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PubMed2005

A novel role for lbx1 in Xenopus hypaxial myogenesis.

We have examined lbx1 expression in early X. laevis tadpoles. In contrast to amniotes, lbx1 is expressed in all of the myoblasts that contribute to the body wall musculature, as well as in a group of cells that migrate into the head. Despite this different expression, the function of lbx1 appears to be conserved. Morpholino (MO) knockdown of lbx1 causes a specific reduction of body wall muscles and hypoglossal muscles originating from the somites. Although myoblast migratory defects are observed in antisense MO injected tadpoles targeting lbx1, this results at least in part from a lack of myoblast proliferation in the hypaxial muscle domain. Conversely, overexpression of lbx1 mRNA results in enlarged somites, an increase in cell proliferation, but a lack of differentiated muscle. The control of cell proliferation is linked to a strong downregulation of myoD expression in gain-of-function experiments. Co-injection of myoD mRNA with lbx1 mRNA eliminates the overproliferation phenotype observed when lbx1 is injected alone. The results indicate that a primary function of lbx1 in hypaxial muscle development is to repress myoD, allowing myoblasts to proliferate before the eventual onset of terminal differentiation.

Animals↗
PubMed1992

Development of the muscle spindles in the human fetal oblique muscles of the eyeball.

The development of muscle spindles in human oblique eye muscles was investigated in 22 fetuses aged 12 to 24 weeks. The muscle spindles appear at 12th week as 1-2 intrafusal fibers surrounded by capsule. With advancement of the development the number of intrafusal myofibers increases. In 14th week the capsule is composed of 2 layers and in 17th week the external capsule appears.

Embryonic and Fetal Development↗
PubMed1968

Mitosis and intermediate-sized filaments in developing skeletal muscle.

A new class of filaments intermediate in diameter between actin and myosin filaments has been demonstrated in skeletal muscle cells cultured from chick embryos. These filaments, which account for the majority of free filaments, average 100 A in diameter. They may run for more than 2 micro in a single section and can be distinguished in size and appearance from the thick and thin filaments assembled into myofibrils. The 100-A filaments are seen scattered throughout the sarcoplasm at all stages of development and show no obvious association with the myofibrils. The 100-A filaments are particularly conspicuous in myotubes fragmented by the mitotic inhibitors, colchicine and Colcemid. In addition, filaments similar in size and appearance to those found in myotubes are present in fibroblasts, chondrocytes, and proliferating mononucleated myoblasts. The 100-A filaments are present in cells arrested in metaphase by mitotic inhibitors. Definitive thick (about 150 A) or thin (about 60 A) myofilaments are not found in skeletal myogenic cells arrested in metaphase. Myogenic cells arrested in metaphase do not bind fluorescein-labeled antibody directed against myosin or actin. For these reasons, it is concluded that not all "thin" filaments in myogenic cells are uniquely associated with myogenesis.

Animals↗
PubMed1995

Regulation of vertebrate muscle differentiation by thyroid hormone: the role of the myoD gene family.

Skeletal myoblasts have their origin early in embryogenesis within specific somites. Determined myoblasts are committed to a myogenic fate; however, they only differentiate and express a muscle-specific phenotype after they have received the appropriate environmental signals. Once proliferating myoblasts enter the differentiation programme they withdraw from the cell cycle and form post-mitotic multinucleated myofibres (myogenesis); this transformation is accompanied by muscle-specific gene expression. Muscle development is associated with complex and diverse protein isoform transitions, generated by differential gene expression and mRNA splicing. The myofibres are in a state of dynamic adaptation in response to hormones, mechanical activity and motor innervation, which modulate differential gene expression and splicing during this functional acclimatisation. This review will focus on the profound effects of thyroid hormone on skeletal muscle, which produce alterations in gene and isoform expression, biochemical properties and morphological features that precipitate in modified contractile/mechanical characteristics. Insight into the molecular events that control these events was provided by the recent characterisation of the MyoD gene family, which encodes helix-loop-helix proteins; these activate muscle-specific transcription and serve as targets for a variety of physiological stimuli. The current hypothesis on hormonal regulation of myogenesis is that thyroid hormones (1) directly regulate the myoD and contractile protein gene families, and (2) induce thyroid hormone receptor-transcription factor interactions critical to gene expression.

