeneration of appendages, spinal cord, and heart - organs and body parts that are highly regenerative among fish and amphibian species but limited in adult mammals. We then describe potential genetic, epigenetic, and post-transcriptional similarities among these different forms of regeneration across vertebrates and discuss several theories for diminished regenerative capacity throughout evolution.

Overexpression of miR-124 in Motor Neurons Plays a Key Role in ALS Pathological Processes

miRNA(miR)-124 is an important regulator of neurogenesis, but its upregulation in SOD1G93A motor neurons (mSOD1 MNs) was shown to associate with neurodegeneration and microglia activation. We used pre-miR-124 in wild-type (WT) MNs and anti-miR-124 in mSOD1 MNs to characterize the miR-124 pathological role. miR-124 overexpression in WT MNs produced a miRNA profile like that of mSOD1 MNs (high miR-125b; low miR-146a and miR-21), and similarly led to early apoptosis. Alterations in mSOD1 MNs were abrogated with anti-miR-124 and changes in their miRNAs mostly recapitulated by their secretome. Normalization of miR-124 levels in mSOD1 MNs prevented the dysregulation of neurite network, mitochondria dynamics, axonal transport, and synaptic signaling. Same alterations were observed in WT MNs after pre-miR-124 transfection. Secretome from mSOD1 MNs triggered spinal microglia activation, which was unno-ticed with that from anti-miR-124-modulated cells. Secretome from such modulated MNs, when added to SC organotypic cultures from mSOD1 mice in the early symptomatic stage, also coun-teracted the pathology associated to GFAP decrease, PSD-95 and CX3CL1-CX3CR1 signaling im-pairment, neuro-immune homeostatic imbalance, and enhanced miR-124 expression levels. Data suggest that miR-124 is implicated in MN degeneration and paracrine-mediated pathogenicity. We propose miR-124 as a new therapeutic target and a promising ALS biomarker in patient sub-populations.

Preclinical Molecular Signatures of Spinal Cord Functional Restoration: Optimizing the Metamorphic Axolotl (Ambystoma mexicanum) Model in Regenerative Medicine

Regenerative medicine offers hope for patients with diseases of the central and peripheral nervous system. Urodele amphibians such as axolotl display an exceptional regenerative capacity and are considered as essential preclinical model organisms in neurology and regenerative medicine research. Earlier studies have suggested that the limb regeneration ability of this salamander notably decreases with induction of metamorphosis by thyroid hormones. Metamorphic axolotl requires further validation as a negative control in preclinical regenerative medicine research, not to mention the study of molecular substrates of its regenerative abilities. In this study, we report new observations on the effect of experimentally induced metamorphosis on spinal cord regeneration in axolotl. Surprisingly, we found that metamorphic animals were successful to functionally restore the spinal cord after an experimentally induced injury. To discern the molecular signatures of spinal cord regeneration, we performed transcriptomics analyses at 1- and 7-days postinjury (dpi) for both spinal cord injury (SCI)-induced (experimental) and laminectomy (sham) groups. We observed 119 and 989 differentially expressed genes at 1- and 7-dpi, respectively, while the corresponding mouse orthologous genes were enriched in junction-, immune system-, and extracellular matrix-related pathways. Taken together, our findings challenge the prior notions of limited regenerative ability of metamorphic axolotl which exhibited successful spinal cord regeneration in our experience. Moreover, we report on molecular signatures that can potentially explain the mechanistic substrates of the regenerative capacity of the metamorphic axolotl. To the best of our knowledge, this is the first report on molecular responses to SCI and functional restoration in metamorphic axolotls. These new findings advance our understanding of spinal cord regeneration, and may thus help optimize the future use of axolotl as a preclinical model in regenerative medicine and integrative biology fields.

microRNA-125b and its downstream Smurf1/KLF2/ATF2 axis as important promoters on neurological function recovery in rats with spinal cord injury

The purpose of this study is to investigate the role of microRNA-125b (miR-125b) and its mechanism in spinal cord injury (SCI) by targeting Smurf1. After loss- and gain-function approaches were conducted in SCI rat models and neural stem cells (NSCs) isolated from foetal rats, the Basso-Beattie-Bresnahan (BBB) score was calculated, and related protein expression was determined by Western blot analysis and cell apoptosis by TUNEL staining. NSC viability was detected by CCK-8, migration abilities by Transwell assay and apoptosis by flow cytometry. The relationship between miR-125b, Smurf1 and KLF2 was evaluated by dual-luciferase reporter gene experiments, Co-IP and in vivo ubiquitin modification assays. Inhibition of miR-125b and KLF2 and the up-regulation of Smurf1 and ATF2 were observed in SCI rats. BBB scores were elevated, the expression of Nestin, NeuN, GFAP, NF-200 and Bcl-2 protein was enhanced but that of Bax protein was reduced, and cell apoptosis was inhibited in SCI rats after up-regulating miR-125b or silencing ATF2. Smurf1 was a target gene of miR-125b, which promoted KLF2 degradation through its E3 ubiquitin ligase function, and KLF2 repressed the expression of ATF2 in NSCs. The results in vivo were replicated in vitro. miR-125b overexpression promotes neurological function recovery after SCI.

