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PubMed1976

The effect of testosterone on skeletal muscle development and protein synthesis in rabbits.

The effect of testosterone administration on muscle development and protein synthesis was studied with intact male rabbits. Rabbits were randomized into three experimental groups; day 0 control (G-1), day 15 control (G-2) and day 15 testosterone (G-3). Testosterone (delta4-Androsten-17beta-ol-3-one in silastic tubing) was surgically implanted into the G-3 rabbits. On day (G-1) and day 15 (G-2 and 3) of the experiment all rabbits were injected IP with 50 mu Ci-3H-leucine. Rabbits were sacrificed at intervals after the 3H-leucine injection. Right and left semitendinosus muscles, pituitary and adrenal glands, testicles and blood samples were obtained for analysis. Testosterone improved (P less than .01) gain and feed efficiency, depressed testicle weight (P less than .01), increased serum testosterone and insulin (P less than 0.01) but did not affect adrenal and pituitary weights. Muscle moisture, fat and total protein, myofibrillar, sarcoplasmic and stromal protein fractions and RNA and DNA content were not significantly affected by testosterone although G-3 semitendinosus muscle had the highest total and myofibrillar protein, RNA, and DNA content. The testosterone treated rabbits (G-3) had higher (P less than 0.05) 3H-leucine incorporation into myofibrillar protein and lower 3H-leucine incorporation into sarcoplasmic protein than the day 0 and day 15 controls.

Adrenal Glands↗
PubMed1984

Effect of maternal alcohol consumption on pre- and post-natal muscle development of mice.

The effect of maternal alcohol consumption during pregnancy on muscle development of the offspring was investigated in 28 mice (14 males, 14 females) at 12 weeks of age. Both the control and alcohol-fed groups received food ad-libitum throughout the period of study. The control group received water ad-libitum also throughout the period of study. The alcohol-fed group, on the other hand, received only water up to six weeks of age. Subsequently, between 6 and 8 weeks of age they received 10% ethanol (v/v) in water and 20% ethanol (v/v) from 8 to 11 weeks age. Both groups were bred at 11 weeks of age. Following diagnosis of pregnancy, the alcohol-fed group received 30% ethanol (v/v) till delivery. The off-spring of both groups were fed water and food ad-libitum throughout the period of study. Each of the off-spring was killed at 12 weeks of age. Body weight, as well as weights of soleus, biceps brachii, long digital extensor and cranial tibial muscles were significantly smaller in off-spring of the alcohol-fed group indicating that maternal consumption of alcohol during pregnancy retards growth, as well as "catch-up growth" in both body weights and muscle mass. The smaller muscle mass, as observed from analyses of soleus muscle, resulted from retardation of muscle growth pre-natally by suppression of normal hyperplasia of muscle fibres during myogenesis and postnatally by suppression of normal hypertrophy of muscle fibres.

Animals↗
PubMed1985

Monoclonal antibodies to desmin: evidence for stage-dependent intermediate filament immunoreactivity during cardiac and skeletal muscle development.

Monoclonal antibodies reactive with desmin (D3 and D76) have been generated and their specificities validated by immunoblots, RIAs, and immunocytochemistry. No cross-reaction with other IFPs has been observed. The McAbs recognized different epitopes but both reside in the amino-terminal rod domain of desmin. Whereas McAb D3 produces a staining pattern characteristic of desmin throughout the development of cardiac and skeletal muscles, McAb D76 was selectively unreactive with certain regions of early (three days in ovo) embryonic cardiac anlage, with cultured cardiac myocytes derived from 7-day-old embryos, and with skeletal myotubes in early stages of myogenesis in vitro. Positive reactivity of D76 was seen at stages of myofibrillogenesis when the sarcomeres assume lateral alignment. Evidence was presented that differential reactivity of D76 did not result from the biosynthesis of a new desmin isoform or the post-translational modification of an existing protein. We suggest that the appearance of D76 immunoreactivity during striated muscle development represents an unmasking of the epitope by some IF-associated protein. Since this transition during skeletal muscle differentiation occurs during lateral alignment of the myofibrils, this antibody may serve as a useful probe for exploring this reorganization of the contractile apparatus during myogenesis and muscle regeneration.

Animals↗
PubMed1992

Differential regulation of the atrial isoforms of the myosin light chains during striated muscle development.