Animals↗
PubMed1993

The epsilon subunit confers fast channel gating on multiple classes of acetylcholine receptors.

During vertebrate skeletal muscle development, multiple forms of long-open-time (slow-type) ACh receptor channels are replaced by at least two different types of short-open-time (fast-type) ACh receptors. Expression of ACh receptors in Xenopus oocytes indicates that the substitution of an epsilon subunit for a gamma subunit may account for both types of fast-gated channel types in adult muscle. Unlike the various forms of the embryonic receptor, in which functional diversity is achieved through alterations in subunit composition, the two major fast-gated forms expressed in oocytes have identical subunit composition. These findings provide a structural basis for both types of short-open-time ACh receptor types found in adult muscle.

Animals↗
PubMed1994

Expression of myosin heavy chain isoforms in developing human muscle spindles.

We studied serial sections of human fetal limb muscles (10-25 weeks of gestation) by light microscopic (LM) immunocytochemistry, using specific antibodies against slow-tonic, slow-twitch, fetal, embryonic, and alpha-cardiac myosin heavy chain (MHC) isoforms, neurofilament protein, laminin, and myomesin. One set of the first-generation myotubes expressed slow-tonic MHCs, and slow-twitch, fetal, and embryonic MHCs from the tenth week of gestation. These primary myotubes were identified as developing nuclear bag fibers. Second-generation myotubes in close apposition to the primary nuclear bag myotubes initially expressed only fetal and embryonic MHCs. One or more of these secondary myotubes acquired expression of slow-tonic and slow-twitch MHCs and gave rise to nuclear bag fibers. Most of the nuclear bag precursors expressed alpha-cardiac MHC. The secondary myotubes that expressed fetal and embryonic MHC but not slow-tonic, slow-twitch, or alpha-cardiac MHCs gave rise to the nuclear chain fibers. This study shows that different populations of fiber precursors, each with a unique sequence of MHC expression, gave rise to the nuclear bag and chain fibers, despite the presence of a common afferent nerve, from the early stages.

Connectin↗
PubMed2002

Muscle power development in preterm infants with periventricular flaring or leukomalacia in relation to outcome at 18 months.

Periventricular flaring (PVF) or periventricular leukomalacia (PVL) was diagnosed by brain ultrasound during the neonatal period in 44 infants (34 males, 10 females; mean gestational age 31 weeks 2 days, SD 2 weeks 1 day) admitted between 1995 and 1997. The infants were divided into three groups according to the severity of their condition. At 0, 3, and 6 months' corrected age an age-adequate neurological examination with special emphasis on the relation between active and passive muscle power was performed and symmetry between right and left sides was assessed. Results for the whole body, as well as for the shoulders, trunk, and legs were classified as optimal, suspect, or abnormal. Motor outcome at 18 months' corrected age was graded in the same way. An overall optimal muscle power regulation was found in one infant at 0, two at 3, and one at 6 months. Suspect outcome was found at all ages in the three groups. At 0 months muscle power regulation did not differ between the three groups. At 3 and 6 months overall poor muscle power, primarily caused by poor muscle power regulation in the shoulders and trunk, was found in infants with PVL grades III or IV. At 18 months' corrected age 24 infants showed no neurological impairment, eight infants had minor impairment, and 12 infants had severe impairment, including all 10 infants categorized as having PVL grades II or IV. The best predictors of impairment at 18 months were the combined results of muscle power in the shoulders and trunk at 3 months with those of the shoulders at 6 months.

Echoencephalography↗
PubMed1993

Function of skeletal muscle myosin heavy and light chain isoforms by an in vitro motility assay.

