Knockout of zebrafish desmin genes does not cause skeletal muscle degeneration but alters calcium flux

Curcumin-activated Wnt5a pathway mediates Ca2+ channel opening to affect myoblast differentiation and skeletal muscle regeneration

BACKGROUND

Skeletal muscle injury is one of the most common sports injuries; if not properly treated or not effective rehabilitation treatment after injury, it can be transformed into chronic cumulative injury. Curcumin, an herbal ingredient, has been found to promote skeletal muscle injury repair and regeneration. The Wnt5a pathway is related to the expression of myogenic regulatory factors, and Ca2+ promotes the differentiation and fusion process of myoblasts. This study explored the effect and mechanism of curcumin on myoblast differentiation during the repair and regeneration of injured skeletal muscle and its relationship with the Wnt5a pathway and Ca2+ channel.

METHODS

Myogenic differentiation of C2C12 cells was induced with 2% horse serum, and a mouse (male, 10 weeks old) model of acute skeletal muscle injury was established using cardiotoxin (20 μL). In addition, we constructed a Wnt5a knockdown C2C12 cell model and a Wnt5a knockout mouse model. Besides, curcumin was added to the cell culture solution (80 mg/L) and fed to the mice (50 mg/kg). Fluorescence microscopy was used to determine the concentration of Ca2+. Western blot and RT-qPCR were used to detect the protein and mRNA levels of Wnt5a, CaN, NFAT2, MyoD, Myf5, Pax7, and Myogenin. The expression levels of MyoD, Myf5, Myogenin, MHC, Desmin, and NFAT2 were detected using immunofluorescence techniques. In addition, MyoD expression was observed using immunohistochemistry, and morphological changes in mouse muscle tissue were observed using HE staining.

RESULTS

During myoblast differentiation and muscle regeneration, Wnt5a expression was upregulated (P < 0.001) and the Wnt5a signalling pathway was activated. Wnt5a overexpression promoted the expression of MyoD, Myf5, Myogenin, MHC, and Desmin (P < 0.05), and conversely, knockdown of Wnt5a inhibited their expression (P < 0.001). The Wnt5a pathway mediated the opening of Ca2+ channels, regulated the expression levels of CaN, NFAT2, MyoD, Myf5, Myogenin, MHC, and Desmin (P < 0.01) and promoted the differentiation of C2C12 myoblasts and the repair and regeneration of injured skeletal muscle. The expression of Wnt5a, CaN, NFAT2, MyoD, Myogenin, Myf5, and MHC in C2C12 myoblast was significantly increased after curcumin intervention (P < 0.05); however, their expression decreased significantly after knocking down Wnt5a on the basis of curcumin intervention (P < 0.05). Similarly, in Wnt5a knockout mice, the promotion of muscle regeneration by curcumin was significantly attenuated.

CONCLUSIONS

Curcumin can activate the Wnt5a signalling pathway and mediate the opening of Ca2+ channels to accelerate the myogenic differentiation of C2C12 cells and the repair and regeneration of injured skeletal muscle.

Mimicking TGFBI Hot-Spot Mutation Did Not Result in Any Deposit Formation in the Zebrafish Cornea

PURPOSE

Mutations in transforming growth factor beta-induced (TGFBI) protein are associated with a group of corneal dystrophies (CDs), classified as TGFBI-associated CDs, characterized by deposits in the cornea. Mouse models were not proper in several aspects for modelling human disease. The goal of this study was to generate zebrafish mutants to investigate the corneal phenotype and to decide whether zebrafish could be a potential model for TGFBI-associated CDs.

METHODS

The conserved arginine residue, codon 117, in zebrafish tgfbi gene was targeted with Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 method. Cas9 VQR variant was used with two target-specific sgRNAs to generate mutations. The presence of mutations was evaluated by T7 Endonuclease Enzyme (T7EI) assay and the type of the mutations were evaluated by Sanger sequencing. The mutant zebrafish at 3 months and 1 year of age were investigated under the microscope for corneal opacity and eye sections were evaluated histopathologically with hematoxylin-eosin, masson-trichrome and congo red stains for corneal deposits.

RESULTS

We achieved indel variation at the target sequence that resulted in p.Ser115_Arg117delinsLeu (c. 347_353delinsT) by nonhomology mediated repair in F1. This zebrafish mutation had the potential to mimic two disease-causing mutations reported in human cases previously: R124L and R124L + del125-126. Mutant zebrafish did not show any corneal opacity or corneal deposits at 3 months and 1 year of age.