We have isolated a cDNA that encodes the human regulatory myosin light chain isoform predominant in adult atrial muscle. The cDNA contains an open reading frame of 175 amino acids and encodes a hydrophilic protein of a largely helical structure with two potential phosphorylation sites. The protein is different from any other regulatory myosin light chain so far described and is the product of a previously uncharacterized single copy gene. An isoform-specific probe was used to analyze the expression of this isoform in adult muscle and in cardiac and skeletal muscle development in vivo and in vitro. Parallel analysis of the corresponding human alkali myosin light chain (predominant in adult atrium) showed that both isoforms are expressed in early heart development, in both atrium and ventricle. Although the atrial alkali light chain is expressed throughout embryonic striated muscle development, the regulatory myosin light chain was not detected in skeletal myogenesis in vivo or in vitro. Thus the atrial isoforms are not universally or exclusively "paired" and can be independently regulated. We propose that the manner in which these particular isoforms fulfill the functional requirements of the muscle at different developmental times may have direct impact on their regulation.

Adult↗
PubMed1989

Genetic analysis of muscle development in Drosophila melanogaster.

The different thoracic muscles of Drosophila are affected specifically in the mutants: stripe (sr), erect wing (ewg), vertical wings (vtw), and nonjumper (nj). We have tested the extent of this specificity by means of a genetic analysis of these loci, multiple mutant combinations, and gene dosage experiments. A quantitative, rather than a qualitative, specificity is found in the mutant phenotypes. All muscles are altered by mutations in any given gene, but the severity of these alterations is muscle specific. The locus stripe seems to have a polar organization where different allelic combinations show quantitative specificity in the muscle affected. In addition to the muscle phenotypes, neural alterations are detected in these mutants. The synergism found between ewg, vtw and ewg, sr as well as the dosage effect of the distal end of the X chromosome upon the expression of ewg and sr suggests the existence of functional relationships among the loci analyzed.

Alleles↗
PubMed1995

Mutations in a novel gene, myoblast city, provide evidence in support of the founder cell hypothesis for Drosophila muscle development.

We have used mutations in the newly identified gene myoblast city to investigate the founder cell hypothesis of muscle development in Drosophila melanogaster. In embryos mutant for myoblast city the fusion of myoblasts into multinucleate muscles is virtually abolished. Nevertheless, a subset of the myoblasts develop specific muscle-like characteristics, including gene expression appropriate to particular muscles, migration to the appropriate part of the segment, correct position and orientation, and contact by motor neurons. We suggest that this subset of myoblasts represents the proposed muscle founder cells and we draw an analogy between these founder cells and the muscle pioneers described for grasshopper muscle development.

Animals↗
PubMed1995

Inactivation of Myf-6 and Myf-5 genes in mice leads to alterations in skeletal muscle development.

Myf-6, alternatively called MRF4 or herculin, is a member of a group of muscle-specific transcription factors which also comprises Myf-5, myogenin and MyoD. All family members show distinct expression patterns during skeletal muscle development and can convert a variety of cell lines to myocytes. We disrupted the Myf-6 gene in mice to investigate its functional role in the network of regulatory factors controlling myogenesis. Homozygous mice carrying the disrupted Myf-6 gene show pronounced down-regulation of Myf-5 transcription for reasons presently unknown. Consequently, these mice represent a double knock-out model for Myf-6 and Myf-5. The mutants resemble most of the Myf-5 phenotype with aberrant and delayed early myotome formation and lack of distal rib structures. In addition, we find a reduction in the size of axial muscles in the back. Apart from changes in the pattern of some contractile protein isoforms, the existing myofibers appear fairly normal. This suggests that Myf-6 has no major role in the maturation of myotubes, as previously proposed. Our results provide evidence that skeletal myogenesis can proceed in the absence of two myogenic factors, Myf-5 and Myf-6, therefore they must exert largely non-redundant functions in vivo.

Animals↗
PubMed1988

Myosin ATPase activity during avian cardiac and skeletal muscle development.

The myosin ATPase activity and myosin light chain composition in developing chick heart and skeletal muscles were studied and compared. Embryonic myosin was purified and characterized from day 7 to day 19 of embryogenesis. Embryonic cardiac myosin generally showed the same Ca2+-activated myosin ATPase activity level as the adult value. In comparison, pooled pectoralis and hindlimb skeletal muscles from day 10 through day 19 showed myosin ATPase activities that were all significantly less than the adult counterpart. The myosin light chain pattern of embryonic cardiac myosin remained relatively constant like the myosin ATPase activity, whereas developmental changes were observed in skeletal myosin light chains.

