Mature Muscle Cells Research Articles

Muscle regeneration in adiponectin knockout mice showed early activation of anti-inflammatory response with perturbations in myogenesis.

Activation, proliferation, and differentiation of satellite cells can be influenced by extracellular factors, such as adiponectin. This adipokine has been proposed as a regulator of in vitro myogenesis, but its action on in vivo regeneration is not still elucidated. We used C57BL/6 (wild-type [WT]) and adiponectin knockout (AdKO) mice injured with barium chloride at periods of 3, 7, and 14 days after injury. The AdKO presented a higher number of centralized nuclei after 7 days, and a reduction in myogenic genes was observed after 3 days. Moreover, these mice presented an increase in anti-inflammatory cytokines after 3 and 7 days, and an increase in the M2 gene marker and proinflammatory cytokines after 7 days. The WT demonstrated an increase in adiponectin messenger RNA after 7 days. These results demonstrate that adiponectin is important in tissue remodeling during regeneration and that its deficiency does not compromise the maturation of muscle fibers, due to an increase in anti-inflammatory response; however, there is a possible impairment in proinflammatory response and an increase in centralized myonuclei.

Expression and functional analysis of the hydrogen peroxide biosensors HyPer and HyPer2 in C2C12 myoblasts/myotubes and single skeletal muscle fibres

Hydrogen peroxide (H2O2) is generated in cells and plays an important role as a signalling molecule. It has been reported that H2O2 is involved in physiological and pathological processes in skeletal muscle. However, H2O2 detection in cells with traditional techniques produces frequent artefacts. Currently, the HyPer biosensor detects intracellular H2O2 specifically in real time using fluorescence microscopy. The aim of this study was to develop and optimize approaches used to express the HyPer biosensor in different models of skeletal muscle cells, such as the C2C12 myoblast/myotube cell line and mature skeletal muscle fibres isolated from C57BL/6J mice, and to measure intracellular H2O2 in real time in these cells. The results show that the expression of the HyPer biosensor in skeletal muscle cells is possible. In addition, we demonstrate that HyPer is functional and that this biosensor detects changes and fluctuations in intracellular H2O2 in a reversible manner. The HyPer2 biosensor, which is a more advanced version of HyPer, presents improved properties in terms of sensitivity in detecting lower concentrations of H2O2 in skeletal muscle fibres. In conclusion, the expression of the HyPer biosensor in the different experimental models combined with fluorescence microscopy techniques is a powerful methodology to monitor and register intracellular H2O2 specifically in skeletal muscle. The innovation of the methodological approaches presented in this study may present new avenues for studying the role of H2O2 in skeletal muscle pathophysiology. Furthermore, the methodology may potentially be adapted to yield other specific biosensors for different reactive oxygen and nitrogen species or metabolites involved in cellular functions.

Production of Innervated Skeletal Muscle Fibers Using Human Induced Pluripotent Stem Cells.

Only a limited number of large-scale protocols describe the production of mature skeletal muscle fibers from human induced pluripotent stem cells (hiPSCs). Here we describe a novel procedure for simultaneous differentiation of hiPSC into muscle cells and motor neurons, that generates innervated and contractile multinucleated skeletal muscle fibers with sarcomeric organization. Our protocol permits the production of expandable skeletal muscle progenitor cells and mature skeletal muscle fibers that can be used for the exploration of skeletal muscle differentiation for basic research, disease modeling, and drug discovery.

Anti-diabetic effect of ethanol extract of Cyclolepis genistoides D. Don (Palo azul), made in Paraguay

Extract of Cyclolepis genistoides D. Don (vernacular name Palo azul; Palo) are traditionally consumed in the Republic of Paraguay in South America for the treatment of diabetes and kidney disease, and is sold in Japan as dietary supplement. This study aimed to elucidate the mechanism of anti-diabetes activity of Palo, especially focused on insulin resistance. Palo promoted adipocytes differentiation and regulated adipokine profiles in 3T3-L1 adipocytes by modulation of PPARγ, a major regulator of adipose differentiation. Human adipocyte showed almost similar profile with 3T3-L1 against Palo treatment. Furthermore, Palo treatment (250 or 1000 mg/kg) was performed with C57BL/6J mice for 14 weeks, being fed high-fat-diet (HFD60) simultaneously. Palo 250 mg/kg exhibited a tendency to decrease subcutaneous adipose volume along with increase of PPARγ and its target, adiponectin mRNA expression. In addition, as the other insulin targeted cell, effect on muscle differentiation was examined. Palo increased differentiation of C2C12 mouse muscle myoblasts by increase of IGF-1, myogenin, and myosine heavy chain (MHC) as well as 5'-AMP-activated protein kinase (AMPK) activation. Palo subsequently promoted myotube formation under differentiation condition. From the above, it was clarified that Palo acts variously on the differentiation and maturation of both adipocytes and muscle cells, and from the viewpoint of the regulatory mechanism for adipocytes, PPARγ-inducing action was shown to be a mechanism that acts across species.