CONCLUSION

This study generated the first zebrafish model mimicking the R124 hot spot mutation in TGFBI-associated CDs. However, evaluations even at 1 year of age did not reveal any deposits in the cornea histopathologically. This study increased the cautions for modelling TGFBI-associated CDs in zebrafish in addition to differences in the corneal structure between zebrafish and humans.

fhl2b mediates extraocular muscle protection in zebrafish models of muscular dystrophies and its ectopic expression ameliorates affected body muscles

In muscular dystrophies, muscle fibers loose integrity and die, causing significant suffering and premature death. Strikingly, the extraocular muscles (EOMs) are spared, functioning well despite the disease progression. Although EOMs have been shown to differ from body musculature, the mechanisms underlying this inherent resistance to muscle dystrophies remain unknown. Here, we demonstrate important differences in gene expression as a response to muscle dystrophies between the EOMs and trunk muscles in zebrafish via transcriptomic profiling. We show that the LIM-protein Fhl2 is increased in response to the knockout of desmin, plectin and obscurin, cytoskeletal proteins whose knockout causes different muscle dystrophies, and contributes to disease protection of the EOMs. Moreover, we show that ectopic expression of fhl2b can partially rescue the muscle phenotype in the zebrafish Duchenne muscular dystrophy model sapje, significantly improving their survival. Therefore, Fhl2 is a protective agent and a candidate target gene for therapy of muscular dystrophies.

Combined Effects of Polystyrene Nanosphere and Homosolate Exposures on Estrogenic End Points in MCF-7 Cells and Zebrafish

BACKGROUND

Micro- and nanoplastics (MNPs) and homosalate (HMS) are ubiquitous emerging environmental contaminants detected in human samples. Despite the well-established endocrine-disrupting effects (EDEs) of HMS, the interaction between MNPs and HMS and its impact on HMS-induced EDEs remain unclear.

OBJECTIVES

This study aimed to investigate the influence of MNPs on HMS-induced estrogenic effects and elucidate the underlying mechanisms in vitro and in vivo.

METHODS

We assessed the impact of polystyrene nanospheres (PNSs; 50  nm , 1.0 mg / L ) on HMS-induced MCF-7 cell proliferation (HMS: 0.01 - 1 μ M , equivalent to 2.62 - 262 μ g / L ) using the E-SCREEN assay and explored potential mechanisms through transcriptomics. Adult zebrafish were exposed to HMS (0.0262 - 262 μ g / L ) with or without PNSs (50  nm , 1.0 mg / L ) for 21 d. EDEs were evaluated through gonadal histopathology, fertility tests, steroid hormone synthesis, and gene expression changes in the hypothalamus-pituitary-gonad-liver (HPGL) axis.

RESULTS

Coexposure of HMS and PNSs resulted in higher expression of estrogen receptor α (ESR1) and the mRNAs of target genes (pS2, AREG, and PGR), a greater estrogen-responsive element transactivation activity, and synergistic stimulation on MCF-7 cell proliferation. Knockdown of serum and glucocorticoid-regulated kinase 1 (SGK1) rescued the MCF-7 cell proliferation induced by PNSs alone or in combination with HMS. In zebrafish, coexposure showed higher expression of SGK1 and promoted ovary development but inhibited spermatogenesis. In addition, coexposure led to lower egg hatchability, higher embryonic mortality, and greater larval malformation. Coexposure also modulated steroid hormone synthesis genes (cyp17a2, hsd17[Formula: see text]1, esr2b, vtg1, and vtg2), and resulted in higher 17 β -estradiol (E 2 ) release in females. Conversely, males showed lower testosterone, E 2 , and gene expressions of cyp11a1, cyp11a2, cyp17a1, cyp17a2, and hsd17[Formula: see text]1.

DISCUSSION

PNS exposure exacerbated HMS-induced estrogenic effects via SGK1 up-regulation in MCF-7 cells and disrupting the HPGL axis in zebrafish, with gender-specific patterns. This offers new mechanistic insights and health implications of MNP and contaminant coexposure. https://doi.org/10.1289/EHP13696.