Salamanders: The molecular basis of tissue regeneration and its relevance to human disease

Salamanders are recognized for their ability to regenerate a broad range of tissues. They have also have been used for hundreds of years for classical developmental biology studies because of their large accessible embryos. The range of tissues these animals can regenerate is fascinating, from full limbs to parts of the brain or heart, a potential that is missing in humans. Many promising research efforts are working to decipher the molecular blueprints shared across the organisms that naturally have the capacity to regenerate different tissues and organs. Salamanders are an excellent example of a vertebrate that can functionally regenerate a wide range of tissue types. In this review, we outline some of the significant insights that have been made that are aiding in understanding the cellular and molecular mechanisms of tissue regeneration in salamanders and discuss why salamanders are a worthy model in which to study regenerative biology and how this may benefit research fields like regenerative medicine to develop therapies for humans in the future.

A Comparative Analysis of Reactive Müller Glia Gene Expression After Light Damage and microRNA-Depleted Müller Glia-Focus on microRNAs

Müller glia (MG) are the predominant glia in the neural retina and become reactive after injury or in disease. microRNAs (miRNAs) are translational repressors that regulate a variety of processes during development and are required for MG function. However, no data is available about the MG miRNAs in reactive gliosis. Therefore, in this study, we aimed to profile miRNAs and mRNAs in reactive MG 7 days after light damage. Light damage was performed for 8 h at 10,000 lux; this leads to rapid neuronal loss and strong MG reactivity. miRNAs were profiled using the Nanostring platform, gene expression analysis was conducted via microarray. We compared the light damage dataset with the dataset of Dicer deleted MG in order to find similarities and differences. We found: (1) The vast majority of MG miRNAs declined in reactive MG 7 days after light damage. (2) Only four miRNAs increased after light damage, which included miR-124. (3) The top 10 genes found upregulated in reactive MG after light damage include Gfap, Serpina3n, Ednrb and Cxcl10. (4) The miRNA decrease in reactive MG 7 days after injury resembles the profile of Dicer-depleted MG after one month. (5) The comparison of both mRNA expression datasets (light damage and Dicer-cKO) showed 1,502 genes were expressed under both conditions, with Maff , Egr2, Gadd45b, and Atf3 as top upregulated candidates. (6) The DIANA-TarBase v.8 miRNA:RNA interaction tool showed that three miRNAs were found to be present in all networks, i.e., after light damage, and in the combined data set; these were miR-125b-5p, let-7b and let-7c. Taken together, results show there is an overlap of gene regulatory events that occur in reactive MG after light damage (direct damage of neurons) and miRNA-depleted MG (Dicer-cKO), two very different paradigms. This suggests that MG miRNAs play an important role in a ubiquitous MG stress response and manipulating these miRNAs could be a first step to attenuate gliosis.

Matrix-Bound Nanovesicles: The Effects of Isolation Method upon Yield, Purity, and Function

Identification of matrix-bound nanovesicles (MBV) as ubiquitous components of the extracellular matrix (ECM) raises questions regarding their biologic functions and their potential theranostic application. Unlike liquid-phase extracellular vesicles (e.g., exosomes), MBV are tightly bound to the ECM, which makes their isolation and harvesting more challenging. The indiscriminate use of different methods to harvest MBV can alter or disrupt their structural and/or functional integrity. The objective of the present study was to compare the effect of various MBV harvesting methods upon yield, purity, and biologic activity. Combinations of four methods to solubilize the ECM (collagenase [COL], liberase [LIB], or proteinase K [PK] and nonenzymatic elution with potassium chloride) and four isolation methods (ultracentrifugation, ultrafiltration [UF], density barrier, and size exclusion chromatography [SEC]) were used to isolate MBV from urinary bladder-derived ECM. All combinations of solubilization and isolation methods allowed for the harvesting of MBV, however, distinct differences were noted. The highest yield, purity, cellular uptake, and biologic activity were seen with MBV isolated by a combination of liberase or collagenase followed by SEC. The combination of proteinase K and UF was shown to have detrimental effects on bioactivity. The results show the importance of selecting appropriate MBV harvesting methods for the characterization and evaluation of MBV and for analysis of their potential theranostic application. Impact statement Identification of matrix-bound nanovesicles (MBV) as ubiquitous components of the extracellular matrix (ECM) has raised questions regarding their biologic functions and their potential theranostic application. This study demonstrates that the harvesting methods used can result in samples with physical and biochemical properties that are unique to the isolation and solubilization methods used. Consequently, developing harvesting methods that minimize sample contamination with ECM remnants and/or solubilization agents will be essential in determining the theranostic potential of MBV in future studies.

