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PubMed1999

Regulation of the p75 neurotrophin receptor in a rat myogenic cell line (L6).

Neurotrophins are expressed in muscle cells both during development and postnatally. Furthermore, during development muscle cells express high levels of the common p75 neurotrophin receptor, which binds all neurotrophins. Only fragmentary and controversial data are available regarding the responsiveness of muscle cells to neurotrophins and the importance of low-affinity p75 receptor in muscle development. The present study investigates in vitro the immunocytochemical expression of p75 in a rat myogenic cell line (L6) at various time points and in response to different coating substrates as a first step in elucidating the regulation of p75 in muscle. We found that in L6 myoblasts, p75 is expressed only at very early stages of maturation and its levels of expression are regulated by the nature of the coating substrates. p75 expression decreases in cells growing on substrates more suitable for myoblast fusion into myotubes. Time course analysis indicates a reverse correlation between myoblast fusion into myotubes and the levels of p75 expression. Myotubes were always p75 negative. Substrates not suitable for the fusion process induced a prolonged presence of p75 in myoblasts with an increase of their apoptosis. We conclude that expression of p75, at least in this in vitro condition, is regulated by the stages of myoblast differentiation and the nature of the coating substrates. According to the observed time- and substrate-related evidences, future studies should investigate in vivo both the regulation of p75 in the myoblast fusion and the effects and the importance of neurotrophins binding during myoblast differentiation.

Animals↗
PubMed1982

Cellular development of liver and skeletal muscles and body composition of pigs from gestationally starved sows.

Liver and skeletal muscle development and changes in body composition were studied in pigs from cross-bred sows subjected to starvation (allowed water and trace mineral salt) during the third trimester of gestation. Two groups of sows were taken off feed on days 93 (21-day) and 107 (7-day) of gestation respectively; a third group fed 1.82 kg of diet per day served as control. The pigs sacrificed at birth, were used to determine liver and skeletal muscle DNA, RNA and protein and body composition. There were no significant differences (P greater than .05) in body weight between the treated groups and the control. Liver weight was depressed in the progeny of 21-day and 7-day starvation groups (P less than .05). Liver cellular DNA was decreased (P less than .05) in the treated animals, RNA and protein content remained unchanged. The skeletal muscles studied responded differently to the treatment imposed; semitendinosus muscle weight, muscle DNA and RNA did not differ among treatments; whereas, gastrocnemius muscle weight, muscle DNA and RNA were significantly lower in the progeny of treated sows (P less than .05, P less than .01 and P less than .05 respectively). Muscle and liver protein content, RNA/DNA, and protein/DNA ratios were not affected by treatments. Body composition analysis showed no differences in per cent dry matter, lipid, ash and protein content. The results suggest that liver and gastrocnemius muscles were adversely affected by prenatal nutritional deficiency imposed while semitendinosus muscles remained unchanged. The differential response of skeletal muscles to prenatal nutritional deficiency indicated a need to study more than a single muscle in similar experiments designed to investigate muscle response. The lack of differences in body composition analysis showed that improved survival of newborn pigs previously reported can be achieved without changes in fetal chemical body composition.

Animals↗
PubMed1992

Contractile properties of the rat external abdominal oblique and diaphragm muscles during development.

We studied the in vitro contractile and fatigue properties of the rat external abdominal oblique (EAO) and costal diaphragm (DIA) muscles during postnatal development. Isometric twitch contraction (CT) and half-relaxation (RT1/2) times were longer in both the EAO and DIA muscles during the early postnatal period and decreased with age. In the first postnatal week, the CT and RT1/2 were longer in the EAO than the DIA muscle. At 14 days of age and thereafter, the CT and RT1/2 were shorter in the EAO than in the DIA muscle. Force-frequency relationships of the EAO and DIA muscles changed during postnatal development such that the relative force (percent maximum) generated at lower frequencies (less than 15 pulses/s) decreased with age. Moreover the relative force generated by the EAO muscle at lower frequencies was greater than that of the DIA muscle during the early postnatal period but less than that of the DIA muscle in adults. The specific force of both the EAO and DIA muscles increased progressively with age. There were no differences in specific force between the EAO and DIA muscles at any age. The fatigability of the EAO and DIA muscles was comparable during the early postnatal period and increased in both muscles with postnatal development. In adults the EAO muscle was more fatigable than the DIA muscle. We conclude that the contractile and fatigue properties of the EAO and DIA muscles undergo significantly different postnatal transitions, which may reflect their functional involvement in sustaining ventilation.