Single-cell analysis of shared signatures and transcriptional diversity during zebrafish development

During development, animals generate distinct cell populations with specific identities, functions, and morphologies. We mapped transcriptionally distinct populations across 489,686 cells from 62 stages during wild-type zebrafish embryogenesis and early larval development (3-120 h post-fertilization). Using these data, we identified the limited catalog of gene expression programs reused across multiple tissues and their cell-type-specific adaptations. We also determined the duration each transcriptional state is present during development and identify unexpected long-term cycling populations. Focused clustering and transcriptional trajectory analyses of non-skeletal muscle and endoderm identified transcriptional profiles and candidate transcriptional regulators of understudied cell types and subpopulations, including the pneumatic duct, individual intestinal smooth muscle layers, spatially distinct pericyte subpopulations, and recently discovered best4+ cells. To enable additional discoveries, we make this comprehensive transcriptional atlas of early zebrafish development available through our website, Daniocell.

Transcriptomic landscape of Atlantic salmon (Salmo salar L.) skin

In this study, we present the first spatial transcriptomic atlas of Atlantic salmon skin using the Visium Spatial Gene Expression protocol. We utilized frozen skin tissue from 4 distinct sites, namely the operculum, pectoral and caudal fins, and scaly skin at the flank of the fish close to the lateral line, obtained from 2 Atlantic salmon (150 g). High-quality frozen tissue sections were obtained by embedding tissue in optimal cutting temperature media prior to freezing and sectioning. Further, we generated libraries and spatial transcriptomic maps, achieving a minimum of 80 million reads per sample with mapping efficiencies ranging from 79.3 to 89.4%. Our analysis revealed the detection of over 80,000 transcripts and nearly 30,000 genes in each sample. Among the tissue types observed in the skin, the epithelial tissues exhibited the highest number of transcripts (unique molecular identifier counts), followed by muscle tissue, loose and fibrous connective tissue, and bone. Notably, the widest nodes in the transcriptome network were shared among the epithelial clusters, while dermal tissues showed less consistency, which is likely attributable to the presence of multiple cell types at different body locations. Additionally, we identified collagen type 1 as the most prominent gene family in the skin, while keratins were found to be abundant in the epithelial tissue. Furthermore, we successfully identified gene markers specific to epithelial tissue, bone, and mesenchyme. To validate their expression patterns, we conducted a meta-analysis of the microarray database, which confirmed high expression levels of these markers in mucosal organs, skin, gills, and the olfactory rosette.

Tryptanthrin inhibits tumor angiogenesis via Notch/Dll4 signaling pathway in zebrafish

Background

Anti-angiogenic pathways are important for inhibiting tumor growth and migration. Tryptanthrin has anticancer properties in vivo but its anti-angiogenesis activities and associated mechanisms remain unclear.

Methods

The effects of tryptanthrin were investigated in vivo using fluorescent labeling of blood vessels in zebrafish. Fluorescence quantitation was conducted to analyze the level of delta-like ligand 4 (Dll4) gene expression. Transcriptome sequencing and quantitative polymerase chain reaction (qPCR) analyses were performed to explore the molecular mechanisms of anti-tumor angiogenesis.

Results

Significant anti-tumor effects were observed in all 48-hpf (hours post-fertilization) zebrafish treated with tryptanthrin (P<0.05). The 6-hpf zebrafish were cultured to 48 and 72 hpf following tryptanthrin treatment. It was found that compared with the control groups, the fluorescence area and the number of complete internode vessels reduced significantly following treatment with medium and high concentrations of tryptanthrin (P<0.05). The relative expression of Dll4 in the 48-hpf zebrafish was significantly inhibited only in the high concentration group (P<0.05). qPCR analysis revealed that the levels of Krt18b, desma, Tnnt2c, and Krt4 gene expression were significantly up-regulated in zebrafish following Dll4 overexpression. After Dll4 knockdown, the level of desma and Tnnt2c gene expression was significantly up-regulated.

Conclusions

Tryptanthrin can inhibit tumor growth in vivo in a concentration-dependent manner by down-regulating Dll4 protein expression, and at the same time up-regulating the level of desma and Tnnt2c gene expression.

Modeling Human Muscular Dystrophies in Zebrafish: Mutant Lines, Transgenic Fluorescent Biosensors, and Phenotyping Assays

