Peripheral axons of the adult zebrafish maxillary barbel extensively remyelinate during sensory appendage regeneration

Myelin repair of spinal cord injury in adult mice induced by treadmill training upregulated peroxisome proliferator-activated receptor gamma coactivator 1 alpha

Growing evidence has proven the efficacy of physical exercise in remyelination and motor function performance after spinal cord injury (SCI). However, the molecular mechanisms of treadmill training on myelin repair and functional recovery after SCI have not yet been fully studied. Here, we explored the effect of treadmill training on upregulating peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1α)-mediated myelin repair and functional recovery in a mouse model of thoracic T10 contusion injury. A 4-week treadmill training scheme was conducted on mice with SCI. The expression levels of oligodendrogenesis-related protein and PGC1α were detected by immunofluorescence, RNA fluorescence in situ hybridization and western blotting. Transmission electron microscopy (TEM) was used to observe myelin structure. The Basso Mouse Scale (BMS) and CatWalk automated gait analysis system were used for motor function recovery evaluation. Motor evoked potentials (MEPs) were also identified. In addition, adeno-associated virus (AAV)-mediated PGC1α knockdown in OLs was used to further unravel the role of PGC1α in exercise-induced remyelination. We found that treadmill training boosts oligodendrocyte precursor cells (OPCs) proliferation, potentiates oligodendrocytes (OLs) maturation, and increases myelin-related protein and myelin sheath thickness, thus impelling myelin repair and hindlimb functional performance as well as the speed and amplitude of nerve conduction after SCI. Additionally, downregulating PGC1α through AAV attenuated these positive effects of treadmill training. Collectively, our results suggest that treadmill training enhances remyelination and functional recovery by upregulating PGC1α, which should provide a step forward in the understanding of the effects of physical exercise on myelin repair.

Dock1 acts cell-autonomously in Schwann cells to regulate the development, maintenance, and repair of peripheral myelin

Schwann cells, the myelinating glia of the peripheral nervous system (PNS), are critical for myelin development, maintenance, and repair. Rac1 is a known regulator of radial sorting, a key step in developmental myelination, and we previously showed in zebrafish that loss of Dock1, a Rac1-specific guanine nucleotide exchange factor, results in delayed peripheral myelination in development. We demonstrate here that Dock1 is necessary for myelin maintenance and remyelination after injury in adult zebrafish. Furthermore, it performs an evolutionary conserved role in mice, acting cell-autonomously in Schwann cells to regulate peripheral myelin development, maintenance, and repair. Additionally, manipulating Rac1 levels in larval zebrafish reveals that dock1 mutants are sensitized to inhibition of Rac1, suggesting an interaction between the two proteins during PNS development. We propose that the interplay between Dock1 and Rac1 signaling in Schwann cells is required to establish, maintain, and facilitate repair and remyelination within the peripheral nervous system.

Systems assessment of statins hazard: Integrating in silico prediction, developmental toxicity profile and transcriptomics in zebrafish

Statins are prescribed widely as lipid-lowering agents. However, statins are associated with an increased harmful risk on public health and the ecosystem. Little is known about statins' toxicity on biological development and the underlying molecular mechanisms. We exposed zebrafish embryos to a series of statins to evaluate their development toxicity. Statins-induced embryonic developmental defects in a concentration-dependent manner. 72 h LC₅₀ values for lovastatin, simvastatin, fluvastatin, atorvastatin, rosuvastatin, and pravastatin were 0.01 μM, 0.04 μM, 1.93 μM, 37.28 μM, 79.29 μM, and 2170 μM, respectively. Moreover, the expression of genes involved in heart contraction, calcium ion binding, transcription factors, nucleus, and G protein-coupled receptor signaling pathway was altered by statins. The early growth response gene (egr4) and transcription factor genes (fosab and fosb) were screened as potential toxicity targets due to their significant upregulation based on protein-protein interaction (PPI) and drug-gene interaction network analysis. Finally, the ecotoxicity profile of statins was predicted by in silico method, and statins were high or moderate risk to aquatic organisms. We provide a systems toxicology strategy to explore the toxicity of statins and illustrate the potential mechanisms of action.