[Non-coding RNAs as therapeutic targets in spinal cord injury]

Spinal cord injury (SCI) may be followed by persistent motor dysfunction and somatosensory disturbances that negatively influences the quality of life of patients and creates a significant economic burden. Analysis of secondary biological processes associated with changes in genetic expression is becoming increasingly important every day in understanding the pathophysiology of spinal cord injury. The results of international sequencing of the human genome were analyzed in 2004. These data revealed about 20,000 protein-coding genes covering near 2% of the total genomic sequence. The vast majority of gene transcripts are actually characterized as non-coding RNAs (ncRNAs). These RNA clusters do not encode functional proteins and ensure post-transcriptional regulation of gene expression. The clusters may be small (approximately 20 nucleotides) known as miRNAs or the transcripts can enroll over 200 nucleotides defined as long non-coding RNAs (lncRNAs). Some modern studies describe transient expression of microRNA in case of spinal cord injury. These RNAs are associated with inflammation and apoptosis, functional recovery and regeneration. Large-scale genomic analysis has demonstrated the existence of multiple lncRNAs whose expression is associated with some processes of spinal cord injury. lncRNA can be divided into two categories depending on the position in relation to the coding genes: intergenic and intragenic. Intergenic lncRNAs is currently the most studied class. Intragenic lncRNAs can be subdivided depending on the overlap of the coding genes (antisense, intron, etc.). According to recent studies, long non-coding RNAs are abundantly present in the tissues of central nervous system and may be crucial in the pathogenesis of certain diseases of nervous system. At the cellular level, it has been shown that lncRNAs regulate the expression of protein-coding RNAs. Moreover, these molecules are involved into such processes as neuronal death, demyelination and glia activation. This review is devoted to the role of ncRNAs in the pathogenesis of spinal cord injury and their potential use as targets for the treatment of consequences of spinal cord injury.

Exploring the role of microRNAs in axolotl regeneration

The axolotl, Ambystoma mexicanum, is used extensively for research in developmental biology, particularly for its ability to regenerate and restore lost organs, including in the nervous system, to full functionality. Regeneration in mammals typically depends on the healing process and scar formation with limited replacement of lost tissue. Other organisms, such as spiny mice (Acomys cahirinus), salamanders, and zebrafish, are able to regenerate some damaged body components. Blastema is a tissue that is formed after tissue injury in such organisms and is composed of progenitor cells or dedifferentiated cells that differentiate into various cell types during regeneration. Thus, identifying the molecules responsible for initiation of blastema formation is an important aspect for understanding regeneration. Introns, a major source of noncoding RNAs (ncRNAs), have characteristic sizes in the axolotl, particularly in genes associated with development. These ncRNAs, particularly microRNAs (miRNAs), exhibit dynamic regulation during regeneration. These miRNAs play an essential role in timing and control of gene expression to order and organize processes necessary for blastema creation. Master keys or molecules that underlie the remarkable regenerative abilities of the axolotl remain to be fully explored and exploited. Further and ongoing research on regeneration promises new knowledge that may allow improved repair and renewal of human tissues.

Dissecting the Molecular Signature of Spinal Cord Regeneration in the Axolotl Model

Thousands of people are affected by central nervous system (CNS) dysfunctions each year, with stroke and spinal cord injury (SCI) being the most frequent causes. Although there is some evidence of partial CNS self-repair (via migration of neural stem cells to the injury zone and adult neurogenesis), due to restricted regeneration capacity in mammals, acute or chronic spinal cord injuries cannot be repaired completely. Therefore, to expand the availability of treatment options for SCI, research on highly regenerative animals has become essential. Among vertebrates, axolotl, a salamander species, has been emerging as a powerful model to explore the molecular mechanisms of regeneration due to its exceptional regenerative capacity. In this study, gene expression modulation for regenerative-capable neotenic axolotl during spinal cord regeneration has been investigated. Next-generation sequencing was applied for the collected regeneration samples at zero and seven days post-amputation (dpa). The data obtained from the analyzed samples revealed 363 genes differentially expressed, mostly downregulated, between zero dpa and seven dpa. The extracellular matrix, cell-cell adhesion, and immune system-related processes and pathways were enriched by gene ontology and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. Based on these data, we conclude that the downregulation of immune system-related biological processes is crucial for spinal cord regeneration.

RNA interference in glial cells for nerve injury treatment

Drivers of RNA interference are potent for manipulating gene and protein levels, which enable the restoration of dysregulated mRNA expression that is commonly associated with injuries and diseases. This review summarizes the potential of targeting neuroglial cells, using RNA interference, to treat nerve injuries sustained in the central nervous system. In addition, the various methods of delivering these RNA interference effectors will be discussed.

The role of the immune system during regeneration of the central nervous system

Central nervous system damage in mammals leads to neuronal cell death, axonal degeneration, and formation of a glial scar resulting in functional and behavioral defects. Other vertebrates, like fish and salamanders, have retained the ability to functionally regenerate after central nervous system injury. To date research from many research organisms has led to a more concise understanding of the response of local neural cells to injury. However, it has become clear that non-neural cells of the immune system play an important role in determining the tissue response to injury. In this review we briefly consider the mammalian response to injury compared to organisms with the natural ability to regenerate. We then discuss similarities and differences in how cells of the innate and adaptive immune system respond and contribute to tissue repair in various species.