The functional significance of the large number of myosin isoforms in skeletal muscles is poorly understood. Myosin molecules that have the same heavy chain, but differ in their essential or alkali light chains, have the same actin-activated ATPase activity. Similarly, the many heavy chain isoforms that appear during the course of muscle development do not show any significant differences in enzymatic activity. By means of an in vitro motility assay, we have measured the analogue of unloaded shortening velocity for myosin isoforms in a reconstituted actomyosin system. We find that both light and heavy chain isoforms translocate actin filaments at distinct velocities. These results support the hypothesis that myosin isoforms are the primary determinant for the range of shortening velocities adopted by a muscle in response to changing functional demands.

Actins↗
PubMed2004

Clathrin isoform CHC22, a component of neuromuscular and myotendinous junctions, binds sorting nexin 5 and has increased expression during myogenesis and muscle regeneration.

The muscle isoform of clathrin heavy chain, CHC22, has 85% sequence identity to the ubiquitously expressed CHC17, yet its expression pattern and function appear to be distinct from those of well-characterized clathrin-coated vesicles. In mature muscle CHC22 is preferentially concentrated at neuromuscular and myotendinous junctions, suggesting a role at sarcolemmal contacts with extracellular matrix. During myoblast differentiation, CHC22 expression is increased, initially localized with desmin and nestin and then preferentially segregated to the poles of fused myoblasts. CHC22 expression is also increased in regenerating muscle fibers with the same time course as embryonic myosin, indicating a role in muscle repair. CHC22 binds to sorting nexin 5 through a coiled-coil domain present in both partners, which is absent in CHC17 and coincides with the region on CHC17 that binds the regulatory light-chain subunit. These differential binding data suggest a mechanism for the distinct functions of CHC22 relative to CHC17 in membrane traffic during muscle development, repair, and at neuromuscular and myotendinous junctions.

Animals↗
PubMed2026

Exploring the Effect of Whole-Genome Duplication on Salmonid LincRNA Repertoire.

Long intergenic non-coding RNAs (lincRNAs) are key epigenetic regulators of genome function, yet their evolutionary dynamics following whole-genome duplication (WGD) events remain poorly understood. Salmonids, which underwent a lineage-specific autotetraploidization (salmonid-specific WGD, ~88-100 million years ago), provide an excellent model to investigate the retention, divergence, and functional potential of recently duplicated non-coding elements. LincRNA repertoires were compared across five genome-annotated salmonids (Oncorhynchus tshawytscha, O. kisutch, O. mykiss, Salmo salar, and S. trutta) and their closest non-duplicated relative, northern pike (Esox lucius). LincRNAs represented ~5-7% of annotated genes in all salmonids except S. salar (18%). Sequence conservation was low relative to coding genes, with only 11-68 highly similar (e-value < 1 &#xd7; 10-30; similarity > 70% and alignments > 100 nucleotides) putative orthologues shared between salmonids and northern pike, and 161-338 among salmonids alone. Synteny conservation was modest in lincRNAs, with lower conservation in putative orthologues (8-16%) compared to putative ohnologues (8-33%). Secondary structure conservation was associated with sequence similarity (&#x3c1; = -0.45; p = 2.2 &#xd7; 10-16), and the association was stronger among WGD ohnologues than orthologues. In S. salar and O. mykiss, lincRNA putative ohnologues showed weaker expression correlations than coding genes, suggesting widespread regulatory divergence, possibly through neo- and subfunctionalisation. Conserved salmonid lincRNAs showed enriched predicted interactions with miRNAs involved in tumour suppression, brain, bone, and muscle development (e.g., miR-455, miR-365, miR124, miR-133a, miR-140, and miR-9), a finding supported by limited transcriptomic data. Although salmonid WGD expanded lincRNA repertoires, lincRNAs have undergone rapid sequence and transcriptional divergence, with limited conservation across species based on sequence similarity, chromosomal position, synteny, and secondary structure. A subset of conserved lincRNAs retains structural features and regulatory signatures consistent with roles as miRNA sponges in brain, skeletal, and muscle development and tumour suppression, potentially acting within conserved regulatory networks. These findings provide new insights into lincRNA evolution following genome duplication and highlight the need for experimental validation of their regulatory functions.