Animals↗
PubMed1990

Migration of myoblasts across basal lamina during skeletal muscle development.

Basal lamina is a sheet of extracellular matrix that separates cells into topologically distinct groups during morphogenesis and is thought to form a barrier to cell migration. We have examined whether, during normal muscle development, myoblasts--mononucleate muscle precursor cells--can cross the basal lamina that surrounds each multinucleate muscle fibre. We marked myoblasts in vivo by injecting replication-defective retroviral vectors encoding LacZ into muscle tissue and analysed the fate of their progeny by the expression of beta-galactosidase. A dual labelling method with broad application to retroviral lineage-marking studies was developed to ensure that most clusters of labelled cells were clones derived from a single precursor cell. Most of the myoblasts that were infected at a late stage of rat hindlimb development, when each fibre with its satellite myoblasts is individually encased in a basal lamina sheath, gave rise to clones that contributed to several labelled fibres. Our results show that myoblasts from healthy fibres migrate across basal lamina during normal development and could contribute to the repair of fibres damaged by injury or disease.

Animals↗
PubMed1979

Contractile protein isozymes in muscle development: identification of an embryonic form of myosin heavy chain.

The nature of the myosin heavy chain in embryonic muscle tissue, cultured muscle cells, and several adult muscles was investigated. After denaturation with sodium dodecyl sulfate, purified rat myosins were subjected to partial proteolytic cleavage or immunological analysis using microcomplement fixation. Three types of myosin heavy chains could be demonstrated by both approaches. Whereas adult muscles contain fast- or slow-type myosin heavy chains, embryonic tissue and cultured muscle cells harbor a distinct embryonic form. The existence of this distinct form further characterizes the isozymic transitions of contractile proteins during muscle development.

Aging↗
PubMed1978

Regulation of skeletal muscle development by the central nervous system in the fetal pig.

The effect of upper motor neuron regulation on skeletal muscle development was studied in the fetal pig. A region of the spinal cord at the level of the upper cervical vertebrae was destroyed by cauterization at 45 days of gestation in four pig fetuses. Five fetuses with intact spinal cords served as controls. Innervation and enzyme activities in the longissimus muscle, the ultrastructure and quantitation of satellite cells in the sartorius muscle, and plasma composition were evaluated at 110 days of gestation. The terminal innervation ratios were similar (P greater than 0.05) for muscles from control and cauterized fetuses. Endplate morphology was also similar. Therefore, innervation of newly formed primary fibers is not controlled by upper motor neurons after 45 days of gestation. Mean values for body weight, percentage of muscle dry weight, percentage of myofibers with myonuclei and plasma levels of protein, glucose, triglycerides, lactate, and creatine phosphokinase activity were similar (P greater than 0.05) between the two groups of fetuses. All but one muscle fiber examined was of the secondary fiber type. These observations suggest that the physiological maturity of the muscle was not appreciably altered even though glucose-6-phosphate dehydrogenase activity was higher (P greater than 0.05) and total phosphorylase activity was lower (P greater than 0.05) in the spinal cauterized fetuses than in the control group. The percentage of satellite cells was lower when based on the number of myofibers observed (P greater than 0.005) or on the number of nuclei contained within the basal lamina (P greater than 0.001) in the muscle of the spinal cauterized fetuses than in the control fetuses. The cytoplasm of satellite cells from the muscles of control fetuses was rich in organelles indicative of metabolic and mitotic activity whereas a paucity of such organelles was observed in the satellite cells of cauterized fetuses. Since the percentage of myofibers that had myonuclei was similar (P greater than 0.05) for the control and cauterized fetuses, it appeared that the myonuclear population was maintained by direct incorporation of the parent satellite cell.

Animals↗
PubMed1985

Muscle development in the grasshopper embryo. II. Syncytial origin of the extensor tibiae muscle pioneers.