Muscle tissue engineering in fibrous gelatin: implications for meat analogs

Bioprocessing applications that derive meat products from animal cell cultures require food-safe culture substrates that support volumetric expansion and maturation of adherent muscle cells. Here we demonstrate scalable production of microfibrous gelatin that supports cultured adherent muscle cells derived from cow and rabbit. As gelatin is a natural component of meat, resulting from collagen denaturation during processing and cooking, our extruded gelatin microfibers recapitulated structural and biochemical features of natural muscle tissues. Using immersion rotary jet spinning, a dry-jet wet-spinning process, we produced gelatin fibers at high rates (~ 100 g/h, dry weight) and, depending on process conditions, we tuned fiber diameters between ~ 1.3 ± 0.1 μm (mean ± SEM) and 8.7 ± 1.4 μm (mean ± SEM), which are comparable to natural collagen fibers. To inhibit fiber degradation during cell culture, we crosslinked them either chemically or by co-spinning gelatin with a microbial crosslinking enzyme. To produce meat analogs, we cultured bovine aortic smooth muscle cells and rabbit skeletal muscle myoblasts in gelatin fiber scaffolds, then used immunohistochemical staining to verify that both cell types attached to gelatin fibers and proliferated in scaffold volumes. Short-length gelatin fibers promoted cell aggregation, whereas long fibers promoted aligned muscle tissue formation. Histology, scanning electron microscopy, and mechanical testing demonstrated that cultured muscle lacked the mature contractile architecture observed in natural muscle but recapitulated some of the structural and mechanical features measured in meat products.

Effect of Hierarchical Scaffold Consisting of Aligned dECM Nanofibers and Poly(lactide-co-glycolide) Struts on the Orientation and Maturation of Human Muscle Progenitor Cells.

Extracellular matrices (ECMs) derived from tissues and decellularized are widely used as biomaterials in tissue engineering applications because they encompass tissue-specific biological and physical cues. In this study, we utilized a solubilized decellularized tissue (dECM) obtained from skeletal muscle to fabricate a nanofibrous structure using the electrospinning technique. The dECM was chemically modified by methacrylate reaction (dECM-MA) to improve the structural stability before electrospinning. The electrospun dECM-MA nanofibers were combined with microscale fibrillated poly(lactide-co-glycolide) (PLGA) constructs fabricated by three-dimensional printing and fibrillation/leaching of poly(vinyl alcohol) to promote skeletal muscle cell orientation and maturation. Using the electrostatic force-assisted fiber-alignment method, a multiscale composite scaffold consisting of fibrillated PLGA and aligned dECM-MA nanofibers was fabricated. The multiscale dECM-MA/PLGA composite scaffold significantly promoted the cellular orientation and myotube formation of human muscle progenitor cells compared to control scaffolds. The results suggested the potential use of the multiscale dECM-MA/PLGA composite scaffold, which contains the biochemical and topographical cues, for bioengineering a skeletal muscle tissue construct.

Interactions among ryanodine receptor isotypes contribute to muscle fiber type development and function.

ABSTRACTMutations affecting ryanodine receptor (RyR) calcium release channels commonly underlie congenital myopathies. Although these channels are known principally for their essential roles in muscle contractility, mutations in the human RYR1 gene result in a broad spectrum of phenotypes, including muscle weakness, altered proportions of fiber types, anomalous muscle fibers with cores or centrally placed nuclei, and dysmorphic craniofacial features. Currently, it is unknown which phenotypes directly reflect requirements for RyRs and which result secondarily to aberrant muscle function. To identify biological processes requiring RyR function, skeletal muscle development was analyzed in zebrafish embryos harboring protein-null mutations. RyR channels contribute to both muscle fiber development and function. Loss of some RyRs had modest effects, altering muscle fiber-type specification in the embryo without compromising viability. In addition, each RyR-encoding gene contributed to normal swimming behavior and muscle function. The RyR channels do not function in a simple additive manner. For example, although isoform RyR1a is sufficient for muscle contraction in the absence of RyR1b, RyR1a normally attenuates the activity of the co-expressed RyR1b channel in slow muscle. RyR3 also acts to modify the functions of other RyR channels. Furthermore, diminished RyR-dependent contractility affects both muscle fiber maturation and craniofacial development. These findings help to explain some of the heterogeneity of phenotypes that accompany RyR1 mutations in humans.