Animals↗
PubMed2005

Dynamics of Z-band based proteins in developing skeletal muscle cells.

During myofibril formation, Z-bodies, small complexes of alpha-actinin and associated proteins, grow in size, fuse and align to produce Z-bands. To determine if there were changes in protein dynamics during the assembly process, Fluorescence Recovery after Photobleaching was used to measure the exchange of Z-body and Z-band proteins with cytoplasmic pools in cultures of quail myotubes. Myotubes were transfected with plasmids encoding Yellow, Green, or Cyan Fluorescent Protein linked to the Z-band proteins: actin, alpha-actinin, cypher, FATZ, myotilin, and telethonin. Each Z-band protein showed a characteristic recovery rate and mobility. All except telethonin were localized in both Z-bodies and Z-bands. Proteins that were present both early in development in Z-bodies and later in Z-bands had faster exchange rates in Z-bodies. These results suggest that during myofibrillogenesis, molecular interactions develop between the Z-band proteins that decrease their mobility and increase the stability of the Z-bands. A truncated construct of alpha-actinin, which localized in Z-bands in myotubes and exhibited a very low rate of exchange, led to disruption of myofibrils, suggesting the importance of dynamic, intact alpha-actinin molecules for the formation and maintenance of Z-bands. Our experiments reveal the Z-band to be a much more dynamic structure than its appearance in electron micrographs of cross-striated muscle cells might suggest.

Animals↗
PubMed2000

Smooth muscle myosin heavy chain isoforms and their role in muscle physiology.

Unlike vertebrate skeletal muscle, smooth muscle myosin heavy chain isoforms are encoded by a single gene. Alternative splicing of the primary transcript from a single gene generates four smooth muscle myosin heavy chain isoforms. These isoforms differ both at the carboxyl terminus (SM1 and SM2 isoforms) and at the amino terminus (SM-A and SM-B isoforms). The smooth muscle myosin heavy chain isoforms are differentially expressed during smooth muscle development and in different smooth muscle cell types. The mechanical properties of smooth muscle may be correlated with the myosin heavy chain content/isoform expression. However, the precise function of each smooth muscle myosin heavy chain isoform to muscle contraction remains to be determined. This review mainly focuses on the molecular basis of smooth muscle myosin heavy chain isoform diversity, its expression during development and disease, and its role in muscle physiology.

Amino Acid Sequence↗
PubMed1991

Transgene expression in the QM myogenic cell line.

We have isolated an avian muscle cell line (QM) which has the essential features of established mammalian muscle cell lines. The experiments reported here were undertaken to determine the suitability of QM cells for the introduction and analysis of cloned transgenes. The promoter of the cardiac troponin T (cTNT) gene has been previously shown to contain sequence elements which govern muscle-specific expression of the chloramphenicol acetyltransferase (CAT) gene in transiently transfected primary cell cultures. We show here that QM cells stably harboring cTNT promoter-CAT fusion genes up-regulate CAT expression in concert with myogenic differentiation, and that as few as 110 upstream nucleotides are sufficient for such differentiation-dependent regulation. In addition, both transient and stable transfection experiments demonstrate that differentiated QM cells possess trans-acting factors necessary for the expression of the skeletal alpha-actin promoter, despite the absence of mRNA or protein product from the endogenous sarcomeric actin genes in these cells. Finally, to follow the developmental potential of QM cells in vivo, we created a clone, QM2ADH, which constitutively expresses the histochemical marker transgene encoding Drosophila alcohol dehydrogenase. When surgically inserted into the limb buds of developing chick embryos, QM2ADH cells are incorporated into endogenous developing muscles, indicating that QM cells are capable of recognizing and responding to host cues governing muscle morphogenesis. Thus, QM cells are versatile as recipients of transgenes for the in vitro and in vivo analysis of molecular events in muscle development.

Actins↗
PubMed2003

[A case with myositis as a manifestation of chronic graft-versus-host-disease (GVHD) with severe muscle swelling developed after aggressive muscular exercise].