Protective Effects of MiR-129-5p on Acute Spinal Cord Injury Rats

BACKGROUND Spinal cord injury (SCI) is a severe devastating condition associated with serious disability and neurologic deficits. Aberrant micro RNA (miRNA) expression has been related to a variety of central nervous system diseases including SCI. In the present study, we aimed to discover the role of miR-129-5p on SCI. MATERIAL AND METHODS An acute SCI rat model was induced, following the modified Allen method. A total of 36 rats were randomly assigned into 4 groups (n=9 in every group): Sham group; Model group (SCI+saline); SCI+NC group; and SCI+miR-129-5p group (100 nm solution, every 2 days). Basso-Beattie-Bresnahan (BBB) locomotor rating score was carried out to determine functional recovery. TUNEL (terminal dUTP nick-end labeling) staining was used to evaluate cell apoptosis. Hematoxylin and eosin staining was performed to assess the pathological state of spinal cord. Furthermore, western blot assay was conducted to measure the calpain1 and calpain2 expression. RESULTS Our data suggested that the expression level of miR-129-5p was markedly reduced in rats after SCI. Then miR-129-5p mimic was injected into the vertebral canal. We found that the SCI+miR-129-5p group had a high score in the BBB test compared with the SCI+NC group and the Model group. The overexpression of miR-129-5p obviously reduced tissue loss, damaged cells, and the number of TUNEL positive cells. Moreover, western blot assay exhibited that overexpression of miR-129-5p decreased calpain1, calpain2, and cleaved caspase-3 expression. CONCLUSIONS Our findings suggested that overexpression of miR-129-5p improved neurological function by promoting functional recovery, reducing tissue loss and cell apoptosis in rats in an SCI model, possibly through downregulation of calpain1 and calpain2.

Transactivation of Met signalling by semaphorin4D in human placenta: implications for the pathogenesis of preeclampsia

OBJECTIVE

The signalling of the receptor tyrosine kinase Met is critical in promoting trophoblast cell invasion, and the deficiency in HGF/Met signalling is associated with preeclampsia. The semaphorin family member semaphorin4D (sema4D) and its receptor Plexin-B1 have been reported to control tumour cell invasion by coupling with Met. We hypothesized that sema4D/Plexin-B1 may promote trophoblast invasion by activating Met, and downregulation of sema4D/Plexin-B1 may account for the deficiency in Met signalling in preeclamptic placenta.

METHODS

In this study, Met and Erk activation and the expression of sema4D/Plexin-B1 in normal and preeclamptic placentas were comparably measured. The role of sema4D in trophoblast cell invasion and tubulogenesis was examined in vitro using the Transwell invasion assay and tube formation assay in trophoblast-endothelial cell co-culture model.

RESULTS

Met, sema4D and Plexin-B1 co-localized in various subtypes of human trophoblast cells, including villous trophoblasts and extravillous trophoblasts (EVTs). In early-onset preeclampsia (E-PE) placentas, the phosphorylated Met and Erk as well as sema4D and Plexin-B1 were much lower than those in gestational week-matched preterm-labour (PTL) placentas. In human trophoblast HTR8/SVneo cell line, sema4D could promote Met and Erk phosphorylation as well as enhance trophoblast cell invasion and tubulogenesis with endothelial cells. Moreover, the effect of sema4D on HTR8/SVneo could be blocked by knocking down Met with specific siRNA.

CONCLUSION

The crosstalk between sema4D and Met could transactivate Met to promote trophoblast cell invasion and differentiation, and decreased expression of sema4D and Plexin-B1 may be responsible for the deficiency in Met signalling and the development of preeclampsia.

Bioelectrical controls of morphogenesis: from ancient mechanisms of cell coordination to biomedical opportunities

Cell-to-cell communication is a cornerstone of multicellular existence. The ancient mechanism of sharing information between cells using the conductance of ions across cell membranes and the propagation of electrical signals through tissue space is a powerful means of efficiently controlling cell decisions and behaviors. Our understanding of how cells use changes in 'bioelectrical' signals to elicit systems-level responses has dramatically improved in recent years. We are now in a position to not just describe these changes, but to also predictively alter them to learn more about their importance for developmental biology and regenerative medicine. Recent work is helping researchers construct a more integrative view of how these simple controls can orchestrate downstream changes in protein signaling pathways and gene regulatory networks. In this review, we highlight experiments and analyses that have led to new insights in bioelectrical controls, specifically as key modulators of complex pattern formation and tissue regeneration. We also discuss opportunities for the development of new therapeutic approaches in regenerative medicine applications by exploiting this fundamental biological phenomenon.

MicroRNAs and Regeneration in Animal Models of CNS Disorders

microRNAs (miRNAs) are recently identified small RNA molecules that regulate gene expression and significantly influence the essential cellular processes associated with CNS repair after trauma and neuropathological conditions including stroke and neurodegenerative disorders. A number of specific miRNAs are implicated in regulating the development and propagation of CNS injury, as well as its subsequent regeneration. The review focuses on the functions of the miRNAs and their role in brain recovery following CNS damage. The article introduces a brief description of miRNA biogenesis and mechanisms of miRNA-induced gene suppression, followed by an overview of miRNAs involved in the processes associated with CNS repair, including neuroprotection, neuronal plasticity and axonal regeneration, vascular reorganization, neuroinflammation, and endogenous stem cell activation. Specific emphasis is placed on the role of multifunctional miRNA miR-155, as it appears to be involved in multiple neurorestorative processes during different CNS pathologies. In association with our own studies on miR-155, I introduce a new and unexplored approach to cerebral regeneration: regulation of brain tissue repair through a direct modulation of specific miRNA activity. The review concludes with discussion on the challenges and the future potential of miRNA-based therapeutic approaches to CNS repair.