Preparation and in vivo evaluation of surface heparinized small diameter tissue engineered vascular scaffolds of poly(ε-caprolactone) embedded with collagen suture.

Herein biodegradable poly(ε-caprolactone) was electrospun into tubular microfibrous scaffolds and modified by the surface heparinization and wrapping of Type I collagen suture for enhancing anticoagulation activity and mechanical properties. The resulting scaffolds were featured by a double distribution of microfiber diameters ranged in 2.74 ± 0.44 and 5.15 ± 0.63 µm on the outer surface with tensile strength of 1.36 ± 0.37 MPa and Young’s modulus of 8.31 ± 1.87 MPa. The burst pressure after embedded with collagen suture was increased to 2419 ± 121 mmHg, remarkably higher than that of the poly(ε-caprolactone)-only scaffolds (1500 ± 136 mmHg) and native vessels. The scaffolds were evaluated in six rabbits for 20 weeks via a carotid artery interpositional model demonstrating a good patency. The effective cell infiltration, and rapid endothelialization and smooth muscle cell maturation were observed. There was no calcification in 20 weeks, and only one developed the aneurysm dilation after 16 weeks. It suggested that the surface heparinization is beneficial to improve the hydrophilicity and anticoagulation property of scaffolds, and embedment of collagen suture is useful to reinforce the mechanical properties and burst pressure.

Skeletal muscle cell transplantation: models and methods.

Xenografts of skeletal muscle are used to study muscle repair and regeneration, mechanisms of muscular dystrophies, and potential cell therapies for musculoskeletal disorders. Typically, xenografting involves using an immunodeficient host that is pre-injured to create a niche for human cell engraftment. Cell type and method of delivery to muscle depend on the specific application, but can include myoblasts, satellite cells, induced pluripotent stem cells, mesangioblasts, immortalized muscle precursor cells, and other multipotent cell lines delivered locally or systemically. Some studies follow cell engraftment with interventions to enhance cell proliferation, migration, and differentiation into mature muscle fibers. Recently, several advances in xenografting human-derived muscle cells have been applied to study and treat Duchenne muscular dystrophy and Facioscapulohumeral muscular dystrophy. Here, we review the vast array of techniques available to aid researchers in designing future experiments aimed at creating robust muscle xenografts in rodent hosts.

Muscle xenografts reproduce key molecular features of facioscapulohumeral muscular dystrophy

Aberrant expression of DUX4, a gene unique to humans and primates, causes Facioscapulohumeral Muscular Dystrophy-1 (FSHD), yet the pathogenic mechanism is unknown. As transgenic overexpression models have largely failed to replicate the genetic changes seen in FSHD, many studies of endogenously expressed DUX4 have been limited to patient biopsies and myogenic cell cultures, which never fully differentiate into mature muscle fibers. We have developed a method to xenograft immortalized human muscle precursor cells from patients with FSHD and first-degree relative controls into the tibialis anterior muscle compartment of immunodeficient mice, generating human muscle xenografts. We report that FSHD cells mature into organized and innervated human muscle fibers with minimal contamination of murine myonuclei. They also reconstitute the satellite cell niche within the xenografts. FSHD xenografts express DUX4 and DUX4 downstream targets, retain the 4q35 epigenetic signature of their original donors, and express a novel protein biomarker of FSHD, SLC34A2. Ours is the first scalable, mature in vivo human model of FSHD. It should be useful for studies of the pathogenic mechanism of the disease as well as for testing therapeutic strategies targeting DUX4 expression.

A 3D culture model of innervated human skeletal muscle enables studies of the adult neuromuscular junction.

Two-dimensional (2D) human skeletal muscle fiber cultures are ill-equipped to support the contractile properties of maturing muscle fibers. This limits their application to the study of adult human neuromuscular junction (NMJ) development, a process requiring maturation of muscle fibers in the presence of motor neuron endplates. Here we describe a three-dimensional (3D) co-culture method whereby human muscle progenitors mixed with human pluripotent stem cell-derived motor neurons self-organize to form functional NMJ connections. Functional connectivity between motor neuron endplates and muscle fibers is confirmed with calcium imaging and electrophysiological recordings. Notably, we only observed epsilon acetylcholine receptor subunit protein upregulation and activity in 3D co-cultures. Further, 3D co-culture treatments with myasthenia gravis patient sera shows the ease of studying human disease with the system. Hence, this work offers a simple method to model and evaluate adult human NMJ de novo development or disease in culture.