The pseudobranch of jawed vertebrates is a mandibular arch-derived gill

The pseudobranch is a gill-like epithelial elaboration that sits behind the jaw of most fishes. This structure was classically regarded as a vestige of the ancestral gill arch-like condition of the gnathostome jaw. However, more recently, hypotheses of jaw evolution by transformation of a gill arch have been challenged, and the pseudobranch has alternatively been considered a specialised derivative of the second (hyoid) pharyngeal arch. Here, we demonstrate in the skate (Leucoraja erinacea) that the pseudobranch does, in fact, derive from the mandibular arch, and that it shares gene expression features and cell types with gills. We also show that the skate mandibular arch pseudobranch is supported by a spiracular cartilage that is patterned by a shh-expressing epithelial signalling centre. This closely parallels the condition seen in the gill arches, where cartilaginous appendages called branchial rays, which support the respiratory lamellae of the gills, are patterned by a shh-expressing gill arch epithelial ridge. Together with similar discoveries in zebrafish, our findings support serial homology of the pseudobranch and gills, and an ancestral origin of gill arch-like anatomical features from the gnathostome mandibular arch.

Summary: The skate pseudobranch is a gill serial homologue and reveals the ancestral gill arch-like nature of the jawed vertebrate mandibular arch.

Zebrafish is a central model to dissect the peripheral neuropathy

The peripheral nervous system (PNS) is composed with all nerves extended from the brain and spinal cord, which are the central nervous system to other organs of the body. Dysfunctional peripheral motion resulting from the regressive neuronal axons in the defected PNS leads to several peripheral neuropathies including both inherited and non-inherited disorders. Because of poor understanding of cellular and molecular mechanisms involved in the peripheral neuropathy, there is currently non-targeted treatment of the disorder. Basic researches have paid attention to dissect roles of causative genes, identified from the inherited peripheral neuropathies, in PNS development. However, recent studies focusing on investigation of therapeutic targets have suggested that successful regeneration of the impaired peripheral nerves may be most effective treatment. The regeneration studies have been limited in the rodents system due to some of practical and physiological disadvantages until zebrafish model has emerged as an ideal system. Hence, this review aims to provide a comprehensive overview of the advantages of zebrafish as a model for the peripheral neuropathy researches and to suggest the disease genes-involved potential mechanisms targeting the PNS regeneration that may be demonstrated in zebrafish.

Transmission Electron Microscopy for Zebrafish Larvae and Adult Lateral Line Nerve

Transmission electron microscopy (TEM) enables visualization of the ultrastructure of the myelin sheath. Schwann cells on the posterior lateral line nerves and motor nerves can be imaged by TEM. Here, we detail the multiday processing of larval trunks and dissected posterior lateral line for TEM, as well as how to trim embedded samples, section, and stain grids for imaging.

Stimulation of morphofunctional repair of the facial nerve with photobiomodulation, using the end-to-side technique or a new heterologous fibrin sealant

This research evaluated the influence of Photobiomodulation Therapy (PBMT) on lesions of the facial nerve repaired with the end-to-side technique or coaptation with a new heterologous fibrin sealant. Thirty-two Wistar rats were separated into 5 groups: Control group (CG), where the buccal branch of the facial nerve was collected; Experimental Suture Group (ESG) and Experimental Fibrin Group (EFG), in which the buccal branch was end-to-side sutured to the zygomatic branch on the right side of the face or coaptated with fibrin sealant on the left side; Experimental Suture Laser Group (ESLG) and Experimental Fibrin Laser Group (EFLG), in which the same procedures were performed as the ESG and EFG, associated with PBMT (wavelength of 830nm, energy density 6.2J/cm², power output 30mW, beam area of 0.116cm², power density 0.26W/cm², total energy per session 2.16J, cumulative dose of 34.56J). The laser was applied for 24s/site at 3 points on the skin's surface, for a total application time of 72s, performed immediately after surgery and 3 times a week for 5weeks. A statistically significant difference was observed in the fiber nerve area between the EFG and EFLG (57.49±3.13 and 62.52±3.56μm², respectively). For the area of the axon, fiber diameter, axon diameter, myelin sheath area and myelin sheath thickness no statistically significant differences were found (p<0.05). The functional recovery of whisker movement occurred faster in the ESLG and EFLG, which were associated with PBMT, with results closer to the CG. Therefore, PBMT accelerated morphological and functional nerve repair in both techniques.

