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PubMed2005

Mechanical signals and IGF-I gene splicing in vitro in relation to development of skeletal muscle.

It has been shown that the insulin-like growth factor (IGF-I) gene is spliced in response to mechanical signals producing forms of IGF-I which have different actions. In order to study how mechanical signals influence this gene splicing in developing muscle, C2C12 cells were grown in three-dimensional (3D) culture and subjected to different regimens of mechanical strain. IGF-IEa which initiates the fusion of myoblasts to form myotubes was found to be constitutively expressed in myoblasts and myotubes (held under endogenous tension) and its expression upregulated by a single ramp stretch of 1-h duration but reduced by repeated cyclical stretch. In contrast, mechano growth factor (MGF), which is involved in the proliferation of mononucleated myoblasts that are required for secondary myotube formation and to establish the muscle satellite (stem) cell pool, showed no significant constitutive expression in static cultures, but was upregulated by a single ramp stretch and by cycling loading. The latter types of force simulate those generated in myoblasts by the first contractions of myotubes. These data indicate the importance of seeking to understand the physiological signals that determine the ratios of splice variants of some growth factor/tissue factor genes in the early stages of development of skeletal muscle.

Alternative Splicing↗
PubMed1986

[Development of connective tissue in mouse skeletal muscle].

The development of the connective tissue in the dorsal forelegs of mouse embryos and sucklings was investigated with the aid of immunofluorescence and electron microscopy. Collagen type III is visible earlier in the muscular connective tissue than collagen type I. However, it seems that collagen does not play a fundamental role in the organization of the muscular tissue. The occurrence of collagen is rather an indication of the mechanical development of the muscles. In early embryos (day 13 to day 15) some desmosome-like cell contacts are visible between fibroblasts and myoblasts, as well as myotubes.

Animals↗
PubMed1989

Load responsiveness of protein synthesis in adult mammalian myocardium: role of cardiac deformation linked to sodium influx.

Exposure of adult mammalian myocardium to increased hemodynamic loads augments cardiac protein synthesis, ultimately leading to hypertrophy of the affected chamber. This established relationship between loading conditions and protein synthesis was examined in terms of two questions. First, is there a basic difference between the anabolic effect of a passive load imposed on diastolic myocardium and that of an active load generated by systolic myocardium? This issue was addressed by measuring [3H]phenylalanine incorporation into muscle protein in either quiescent or contracting ferret papillary muscles, set at known isometric lengths. Myocardial protein synthesis increased in proportion to total muscle tension in each case, with an equivalent relation describing both quiescent and contracting muscles. Synthesis of two contractile proteins, actin and myosin heavy chain, were enhanced by muscle loading. Thus, a quantitative rather than qualitative difference between the anabolic effects of diastolic and systolic loading was demonstrated. Second, since increased sodium influx is an initial cellular response requisite to the growth-inducing activity of many substances, and since sodium entry through stretch-activated ion channels is stimulated by deformation of the sarcolemma, does cardiac deformation during increased loading promote sodium influx as a signal to increase anabolic activity? In either quiescent or contracting papillary muscles, the rate of 24Na+ uptake was found to increase with load. Streptomycin, a cationic blocker of the mechanotransducer ion channels, was without effect on protein synthesis in stimulated but slack muscles; however, it inhibited, in a dose-related manner, the augmented protein synthesis otherwise observed in contracting muscles developing tension. At 500 microM, streptomycin did not reduce active tension, but it did reduce the synthesis of both actin and myosin heavy chain. In a second pharmacologic approach, inotropic agents were chosen which uniformly increased muscle tension development but which had contrasting effects on sodium influx. Protein synthesis increased in the presence of Na+ influx enhancers, monensin or veratridine; however, protein synthesis decreased in the presence of amiloride, a sodium influx inhibitor. Thus, myocardial protein synthesis varied directly with sodium influx despite the positive inotropic effect observed with each of these agents. In addition, inhibition of protein synthesis by ouabain demonstrated that activation of the Na+ pump is required for the anabolic effect of load.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Subcellular distribution of acetylcholinesterase asymmetric forms during postnatal development of mammalian skeletal muscle.

This study describes the changes which occur in intra- and extracellular asymmetric acetylcholinesterase (AChE) forms in rat gracilis muscle during postnatal development. Initially (day 7) these forms (12.5 S and 16 S AChE) were evenly distributed along the muscle and only present intracellularly. With advancing age (days 7-28) they gradually became concentrated in endplate (vs non-endplate) muscle regions where a certain proportion of them was subsequently externalized. In contrast, no externalization was observed in the non-endplate regions. Our results support the view that AChE asymmetric forms are assembled within the muscle cell prior to their deposition on the extracellular synaptic compartment.