We report a 21-year-old-man, with myositis as a manifestation of chronic graft-versus-host-disease (GVHD). He was diagnosed as having acute myelogenous leukemia at the age of 18 years, and had bone marrow transplantation (BMT) two years after the onset of the disease. Cutaneous manifestation of acute GVHD appeared on the twelfth day following BMT, which responded to prednisolone. Thereafter, GVHD has been well-controlled except for mild liver dysfunction which was thought to be a sign of chronic GVHD. Eleven months after BMT, he enjoyed snowboarding for two days from morning till night. Two days later, he experienced muscle swelling with pain and fever, which gradually worsened for which he was admitted to our hospital. Neurological examination revealed severe proximal and distal muscle swelling with fever and tenderness in all extremities. Mild, symmetrical, proximal weakness was observed in all four limbs. Severity of muscle swelling and its generalized nature restricted the movements of shoulder-, elbow- and ankle-joints and he was unable to walk. Laboratory investigations revealed creatine kinase (CK) of 7,860 IU/L, C-reactive protein (CRP) of 21.5 mg/dL and raised biliary enzymes. MRI generated high intensity signals from the swollen muscles. Muscle biopsy examination of involved areas showed severe interstitial edema and mononuclear cells infiltration. Macrophages were scattered through out the perimysium and endomysium. On the other hand, T cells and B cells were localized to the endomysium. Although a lot of CD8 positive T cells were seen adjacent to non-necrotic fibers, none of them was obviously invading the non-necrotic fibers. Perifascicular atrophy was not seen. Symptoms gradually worsened over two weeks or so when prednisolone was started to which he responded rapidly. While tapering steroids, the symptoms relapsed on resuming aggressive exercise. Resumption of the treatment regime promptly controlled the symptoms. The cause of myositis as a manifestation of chronic GVHD is unclear. T-cell or B-cell dysfunction, collagen-vascular-like processes, viral infection and direct damage by radiation or chemotherapy have been supposed to involve in the disease process. Our case suggests that aggressive muscular exercise could play as a initiator of myositis as a manifestation of chronic GVHD.

Adult↗
PubMed1992

Expression of type-specific MHC isoforms in rat intrafusal muscle fibers.

Myosin heavy chain (MHC) expression by intrafusal fibers was studied by immunocytochemistry to determine how closely it parallels MHC expression by extrafusal fibers in the soleus and tibialis anterior muscles of the rat. Among the MHC isoforms expressed in extrafusal fibers, only the slow-twitch MHC of Type 1 extrafusal fibers was expressed along much of the fibers. Monoclonal antibodies (MAb) specific for this MHC bound to the entire length of bag2 fibers and the extracapsular region of bag1 fibers. The fast-twitch MHC isoform strongly expressed by bag2 and chain fibers had an epitope not recognized by MAb to the MHC isoforms characteristic of developing muscle fibers or the three subtypes (2A, 2B, 2X) of Type 2 extrafusal fibers. Therefore, intrafusal fibers may express a fast-twitch MHC that is not expressed by extrafusal fibers. Unlike extrafusal fibers, all three intrafusal fiber types bound MAb generated against mammalian heart and chicken limb muscles. The similarity of the fast-twitch MHC of bag2 and chain fibers and the slow-tonic MHC of bag1 and bag2 fibers to the MHC isoforms expressed in avian extrafusal fibers suggests that phylogenetically primitive MHCs might persist in intrafusal fibers. Data are discussed relative to the origin and regional regulation of MHC isoforms in intrafusal and extrafusal fibers of rat hindlimb muscles.

Aging↗
PubMed1985

The postnatal functional development of muscle stretch receptors in the rat.