Functional validation of ABHD12 mutations in the neurodegenerative disease PHARC

ABHD12 mutations have been linked to neurodegenerative PHARC (polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and early-onset cataract), a rare, progressive, autosomal, recessive disease. Although ABHD12 is suspected to play a role in the lysophosphatidylserine and/or endocannabinoid pathways, its precise functional role(s) leading to PHARC disease had not previously been characterized. Cell and zebrafish models were designed to demonstrate the causal link between an identified new missense mutation p.T253R, characterized in ABHD12 from a young patient, the previously characterized p.T202I and p.R352* mutations, and the associated PHARC. Measuring ABHD12 monoacylglycerol lipase activity in transfected HEK293 cells demonstrated inhibition with mutated isoforms. Both the expression pattern of zebrafish abhd12 and the phenotype of specific antisense morpholino oligonucleotide gene knockdown morphants were consistent with human PHARC hallmarks. High abhd12 transcript levels were found in the optic tectum and tract, colocalized with myelin basic protein, and in the spinal cord. Morphants have myelination defects and concomitant functional deficits, characterized by progressive ataxia and motor skill impairment. A disruption of retina architecture and retinotectal projections was observed, together with an inhibition of lens clarification and a low number of mechanosensory hair cells in the inner ear and lateral line system. The severe phenotypes in abhd12 knockdown morphants were rescued by introducing wild-type human ABHD12 mRNA, but not by mutation-harboring mRNAs. Zebrafish may provide a suitable vertebrate model for ABHD12 insufficiency and the study of functional impairment and potential therapeutic rescue of this rare, neurodegenerative disease.

Analysis of myelinated axon formation in zebrafish

Myelin is a lipid-rich sheath formed by the spiral wrapping of specialized glial cells around axon segments. Myelinating glia allow for rapid transmission of nerve impulses and metabolic support of axons, and the absence of or disruption to myelin results in debilitating motor, cognitive, and emotional deficits in humans. Because myelin is a jawed vertebrate innovation, zebrafish are one of the simplest vertebrate model systems to study the genetics and development of myelinating glia. The morphogenetic cellular movements and genetic program that drive myelination are conserved between zebrafish and mammals, and myelin develops rapidly in zebrafish larvae, within 3-5days postfertilization. Myelin ultrastructure can be visualized in the zebrafish from larval to adult stages via transmission electron microscopy, and the dynamic development of myelinating glial cells may be observed in vivo via transgenic reporter lines in zebrafish larvae. Zebrafish are amenable to genetic and pharmacological screens, and screens for myelinating glial phenotypes have revealed both genes and drugs that promote myelin development, many of which are conserved in mammalian glia. Recently, zebrafish have been employed as a model to understand the complex dynamics of myelinating glia during development and regeneration. In this chapter, we describe these key methodologies and recent insights into mechanisms that regulate myelination using the zebrafish model.

The new heterologous fibrin sealant in combination with low-level laser therapy (LLLT) in the repair of the buccal branch of the facial nerve

This study aimed to evaluate the effects of low-level laser therapy (LLLT) in the repair of the buccal branch of the facial nerve with two surgical techniques: end-to-end epineural suture and coaptation with heterologous fibrin sealant. Forty-two male Wistar rats were randomly divided into five groups: control group (CG) in which the buccal branch of the facial nerve was collected without injury; (2) experimental group with suture (EGS) and experimental group with fibrin (EGF): The buccal branch of the facial nerve was transected on both sides of the face. End-to-end suture was performed on the right side and fibrin sealant on the left side; (3) Experimental group with suture and laser (EGSL) and experimental group with fibrin and laser (EGFL). All animals underwent the same surgical procedures in the EGS and EGF groups, in combination with the application of LLLT (wavelength of 830 nm, 30 mW optical power output of potency, and energy density of 6 J/cm(2)). The animals of the five groups were euthanized at 5 weeks post-surgery and 10 weeks post-surgery. Axonal sprouting was observed in the distal stump of the facial nerve in all experimental groups. The observed morphology was similar to the fibers of the control group, with a predominance of myelinated fibers. In the final period of the experiment, the EGSL presented the closest results to the CG, in all variables measured, except in the axon area. Both surgical techniques analyzed were effective in the treatment of peripheral nerve injuries, where the use of fibrin sealant allowed the manipulation of the nerve stumps without trauma. LLLT exhibited satisfactory results on facial nerve regeneration, being therefore a useful technique to stimulate axonal regeneration process.

