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At least 667 records · Page 37Linked to original sources
PubMed2000

Apterous mediates development of direct flight muscles autonomously and indirect flight muscles through epidermal cues.

Two physiologically distinct types of muscles, the direct and indirect flight muscles, develop from myoblasts associated with the Drosophila wing disc. We show that the direct flight muscles are specified by the expression of Apterous, a Lim homeodomain protein, in groups of myoblasts. This suggests a mechanism of cell-fate specification by labelling groups of fusion competent myoblasts, in contrast to mechanisms in the embryo, where muscle cell fate is specified by single founder myoblasts. In addition, Apterous is expressed in the developing adult epidermal muscle attachment sites. Here, it functions to regulate the expression of stripe, a gene that is an important element of early patterning of muscle fibres, from the epidermis. Our results, which may have broad implications, suggest novel mechanisms of muscle patterning in the adult, in contrast to embryonic myogenesis.

Animals↗
PubMed1996

Differential assembly of cytoskeletal and sarcomeric actins in developing skeletal muscle cells in vitro.

Monoclonal antibodies (McAb) to actin were prepared to analyze the assembly of actin isoforms in developing muscle cells in vitro. One of the antibodies (SkA-06) was specific for alpha-sarcomeric actin isoforms in skeletal and cardiac muscles, while the others recognized cytoskeletal (beta, gamma) actin isoforms in smooth muscle and non-muscle tissues as well as the sarcomeric (alpha) actins. Using SkA-06 and a polyclonal antibody (PcAb) specific for cytoskeletal actins, the subcellular localization of the actin isoforms was examined by immunocytochemical methods. While in developing young myotubes, cytoskeletal and sarcomeric actins were co-localized in nascent myofibrils or stress-fiber-like structures, sarcomeric actins predominated in striated myofibrils in more developed myotubes. When FITC-labeled cytoskeletal and sarcomeric actins were introduced into young myotubes by a microinjection method, the latter became detectable in striated structures sooner than the former but they were finally incorporated into striated myofibrils. These results suggest that alpha-actin(s) as well as beta- and gamma-actins can be incorporated into myofibrils, but alpha-actin(s) is assembled preferentially into myofibrils in developing muscle cells.

Actins↗
PubMed2000

Expression of cofilin isoforms during development of mouse striated muscles.

Cofilin (CF) is an actin regulatory protein that plays a critical role in actin filament dynamics in a variety of cells. Two cofilin isoforms. muscle-type (M-CF) and nonmuscle-type (NM-CF) encoded by different genes, exist in mammals; in the adult, the former is predominantly expressed in muscle tissues, while the latter is distributed in various non-muscle tissues (Ono et al., 1994). In this study, we examined cofilin isoform expression during skeletal and cardiac muscle development in mice using cDNA probes and antibodies which distinguish the isoforms. We found that the expression of M-CF was initiated in terminally differentiated myogenic cells in both the myotome and limb buds. In myogenic cell cultures, its expression occurred coupled with myotube formation. NM-CF was expressed in developing skeletal and cardiac muscles but disappeared from skeletal muscle during postnatal development, while its expression persisted in the heart, even in adult mice. A similar situation was observed in the heart of other mammals. Thus, it is likely that the both cofilin isoforms are involved in the regulation of actin assembly during myofibrillogenesis. Only M-CF could be involved in actin dynamics in mature skeletal muscle, while both isoforms could be in the mature heart.

Actin Depolymerizing Factors↗
PubMed1995

Changes in responsiveness to extracellular ATP in chick skeletal muscle during development and upon denervation.