Acetylcholinesterase↗
PubMed1989

Specific programs of myosin expression in the postnatal development of rat muscles.

The expression of myosin during postnatal development was studied in a dozen muscles of the rat. All muscles displayed the usual sequential transitions from embryonic to neonatal and to adult isomyosins. However, we observed that these transitions did not take place uniformly. Thus, half-transition times for the appearance of the adult intermediate and fast myosin extended from seven days for diaphragm, the most precocious muscle of all those examined, to 23 days for male rat masseter. Besides the large differences between their half-transition times, we noticed that the transition curves displayed different slopes, covering different periods. Differences between muscles mainly affected the neonatal-to-adult transition rather than the embryonic-to-neonatal transition, since the embryonic-type myosin disappeared from all muscles examined except for one, at about the same time, by the end of the first week after birth. In addition, the appearance of slow myosin varied for each muscle and did not follow curves parallel to those for intermediate and fast myosins. These results indicate that each muscle of the rat is subjected to a specific program of myosin isoform transitions during postnatal development.

Aging↗
PubMed1993

Analyses of PS integrin functions during Drosophila development.

The Drosophila position-specific (PS) antigens are homologues of the vertebrate integrins, a family of transmembrane proteins that function in cell-matrix and cell-cell adhesion. The common beta subunit of PS integrins (PS beta) is encoded by the lethal(l)myospheroid gene (mys) and is required during wing, eye and muscle development. By expressing PS beta protein at defined developmental periods, we have shown that PS integrins are required throughout pupation, but not earlier, for normal development of wings. In contrast, the key requirement for PS integrins in eye development occurs only in the late pupa. Furthermore, PS integrins are apparently not required for the differentiation of the ommatidial cells; only for their organization. These results are consistent with roles for PS integrins in the interactions between the wing epithelia during the two phases of pupal wing expansion and in maintaining the attachment of a fully formed fenestrated membrane to the basement membrane of the retina. We have also examined the functional significance of alternative splicing of the transcript of the mys gene using P element-mediated transformation to introduce transgenes producing only one of the two spliced forms of PS beta. We find that either form is sufficient to rescue postembryonic mys phenotypes in the wing, eye and muscle but that both of the two splice forms are necessary to rescue the mys embryonic defects. This result indicates a requirement for the alternative splicing of mys during embryogenesis. The location of the alternative exons suggests that the two forms of the PS beta integrin subunit may interact with alternative alpha subunits and/or ligands.

Animals↗
PubMed1985

Factors determining the subunit composition of tropomyosin in mammalian skeletal muscle.

Adult rat fast-twitch skeletal muscle such as extensor digitorum longus contains alpha- and beta-tropomyosin subunits, as is the case in the corresponding muscles of rabbit. Adult rat soleus muscle contains beta-, gamma- and delta-tropomyosins, but no significant amounts of alpha-tropomyosin. Evidence for the presence of phosphorylated forms of at least three of the four tropomyosin subunit isoforms was obtained, particularly in developing muscle. Immediately after birth alpha- and beta-tropomyosins were the major components of skeletal muscle, in both fast-twitch and slow-twitch muscles. Differentiation into slow-twitch skeletal muscles was accompanied by a fall in the amount of alpha-tropomyosin subunit and its replacement with gamma- and delta-subunits. After denervation and during regeneration after injury, the tropomyosin composition of slow-twitch skeletal muscle changed to that associated with fast-twitch muscle. Thyroidectomy slowed down the changes in tropomyosin composition resulting from the denervation of soleus muscle. The results suggest that the 'ground state' of tropomyosin-gene expression in the skeletal muscle gives rise to alpha- and beta-tropomyosin subunits. Innervation by a 'slow-twitch' nerve is essential for the expression of the genes controlling gamma- and delta-subunits. There appears to be reciprocal relationship between expression of the gene controlling the synthesis of alpha-tropomyosin and those controlling the synthesis of gamma- and delta-tropomyosin subunits.

Animals↗
PubMed1992

Determinants of vascular structure.

