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PubMed2004

Smooth muscle development during postnatal growth of distal bronchioles in infant rhesus monkeys.

Development of smooth muscle in conducting airways begins early in fetal life. Whereas the pattern and regulation of smooth muscle differentiation are well-defined, the impact of airway growth on the process is not. To evaluate the transformations in organization during postnatal growth, smooth muscle bundle organization (size, abundance, and orientation) was mapped in five generations of distal airways of infant rhesus monkeys (5 days and 1, 2, 3, and 6 mo old). On the basis of direct measurement of the bronchiole proximal to the terminal bronchiole, length increased by 2-fold, diameter by 1.35-fold, and surface area by 2.8-fold between 5 days and 6 mo of age. Smooth muscle bundle size was greater in proximal bronchioles than in respiratory bronchioles and did not change with age. However, relative bundle size decreased in proportion to airway size as the airways grew. Relative bundle abundance was constant regardless of airway generation or age. The distribution of smooth muscle bundle orientation changed with age in each airway generation, and there were significant changes in the terminal and respiratory bronchioles. We conclude that smooth muscle undergoes marked organizational changes as airways grow during postnatal development.

Age Factors↗
PubMed1988

Shedding of cytoplasmic actins by developing muscle cells.

Young myotubes develop spots or macules of actin and alpha actinin under and adjacent to slender actin strands. Macules are found only before sarcomere formation. They contain cytoplasmic actin, small amounts of alpha actin, and alpha actinin but are devoid of tubulin, myosin and vimentin. In the electron microscope, they are seen to contain small filaments but no other organelles. Macules are found on the culture dish and in the culture medium, as well as on the lower and lateral surfaces of the cells. Both emetine and cycloheximide, at doses that inhibit protein synthesis, accelerate formation and shedding of macules. This presents the first observation of a cellular system in which the changeover from a generalized cytoskeleton to a tissue-specific cytoskeleton involves shedding of the cytoplasmic isoforms of cytoskeletal proteins.

Actins↗
PubMed1985

Muscle development in the grasshopper embryo. III. Sequential origin of the flexor tibiae muscle pioneers.

The flexor (FlTi) and extensor (ETi) tibiae are antagonist muscles located in the femur of the metathoracic leg of the grasshopper. Both are complex, consisting of an array of bundles of muscle fibers connecting the ectoderm of the wall of the femur with their respective apodemes. In the previous paper (E. E. Ball and C. S. Goodman, 1985, Dev. Biol. 111, 399-416) we described the embryonic development of the ETi muscle, focusing in particular on its syncytial origin from a giant supramuscle pioneer which later divides into an array of individual muscle pioneers. Here we describe the embryonic development of the FlTi muscle. In contrast to the development of the ETi muscle, the array of individual muscle pioneers for the FlTi does not have a syncytial origin but rather arises by sequential recruitment from the mass of smaller, undifferentiated mesoderm cells. The FlTi MPs first appear as two cells symmetrically placed on the corners of the FlTi apodeme at around 37%. A third MP is then added between these two; this third MP later dies. Subsequent growth occurs by symmetrical addition of MPs distally along the sides of the developing apodeme and by enlargement of the individual MPs. Initially each MP contains only a single nucleus; by about 50% there are at least two to three nuclei per MP and each is surrounded by a cluster of smaller, undifferentiated mesoderm cells. Each MP develops into a bundle of muscle fibers by a cycle of fusion and division. The individual mesoderm cells surrounding each MP fuse with it starting at about 60%. At the same time, the large MP begins to divide into smaller muscle fibers.

Animals↗
PubMed2001

Effect of visual display terminal height on the trapezius muscle hardness: quantitative evaluation by a newly developed muscle hardness meter.