A Human Pluripotent Stem Cell-Based Screen for Smooth Muscle Cell Differentiation and Maturation Identifies Inhibitors of Intimal Hyperplasia.

SummaryContractile to synthetic phenotypic switching of smooth muscle cells (SMCs) contributes to stenosis in vascular disease and vascular transplants. To generate more contractile SMCs, we performed a high-throughput differentiation screen using a MYH11-NLuc-tdTomato human embryonic stem cell reporter cell line. We identified RepSox as a factor that promotes differentiation of MYH11-positive cells by promoting NOTCH signaling. RepSox induces SMCs to exhibit a more contractile phenotype than SMCs generated using PDGF-BB and TGF-β1, two factors previously used for SMC differentiation but which also cause intimal hyperplasia. In addition, RepSox inhibited intimal hyperplasia caused by contractile to synthetic phenotypic switching of SMCs in a rat balloon injury model. Thus, in addition to providing more contractile SMCs that could prove useful for constructing artificial blood vessels, this study suggests a strategy for identifying drugs for inhibiting intimal hyperplasia that act by driving contractile differentiation rather than inhibiting proliferation non-specifically.

Regulation of SETD7 Methyltransferase by SENP3 Is Crucial for Sarcomere Organization and Cachexia

Precise assembly of the sarcomere, a force-generating unit in striated muscles, is critical for muscle contraction. Defective sarcomere organization is linked to myopathies and cachexia. The molecular mechanisms concerning sarcomere assembly are poorly understood. Here, we report that the SUMO-specific isopeptidase SENP3 determines sarcomere assembly by specifically regulating the sarcomeric contractile myosin heavy-chain gene MyHC-II. The contractile ability of mature muscle cells is severely compromised in SENP3-depleted cells. Mechanistically, SENP3 is associated with the SETD7 histone methyltransferase and deSUMOylates SETD7. By recruiting SETD7 to MyHC-II, SENP3 promotes association of SETD7 with transcriptionally active RNA polymerase II and precludes the opposing methyltransferase Suv39h1. Strikingly, SENP3 is degraded in cachexia, characterized by dramatic loss of sarcomeric protein, particularly MyHC-II. SENP3 regulation of SETD7 is impaired in cachexia, leading to perturbed MyHC-II expression and disorganized sarcomeres. Our findings reveal an unanticipated role of SENP3 in sarcomere assembly and cachexia.

Age-dependent variations in the expression of myosin isoforms and myogenic factors during the involution of the proximal sesamoidean ligament of sheep

In ungulates the stability of the fetlock joint is dependent on several muscles, which are exposed to high stress and strain. Among those muscles, the proximal sesamoidean ligament or PSL (also known as the suspensory ligament or Ruini's elasto-tendinous organ) is organized at birth in layers of muscle fibres alternated with abundant tendinous tissue that, during the postnatal development, becomes the predominant tissue.In this study we analysed the PSL of the sheep at the age of 1, 30 and 180 days and determined the expression of several genes which either (a) are markers of muscle fibre growth and maturation, or (b) play a role as signal molecules. We observed an accelerated maturation, as indicated by the transition of MyHC isoform expression towards the slow isoforms and a reduced regenerative potential indicated by the low Pax7 expression and the altered Wnt signalling. We also found a specific myogenic expression pattern of MyoD, Myf5 and Myogenin in the developing PSL and high mRNA levels of specific fibrogenic factors, as TGF-β1, that, undoubtedly, stimulate the growth of connective tissue. Our observations confirmed, at molecular level, the peculiarity of the fast involution observed in PSL a muscle that undergoes a very specific active differentiation process during early development, which implies myofibres involution and their replacement with connective tissue.