The development of the vasculature is a complex process, the end result of which enables the cardiovascular system to supply each tissue with the required amount of blood at the correct pressure. The mechanisms controlling this development are poorly understood, and this article seeks to review briefly some of the mechanisms that may be involved. At the capillary level, it appears that capillary proliferation is closely related to tissue metabolism. The lumen diameter of the feeding arterioles and arteries then develops (through a mechanism that appears to be dependent on endothelial factors) to accommodate the new flow requirements. In studies of the development of esophageal varices, it seems that the increased lumen diameter resulting from increased flow is due to the rapid synthesis of wall material. Within the walls of the feeding arterioles and arteries, the smooth muscle develops to insure a constant loading of the individual smooth muscle cells. This development is not necessarily associated with alterations in the amount of smooth muscle, but can be due to "remodeling," i.e., the rearrangement of existing smooth muscle cells to allow them to perform their function more effectively. Clearly, if we assume that antihypertensive therapy should seek not only to reduce blood pressure but also to normalize vascular structure, a better understanding of the mechanisms controlling vascular development is needed.

Animals↗
PubMed1992

Fine structure of developed human tongue muscle.

The purpose of this study was to clarify the relationship myofibrils, mitochondoria and other cytoplasmic organella in the developed lingual muscle (vertical, transverse, and longitudinal) by using various microscopic levels: light, scanning electron, and transmission electron. The tongue muscles were examined in seventeen autopsy specimens: eight, 12-32 weeks gestation and ten adults (five male, five female; 54-93 years). The muscle fiber rapidly developed. A large number of mitochondoria and glycogen granules increased and the size of myofibrils in the middle stage also increased, ranging from 24 to 28 weeks gestations. The developed myofibrils were differentiated, the VL and TL at first are developed before the LL developed. These results suggest that the lingual intrinsic muscle have differences in properties during development.

Aged↗
PubMed1987

Force-time measurements of knee muscle functions of subjects with multiple sclerosis.

The purpose of this study was to determine whether the time-rate of muscle tension development, the muscle tension-maintaining capacity, and the reciprocal inhibition time of muscles in subjects with multiple sclerosis were significantly different from those of healthy subjects. An isokinetic dynamometer was used to evaluate the quadriceps femoris and hamstring muscles of 15 Experimental Group subjects with multiple sclerosis and 17 healthy Control Group subjects. The muscles were tested isometrically at 45 degrees of knee flexion and isokinetically at speeds of 30 degrees/sec and 90 degrees/sec. The subjects with multiple sclerosis demonstrated a significant (p less than .001) slowing of the time-rate of muscle tension development and a significant (p less than .005) decrease in muscle tension-maintaining capacity when compared with healthy subjects. The difference in the reciprocal inhibition time of muscles of the Experimental and Control Groups was not significant. When the reciprocal inhibition time of muscles was expressed as a percentage of the total torque curve, however, a significant prolongation (p less than .001) was observed in the subjects with multiple sclerosis.

Adolescent↗
PubMed1988

Functional interactions between unlinked muscle genes within haploinsufficient regions of the Drosophila genome.

Mutations in 13 genes affecting muscle development in Drosophila have been examined in pairwise combinations for evidence of genetic interactions. Heterozygous combinations of mutations in five genes, including the gene coding for myosin heavy chain, result in more severe phenotypes than respective single heterozygous mutant controls. The various mutant interactions include examples showing allele-specific intergenic interactions, gene specific interactions, and allele-specific intragenic complementations, suggesting that some interactions result from the manner in which mutant gene products associate. Interactions that result from alterations in "+" gene copy number were also uncovered, suggesting that normal myofibril development requires that the relative amounts of respective gene products produced be tightly regulated. The importance of the latter parameter is substantiated by the finding that all five interacting loci map to disperse haploinsufficient or haplolethal regions of the genome. The implications of the present findings are discussed in relation to pursuing the phenomena involving genetic interactions to identify new genes encoding interacting myofibrillar proteins, to examine the nature of intermolecular interactions in mutant and normal development and to decipher the quantitative and temporal regulation of a large family of functionally related gene products.

Alleles↗
PubMed1985

Development and subsequent neural tube effects on the excitability of cultured Xenopus myocytes.