Skeletal muscles in developing chick embryos were tested for responsiveness to adenosine 5'-triphosphate (ATP), a substance known to depolarize chick skeletal muscle in culture. The sensitivity to extracellular ATP was tested at various stages of development in five different muscles; pectoralis superficia, anterior latissimus dorsi, posterior latissimus dorsi, sartorious, and gastrocnemius. At the earliest time that muscles were tested (Embryonic Day 6, stage 30 of Hamburger and Hamilton, 1951) application of ATP(50-100 microM) elicited vigorous contractions in all five muscles, but within a few days (Embryonic Day 17, stage 43) none of the muscles contracted in response to ATP. Sensitivity declined at approximately the same time in all five of these muscles. Intracellular recordings made from muscle fibers near the time of hatching (Embryonic Days 18-21 or Postnatal Days 1-2) indicated that the loss of the ability to contract in response to ATP was due to the total loss of responsiveness to ATP. Surgical denervation of the anterior latissimus dorsi and posterior latissimus dorsi was performed in a series of chicks 1-2 days after hatching, and the ability of these muscles to contract in response to ATP was tested 3-10 days after the surgery. Contractions in response to ATP were present in many of the muscles. Thus denervation of muscles in newly hatched chicks led to the reappearance of sensitivity to ATP. The disappearance of ATP responsiveness shortly after muscles become innervated and the reappearance of ATP responsiveness following denervation suggest that the expression of ATP responsiveness is regulated by motor neurons.

Adenosine Triphosphate↗
PubMed1983

Studies on glycoconjugate metabolism in developing skeletal muscle membranes.

The postnatal development of mammalian skeletal muscle is characterized by changes in the properties of several key membrane glycoprotein enzymes and receptors. In the present study, CMP-sialic acid: fetuin sialyltransferase and CMP-sialic acid: lactosylceramide sialyltransferase activity was characterized in sarcolemma and sarcoplasmic reticulum membranes isolated from neonatal (0-1 week) and adult (8 week) rabbit skeletal muscle. CMP-sialic acid: fetuin sialyltransferase decreased by a factor of 10 in sarcolemma and 6 in sarcoplasmic reticulum during development, whereas CMP-sialic acid: lactosylceramide sialyltransferase activity decreased by a factor of 6 in sarcolemma and 18 in sarcoplasmic reticulum. The Km for CMP-sialic acid using the lipid acceptor declined during the development of sarcoplasmic reticulum (neonate vs. adult: 538 vs. 33 microM), but not in sarcolemma. The carbohydrate composition of sarcolemma was changed only with respect to total sialic acid content (neonate vs. adult: 67 vs. 44 nmol/mg). Similar analysis of sarcoplasmic reticulum carbohydrates showed decreases in total sialic acid, lipid-bound sialic acid, hexosamines and hexoses. The major ganglioside was GM3 for both types of membrane. No qualitative changes were observed in ganglioside composition comparing neonatal and adult membranes.

Aging↗
PubMed1996

Quantitative analysis of low molecular weight G-actin-binding proteins, cofilin, ADF and profilin, expressed in developing and degenerating chicken skeletal muscles.

A large amount of G-actin is pooled in the cytoplasm of young embryonic skeletal muscle and, although its concentration is reduced as muscle develops, the total amount of actin in muscle cells increases remarkably. Three G-actin-binding proteins, cofilin, ADF and profilin, are known to be involved in creating the G-actin pool in the embryonic muscle. To better understand how they are responsible for the regulation of assembly and disassembly of actin in developing and degenerating muscles, we measured the amounts of the three G-actin-binding proteins by means of quantitative immunoblotting and compared them with that of G-actin. The sum of the amounts of the three actin-binding proteins was insufficient at early developmental stages but sufficient at later stages to account for the pool of G-actin in young muscle cells. It decreased in parallel with the decrease in the G-actin pool as muscle developed. Expression of thymosin beta 4, which is known to be extremely important for G-actin-sequestering in a variety of non-muscle cells, was detected at a considerable level in young embryonic but not in adult skeletal muscles according to Northern and Western blotting. In degenerating denervated and dystrophic muscles, cofilin and profilin, but not ADF, were significantly increased in amount. From these results, we conclude that the G-actin pool in young embryonic skeletal muscle is mainly due to cofilin, ADF, profilin and thymosin beta 4, but thymosin beta 4 as well as ADF becomes less important as muscle develops. Cofilin and profilin may also be involved in the redistribution of actin during myofibrillogenesis and in the process of actin disassembly in degenerating muscles.

Actin Depolymerizing Factors↗
PubMed1974

The formation of synapses in reinnervated and cross-reinnervated striated muscle during development.