Cost‐effective synthesis of polyethylene glycol diacrylate‐acrylic acid (PEGDA‐AA), a tissue engineering hydrogel ideal for C2C12 mouse muscle cells

Current research in tissue engineering focuses on growing and functionalizing cells in vitro to assemble viable constructs that restore, maintain, or improve damaged tissues or whole organs. Specific to the field of tissue engineering, hydrogels have proven successful in the development of multiple cell types with the goal of one day serving as grafts that will replace large areas of lost or damaged tissue. This assembly depends on the presence of a scaffold, or three‐dimensional structure that guides the growth of new tissue, and hydrogel polymers in particular have been known to be an excellent building block for scaffold formation. This research focused on the synthesis and characterization of the hydrogel polyethylene glycol diacrylate‐acrylic acid (PEGDA‐AA), a hydrophilic material that provides a viable environment for cell maturation because of its favorable characteristics for the development and maturation of mouse C2C12 muscle cells. Using modified procedures adapted from Browe et al. (2016) to create a cost‐effective way of synthesizing this precursor, PEGDA was successfully synthesized and characterized through 13C and 1H‐NMR spectroscopy. Current research focuses on analyzing the effects of the hydrogel on the growth and development of C2C12 cells with the long‐term goal of establishing an efficient model for human tissue engineering.Support or Funding InformationHampden‐Sydney College Office of Undergraduate ResearchThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A critical role for the nuclear protein Akirin2 in the formation of mammalian muscle in vivo.

Evolutionarily conserved Akirin nuclear proteins interact with chromatin remodeling complexes at gene enhancers and promoters, and have been reported to regulate cell proliferation and differentiation. Of the two mouse Akirin genes, Akirin2 is essential during embryonic development, with known in vivo roles in immune system function and the formation of the cerebral cortex. Here we demonstrate that Akirin2 is critical for mouse myogenesis, a tightly regulated developmental process through which myoblast precursors fuse to form mature skeletal muscle fibers. Loss of Akirin2 in somitic muscle precursor cells via Sim1-Cre-mediated excision of a conditional Akirin2 allele results in neonatal lethality. Mutant embryos exhibit a complete lack of forelimb, intercostal, and diaphragm muscles due to extensive apoptosis and loss of Pax3-positive myoblasts. Severe skeletal defects, including craniofacial abnormalities, disrupted ossification, and rib fusions are also observed, attributable to lack of skeletal muscles as well as patchy Sim1-Cre activity in the embryonic sclerotome. We further show that Akirin2 levels are tightly regulated during muscle cell differentiation in vitro, and that Akirin2 is required for the proper expression of muscle differentiation factors myogenin and myosin heavy chain. Our results implicate Akirin2 as a major regulator of mammalian muscle formation in vivo.

R482L Mutation of the LMNA Gene Affects Dynamics of C2C12 Myogenic Differentiation and Stimulates Formation of Intramuscular Lipid Droplets.

Mutations in the LMNA gene resulting in the substitution of the highly conserved arginine 482 residue in the globular C-terminal domain of lamin A/C are associated with the Dunnigan-type familial partial lipodystrophy (FPLD2) often accompanied by impairments in the muscle tissue development. The mechanisms underlying these impairments remain unknown. The purpose of our work was to investigate the effects of the LMNA gene mutation R482L on the muscle differentiation and intramuscular fat accumulation using C2C12 mouse myoblasts transduced with the lentiviral constructs carrying the wild-type human LMNA gene (LMNA-WT) or the LMNA-R482L mutant gene. After stimulation of myogenesis and adipogenesis in the transduced cell, expression of muscle and adipose tissue differentiation markers, morphology of differentiated myotubes, and formation of intramuscular lipid droplets were analyzed. C2C12 cells carrying the LMNA-R482L construct exhibited upregulated desmin expression at all stages of muscle differentiation and transformed into hypertrophied myotubules (in comparison with C2C12 myoblasts transduced with LMNA-WT). Reduced expression levels of the myogenic transcription factor Myf6 in the cells with the LMNA-R482L mutant indicated delayed maturation of muscle fibers. These cells more actively accumulated fat in response to the stimulation of adipose differentiation than myoblasts modified with the wild-type LMNA; they also expressed the markers of lipid droplets, such as FABP4 (fatty acid-binding protein 4), ATGL (adipose triglyceride lipase), and PLIN2 (perilipin 2). Therefore, the R482L mutation of the LMNA gene affects the dynamics of C2C12 myoblast differentiation into myotubules and stimulates formation of fat deposits in the myoblasts and myotubules in a tissue-specific manner.

Reduced Myogenic and Increased Adipogenic Differentiation Capacity of Rotator Cuff Muscle Stem Cells.