Animals↗
PubMed2004

Effects of a quantitative trait locus for muscle hypertrophy from Belgian Texel sheep on carcass conformation and muscularity.

A QTL for muscle hypertrophy has been identified in the Belgian Texel breed. A population of F2 and backcross lambs created from crosses of Belgian Texel rams with Romanov ewes was studied. Effects on carcass traits and muscle development of the Belgian Texel breed polygenes and Belgian Texel single QTL were compared. In both cases, carcass conformation and muscularity were improved. The Texel polygenic environment improved conformation mainly through changes in skeletal frame shape. Segments were shorter and bone weight lower. Muscles were more compact, shorter, and thicker. The single QTL affected muscle development. Thickness and weight of muscles were increased. Composition in myosin changed toward an increase of fast contractile type. The relative contribution of hind limb joint to carcass weight was increased. Differences in skeletal frame morphology among the three genotypes of the single QTL were small. Conformation scoring was mainly influenced by leg muscularity. Back and shoulder muscle development, which largely contributed to variability of muscularity, were less involved in the conformation scoring. Lastly, the QTL explains a small part of differences between these Belgian Texel and Romanov breeds for conformation or muscle development. A large part of genetic variability remains to be explored.

Animals↗
PubMed1988

Binding of Ricinus communis I lectin to developing dystrophic muscle in human fetus.

In previous studies it was shown that a D-galactose-specific lectin, Ricinus communis I (RCA I), does not bind to the plasma membrane of muscle fibres from patients with Duchenne muscular dystrophy (DMD) in contrast to normal muscle. We have now studied RCA I binding to the membranes of developing human fetal muscle in fetuses at 95% risk of DMD (n = 6) and normal controls (n = 5) with a developmental range of 12-20 weeks of gestation. The results were compared to the membrane appearance with conventional ultrastructure. Binding of RCA I to the muscle basement membrane was consistently strong from the early stages of myogenesis, such as in fusing myoblasts/myocytes. RCA I binding to the plasma membrane was weak but detectable in both DMD and normal fetuses at 12-14 weeks of gestation. Both the normal and diseased condition showed an increase of RCA I labelling of the muscle plasma membrane at 15-17 weeks and strong labelling at 18-20 weeks of gestation. No difference was observed in the RCA I localization of normal and diseased human fetal muscle plasma membrane. It is concluded that (a) the plasma membrane in developing fetal muscle undergoes a maturation process between 12 and 20 weeks gestational age leading to an increase in expression of RCA I binding carbohydrate moieties; and (b) that the absence of RCA I binding glycoprotein in mature DMD muscle plasma membrane reflects a change acquired during the course of disease.

Cell Membrane↗
PubMed2001

Functional reconstruction of the lateral face after ablative tumor resection: use of free muscle and musculocutaneous flaps.

BACKGROUND: Wide resection of tumors of the middle third of the face often results in complex three-dimensional defects and facial paralysis either due to removal of the facial nerve within the tumoral tissue or to extensive resection of the facial muscles. METHODS: We report the cases of three patients who underwent wide excision of tumors of the cheek region, operations that resulted in tissue defects and facial palsy. Defect reconstruction and facial reanimation was accomplished in one stage through functional muscle transplantation. RESULTS: Follow-up of more than 1 year showed good symmetry at rest and reanimation of the corner of the mouth in all cases, but one patient, in which the ipsilateral facial main trunk was used as motor nerve supply to the transplanted muscle, developed significant muscle contracture and binding of the cheek skin. CONCLUSIONS: Every effort should be made to optimize the functional and cosmetic outcomes of neurovascular muscle transfers through precise planning and careful execution of the intricate details of the surgical technique for muscle transplantation.