We examined both the development of electrical excitability in cultured Xenopus muscle over a period of 7 days, and the effects of neural tube on the muscle action potential. During muscle development, delayed and anomalous rectification were present in most cases within 24 hr. The action potential was dependent on Na at all times examined, and the rate of rise of the action potential (Vmax) increased substantially (seven-fold) from the first 2 days to 6 to 7 days in vitro, reflecting an increase in Na current density. In order to determine the mechanism for the increase in Vmax, we examined single-channel Na currents using the gigaseal technique. Single-channel conductance (gamma) did not increase substantially when measured using the patch clamp technique: gamma = 24 pS at 1 to 2 days, and gamma = 28 pS at 4 to 6 days. The channel open time at 14 degrees C was 0.6 msec for 1- to 2-day-old cells and 0.5 msec in 4- to 6-day-old cells at a step potential 40 mV from rest. The time constant for current decay as well as the time-to-peak current also did not change over time. Thus, channel kinetics appear unchanged. The maximum inward current from summed records was statistically greater for older cells, and the frequency of patches displaying single-channel events increased from 75 to 98%. Thus, we conclude that during development in vitro, Na current density increases as a result of an increase in channel density without detectable alterations in single-channel properties. Neural tube addition led to a further increase in Vmax (two-fold), even in muscle cells with no apparent nerve contact. Single channel analysis of cells in coculture revealed gamma to be 28 pS in three cells displaying a single amplitude peak for individual Na currents. In the majority of cases (9/12), however, there appeared to be two classes of Na channels present which were difficult to separate. The larger conductance channel likely corresponds to the 28 pS class. The smaller channels, when present, did not contribute substantially to the population of events comprising the amplitude histogram. Other single-channel kinetic parameters also did not change. We, therefore, conclude that neural tube addition does not effect activation or inactivation kinetics but likely causes a further increase in channel density and possibly the induction of a second type of Na channel.

Action Potentials↗
PubMedDate not supplied

[Morphogenesis of transverse straited muscles].

During the past 50 years there have been significant advances in our understanding of striated muscle development, both from tissue culture studies and from observations of myogenesis in the developing foetus. Experiments, using the distinctive nucleolar marker of quail nuclei, have led to reexamination of the source of the body's muscle masses. Advances have been made in our understanding of the events which occur and mechanisms involved in the formation of multinucleated myofibers from mononucleated myoblasts. Recently, the development of entire muscle organs has been studied. The present review attempts to synthesize the results of both in vivo and in vitro studies of myogenesis, comparing both their similarities and their differences. Attention has been focused on recent advances in our understanding of the source of muscles in the intact foetus, the formation of extrafusal and intrafusal fibers, and the development of the afferent and efferent neuromuscular relationships.

Animals↗
PubMed1975

The development of alkaline phosphatase in trichinous muscle.

The development of alkaline phosphatase during invasion and encystment of Trichinella spiralis in rat skeletal muscle fibres was studied at the ultrastructural level. On day 14 after infection, the enzymatic activity is found in proliferating parts of the T-tubular system and in parts of the plasmalemma. In cells, in which a strong hyperplasia of this system is noted. AlPase is present in the abundant network of stratified and concentric membranes from which a large number of pinocytic vesicles arise. From day 50 till 1 year after infection the enzyme activity was invariably present in the matrix surrounding the larvae and was confined to the enormous amounts of cytoplasmic membranes. The possible functional significance of this enzyme in the matrix, in view of its peculiar localization in the immediate vicinity of the parasite, is discussed. In the presence of 0.1 mM of the levamisole analogue, compound R 30402, which is a stereospecific inhibitor of AlPase, the activity is completely lost.

Alkaline Phosphatase↗
PubMed2001

A light microscope study of the distribution of muscle in the frog esophagus and stomach.

The present study reports light microscopical observations of the distribution of muscle in the esophagus and stomach of both the bull frog (Rana catesbeiana) and the African clawed frog (Xenopus laevis). The external muscle coat of the upper half of the esophagus in both species had several collagen coated bundles of striated muscle fibres around the circumference. These striated muscle bundles ran longitudinally from the pharynx to around the vicinity of the center of the esophagus. Beneath these striated muscle bundles was an inner circular layer of smooth muscle. In both species, the inner circular layer of smooth muscle was particularly thick in the region close to the pharynx. In the bull frog, the lower half of the esophagus lacked striated muscle. However, the circular smooth muscle layer, extending from the upper half of the esophagus, was also observed throughout the lower half of the esophagus. An outer longitudinal layer of smooth muscle developed towards the terminal portion of the esophagus such that in this region, both outer longitudinal and inner circular layers of smooth muscle were observed. Similarly in the African clawed frog, the inner circular layer of smooth muscle was continuous along the full length of the esophagus. Again, no striated muscle bundles were observed in the lower half of the esophagus. However, the outer longitudinal layer of smooth muscle was seen to develop in the middle region of the esophagus. Its muscle layer extended to the terminal portion of the esophagus. Thus, both outer longitudinal and inner circular layers of smooth muscle were observed throughout the lower half of the esophagus. In both frogs, the thickness of the outer longitudinal and inner circular layers of smooth muscle changed before and after the esophago-gastric junction. In both frogs, no muscularis mucosa was observed in the esophageal wall. However, in the lower half of the esophagus of the African clawed frog, small bundles of smooth muscle were observed here and there in the submucosa. A fully developed muscularis mucosa with both outer longitudinal and inner circular layers was observed in the upper stomach of both frogs.