AP-1cFos/JunB/miR-200a regulate the pro-regenerative glial cell response during axolotl spinal cord regeneration

Salamanders have the remarkable ability to functionally regenerate after spinal cord transection. In response to injury, GFAP⁺ glial cells in the axolotl spinal cord proliferate and migrate to replace the missing neural tube and create a permissive environment for axon regeneration. Molecular pathways that regulate the pro-regenerative axolotl glial cell response are poorly understood. Here we show axolotl glial cells up-regulate AP-1^cFos/JunB after injury, which promotes a pro-regenerative glial cell response. Injury induced upregulation of miR-200a in glial cells supresses c-Jun expression in these cells. Inhibition of miR-200a during regeneration causes defects in axonal regrowth and transcriptomic analysis revealed that miR-200a inhibition leads to differential regulation of genes involved with reactive gliosis, the glial scar, extracellular matrix remodeling and axon guidance. This work identifies a unique role for miR-200a in inhibiting reactive gliosis in axolotl glial cells during spinal cord regeneration.

Keith Sabin et al. showed that upregulation of the AP-1 complex, composed of c-Fos and JunB, in the axolotl spinal cord promotes a pro-regenerative glial cell response. This response is impaired by inhibition of miR-200a; suggesting an important role for this microRNA in axolotl spinal cord regeneration.

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.

The role of microRNAs in newborn brain development and hypoxic ischaemic encephalopathy

Neonates can develop hypoxic-ischaemic encephalopathy (HIE) due to lack of blood supply or oxygen, resulting in a major cause of death and disability among term newborns. However, current definitive treatment of therapeutic hypothermia, will only benefit one out of nine babies. Furthermore, the mechanisms of HIE and therapeutic hypothermia are not fully understood. Recently, microRNAs (miRNAs) have become of interest to many researchers due to their important role in post-transcriptional control and deep evolutionary history. Despite this, role of miRNAs in newborns with HIE remains largely unknown due to limited research in this field. Therefore, this review aims to understand the role of miRNAs in normal brain development and HIE pathophysiology with reliance on extrapolated data from other diseases, ages and species due to current limited data. This will provide us with an overview of how miRNAs in normal brain development changes after HIE. Furthermore, it will indicate how miRNAs are affected specifically or globally by the various pathophysiological events. In addition, we discuss about how drugs and commercially available agents can specifically target certain miRNAs as a mechanism of action and potential safety issue with off-target effects. Improving our understanding of the role of miRNAs on the cellular response after HIE would enhance the success of effective diagnosis, prognosis, and treatment of newborns with HIE.

A clinically relevant blunt spinal cord injury model in the regeneration competent axolotl (Ambystoma mexicanum) tail

A randomized controlled and blinded animal trial was conducted in the axolotl (Ambystoma mexicanum), which has the ability to regenerate from transectional spinal cord injury (SCI). The objective of the present study was to investigate the axolotl's ability to regenerate from a blunt spinal cord trauma in a clinical setting. Axolotls were block-randomized to the intervention (n=6) or sham group (n=6). A laminectomy of two vertebrae at the level caudal to the hind limbs was performed. To induce a blunt SCI, a 25 g rod was released on the exposed spinal cord. Multiple modalities were applied at baseline (pre-surgery), and subsequently every third week for a total of 9 weeks. Gradient echo magnetic resonance imaging (MRI) was applied to assess anatomical regeneration. To support this non-invasive modality, regeneration was assessed by histology, and functional regeneration was investigated using swimming tests and functional neurological examinations. MRI suggested regeneration within 6 to 9 weeks. Histological analysis at 9 weeks confirmed regeneration; however, this regeneration was not complete. By the experimental end, all animals exhibited restored full neurological function. The present study demonstrated that the axolotl is capable of regenerating a contusion SCI; however, the duration of complete regeneration required further investigation.

Comparative Transcriptomics of Rat and Axolotl After Spinal Cord Injury Dissects Differences and Similarities in Inflammatory and Matrix Remodeling Gene Expression Patterns

Following spinal cord injury in mammals, maladaptive inflammation, and matrix deposition drive tissue scarring and permanent loss of function. In contrast, axolotls regenerate their spinal cord after severe injury fully and without scarring. To explore previously unappreciated molecules and pathways that drive tissue responses after spinal cord injury, we performed a 4-way intersection of rat and axolotl transcriptomics datasets and isolated shared genes with similar or differential expression at days 1, 3, and 7 after spinal cord injury in both species. Systems-wide differences and similarities between the two species are described in detail using public-domain computational tools and key differentially regulated genes are highlighted. Amongst persistent differential expression in matching neuronal genes (upregulated in axolotls but downregulated in rats) and nucleic acid metabolism genes (downregulated in axolotls but upregulated in rats), we found multiple extracellular matrix genes that were upregulated in both species after spinal cord injury and all time-points (days 1, 3, and 7), indicating the importance of extracellular matrix remodeling in wound healing. Moreover, the archetypal transcription factor SP1, which was consistently upregulated in rats but was unchanged in axolotls, was predicted as a potential transcriptional regulator of classic inflammatory response genes in rats most of which were not regulated in regenerating axolotls. This analysis offers an extensive comparative platform between a non-regenerating mammal and a regenerating urodele after spinal cord injury. To better understand regeneration vs. scarring mechanisms it is important to understand consistent molecular differences as well as similarities after experimental spinal cord injury.