Adolescent↗
PubMed2004

Electrodynamic smooth muscle sphincter: development and biomechanical evaluation of a novel porcine artificial smooth muscle sphincter in a new in vitro stoma simulator.

AIM: Many authors have suggested that the activity of the enteric inhibitory nerves is important in regulating normal gastrointestinal motility and inducing smooth muscle relaxation. Hitherto, no experimental or clinical models exist that transfer these physiological aspects to creating an autologous artificial sphincter for the treatment of major incontinence. Therefore, this study was performed to determine the contractile and relaxant capacity of gastrointestinal muscle types and to investigate the efficiency of a novel smooth muscle sphincter, based on the non-adrenergic, non-cholinergic (NANC) receptive relaxation under electrical field stimulation (EFS). METHODS: For the first step, the isometric tension from isolated circular porcine fundus and colon muscle strips was recorded during pharmacological stimulation (TTX, L-NNA and atropine) and EFS. As a result, a continent electrodynamic smooth muscle sphincter (ESMS) was created by wrapping a fundus muscle flap around an isolated segment of porcine distal colon. The EFS of the free nerve fibers of the flap was realized using a circular platinum wire electrode. Parameters such as threshold of continence, intra/preluminal pressure and fluid passage were analyzed in a newly designed in vitro stoma simulator. RESULTS: Electrical field stimulation produced a maximal and voltage-dependent fundus relaxation to --12.4 mN/mm(2) (frequency of 40 Hz, pulse duration, train duration and voltage of 5 ms, 1 s and 60 mA respectively), which were abolished by N-nitro-L -arginine (L-NNA; 10(-4) M) in a dose-dependent manner, confirming that relaxant responses were mediated by NANC nerves. The results of eight ESMS showed that circular electrical stimulation of the muscle flap caused muscle relaxation with a concomitant and effective reduction in the occlusion pressure. CONCLUSION: The NANC-induced relaxation mechanism of porcine fundus preparations could be transferred to an efficient smooth muscle sphincter with a high threshold of continence and electrically controlled defecation.

Anal Canal↗
PubMed2005

Desmin filaments are stably associated with the outer nuclear surface in chick myoblasts.

Eukaryotic cells have highly organized, interconnected intracellular compartments. The nuclear surface and cytoplasmic cytoskeletal filaments represent compartments involved in such an association. Intermediate filaments are the major cytoskeletal elements in this association. Desmin is a muscle-specific structural protein and one of the earliest known muscle-specific genes to be expressed during cardiac and skeletal muscle development. Desmin filaments have been shown to be associated with the nuclear surface in the myogenic cell line C2C12. Previous studies have revealed that mice lacking desmin develop imperfect muscle, exhibiting the loss of nuclear shape and positioning. In the present work, we have analyzed the association between desmin filaments and the outer nuclear surface in nuclei isolated from pectoral skeletal muscle of chick embryos and in primary chick myogenic cell cultures by using immunofluorescence microscopy, negative staining, immunogold, and transmission electron microscopy. We show that desmin filaments remain firmly attached to the outer nuclear surface after the isolation of nuclei. Furthermore, positive localization of desmin persists after gentle washing of the nuclei with high ionic strength solutions. These data suggest that desmin intermediate filaments are stably and firmly connected to the outer nuclear surface in skeletal muscles cells in vivo and in vitro.

Animals↗
PubMed2000

Nutrient absorption and utilization by wing and flight muscle morphs of the cricket Gryllus firmus: implications for the trade-off between flight capability and early reproduction.