Animals↗
PubMed1991

Histomorphometrical aspects of the postnatal development of masticatory muscle in the muscular dystrophic mouse.

Histomorphological and histomorphometrical observations were used to describe the development of masticatory muscles from normal and muscular dystrophic mice. The masseter and the digastric muscle were described from the birth to 35-40 week of age. It has not been possible by histomorphological criteria to separate dystrophic muscles from normal muscles at birth. From 2 weeks onwards marked differences between the affected and unaffected muscles appeared, as the affected fibres from this age are rounded with marked variations in size. Central nucleation is frequent and there is an increased amount of connective tissue between the fibres. The histomorphometrical observations revealed an increase in mean size of the fibres with age, both in normal and dystrophic masticatory muscles. The fibre size variance which has been shown to be a reliable parameter for description of degree of affection of dystrophic muscles, increased with increasing age in both groups. However, the variance is at all ages greater in the dystrophic muscles than in the normal ones, and is always greater in the masseter muscle than in the digastric muscle. There seems to be some small differences between male and female masticatory muscles, whereas no differences could be revealed between muscles from normal and heterozygous animals. Possible explanations of the obvious differences in degree and progression of the disease between the masseter and digastric muscle are proposed.

Animals↗
PubMed2004

MyoD-lacZ transgenes are early markers in the neural retina, but MyoD function appears to be inhibited in the developing retinal cells.

Recent findings suggest that eye and skeletal muscle development in vertebrates share the same regulatory network. In that network, Pax3 gene is apparently activated through Dach/Eya/Six feedback loop to mediate MyoD-driven myogenesis. The purpose of this study was to investigate previously reported MyoD-lacZ expression in the developing mouse neural retina and to gain insight into the potential role of MyoD in the embryonic retinal cells. The analysis of MD6.0-lacZ and 258/-2.5lacZ transgenic embryos revealed that the retinal temporal expression pattern of the two transgenes resembled their expression pattern in the MyoD-dependent precursor muscle cells. However, MyoD transcripts and protein could not be found in the sites of MyoD-lacZ retinal expression. Furthermore, our immunohistochemical analysis suggests the existence of diverse factors (e.g., Pax6 and Chx10) within the retinal cells that differentially and inappropriately activate the two transgenes. Finally, the retinal phenotype observed in Pax7-/- knock-out mice suggests a role for Pax7 in photoreceptor cell differentiation, retinal lamination and in the etiopathology of retinoblastoma. Taken together, our data suggest that the MyoD gene evolved a different mechanism to achieve its down-regulation within the retina than that of the Myf5 gene.

Animals↗
PubMed1985

Changes of the NADP-linked malic enzyme in the developing rat skeletal muscle.

The activities of NADP-linked malic enzyme, hexose monophosphate shunt dehydrogenases and NADP-linked isocitrate dehydrogenase were studied during development of skeletal muscle and compared with those in the liver. The variation patterns of malic enzyme activity in the liver and in the skeletal muscle were very similar, however the amplitude of the changes was different. The enzyme activity increased approx 16-fold in the liver and about 2-fold in skeletal muscle at the same stage of development. In skeletal muscle the increase of the malic enzyme activity was only slightly higher than of lactic dehydrogenase and citrate synthase. Studies on the intracellular distribution of malic enzyme in skeletal muscle showed that both mitochondrial and extramitochondrial enzymes increased between 20th and 37th day of life, the increase of the extramitochondrial enzyme being more pronounced. The hexose monophosphate shunt dehydrogenases activity showed an increase in the liver but no change was observed in the skeletal muscle at the weaning time. Changes in the activity of the liver and skeletal muscle isocitrate dehydrogenase were not significant between 10th and 80th day of life. The results suggest that the malic enzyme in the liver is playing a different physiological role than in the skeletal muscle.

Animals↗