Identification and Characterization of microRNAs during Retinoic Acid-Induced Regeneration of a Molluscan Central Nervous System

Retinoic acid (RA) is the biologically active metabolite of vitamin A and has become a well-established factor that induces neurite outgrowth and regeneration in both vertebrates and invertebrates. However, the underlying regulatory mechanisms that may mediate RA-induced neurite sprouting remain unclear. In the past decade, microRNAs have emerged as important regulators of nervous system development and regeneration, and have been shown to contribute to processes such as neurite sprouting. However, few studies have demonstrated the role of miRNAs in RA-induced neurite sprouting. By miRNA sequencing analysis, we identify 482 miRNAs in the regenerating central nervous system (CNS) of the mollusc Lymnaeastagnalis, 219 of which represent potentially novel miRNAs. Of the remaining conserved miRNAs, 38 show a statistically significant up- or downregulation in regenerating CNS as a result of RA treatment. We further characterized the expression of one neuronally-enriched miRNA upregulated by RA, miR-124. We demonstrate, for the first time, that miR-124 is expressed within the cell bodies and neurites of regenerating motorneurons. Moreover, we identify miR-124 expression within the growth cones of cultured ciliary motorneurons (pedal A), whereas expression in the growth cones of another class of respiratory motorneurons (right parietal A) was absent in vitro. These findings support our hypothesis that miRNAs are important regulators of retinoic acid-induced neuronal outgrowth and regeneration in regeneration-competent species.

Salamander spinal cord regeneration: The ultimate positive control in vertebrate spinal cord regeneration

Repairing injured tissues / organs is one of the major challenges for the maintenance of proper organ function in adulthood. In mammals, the central nervous system including the spinal cord, once established during embryonic development, has very limited capacity to regenerate. In contrast, salamanders such as axolotls can fully regenerate the injured spinal cord, making this a very powerful vertebrate model system for studying this process. Here we discuss the cellular and molecular requirements for spinal cord regeneration in the axolotl. The recent development of tools to test molecular function, including CRISPR-mediated gene editing, has lead to the identification of key players involved in the cell response to injury that ultimately leads to outgrowth of neural stem cells that are competent to replay the process of spinal cord development to replace the damaged/missing tissue.

Propofol (2,6-diisopropylphenol) is an applicable immersion anesthetic in the axolotl with potential uses in hemodynamic and neurophysiological experiments

The Mexican axolotl (Ambystoma mexicanum) is an important model species in regenerative biology. Traditionally, axolotls are anesthetized using benzocaine or MS-222, both of which act to inhibit voltage gated sodium channels thereby preventing action potential propagation. In some neurophysiological experiments this is not desirable; therefore we tested propofol as an alternative anesthetic in the axolotl. We evaluated benzocaine, MS-222, and propofol's cardiovascular effects, effects on action potential propagation in the spinal cord, and gross limb regenerative effects. We found that propofol is applicable as a general anesthetic in the axolotl allowing for neurophysiological experiments and yielding a stable anesthesia with significantly less cardiovascular effect than both benzocaine and MS-222. Additionally, propofol did not affect gross limb regeneration. In conclusion we suggest the consideration of propofol as an alternative immersion anesthetic to benzocaine and MS-222.

Endogenous Bioelectric Signaling Networks: Exploiting Voltage Gradients for Control of Growth and Form

Living systems exhibit remarkable abilities to self-assemble, regenerate, and remodel complex shapes. How cellular networks construct and repair specific anatomical outcomes is an open question at the heart of the next-generation science of bioengineering. Developmental bioelectricity is an exciting emerging discipline that exploits endogenous bioelectric signaling among many cell types to regulate pattern formation. We provide a brief overview of this field, review recent data in which bioelectricity is used to control patterning in a range of model systems, and describe the molecular tools being used to probe the role of bioelectrics in the dynamic control of complex anatomy. We suggest that quantitative strategies recently developed to infer semantic content and information processing from ionic activity in the brain might provide important clues to cracking the bioelectric code. Gaining control of the mechanisms by which large-scale shape is regulated in vivo will drive transformative advances in bioengineering, regenerative medicine, and synthetic morphology, and could be used to therapeutically address birth defects, traumatic injury, and cancer.

A novel role for SALL4 during scar-free wound healing in axolotl

The human response to serious cutaneous damage is limited to relatively primitive wound healing, whereby collagenous scar tissue fills the wound bed. Scars assure structural integrity at the expense of functional regeneration. In contrast, axolotls have the remarkable capacity to functionally regenerate full thickness wounds. Here, we identified a novel role for SALL4 in regulating collagen transcription after injury that is essential for perfect skin regeneration in axolotl. Furthermore, we identify miR-219 as a molecular regulator of Sall4 during wound healing. Taken together, our work highlights one molecular mechanism that allows for efficient cutaneous wound healing in the axolotl.

The Role of microRNA Markers in the Diagnosis, Treatment, and Outcome Prediction of Spinal Cord Injury

Spinal cord injury (SCI) is a devastating condition that affects many people worldwide. Treatment focuses on controlling secondary injury cascade and improving regeneration. It has recently been suggested that both the secondary injury cascade and the regenerative process are heavily regulated by microRNAs (miRNAs). The measurement of specific biomarkers could improve our understanding of the disease processes, and thereby provide clinicians with the opportunity to guide treatment and predict clinical outcomes after SCI. A variety of miRNAs exhibit important roles in processes of inflammation, cell death, and regeneration. These miRNAs can be used as diagnostic tools for predicting outcome after SCI. In addition, miRNAs can be used in the treatment of SCI and its symptoms. Significant laboratory and clinical evidence exist to show that miRNAs could be used as robust diagnostic and therapeutic tools for the treatment of patients with SCI. Further clinical studies are warranted to clarify the importance of each subtype of miRNA in SCI management.