Absorption efficiency (AD, approximate digestibility, assimilation efficiency) of various macronutrients and conversion of absorbed nutrients to biomass (ECD) were compared among the two types of flightless morph and the flight-capable morph of the cricket, Gryllus firmus. No biologically significant phenotypic or genetic difference in AD for carbohydrate, protein or lipid was observed among morphs fed either a high-nutrient (100%) or a low-nutrient (25%) diet. Thus, previously-documented differences among adult morphs in carbohydrate and lipid content must be caused by processes other than variation in nutrient absorption by morphs during adulthood. Relative absorption efficiency of total dry mass of food by morphs of G. firmus appears to be a valid indicator of relative AD of total calories. Morphs did not differ phenotypically or genetically in the excretion of end products of nitrogen metabolism (uric acid, hypoxanthine plus xanthine) on either the high nutrient or the low nutrient diet. Nutritional indices corrected for excreted nitrogenous metabolites were very similar to uncorrected indices, and the pattern of variation among the morphs was the same for corrected or uncorrected values. Each of the two types of flightless morph converted a greater proportion of absorbed nutrients into body mass, mainly ovaries, and allocated a smaller proportion of assimilated nutrients to respiration than did the flight-capable morph. Moreover, the trade-off between respiration and early reproduction was substantially magnified on the low nutrient diet. These results extend previous findings of a trade-off between flight capability and early reproduction in wing-polymorphic Gryllus species (1) to diets of very different nutrient quantity, and (2) to flightlessness arising from different causes: blockage of flight muscle development in juveniles vs histolysis of fully-developed flight muscles in adults.

Journal Article↗
PubMed1998

Functional Changes Of Fetal Muscle Acetylcholine Receptor During Mouse Development.

In developing muscles in vivo and in vitro, the acetylcholine receptor gamma-subunit exists in two splice variants, conferring different single-channel open durations (tau(op)) to reconstituted receptors. In mouse muscles, tau(op) changes around birth, possibly as receptors incorporate either variant of gamma-subunit. This might be relevant to the concomitant maturation of muscle innervation.

Journal Article↗
PubMed1998

Levels of MyoD protein expression following injury of mdx and normal limb muscle are modified by thyroid hormone.

Thyroid hormone (T3) affects muscle development and muscle regeneration. It also interacts with the muscle regulatory gene MyoD in culture and affects myoblast proliferation. We studied the localization of MyoD protein using a well-characterized polyclonal antibody for immunohistochemistry. Relative numbers of myogenic precursor cells per field were identified by their MyoD expression during muscle regeneration in normal and mdx dystrophic mice, with particular reference to the expression in mononuclear cells and myotubes at various T3 levels. In regeneration by normal muscles, relatively few MyoD+ nuclei per field were present in mononuclear cells of euthyroid and hypothyroid mice. MyoD staining of mononuclear cell nuclei was approximately doubled in fields of regenerating muscles of normal hyperthyroid compared to euthyroid mice, and was observed in precursors that appeared to be aligned before fusion into myotubes. In mdx regenerating muscle, twofold more mononuclear cells positive for MyoD were present in all three treatment groups compared to normal muscles regenerating under the same conditions. Localization was similar to the pattern in normal euthyroid mice. However, in muscles regenerating in hyperthyroid mdx mice, both mononuclear cell nuclei and centrally located nuclei in a subpopulation (about 15%) of new myotubes formed after the crush injury were intensely stained for MyoD protein. The changes observed are consistent with reports on T3-induced alteration of muscle repair, and propose a link between MyoD regulation and the accelerated differentiation during regeneration under high T3 conditions. (J Histochem Cytochem 46:59-67, 1998)

Animals↗
PubMed1995

Utrophin actin binding domain: analysis of actin binding and cellular targeting.

Utrophin, or dystrophin-related protein, is an autosomal homologue of dystrophin. The protein is apparently ubiquitously expressed and in muscle tissues the expression is developmentally regulated. Since utrophin has a similar domain structure to dystrophin it has been suggested that it could substitute for dystrophin in dystrophic muscle. Like dystrophin, utrophin has been shown to be associated with a membrane-bound glycoprotein complex. Here we demonstrate that expressed regions of the predicted actin binding domain in the NH2 terminus of utrophin are able to bind to F-actin in vitro, but do not interact with G-actin. The utrophin actin binding domain was also able to associate with actin-containing structures, stress fibres and focal contacts, when microinjected into chick embryo fibroblasts. The expressed NH2-terminal 261 amino acid domain of utrophin has an affinity for skeletal F-action (Kd 19 +/- 2.8 microM), midway between that of the corresponding domains of alpha-actinin (Kd 4 microM) and dystrophin (Kd 44 microM). Moreover, this utrophin domain binds to non-muscle actin with a approximately 4-fold higher affinity than to skeletal muscle actin. These data (together with those of Matsumura et al. (1992) Nature, 360, 588-591) demonstrate for the first time that utrophin is capable of performing a functionally equivalent role to that of dystrophin. The NH2 terminus of utrophin binds to actin and the COOH terminus binds to the membrane associated glycoprotein complex, thus in non-muscle and developing muscle utrophin performs the same predicted 'spacer' or 'shock absorber' role as dystrophin in mature muscle tissues. These data suggest that utrophin could replace dystrophin functionally in dystrophic muscle.