The extensor tibiae muscle (ETi) in the metathoracic leg of the grasshopper, which powers the jump, is among the most studied insect muscles. In contrast to many insect muscles which are simple (consisting of only a single bundle of muscle fibers), the ETi is a complex muscle which consists of an array of bundles of muscle fibers, each with a separate site of insertion on the body wall ectoderm and on the ETi apodeme ectoderm. Here we describe the embryonic development of this complex muscle. The ETi muscle develops from a single muscle pioneer (MP) which connects the initial invagination of the ETi apodeme to the wall of the femur. This MP then dramatically expands around the developing apodeme to form a large horseshoe-shaped, multinucleate cell, called the supramuscle pioneer (supra-MP); the number of nuclei in the supra-MP increases by cell fusion rather than by nuclear division. The arms of the supra-MP grow steadily longer and their outer edges begin to appear scalloped, certain areas remaining tightly apposed to the ectoderm of the wall of the leg while adjacent areas lose their adhesion and are pulled away. By about 50% of embryonic development the ETi supra-MP consists of a periodic series of bridges (cytoplasmic extensions) connecting the leg wall ectoderm with the apodeme, and linked into a giant syncytium near their inner, apodeme surface by a thin layer of cytoplasm containing hundreds of nuclei. Each bridge is surrounded by a cluster of many smaller mesoderm cells. Next the syncytium begins to divide such that by 60% the periodic bridges of the supra-MP have lost syncytial contact with each other and now themselves form an array of smaller, individual, multinucleate MPs connecting the body wall to the apodeme, each surrounded by a mass of undifferentiated mesoderm cells. This initial cycle of fusion and division is followed by a second similar cycle in which the individual mesoderm cells surrounding each MP fuse with the MP. At the same time, the MP divides into the initial bundle of smaller muscle fibers. Coincident with this division into muscle fibers is the further development of thick and thin filaments and the T-tubule system.

Animals↗
PubMed1990

Biogenesis of transverse tubules: immunocytochemical localization of a transverse tubular protein (TS28) and a sarcolemmal protein (SL50) in rabbit skeletal muscle developing in situ.

To study the biogenesis of transverse tubules, the temporal appearance and distribution of TS28 (a specific marker of transverse tubules absent from the sarcolemma in adult skeletal muscle; 28,000 Mr) and SL50 (specifically associated with the sarcolemma and absent from the region of the transverse tubules in adult rabbit skeletal muscle) (Jorgensen, A.O., W. Arnold, A. C.-Y. Shen, S. Yuan, M. Gaver, and K.P. Campbell. 1990. J. Cell Biol. 110:1173-1185) were determined in rabbit skeletal muscle developing in situ (day 17 of gestation to day 15 newborn) by indirect immunofluorescence labeling. The results presented show that the temporal appearance and subcellular distribution of TS28 is distinct from that of SL50 at the developmental stages examined. TS28 was first detected in some, but not all, multinucleated myotubes on day 17 of gestation. At this stage of development, SL50 and the Ca2(+)-ATPase of the sarcoplasmic reticulum were already present in all myotubes. TS28 first appeared in discrete foci mostly confined to the cell periphery of the myotubes. At subsequent stages of development (days 19-24 of gestation), TS28 was also found in shoft finger-like structures extending obliquely and transversely from the cell periphery towards the center of the myotubes. 1-2 d after birth, TS28 was observed in an anastomosing network composed of transversely oriented chickenwire-like networks extending throughout the cytoplasm and interconnected by longitudinally oriented fiber-like structures. As development proceeded, the transversely oriented network became increasingly dominant. By day 10 of postnatal development, the longitudinally oriented component of the tubular network was not regularly observed. At none of the developmental stages examined was TS28 observed to be uniformly distributed at the cell periphery. SL50, like TS28, first appeared in discrete foci at the cell periphery. However, shortly after its first appearance it appeared to be distributed along the entire cell periphery. Although the intensity of SL50 labeling increased with development, it remained confined to the sarcolemma and was absent from the interior regions of the myofibers, where transverse tubules were present at all subsequent developmental stages examined. Immunoblotting of cell extracts from skeletal muscle tissue at various stages of development showed that SL50 was first detected on day 24 of gestation, while TS28 was not detected until days 1-2 after birth. Comparison of these results with previous ultrastructural studies of the formation of transverse tubules supports the idea that the temporal appearance and subcellular distribution of TS28 correspond very closely to that of the distribution of forming transverse tubules in rabbit skeletal muscle developing in situ.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1976

Insulin action on glucose transport and calcium fluxes in developing muscle cells in vitro.