The scales and tales of myelination: using zebrafish and mouse to study myelinating glia

Myelin, the lipid-rich sheath that insulates axons to facilitate rapid conduction of action potentials, is an evolutionary innovation of the jawed-vertebrate lineage. Research efforts aimed at understanding the molecular mechanisms governing myelination have primarily focused on rodent models; however, with the advent of the zebrafish model system in the late twentieth century, the use of this genetically tractable, yet simpler vertebrate for studying myelination has steadily increased. In this review, we compare myelinating glial cell biology during development and regeneration in zebrafish and mouse and enumerate the advantages and disadvantages of using each model to study myelination. This article is part of a Special Issue entitled SI: Myelin Evolution.

Anatomy and ontogeny of a novel hemodynamic organ in zebrafish

The zebrafish maxillary barbel can protract and retract in response to stimuli, and appears connected to a prominent blood sinus on the lateral aspect of the maxillary bone. However, the mechanism of barbel movement is not described. Using whole-mount phalloidin staining of the sinus region, we observed long filamentous actin cables, suggesting highly organized vascular smooth muscle cells, surrounding an endothelial chamber. Although the chamber is variably filled by erythrocytes in vivo, cardiac injection of fluorescent dextrans shows that it consistently contains plasma. Full-thickness confocal imaging of dextran-injected adults containing EGFP(+) endothelial cells revealed a vascular complex with three compartments, here named the distal bulb, central chamber, and accessory chamber. The early ontogeny of all three compartments was confirmed in a whole-mount series of Tg(fli1a:EGFP) juveniles. In wild type adults, the fine structure of each chamber was studied using paraffin- and plastic-section histochemistry and transmission electron microscopy. The distal bulb and central chamber have smooth muscle coats with luminally-elongated septa, forming semi-detached blood-filled lacunae. The central chamber walls and septa are extensively innervated by small, unmyelinated axons, as confirmed by immunohistochemical detection of acetylated tubulin, a component of axonal cytoplasm. The accessory chamber appears neither innervated nor muscularized, but is an endothelial cul-de-sac with a thickened elastic adventitia, suggesting an extensible fluid reservoir. We propose that we have identified a new organ in zebrafish, the maxillary barbel blood sinus, whose neurovascular specializations may contribute to zebrafish sensory biology and appendage control.

Divergent requirements for fibroblast growth factor signaling in zebrafish maxillary barbel and caudal fin regeneration

The zebrafish maxillary barbel is an integumentary organ containing skin, glands, pigment cells, taste buds, nerves, and endothelial vessels. The maxillary barbel can regenerate (LeClair & Topczewski 2010); however, little is known about its molecular regulation. We have studied fibroblast growth factor (FGF) pathway molecules during barbel regeneration, comparing this system to a well-known regenerating appendage, the zebrafish caudal fin. Multiple FGF ligands (fgf20a, fgf24), receptors (fgfr1-4) and downstream targets (pea3, il17d) are expressed in normal and regenerating barbel tissue, confirming FGF activation. To test if specific FGF pathways were required for barbel regeneration, we performed simultaneous barbel and caudal fin amputations in two temperature-dependent zebrafish lines. Zebrafish homozygous for a point mutation in fgf20a, a factor essential for caudal fin blastema formation, regrew maxillary barbels normally, indicating that the requirement for this ligand is appendage-specific. Global overexpression of a dominant negative FGF receptor, Tg(hsp70l:dn-fgfr1:EGFP)(pd1) completely blocked fin outgrowth but only partially inhibited barbel outgrowth, suggesting reduced requirements for FGFs in barbel tissue. Maxillary barbels expressing dn-fgfr1 regenerated peripheral nerves, dermal connective tissue, endothelial tubes, and a glandular epithelium; in contrast to a recent report in which dn-fgfr1 overexpression blocks pharyngeal taste bud formation in zebrafish larvae (Kapsimali et al. 2011), we observed robust formation of calretinin-positive tastebuds. These are the first experiments to explore the molecular mechanisms of maxillary barbel regeneration. Our results suggest heterogeneous requirements for FGF signaling in the regeneration of different zebrafish appendages (caudal fin versus maxillary barbel) and taste buds of different embryonic origin (pharyngeal endoderm versus barbel ectoderm).