Actins↗
PubMed1985

Deep pectoral myopathy: a penalty of successful selection for muscle growth.

Deep pectoral myopathy (DPM) is a disease that affects commercial poultry selected for large breast muscle development. The muscle affected by the disease is the supracoracoid muscle and usually one side of the breast musculature atrophies. The necrotic muscle has a characteristic pale green color. Heavy breeds of turkeys and broilers can be induced to show DPM by electrical stimulation of the breast muscle itself or by vigorous wing flapping; older birds are more susceptible. The cause of DPM is a fascial compartment too small to accommodate the enclosed supracoracoid muscle during vigorous exercise when the muscle increases its weight (and overall size) by about 20%. The inelastic compartment essentially strangulates the swollen, activated muscle. A possible means of correcting DPM is to train or exercise the flight muscles during the rapid growth phase of chicks or poults. Feed, for example, could be positioned above floor level so that birds would have to flutter up to reach it. There is also evidence to suggest a genetic component to the disease. Hence, an indicator such as high plasma creatine kinase levels may be used as a selection criterion.

Age Factors↗
PubMed1990

Muscle-specific RNA processing continues in the absence of myogenin expression.

During muscle development, muscle-specific gene expression is achieved by a complex set of transcriptional and post-transcriptional mechanisms. We examined the requirement of new protein synthesis and myogenin expression for muscle-specific tropomyosin expression during myogenesis of the rat muscle cell line L6E9. The results show that new protein synthesis is required for both muscle gene transcription and muscle-specific alternate RNA processing. However, once initiated, the synthesis of muscle tropomyosin mRNA continued in the presence of cycloheximide, while the expression of muscle actin, myosin heavy chain, and myogenin mRNA was abolished. These results suggest that muscle-specific processing of tropomyosin transcripts can continue to occur in the absence of myogenin expression unlike the expression of muscle actin and myosin heavy chain mRNAs. However, the transfection of myogenin cDNA into nonmuscle cells induced muscle-specific RNA processing of tropomyosin, suggesting indirect involvement of myogenic factors in the initiation of muscle-specific RNA processing pathways.

Actins↗
PubMed2002

Development-dependent disappearance of caspase-3 in skeletal muscle is post-transcriptionally regulated.

Caspase-3, a major player in apoptosis, engages apoptosis-activated cells into an irreversible pathway leading to cell death. In this article, we report that caspase-3 protein is absent from rat and mouse adult skeletal muscles, despite the abundant presence of its mRNA. During skeletal muscle development, caspase-3 protein is present in neonatal animals, but its expression gradually decreases, and disappears completely by 1 month of age, when there is still abundant caspase-3 mRNA. This discordance between caspase-3 message and protein expression is unique to skeletal muscle, as in all other analyzed tissues the protein presence correlates with the presence of the mRNA. The only circumstance in which caspase-3 protein appears in adults is in regenerating muscles; once regeneration is complete, however, it again becomes undetectable in repaired muscles. We conclude that caspase-3 protein in skeletal muscle is uniquely regulated at the post-transcriptional level, unseen in other tissues such as brain, heart, lung, kidney, thymus, spleen, liver, or testis. The post-transcriptional regulation of caspase-3 might serve as a fail-safe mechanism to avoid accidental cell death.

Aging↗
PubMed1975

The influence of innervation on the differentiation of contractile speeds of developing chick muscles.