Muscular dystrophies (MDs) are a heterogeneous group of myopathies characterized by progressive muscle weakness leading to death from heart or respiratory failure. MDs are caused by mutations in genes involved in both the development and organization of muscle fibers. Several animal models harboring mutations in MD-associated genes have been developed so far. Together with rodents, the zebrafish is one of the most popular animal models used to reproduce MDs because of the high level of sequence homology with the human genome and its genetic manipulability. This review describes the most important zebrafish mutant models of MD and the most advanced tools used to generate and characterize all these valuable transgenic lines. Zebrafish models of MDs have been generated by introducing mutations to muscle-specific genes with different genetic techniques, such as (i) N-ethyl-N-nitrosourea (ENU) treatment, (ii) the injection of specific morpholino, (iii) tol2-based transgenesis, (iv) TALEN, (v) and CRISPR/Cas9 technology. All these models are extensively used either to study muscle development and function or understand the pathogenetic mechanisms of MDs. Several tools have also been developed to characterize these zebrafish models by checking (i) motor behavior, (ii) muscle fiber structure, (iii) oxidative stress, and (iv) mitochondrial function and dynamics. Further, living biosensor models, based on the expression of fluorescent reporter proteins under the control of muscle-specific promoters or responsive elements, have been revealed to be powerful tools to follow molecular dynamics at the level of a single muscle fiber. Thus, zebrafish models of MDs can also be a powerful tool to search for new drugs or gene therapies able to block or slow down disease progression.

Single-cell analysis of shared signatures and transcriptional diversity during zebrafish development

During development, animals generate distinct cell populations with specific identities, functions, and morphologies. We mapped transcriptionally distinct populations across 489,686 cells from 62 stages during wild-type zebrafish embryogenesis and early larval development (3-120 hours post-fertilization). Using these data, we identified the limited catalog of gene expression programs reused across multiple tissues and their cell-type-specific adaptations. We also determined the duration each transcriptional state is present during development and suggest new long-term cycling populations. Focused analyses of non-skeletal muscle and the endoderm identified transcriptional profiles of understudied cell types and subpopulations, including the pneumatic duct, individual intestinal smooth muscle layers, spatially distinct pericyte subpopulations, and homologs of recently discovered human best4+ enterocytes. The transcriptional regulators of these populations remain unknown, so we reconstructed gene expression trajectories to suggest candidates. To enable additional discoveries, we make this comprehensive transcriptional atlas of early zebrafish development available through our website, Daniocell.

α-1,6-Fucosyltransferase Is Essential for Myogenesis in Zebrafish

Glycosylation is an important mechanism regulating various biological processes, including intercellular signaling and adhesion. α-1,6-fucosyltransferase (Fut8) belongs to a family of enzymes that determine the terminal structure of glycans. Fut8 is widely conserved from Caenorhabditis elegans to humans, and its mutants have been reported in humans, mice, and zebrafish. Although mutants show various symptoms, such as spinal deformity and growth retardation, its effects on skeletal muscles are unknown. We aimed to elucidate the function of Fut8 in skeletal muscle using zebrafish and C2C12 cells for evaluation. We observed that most fut8a morphants died at 2 days post-fertilization (dpf) or in earlier developmental stages even at low concentrations of morpholino oligonucleotides (MOs). Mutant juveniles also had small body sizes, and abnormal myocepta and sarcomere structures, suggesting that Fut8a plays important roles in myogenesis. Moreover, treatment of C2C12 cells with 2-fluorofucose (2FF), a fucosylation inhibitor, during cell differentiation dramatically reduced the expression of myogenic genes, such as Myomaker and other myogenic fusion genes, and inhibited myotube formation. These results indicate that Fut8 is an important factor in myogenesis, and myofusion in particular.

Characterization of a novel zebrafish model of SPEG-related centronuclear myopathy

Centronuclear myopathy (CNM) is a congenital neuromuscular disorder caused by pathogenic variation in genes associated with membrane trafficking and excitation–contraction coupling (ECC). Bi-allelic autosomal-recessive mutations in striated muscle enriched protein kinase (SPEG) account for a subset of CNM patients. Previous research has been limited by the perinatal lethality of constitutive Speg knockout mice. Thus, the precise biological role of SPEG in developing skeletal muscle remains unknown. To address this issue, we generated zebrafish spega, spegb and spega;spegb (speg-DKO) mutant lines. We demonstrated that speg-DKO zebrafish faithfully recapitulate multiple phenotypes associated with CNM, including disruption of the ECC machinery, dysregulation of calcium homeostasis during ECC and impairment of muscle performance. Taking advantage of zebrafish models of multiple CNM genetic subtypes, we compared novel and known disease markers in speg-DKO with mtm1-KO and DNM2-S619L transgenic zebrafish. We observed Desmin accumulation common to all CNM subtypes, and Dnm2 upregulation in muscle of both speg-DKO and mtm1-KO zebrafish. In all, we establish a new model of SPEG-related CNM, and identify abnormalities in this model suitable for defining disease pathomechanisms and evaluating potential therapies.