The response to a 5-sec stretch of the triceps muscle was studied in dorsal root filaments L5 of 72 infant rats (1-19 days old) under urethane anesthesia. More than 50% of all units in 1-day-old rats responded by repetitive firing until the end of the 5-sec stretch (slowly adapting or SA receptors), while the rest ceased to fire earlier (relatively rapidly adapting or 1/2 SA receptors), or gave an "on" response only. The number of units exhibiting an SA response increased with age and attained 80% in 5-day-old rats. By the 10th day of life, almost 90% of endings behaved as SA receptors. During development, the maximal discharge frequencies at the peak of stretch increased markedly, and their values in 18-day-old rats were comparable to those in adult rats. The phasic component of the response to stretch, although less well defined in the younger animals, was already present even in 1-day-old rats. Adaptation of the static response during maintained stretch was relatively steep in all the age groups studied. The results indicate that, in the rat, large numbers of muscle stretch receptors are capable of responding to sustained stretch as SA receptors, even at an age when their morphological and ultrastructural maturation is not yet fully accomplished.

Adaptation, Physiological↗
PubMed2006

The development of the larval nervous system, musculature and ciliary bands of Pomatoceros lamarckii (Annelida): heterochrony in polychaetes.

BACKGROUND: To understand the evolution of animals it is essential to have taxon sampling across a representative spread of the animal kingdom. With the recent rearrangement of most of the Bilateria into three major clades (Ecdysozoa, Lophotrochozoa and Deuterostomia) it has become clear that the Lophotrochozoa are relatively poorly represented in our knowledge of animal development, compared to the Ecdysozoa and Deuterostomia. We aim to contribute towards redressing this balance with data on the development of the muscular, nervous and ciliary systems of the annelid Pomatoceros lamarckii (Serpulidae). We compare our data with other lophotrochozoans. RESULTS: P. lamarckii develops locomotory and feeding structures that enable it to become a swimming, planktotrophic larva within 24 hours. Formation of the trochophore includes development of a prototroch, metatroch and neurotroch, development of apical and posterior nervous elements at similar times, and development of musculature around the ciliary bands and digestive tract prior to development of any body wall muscles. The adult nervous and muscular systems are essentially preformed in the late larva. Interestingly, the muscular systems of the larvae and juvenile worms do not include the circular muscles of the body wall, which are considered to be plesiomorphic for annelids, although the possibility that circular muscles develop after these stages cannot be ruled out at this point. CONCLUSION: A comparison between polychaetes shows variability in the timing (heterochrony) of development of body wall muscles and elements of the nervous system. These heterochronies are one route for evolution of different life history strategies, such as adaptations to feeding requirements.

Journal Article↗
PubMed2001

Assembly of thick, thin, and titin filaments in chick precardiac explants.

De novo cardiac myofibril assembly has been difficult to study due to the lack of available cell culture models that clearly and accurately reflect heart muscle development in vivo. However, within precardiac chick embryo explants, premyocardial cells differentiate and commence beating in a temporal pattern that corresponds closely with myocyte differentiation in the embryo. Immunofluorescence staining of explants followed by confocal microscopy revealed that distinct stages of cardiac myofibril assembly, ranging from the earliest detection of sarcomeric proteins to the late appearance of mature myofibrils, were consistently recognized in precardiac cultures. Assembly events involved in the early formation of sarcomeres were clearly visualized and accurately reflected observations described by others during chick heart muscle development. Specifically, the early colocalization of alpha-actinin and titin dots was observed near the cell periphery representing I-Z-I-like complex formation. Myosin-containing thick filaments assembled independently of actin-containing thin filaments and appeared centered within sarcomeres when titin was also linearly aligned at or near cell borders. An N-terminal epitope of titin was detected earlier than a C-terminal epitope; however, both epitopes were observed to alternate near the cell periphery concomitant with the earliest formation of myofibrils. Although vascular actin was detected within cells during early assembly stages, cardiac actin predominated as the major actin isoform in mature thin filaments. Well-aligned thin filaments were also observed in the absence of organized staining for tropomodulin at thin filament pointed ends, suggesting that tropomodulin is not required to define thin filament lengths. Based on these findings, we conclude that the use of the avian precardiac explant system accurately allows for direct investigation of the mechanisms regulating de novo cardiac myofibrillogenesis.

Actin Cytoskeleton↗