1. The role of innervation of the differentiation of contractile speeds was studied in the slow anterior latissimus dorsi (ALD) and fast posterior latissimus dorsi (PLD) muscle of the chick. 2. These muscles become innervated during the 12th and 15th day of embryonic development. At this time both muscles contract and relax extremely slowly and their contractile speeds are very similar. By the 18th day their contraction and relaxation becomes more rapid. It is at this time that the contractile characteristics of both muscles also become very different from each other, ALD being about 3 times slower than PLD. Thus innervation percedes differentiation of contractile speeds by several days. 3. The influence of innervation on the contractile characteristics of developing slow and fast muscles was studied during muscle regeneration in adults. When a slow ALD muscle was minced and implanted in place of a fast PLD the newly regenerated ALD became innervated by a PLD nerve and resembled a fast PLD. Conversely, when PLD muscles were minced and replaced ALD the regenerated PLD was innervated by ALD nerve and became slow. 4. Histological examination revealed that the regenerated ALD became focally innervated, and the regenerated PLD multiply innervated. 5. Thus, the contractile speeds are not predetermined properties of the muscle fibre. Both contractile characteristic and the pattern of innervation of developing muscles are determined by the motor nerve.

Animals↗
PubMed1999

Immunolocalization of mitsugumin29 in developing skeletal muscle and effects of the protein expressed in amphibian embryonic cells.

The temporal appearance and subcellular distribution of mitsugumin29 (MG29), a 29-kDa transmembrane protein isolated from the triad junction in skeletal muscle, were examined by immunohistochemistry during the development of rabbit skeletal muscle. MG29 appeared in the sarcoplasmic reticulum (SR) in muscle cells at fetal day 15 before the onset of transverse tubule (T tubule) formation. In muscle cells at fetal day 27, in which T tubule and triad formation is ongoing, both SR and triad were labeled for MG29. In muscle cells at newborn 1 day, the labeling of the SR had become weak and the triads were well developed and clearly labeled for MG29. Specific and clear labeling for MG29 was restricted to the triads in adult skeletal muscle cells. When MG29 was expressed in amphibian embryonic cells by injection of the cRNA, a large quantity of tubular smooth-surfaced endoplasmic reticulum (sER) was formed in the cytoplasm. The tubular sER was 20-40 nm in diameter and appeared straight or reticular in shape. The tubular sER was formed by the fusion of coated vesicles [budded off from the rough-surfaced endoplasmic reticulum (rER)] and vacuoles of rER origin. The present results suggest that MG29 may play important roles both in the formation of the SR and the construction of the triads during the early development of skeletal muscle cells.

Amphibians↗
PubMed1989

Two components of calcium channel current in embryonic chick skeletal muscle cells developing in culture.

The properties of the Ca channel currents in chick skeletal muscle cells (myoballs) in culture were studied using a suction pipette technique which allows internal perfusion and voltage clamp. The Ca channel currents as carried by Ba ions were recorded, after suppression of currents through ordinary Na, K and Cl channels by absence of Na, K and Cl ions, by external TEA, by internal EGTA and by observing the Ba currents instead of the Ca currents. Two components of Ba current could be distinguished. One was present only if the myoballs were held at relatively negative holding potentials below -50 mV. This component first became detectable at clamp potentials of about -50 mV and reached a maximum between -10 and -20 mV. During long clamp steps, it became inactivated completely. The inactivation process of this component at a clamp potential of -30 mV was well fitted to a single exponential with a time constant of about -20 ms. Half-maximal steady-state inactivation was observed at -63 mV. The other component persisted even at relatively positive holding potentials above -40 mV, was observed during clamp pulses to -20 mV and above, and reached a maximum between +10 and +20 mV. This component inactivated very little; a substantial fraction of this component remained at the end of clamp pulses lasting 1 s. The inactivation process of this component at a clamp potential of -10 mV apparently followed a single exponential with a time constant of about 1 s. Half-maximal steady-state inactivation was attained at -33 mV. Both components of Ba current were blocked by Co ions, but organic Ca channel blocker D600 preferentially blocked the high-threshold, slowly inactivating component. The relationship between the current amplitude and the concentration of the external Ba ions was different between the two components. Furthermore, the two components of Ba current also differed in their developmental profile. These findings demonstrate the existence of two distinct types of Ca channels in the early stages of chick muscle cell development.

Animals↗