Extrinsic and Intrinsic Regulation of Axon Regeneration by MicroRNAs after Spinal Cord Injury

Spinal cord injury is a devastating disease which disrupts the connections between the brain and spinal cord, often resulting in the loss of sensory and motor function below the lesion site. Most injured neurons fail to regenerate in the central nervous system after injury. Multiple intrinsic and extrinsic factors contribute to the general failure of axonal regeneration after injury. MicroRNAs can modulate multiple genes' expression and are tightly controlled during nerve development or the injury process. Evidence has demonstrated that microRNAs and their signaling pathways play important roles in mediating axon regeneration and glial scar formation after spinal cord injury. This article reviews the role and mechanism of differentially expressed microRNAs in regulating axon regeneration and glial scar formation after spinal cord injury, as well as their therapeutic potential for promoting axonal regeneration and repair of the injured spinal cord.

The Role of microRNAs in Animal Cell Reprogramming

Our concept of cell reprogramming and cell plasticity has evolved since John Gurdon transferred the nucleus of a completely differentiated cell into an enucleated Xenopus laevis egg, thereby generating embryos that developed into tadpoles. More recently, induced expression of transcription factors, oct4, sox2, klf4, and c-myc has evidenced the plasticity of the genome to change the expression program and cell phenotype by driving differentiated cells to the pluripotent state. Beyond these milestone achievements, research in artificial cell reprogramming has been focused on other molecules that are different than transcription factors. Among the candidate molecules, microRNAs (miRNAs) stand out due to their potential to control the levels of proteins that are involved in cellular processes such as self-renewal, proliferation, and differentiation. Here, we review the role of miRNAs in the maintenance and differentiation of mesenchymal stem cells, epimorphic regeneration, and somatic cell reprogramming to induced pluripotent stem cells.

Dynamic membrane depolarization is an early regulator of ependymoglial cell response to spinal cord injury in axolotl

Salamanders, such as the Mexican axolotl, are some of the few vertebrates fortunate in their ability to regenerate diverse structures after injury. Unlike mammals they are able to regenerate a fully functional spinal cord after injury. However, the molecular circuitry required to initiate a pro-regenerative response after spinal cord injury is not well understood. To address this question we developed a spinal cord injury model in axolotls and used in vivo imaging of labeled ependymoglial cells to characterize the response of these cells to injury. Using in vivo imaging of ion sensitive dyes we identified that spinal cord injury induces a rapid and dynamic change in the resting membrane potential of ependymoglial cells. Prolonged depolarization of ependymoglial cells after injury inhibits ependymoglial cell proliferation and subsequent axon regeneration. Using transcriptional profiling we identified c-Fos as a key voltage sensitive early response gene that is expressed specifically in the ependymoglial cells after injury. This data establishes that dynamic changes in the membrane potential after injury are essential for regulating the specific spatiotemporal expression of c-Fos that is critical for promoting faithful spinal cord regeneration in axolotl.

MicroRNA dysregulation in response to RARβ2 inhibition reveals a negative feedback loop between MicroRNAs 1, 133a, and RARβ2 during tail and spinal cord regeneration in the adult newt

BACKGROUND

The molecular events underlying epimorphic regeneration of the adult urodele amphibian tail and caudal spinal cord are undetermined. Given the dynamic nature of gene expression control by retinoic acid (RA) signaling and the pleiotropic effects of microRNAs (miRNAs) on multiple mRNA targets in this complex system, we examined whether RA signaling through a specific receptor, RARβ2, alters expression of select miRNAs during spinal cord regeneration.

RESULTS

An initial screen identified 18 highly conserved miRNAs dysregulated in regenerating tail and spinal cord tissues after inhibition of RARβ2 signaling with a selective antagonist, LE135. miRNAs let-7c, miR-1, and miR-223 were expressed within the ependymoglial cells, coincident spatially with the expression of RARβ2. Altering the expression pattern of these three miRNAs led to a significant inhibition of caudal ependymal tube outgrowth by 21 days post tail amputation. We demonstrated that miR-1 targets the 3'-untranslated region of RARβ2 mRNA in vitro; and in vivo, up-regulation of miR-1 led to a significant decrease in RARβ2 protein.

CONCLUSIONS

These and previous data suggest that miR-1 and miR-133a, both members of the same miRNA gene cluster, may participate with RARβ2 in a negative feedback loop contributing to the regulation of the ependymal response after tail amputation.