The aim of this study was to determine trapezius muscle hardness in 9 healthy volunteers before and after word processing tasks with a video display terminal (VDT) at three different heights. When using a desktop personal computer (PC), no change was observed in muscle hardness even after a 30-min task if a subject was in the reference posture with a declination angle formed by the Reid's line directed toward the upper edge of the PC screen and the horizontal plane within 5-10 degrees. However, an increase in muscle hardness was observed after a 15-min task in a posture of looking up at the screen (angle of elevation: 15-20 degrees) and after a 30-min task in a posture of looking down at the screen (angle of declination: 15-20 degrees). When the same tasks were performed with a notebook PC, muscle hardness increased after 15 min. Fifteen minutes of relaxation exercise reduced the muscle hardness caused by VDT work.

Adult↗
PubMed2005

Effect of genetic increases in egg production, age, and sex on muscle development in turkeys.

Breast muscle morphology was studied at 8 and 16 wk of age in a line (E) selected over 44 generations for increased egg production and its randombred control line (RBC1). A sample of 20 birds per sex-line-age subgroup was killed with restraint to prevent flapping of the wings. The skin was removed from the breast region, and a sample of breast muscle was obtained in a manner to prevent contraction. The muscle samples were dehydrated, cleared, embedded in paraffin, sectioned, and incubated and rehydrated prior to staining with hematoxylin and eosin. Four sections from the same muscle from each bird were placed on a slide, and the slides were viewed for muscle morphological characteristics with a microscope and digitally recorded. Five fields of each section were viewed. Representative sections for each bird were given a score by 4 individuals based on breast muscle morphology. The scores ranged from 1 (little extracellular matrix and indistinct muscle fibers) to 5 (large extracellular space and distinct muscle fibers). Scores from 2 to 4 were intermediate to these extremes. Breast muscle morphology scores did not differ between lines or ages but there was a significant interaction between lines and ages. The scores increased in the RBC1 line from 8 to 16 wk of age, but the reverse was true for the E line. Scores were higher in males than females. The results of the present study suggest that selection for increased egg production in dam lines should not greatly influence breast muscle morphology in commercial turkeys.

Aging↗
PubMed1997

Ectopic expression of MEF2 in the epidermis induces epidermal expression of muscle genes and abnormal muscle development in Drosophila.

Myocyte-specific enhancer-binding factor 2 (MEF2) is a myogenic regulatory factor in vertebrates and Drosophila. Whereas the role of MEF2 in regulating vertebrate myogenesis and muscle genes has been extensively studied, little is known of the role of MEF2 in regulating Drosophila myogenesis. We have shown in a recent analysis of the regulation of the Drosophila Tropomyosin I (TmI) gene in transgenic flies that MEF2 is a positive regulator of TmI expression in the somatic body-wall muscles of embryos, larvae, and adults. To understand further the role of MEF2 in myogenesis and test the role of MEF2 in regulating TmI expression, we have used the yeast GAL4/UAS system to generate embryos in which MEF2 is ectopically expressed in tissues where it is not normally expressed or embryos in which MEF2 is overexpressed in the mesoderm and muscles. We observe that ectopic expression of MEF2 in the epidermis and the ventral midline cells in embryos activates the expression of TmI and other muscle genes in these tissues and that this activation is stage-dependent suggesting a requirement for additional factors. Furthermore, ectopic expression of MEF2 in the epidermis results in a decrease in the expression of signaling molecules in the epidermis and a failure of the embryo to properly form body-wall muscles. These results indicate that MEF2 can function out of context in the epidermis to induce the expression of muscle genes and interfere with a requirement for the epidermis in muscle development. We also find that the level of MEF2 in the mesoderm and/or muscles in embryos is critical to body-wall muscle formation; however, no effect is observed on the development of the visceral muscle or dorsal vessel.

Animals↗
PubMed2006

Expression and functional activity of ryanodine receptors (RyRs) during skeletal muscle development.