This article has an associated First Person interview with the joint first authors of the paper.

Summary: We created a novel zebrafish Speg mutant model of centronuclear myopathy that recapitulates key features of the human disorder and provides insight into pathomechanisms of the disease.

Toxicogenomic profiling after sublethal exposure to nerve- and muscle-targeting insecticides reveals cardiac and neuronal developmental effects in zebrafish embryos

For specific primary modes of action (MoA) in environmental non-target organisms, EU legislation restricts the usage of active substances of pesticides or biocides. Corresponding regulatory hazard assessments are costly, time consuming and require large numbers of non-human animal studies. Currently, predictive toxicology of development compounds relies on their chemical structure and provides little insights into toxicity mechanisms that precede adverse effects. Using the zebrafish embryo model, we characterized transcriptomic responses to a range of sublethal concentrations of six nerve- and muscle-targeting insecticides with different MoA (abamectin, carbaryl, chlorpyrifos, fipronil, imidacloprid & methoxychlor). Our aim was to identify affected biological processes and suitable biomarker candidates for MoA-specific signatures. Abamectin showed the most divergent signature among the tested insecticides, linked to lipid metabolic processes. Differentially expressed genes (DEGs) after imidacloprid exposure were primarily associated with immune system and inflammation. In total, 222 early responsive genes to either MoA were identified, many related to three major processes: (1) cardiac muscle cell development and functioning (tcap, desma, bag3, hspb1, hspb8, flnca, myoz3a, mybpc2b, actc2, tnnt2c), (2) oxygen transport and hypoxic stress (alas2, hbbe1.1, hbbe1.3, hbbe2, hbae3, igfbp1a, hif1al) and (3) neuronal development and plasticity (npas4a, egr1, btg2, ier2a, vgf). The thyroidal function related gene dio3b was upregulated by chlorpyrifos and downregulated by higher abamectin concentrations. Important regulatory genes for cardiac muscle (tcap) and forebrain development (npas4a) were the most frequently ifferentially expressed across all insecticide treatments. We consider the identified gene sets as useful early warning biomarker candidates, i.e. for developmental toxicity targeting heart and brain in aquatic vertebrates. Our findings provide a better understanding about early molecular events in response to the analyzed MoA. Perceptively, this promotes the development for sensitive and informative biomarker-based in vitro assays for toxicological MoA prediction and AOP refinement, without the suffering of adult fish.

What does desmin do: A bibliometric assessment of the functions of the muscle intermediate filament

Intermediate filaments were first described in muscle in 1968, and desmin was biochemically identified about 10 years afterwards. Its importance grew after the identification of desminopathies and desmin mutations that cause mostly cardiopathies. Since its characterization until recently, different functions have been attributed to desmin. Here, we use bibliometric tools to evaluate the articles published about desmin and to assess its several putative functions. We identified the most productive authors and the relationships between research groups. We studied the more frequent words among 9734 articles (September 2021) containing "desmin" on the title and abstract, to identify the major research focus. We generated an interactive spreadsheet with the 934 papers that contain "desmin" only on the title that can be used to search and quantify terms in the abstract. We further selected the articles that contained the terms "function" or "role" from the spreadsheet, which we then classified according to type of function, organelle, or tissue involved. Based on the bibliographic analysis, we assess comparatively the putative functions, and we propose an alternative explanation for the desmin function.

The EMT transcription factor Snai1 maintains myocardial wall integrity by repressing intermediate filament gene expression

The transcription factor Snai1, a well-known regulator of epithelial-to-mesenchymal transition, has been implicated in early cardiac morphogenesis as well as in cardiac valve formation. However, a role for Snai1 in regulating other aspects of cardiac morphogenesis has not been reported. Using genetic, transcriptomic, and chimeric analyses in zebrafish, we find that Snai1b is required in cardiomyocytes for myocardial wall integrity. Loss of snai1b increases the frequency of cardiomyocyte extrusion away from the cardiac lumen. Extruding cardiomyocytes exhibit increased actomyosin contractility basally as revealed by enrichment of p-myosin and α-catenin epitope α-18, as well as disrupted intercellular junctions. Transcriptomic analysis of wild-type and snai1b mutant hearts revealed the dysregulation of intermediate filament genes, including desmin b (desmb) upregulation. Cardiomyocyte-specific desmb overexpression caused increased cardiomyocyte extrusion, recapitulating the snai1b mutant phenotype. Altogether, these results indicate that Snai1 maintains the integrity of the myocardial epithelium, at least in part by repressing desmb expression.