1. A study has been made of the formation of synapses in reinnervated and cross-reinnervated developing striated muscles which normally receive either a focal or distributed innervation, using histological, ultrastructural and electrophysiological techniques.2. The focally innervated mammalian tibialis anterior muscle, denervated soon after birth, was reinnervated at both the original end-plates as well as on the new muscle added during the period of denervation; but not on the muscle present at the time of denervation. Nearly all the synapses which had formed, other than at the original end-plates, disappeared by 6 weeks post-natal.3. The avian anterior latissimus dorsi muscle (ALD), which receives a distributed innervation, was denervated during the first week post-hatched, and became reinnervated both at the original synaptic sites as well as on the new muscle added during the period of denervation; all these synapses were spaced approximately 200 mum apart along the length of individual muscle cells.4. The myofibres of the ALD muscle cross-reinnervated at hatching with the superior brachialis nerve, which contains fast motor axons that normally form a focal innervation, were each focally innervated by a single ;en plaque' terminal; these synapses had the same electrical properties as normal synapses formed by fast motor axons.5. Many of the myofibres of the avian posterior latissimus dorsi (PLD), which normally receive a focal innervation, received a distributed innervation from ;en grappe' terminals when cross-reinnervated with the ALD nerve at hatching.6. It is suggested that during development the nerve type determines the pattern of synapses over an effector; this is achieved by the nerve, after forming the initial synaptic contact, making the rest of the muscle cell membrane refractory to further synapse formation for some distance, this distance being determined by the nerve type.

Action Potentials↗
PubMed1988

Reorganization of synaptic inputs to developing skeletal muscle fibres.

During early stages of postnatal development skeletal muscle fibres of mammals are contacted by several axons. The transition from poly- to mononeuronal innervation has been extensively studied on the rat soleus. The role of activity in this process has been acknowledged but the mechanisms leading to synapse remodelling are not understood. The participation of the muscle has to be taken into account; if muscles are paralysed by alpha-bungarotoxin, the elimination of terminals is arrested. Changes in Ca2+ also influence the rate of removal of terminals. Calcium seems to act through a calcium-activated neutral protease (CANP) present in nerve endings. If CANP is inhibited, elimination fails to take place. Thus Ca2+ enters the terminal and activates the CANP. Release of K+ ions from active muscle could link muscle activity and synapse elimination. Excess K+ was found to reduce nerve-muscle contacts, by depolarizing terminals and allowing Ca2+ entry. A greater increase of Ca2+ concentration in smaller terminals would be expected, because of their surface-to-volume ratio, and they are preferentially eliminated. Thus elimination depends on the unequal size of terminals at the endplate. Therefore the 'survivability' of individual nerve endings may already be determined at the time of synapse elimination.

Acetylcholine↗
PubMed1984

Immunochemical analysis of C-protein isoform transitions during the development of chicken skeletal muscle.

Isoforms of C-protein in adult chickens which differ in fast (pectoralis major, PM) and slow (anterior latissimus dorsi, ALD) skeletal muscles can be distinguished immunochemically with monoclonal antibodies (McAbs) specific for the respective fast (MF-1) and slow (ALD-66) protein variants (Reinach et al., 1982 and 1983). The expression of these C-proteins during chick muscle development in vivo has been analyzed by immunoblot and immunofluorescence procedures. Neither MF-1 nor ALD-66 reacted with whole-cell lysates or myofibrils from PM of 12-day-old embryos. However, both McAbs bound to peptides of 145 kDa in PM from late embryonic and young posthatched chickens. All of the myofibers in these muscles reacted with both antibodies, but the binding of the anti-slow McAb (ALD-66) diminished progressively with age and was completely negative with PM by 2 weeks after hatching. In contrast, the ALD muscle from 17 days in ovo thru adulthood only reacted with ALD-66; no binding of MF-1 could be detected at these stages. Since both fast and slow myosin light chains (LC) coexist within embryonic pectoralis and ALD muscles (e.g., G. F. Gauthier, S. Lowey, P. A. Benfield, and A. W. Hobbs, 1982, J. Cell Biol. 92, 471-484) yet segregate to specific fast and slow muscle fibers at different stages of development, the temporal transitions of C-protein and myosin LC were compared during myogenesis. "Slow-type" C-protein appeared after the disappearance of slow myosin light chains, whereas the accumulation of the "fast-type" light chains occurred before the expression of "fast-type" C-protein. The pattern of isoform transitions appears to be far more complex than previously suspected.