Two isoforms of ryanodine receptors are expressed in skeletal muscles, RyR1 and RyR3. We investigated the relative level of expression of RyRs in developing murine skeletal muscles using [3H]ryanodine binding and immunoprecipitation experiments. In the diaphragm RyR3 accounted for 11% of total RyRs in 5-day-old mice and for 3% of total RyRs in 60-day-old mice. In hindlimb muscles, RyR3 accounted for 3% and 1% of total RyRs in 5-day-old and adult mice, respectively. The activity of RyR1 channels in native microsomal vesicles from murine muscles was found to be as low as 35% of that measured after CHAPS exposure, while no inhibition was observed for RyR3. CHAPS sensitivity of recombinant RyR1 and RyR3 expressed in HEK293 cells was also investigated. The activity of recombinant RyR1 but not RyR3 channels was found to be inhibited in native conditions, suggesting that this property may not be dependent on a muscle environment.

Animals↗
PubMed2003

Myosin heavy chain isoforms in postnatal muscle development of mice.

In this study, using a high-resolution gel electrophoresis technique, we have characterized the myosin heavy chain composition in different skeletal muscle of the mouse during postnatal development. The pattern of myosin heavy chain expression was studied in four hind limb muscles, the diaphragm, the tongue and the masseter. All of these muscles displayed the usual sequential transitions from embryonic to neonatal and to adult myosin heavy chain isoforms but more interestingly these transitions occur with a distinct chronology in the different muscles. In addition, our results demonstrated a transitory pattern of expression for certain adult myosin heavy chain isoforms in the soleus and the tongue. In the soleus muscle IIB and in the tongue IIA myosin heavy chain isoforms were detected only for a short time during postnatal life. Our results demonstrate that muscles of the mouse with different functions are subjected to a distinct programs of myosin isoform transitions during postnatal muscle development. This study describes new data which will help us to understand both postnatal muscle development in transgenic mouse muscles as well as in muscle pathology.

Aging↗
PubMed2006

Hhip regulates zebrafish muscle development by both sequestering Hedgehog and modulating localization of Smoothened.

Sharp borders between cells with different developmental fates are important for patterning of invertebrates, but are not well understood in vertebrates. Zebrafish slow muscle cells develop from adaxial cells, a one-cell-diameter-thick pseudo-epithelium immediately adjacent to the notochord. Hedgehog (Hh) signals from notochord specify adaxial cells to form slow muscle cells. Cells next to adaxial cells form fast muscle. This suggests that Hh signaling is locally regulated to produce a sharp border that separates slow and fast muscle precursors. To understand how Hh activity is locally regulated, we characterized the dynamic roles of Hhip, a protein that binds Hedgehog at the cell surface. Hhip is strongly expressed by adaxial cells and, together with Patched, the Hedgehog receptor, limits transduction of the Hedgehog signaling by Smoothened to adaxial cells. Hhip protein lacking its membrane associated domain still suppresses Hh activity but no longer acts synergistically with Patched. Hhip and Smoothened colocalize at the cell surface and, in response to Hedgehog, internalize together. Knockdown of Hhip blocks Smoothened internalization while increasing Hedgehog signaling and slow muscle formation. These data support a model in which Hhip regulates muscle development both by sequestering Hedgehog and by modulating localization of Smoothened.

Animals↗
PubMed2001

Regulation of myosin heavy chain expression during rat skeletal muscle development in vitro.

Signals that determine fast- and slow-twitch phenotypes of skeletal muscle fibers are thought to stem from depolarization, with concomitant contraction and activation of calcium-dependent pathways. We examined the roles of contraction and activation of calcineurin (CN) in regulation of slow and fast myosin heavy chain (MHC) protein expression during muscle fiber formation in vitro. Myotubes formed from embryonic day 21 rat myoblasts contracted spontaneously, and approximately 10% expressed slow MHC after 12 d in culture, as seen by immunofluorescent staining. Transfection with a constitutively active form of calcineurin (CN*) increased slow MHC by 2.5-fold as determined by Western blot. This effect was attenuated 35% by treatment with tetrodotoxin and 90% by administration of the selective inhibitor of CN, cyclosporin A. Conversely, cyclosporin A alone increased fast MHC by twofold. Cotransfection with VIVIT, a peptide that selectively inhibits calcineurin-induced activation of the nuclear factor of activated T-cells, blocked the effect of CN* on slow MHC by 70% but had no effect on fast MHC. The results suggest that contractile activity-dependent expression of slow MHC is mediated largely through the CN-nuclear factor of activated T-cells pathway, whereas suppression of fast MHC expression may be independent of nuclear factor of activated T-cells.