Fat accumulation commonly occurs in chronically torn rotator cuff muscles, and increased fat within the rotator cuff is correlated with poor clinical outcomes. The extent of lipid deposition is particularly pronounced in injured rotator cuff muscles compared with other commonly injured muscles such as the gastrocnemius. Satellite cells, which are a tissue-resident muscle stem-cell population, can differentiate into fat cells. We hypothesized that satellite cells from the rotator cuff have greater intrinsic adipogenic differentiation potential than do gastrocnemius satellite cells, and this difference is due to variations in epigenetic imprinting between the cells. Satellite cells from gastrocnemius and rotator cuff muscles of mice were cultured in adipogenic media, and the capacity to differentiate into mature muscle cells and adipogenic cells was assessed (n ≥ 9 plates per muscle group). We also performed DNA methylation analysis of gastrocnemius and rotator cuff satellite cells to determine whether epigenetic differences were present between the 2 groups (n = 5 mice per group). Compared with the gastrocnemius, satellite cells from the rotator cuff had a 23% reduction in myogenic differentiation and an 87% decrease in the expression of the differentiated muscle cell marker MRF4 (myogenic regulatory factor 4). With respect to adipogenesis, rotator cuff satellite cells had a 4.3-fold increase in adipogenesis, a 12-fold increase in the adipogenic transcription factor PPARγ (peroxisome proliferator-activated receptor gamma), and a 65-fold increase in the adipogenic marker FABP4 (fatty-acid binding protein 4). Epigenetic analysis identified 355 differentially methylated regions of DNA between rotator cuff and gastrocnemius satellite cells, and pathway enrichment analysis suggested that these regions were involved with lipid metabolism and adipogenesis. Satellite cells from rotator cuff muscles have reduced myogenic and increased adipogenic differentiation potential compared with gastrocnemius muscles. There appears to be a cellular and genetic basis behind the generally poor rates of rotator cuff muscle healing. The reduced myogenic and increased adipogenic capacity of rotator cuff satellite cells is consistent with the increased fat content and poor muscle healing rates often observed for chronically torn rotator cuff muscles. For patients undergoing rotator cuff repair, transplantation of autologous satellite cells from other muscles less prone to fatty infiltration may improve clinical outcomes.

Loss of the neurodevelopmental Joubert syndrome causing protein, Ahi1, causes motor and muscle development delays independent of central nervous system involvement

Joubert syndrome (JBTS) is a predominantly autosomal recessive neurodevelopmental disorder that presents with characteristic malformations of the cerebellar vermis, superior cerebellar peduncles and midbrain in humans. Accompanying these malformations are a heterogeneous set of clinical symptoms, which frequently include deficits in motor and muscle function, such as hypotonia (low muscle tone) and ataxia (clumsiness). These symptoms are attributed to improper development of the hindbrain, but no direct evidence has been reported linking these in JBTS. Here, we describe muscle developmental defects in a mouse with a targeted deletion of the Abelson helper integration site 1 gene, Ahi1, one of the genes known to cause JBTS in humans. While FVB/NJ Ahi1-/- mice display no gross malformations of the cerebellum, deficits are observed in several measures of motor function, strength, and body development. Specifically, Ahi1-/- mice show delayed physical development, delays in surface reflex righting as neonates, and reductions in grip strength and spontaneous locomotor activity as adults. Additionally, Ahi1-/- mice showed evidence of muscle-specific contributions to this phenotype, such as reductions in 1) myoblast differentiation potential in vitro, 2) muscle desmin expression, and 3) overall muscle mass, myonuclear domain, and muscle fiber cross-sectional area. Together, these data suggest that loss of Ahi1 may cause abnormalities in the differentiation of myoblasts to mature muscle cells. Moreover, Ahi1 loss impacts muscle development directly, outside of any indirect impact of cerebellar malformations, revealing a novel myogenic cause for hypotonia in JBTS.

Membrane Curvature and Tension Control the Formation and Collapse of Caveolar Superstructures

Caveolae, flask-shaped pits covered by caveolin-cavin coats, are abundant features of the plasma membrane of many cells. Besides appearing as single-membrane indentations, caveolae are organized as superstructures in the form of rosette-like clusters, whose mechanism of assembly and biological functions have been elusive. Here, we propose that clustering of caveolae in mature muscle cells is driven by forces originating from the elastic energy of membrane-bending deformations and membrane tension. We substantiate this mechanism by computational modeling, which recovers the unique shapes observed for the most ubiquitous caveolar clusters. We support the agreement between the calculated and observed configurations by electron tomography of caveolar clusters. The model predicts the experimentally assessable dependence of caveolar clustering on membrane tension and on the degree of the caveolar coat assembly. We reveal a difference in conformation and, possibly, in function and formation mechanism between caveolar clusters of muscle cells and of adipocytes.