The glucose transport system of developing muscle cells in vitro is described. Uptake experiments showed stereospecificity but no saturation or competition. Km-values for early myoblasts could not be determined; with progressive development, the absolute amount of uptake increases and becomes insulin sensitive. Km-values of about 13 mM basal and 32 mM for insulin stimulation were determined and discussed with respect to the glucose transport mechanism. Basal and insulin-dependent transport were shown to be dependent on the presence of calcium in the medium. Moreover, the ionophore A 23187 could be shown to mimic the insulin effect on glucose uptake. 45Ca saturation and desaturation experiments showed that insulin enhances the "mitochondrial" calcium pool by 35% and increases the apparent "cytoplasmic" efflux rate constant by 50%. We propose that insulin increases the free cytoplasmic calcium concentration, which may be the intracellular signal for the stimulation of glucose transport.

Animals↗
PubMed1995

Synapse-associated expression of an acetylcholine receptor-inducing protein, ARIA/heregulin, and its putative receptors, ErbB2 and ErbB3, in developing mammalian muscle.

Developing motor axons induce synaptic specializations in muscle fibers, including preferential transcription of acetylcholine receptor (AChR) subunit genes by subsynaptic nuclei. One candidate nerve-derived signaling molecule is AChR-inducing activity (ARIA)/heregulin, a ligand of the erbB family of receptor tyrosine kinases. Here, we asked whether ARIA and erbB kinases are expressed in patterns compatible with their proposed signaling roles. In developing muscle, ARIA was present not only at synaptic sites, but also in extrasynaptic regions of the muscle fiber. ARIA was synthesized, rather than merely taken up, by muscle cells, as indicated by the presence of ARIA mRNA in muscle and of ARIA protein in a clonal muscle cell line. ARIA-responsive myotubes expressed both erbB2 and erbB3, but little EGFR/erbB1 or erbB4. In adults, erbB2 and erbB3 were localized to the postsynaptic membrane. ErbB3 was restricted to the postsynaptic membrane perinatally, at a time when ARIA was still broadly distributed. Thus, our data are consistent with a model in which ARIA interacts with erbB kinases on the muscle cell surface to provide a local signal that induces synaptic expression of AChR genes. However, much of the ARIA is produced by muscle, not nerve, and the spatially restricted response may result from the localization of erbB kinases as well as of ARIA. Finally, we show that erbB3 is not concentrated at synaptic sites in mutant mice that lack rapsyn, a cytoskeletal protein required for AChR clustering, suggesting that pathways for synaptic AChR expression and clustering interact.

Aging↗
PubMed1987

Evidence for sequential expression of multiple AMP deaminase isoforms during skeletal muscle development.

AMP deaminase (myoadenylate deaminase; EC 3.5.4.6) is an integral part of the myofibril in skeletal muscle, and this enzyme plays an important role in energy metabolism in this tissue. We report here the identification of three AMP deaminase isoforms during skeletal muscle development in the rat. An embryonic isoform is expressed in the developing hindlimb of the rat between 7 and 14 days of gestation. This isoform is not unique to skeletal muscle or the embryo as it is also expressed in many nonmuscle tissues of the perinatal and adult rat. A perinatal isoform of AMP deaminase that is restricted to skeletal muscle is produced 4-6 days before birth and persists for 2-3 weeks of postnatal life. An adult, skeletal muscle-specific isoform of AMP deaminase appears at birth and reaches maximal levels after 3 weeks of postnatal development. We conclude from these studies there is a developmentally controlled program that leads to the sequential expression of AMP deaminase isoforms during the transition from embryonic to adult skeletal muscle.

AMP Deaminase↗
PubMed1992

Formation of highly organized skeletal muscle fibers in vitro. Comparison with muscle development in vivo.

Two methods were developed in which long-term cultures of quail skeletal muscle were established so that all of the muscle fibers develop in a highly oriented manner. The muscle fibers became spontaneously and vigorously contractile and established strong connections with the extracellular matrix at their ends that closely duplicate the structure of the myotendinous junction. A continuous basal lamina was formed around each muscle fiber that contained type IV collagen, laminin and heparan sulfate proteoglycan. With one of the methods, an extensive extracellular matrix developed around each muscle fiber that was highly organized with the formation of a distinctive epimysium, perimysium and endomysium. Analysis of the cultures by both methods for different isoforms of myosin showed expression of an adult form of myosin by some of the muscle cells. The results therefore demonstrate that muscle development in the present culture systems proceeds extensively for several weeks. It will now be possible to investigate directly the structure of the connections between muscle fibers and the extracellular matrix.

Animals↗