Animals↗
PubMed1995

Posthatching growth and pectoralis muscle development in broiler strain chickens, bantam chickens and the reciprocal crosses between them.

Body weight, pectoralis muscle weight, pectoralis protein and DNA concentration, and plasma GH and IGF-I concentrations of broiler chicks (BrBr), bantam chicks (BaBa) and reciprocal crosses between them (BaBr and BrBa) were measured between 0 and 42 days after hatching. At hatch, body weight and pectoralis weight of the two types of chicks from broiler eggs (BrBr and BaBr) were equal to each other but greater than the two types of chicks from bantam eggs (BaBa and BrBa), which were not different from each other. BrBr chicks grew more rapidly than crossbreds and BaBa chicks grew more slowly. Weights of the reciprocal crosses (BaBr and BrBa) were markedly different at day of age, but converged by day 14. The increase in pectoralis muscle mass of BrBr chicks exceeded that of the reciprocal crosses which in turn exceeded that of BaBa chicks. The increase in pectoralis DNA content and protein content followed the same pattern. The DNA unit size, as expressed by the protein:DNA ratio, was markedly lower in pure bantam chicks from 14 to 42 days of ages, whereas the unit size did not differ between the intermediate sized reciprocal crosses and the large bodied broiler chicks. Differences in muscle mass were primarily achieved by differences in the number of DNA units although a difference in unit size was also a factor. There were no clear relationships between growth and plasma growth hormone or insulin-like growth factor I concentrations. Thus while satellite cell proliferation is primarily responsible for genotypic differences in muscle mass, the plasma growth hormone-IGF-I axis does not appear to be regulating their proliferation.

Age Factors↗
PubMed1996

Uncoupling of Grb2 from the Met receptor in vivo reveals complex roles in muscle development.

Hepatocyte growth factor (HGF) and its receptor, the Met tyrosine kinase, are determinants of placenta, liver, and muscle development. Here, we show that Met function in vivo requires signaling via two carboxy-terminal tyrosines. Mutation of both residues in the mouse genome caused embryonal death, with placenta, liver, and limb muscle defects, mimicking the phenotype of met null mutants. In contrast, disrupting the consensus for Grb2 binding allowed development to proceed to term without affecting placenta and liver but caused a striking reduction in limb muscle coupled to a generalized deficit of secondary fibers. These data show that the requirements for Met signaling vary depending on the tissue and reveal a novel role for HGF/ Met in late myogenesis.

Adaptor Proteins, Signal Transducing↗
PubMed1975

Physiological properties of junctions between nerve and muscle developing during salamander limb regeneration.

1. Physiological properties of developing nerve-muscle junctions were studied in regenerating limbs of adult salamanders. 2. During the period of synapse formation the muscle fibres had diameters of 4-10 mum, resting potentials of minus 90 to minus 100 mV and input resistances of 10-50 Momega. Some, but not all, pairs of adjacent muscle fibres were electrically coupled. 3. At the stage when muscle fibres could first be identified, some of them were not innervated, at least as determined by electrophysiological criteria. 4. During muscle innervation the neuromuscular synapses were encountered in several intermediate phases of maturity. (i) At the least mature junctions small spontaneous synaptic potentials occurred, but stimulation of the motor nerve trunk did not evoke synchronous transmitter release. (ii) At other junctions maximal nerve stimulation evoked only a single end-plate potential of low quantum content. (iii) More mature fibres received synaptic input from as many as four motor neurons, which could be distinguished by their discrete stimulus thresholds. 5. During this period of synapse development the fibres lacked an action potential but often showed a prolonged response to depolarization. 6. Fibres in normal adult muscles had from one to three synaptic inputs, were not electrically coupled, and responded to depolarization with an action potential.

Action Potentials↗
PubMed1998

Expression of myogenic regulatory factors during muscle development of Xenopus: myogenin mRNA accumulation is limited strictly to secondary myogenesis.