Age Factors↗
PubMed1992

Muscle fiber pattern is independent of cell lineage in postnatal rodent development.

Muscle fibers specialized for fast or slow contraction are arrayed in characteristic patterns within developing limbs. Clones of myoblasts analyzed in vitro express fast and slow myosin isoforms typical of the muscle from which they derive. As a result, it has been suggested that distinct myoblast lineages generate and maintain muscle fiber pattern. We tested this hypothesis in vivo by using a retrovirus to label myoblasts genetically so that the fate of individual clones could be monitored. Both myoblast clones labeled in muscle in situ and clones labeled in tissue culture and then injected into various muscles contribute progeny to all fiber types encountered. Thus, extrinsic signals override the intrinsic commitment of myoblast nuclei to particular programs of gene expression. We conclude that in postnatal development, pattern is not dictated by myoblast lineage.

Animals↗
PubMed2002

Deficiency of triad formation in developing skeletal muscle cells lacking junctophilin type 1.

Junctophilins (JP-1, JP-2, and JP-3) are transmembrane proteins expressed in the junctional membrane complexes in excitable cells. Both JP-1 and JP-2 are co-expressed in the triads of skeletal muscle, but only JP-2 is expressed in cardiac muscle. We analyzed the roles played by JP-1 and JP-2 in triad formation in skeletal muscle by comparing developing skeletal muscles in wild-type and JP-1-knockout (KO) mice (both before and after birth). In the skeletal muscles of embryos, most of the couplings between sarcoplasmic reticulum (SR) and transverse tubule (T-tubule) were diads, with triads being very scarce. The number of triads increased markedly after birth in wild-type mice. However, there was no increase in the number of triads in the neonates of JP-1-KO mice, and they died within 1 day after birth. JP-2 expression was constant before and after birth, while expression of JP-1 increased with birth. Quantitative and morphological differences were not seen between wild-type and JP-1-KO mice in the formation of diads in the period just before the JP-1-KO mice died. The SR swelled and developed large vacuoles in skeletal muscle cells just before the JP-1-KO mice died. The present results strongly suggest that JP-1 and JP-2 play important roles in the formation of triads and diads, respectively, during the development of skeletal muscle in mouse.

Animals↗
PubMed2001

Actinin-associated LIM protein-deficient mice maintain normal development and structure of skeletal muscle.

The actinin-associated LIM protein, ALP, is the prototype of a large family of proteins containing an N-terminal PDZ domain and a C-terminal LIM domain. These PDZ-LIM proteins are components of the muscle cytoskeleton and occur along the Z lines owing to interaction of the PDZ domain with the spectrin-like repeats of alpha-actinin. Because PDZ and LIM domains are typically found in proteins that mediate cellular signaling, PDZ-LIM proteins are suspected to participate in muscle development. Interestingly the ALP gene occurs at 4q35 near the heterochromatic region mutated in facioscapulohumeral muscular dystrophy, indicating a possible role for ALP in this disease. Here, we describe the generation and analysis of mice lacking the ALP gene. Surprisingly, the ALP knockout mice show no gross histological abnormalities and maintain sarcolemmal integrity as determined by serum pyruvate kinase assays. The absence of a dystrophic phenotype in these mice suggests that down-regulation of ALP does not participate in facioscapulohumeral muscular dystrophy. These data suggest that ALP does not participate in muscle development or that an alternative PDZ-LIM protein can compensate for the lack of ALP.

Animals↗
PubMed1995

Muscle-specific gene expression during myogenesis in the mouse.

Over the past decade, significant advances in molecular biological techniques have substantially increased our understanding of in vivo myogenesis, supplementing the information that previously had been obtained from classical embryological and morphological studies of muscle development. In this review, we have attempted to correlate morphogenetic events in developing murine muscle with the expression of genes encoding the MyoD family of myogenic regulatory factors and the contractile proteins. Differences in the pattern of expression of these genes in murine myotomal and limb muscle are discussed in the context of muscle cell lineage and environmental factors. The differences in gene expression in these two types of muscle suggest that no single coordinated pattern of gene activation is required during the initial formation of the muscles of the mouse.

Animals↗