Identification of Conserved and Novel MicroRNAs during Tail Regeneration in the Mexican Axolotl

The Mexican axolotl salamander (Ambystoma mexicanum) is one member of a select group of vertebrate animals that have retained the amazing ability to regenerate multiple body parts. In addition to being an important model system for regeneration, the axolotl has also contributed extensively to studies of basic development. While many genes known to play key roles during development have now been implicated in various forms of regeneration, much of the regulatory apparatus controlling the underlying molecular circuitry remains unknown. In recent years, microRNAs have been identified as key regulators of gene expression during development, in many diseases and also, increasingly, in regeneration. Here, we have used deep sequencing combined with qRT-PCR to undertake a comprehensive identification of microRNAs involved in regulating regeneration in the axolotl. Specifically, among the microRNAs that we have found to be expressed in axolotl tissues, we have identified 4564 microRNA families known to be widely conserved among vertebrates, as well as 59,811 reads of putative novel microRNAs. These findings support the hypothesis that microRNAs play key roles in managing the precise spatial and temporal patterns of gene expression that ensures the correct regeneration of missing tissues.

Integrated analyses of zebrafish miRNA and mRNA expression profiles identify miR-29b and miR-223 as potential regulators of optic nerve regeneration

Background

Unlike mammals, zebrafish have the ability to regenerate damaged parts of their central nervous system (CNS) and regain functionality of the affected area. A better understanding of the molecular mechanisms involved in zebrafish regeneration may therefore provide insight into how CNS repair might be induced in mammals. Although many studies have described differences in gene expression in zebrafish during CNS regeneration, the regulatory mechanisms underpinning the differential expression of these genes have not been examined.

Results

We used microarrays to analyse and integrate the mRNA and microRNA (miRNA) expression profiles of zebrafish retina after optic nerve crush to identify potential regulatory mechanisms that underpin central nerve regeneration. Bioinformatic analysis identified 3 miRNAs and 657 mRNAs that were differentially expressed after injury. We then combined inverse correlations between our miRNA expression and mRNA expression, and integrated these findings with target predictions from TargetScan Fish to identify putative miRNA-gene target pairs. We focused on two over-expressed miRNAs (miR-29b and miR-223), and functionally validated seven of their predicted gene targets using RT-qPCR and luciferase assays to confirm miRNA-mRNA binding. Gene ontology analysis placed the miRNA-regulated genes (eva1a, layna, nefmb, ina, si:ch211-51a6.2, smoc1, sb:cb252) in key biological processes that included cell survival/apoptosis, ECM-cytoskeleton signaling, and heparan sulfate proteoglycan binding,

Conclusion

Our results suggest a key role for miR-29b and miR-223 in zebrafish regeneration. The identification of miRNA regulation in a zebrafish injury model provides a framework for future studies in which to investigate not only the cellular processes required for CNS regeneration, but also how these mechanisms might be regulated to promote successful repair and return of function in the injured mammalian brain.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1772-1) contains supplementary material, which is available to authorized users.

[Micro RNA and its role in the pathophysiology of spinal cord injury - a further step towards neuroregenerative medicine]

In the pathophysiology of spinal cord injury, the secondary biological processes involving changes in gene expression become more important day a day. Within these changes, the expression of different microRNAs has been involved in some of the pathophysiological processes of spinal cord injury. There are several studies that describe the transient expression of microRNA in spinal cord injury, some of them related to inflammation and apoptosis and others to functional recovery and regeneration. MicroRNA may be a potential target for the treatment of spinal cord injury, modifying the processes of inflammation, oxidation, apoptosis, functional recovery and regeneration. It is necessary to continue the study of microRNAs in spinal cord injury, as well as the identification of their target genes and signaling mechanisms involved in its neurological effects. With this, the ultimate goal is the development of effective and safe therapeutic and diagnostic strategies for patients with spinal cord injury.

In vivo modulation and quantification of microRNAs during axolotl tail regeneration

The ability to regenerate diseased, injured, or missing complex tissue is widespread throughout lower vertebrates and invertebrates; however, our knowledge of the molecular mechanisms that regulate this amazing ability is still in its infancy. Many recent papers have shown important roles for microRNAs in regulating regeneration in a number of species. The ability to detect and quantify miRNA expression fluctuations at a single cell level in vivo in different cell types during processes like regeneration is very informative. In this chapter, we describe how to use a dual-fluorescent green fluorescent protein (GFP)-reporter/monomeric red fluorescent protein (mRFP)-sensor (DFRS) plasmid to quantitate the dynamics of specific miRNAs over time following miRNA mimic injection as well as during regeneration. In this bicistronic vector, the mRFP allows for verification of miRNA expression, while the GFP functions as an internal control to normalize miRNA expression and thus obtain quantitative results. In addition, we demonstrate how this technique revealed dynamic miR-23a expression and function during tail regeneration.

The link between injury-induced stress and regenerative phenomena: A cellular and genetic synopsis

Injury is an inescapable phenomenon of life that affects animals at every physiological level. Yet, some animals respond to injury by rebuilding the damaged tissues whereas others are limited to scarring. Elucidating how a tissue insult from wounding leads to a regenerative response at the genetic level is essential to make regenerative advantages translational. It has become clear that animals with regenerative abilities recycle developmental programs after injury, reactivating genes that have lied dormant throughout adulthood. The question that is critical to our understanding of regeneration is how a specific set of developmentally important genes can be reactivated only after an acute tissue insult. Here, we review how injury-induced cellular stresses such as hypoxic, oxidative, and mechanical stress may contribute to the genomic and epigenetic changes that promote regeneration in animals. This article is part of a Special Issue entitled: Stress as a fundamental theme in cell plasticity.