To clarify the acquisition of the adult muscle pattern in Xenopus laevis, in situ hybridization and reverse transcriptase-polymerase chain reaction were used to correlate the time course of gene expression for myogenic regulatory factors (Myf-5, MyoD, and myogenin) with the expression of contractile protein (myosin heavy chain; MHC) genes during hindlimb formation compared with their expression in dorsal body muscles. After the precocious expression of Myf-5 and MyoD mRNA in limb bud (stage 50), myogenin mRNA strongly accumulated later at paddle stages (stages 52/53) concomitantly with the accumulation of both the larval and the adult MHC mRNAs. In dorsal body muscles, as early as stage 52, myogenin transcripts accumulated in a few small, secondary myofibers expressing the adult MHC mRNA that were located along the dorsomedial edge, but they were never detected in the large, primary myofibers of the body expressing the larval MHC mRNA. During metamorphosis, the areas expressing both the adult MHC and the myogenin transcripts gradually expanded from the dorsomedial edge to the ventral side of the dorsal body muscles, accounting for the progression of the secondary "adult" myogenesis described previously (Nishikawa and Hayashi [1994] Dev. Biol. 165:86-94). This work shows that, in Xenopus, the accumulation of myogenin mRNA is restricted to secondary myogenesis, including the formation of new muscles in developing limbs as well as in dorsal muscles during body remodeling. This shows that myogenin is not required for primary myogenesis, and it suggests a crucial role for myogenin in the terminal differentiation program, including myoblast fusion and the activation of adult-type muscle genes.

Animals↗
PubMedDate not supplied

Muscle development in dendrobranchiate shrimp, with comparison with Artemia.

The muscle pattern of malacostracan and entomostracan crustacean nauplius larvae was compared using fluorescent phallotoxins. In the dendrobranchiate malacostracan Sicyonia ingentis, F-actin staining was first detected in limb setae at 12 h, likely within sensory nerves. Staining of F-actin was detected in the trunk at 15 h and grew into the naupliar limbs. Sarcomeres were detected at 19 h, identifying the structures as extrinsic limb muscles. The extrinsic limb muscles enlarged but retained their general pattern during the later nauplius stages. Longitudinal trunk muscles and circumferential visceral muscle (VM) developed in the post-naupliar region during nauplius instars 4 and 5, at the time when the gut also formed. In the anostracan branchiopod Artemia salina, the newly hatched nauplius contained an extensive system of extrinsic and intrinsic limb muscles. The gut was almost complete at hatching, along with its associated circumferential VM. Muscles similar in position and structure could be identified in nauplii from the two taxa, but different anatomical origins of extrinsic muscles were evident. Whether the naupliar limb muscles are homologous in malacostracans and branchiopods remains an open question. The strong musculature of the dendrobranchiate naupliar limbs correlates with the use of all three pairs of limbs for swimming.

Actins↗
PubMed2006

Cytoplasmic gamma-actin is not required for skeletal muscle development but its absence leads to a progressive myopathy.

Nonmuscle gamma(cyto)-actin is expressed at very low levels in skeletal muscle but uniquely localizes to costameres, the cytoskeletal networks that couple peripheral myofibrils to the sarcolemma. We generated and analyzed skeletal muscle-specific gamma(cyto)-actin knockout (Actg1-msKO) mice. Although muscle development proceeded normally, Actg1-msKO mice presented with overt muscle weakness accompanied by a progressive pattern of muscle fiber necrosis/regeneration. Functional deficits in whole-body tension and isometric twitch force were observed, consistent with defects in the connectivity between muscle fibers and/or myofibrils or at the myotendinous junctions. Surprisingly, gamma(cyto)-actin-deficient muscle did not demonstrate the fibrosis, inflammation, and membrane damage typical of several muscular dystrophies but rather presented with a novel progressive myopathy. Together, our data demonstrate an important role for minimally abundant but strategically localized gamma(cyto)-actin in adult skeletal muscle and describe a new mouse model to study the in vivo relevance of subcellular actin isoform sorting.

Actins↗