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PubMed1980

Beta-adrenergic receptor-adenylate cyclase alterations during the postnatal development of skeletal muscle.

The postnatal development of mammalian skeletal muscle is associated with an increased capacity for glycogenolysis. In the present study rabbit skeletal muscle underwent a 7-fold increase in glycogen synthase and glycogen phosphorylase activity over the postnatal period of 0--8 weeks. An enriched fraction of sarcolemma was prepared from neonatal and adult muscle to examine the development of the beta-adrenergic receptor-adenylate cyclase system. Adult membranes possessed a 2-fold greater Na+K+(Mg2+)-ATPase activity and a 6--8 fold greater sodium fluoride- and epinephrine-stimulated adenylate cyclase activity. The activation ratio (effector activity/basal activity) increased 2--3 fold for epinephrine and sodium fluoride in adult sarcolemma. The activation by catecholamines conformed to the physiological beta 2 type response with isoproterenol (1.8 . 10(-8) M) > epinephrine (1.1 . 10(-7) M) > norinephrine (3.2 . 10(-6) M). In contrast, binding studies employing (-)-[3H]dihydroalprenolol showed little difference between neonatal and adult membranes with respect to (1) number of binding sites, (2) equilibrium dissociation constant and (3) displacement of (-)-[3H]dihydroalprenolol by catecholamine agonists. Protein and lipid components of the sarcolemma were also modified during development. Neonatal membranes possessed two glycopeptides of Mr 80000 and 86000, whereas in the adult only a single Mr 113000 species was evident. The total lipid phosphorus and phospholipid composition was unchanged during development. The content of linoleic acid increased approx. 3-fold during development in the phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine phospholipids. The cholesterol content of adult membranes was decreased by 29% compared to neonatal membranes.

Adenylyl Cyclases↗
PubMed2006

The relative contributions of compression and hypoxia to development of muscle tissue damage: an in vitro study.

Deep pressure ulcers develop in tissues subjected to sustained mechanical loading. Though it has been hypothesized that this damage mechanism results from local tissue ischemia, it has recently been shown with a cell model that sustained compression can cause cell deformation, leading to tissue breakdown. The present study focuses on the assessment of cell viability during compression and ischemia in an in vitro muscle model to determine their relative contributions to damage development. A model system was developed consisting of engineered skeletal muscle produced from the culture of murine muscle cells in a collagen gel. The tissue was subjected to 0, 20, or 40% compression under hypoxic or normoxic conditions. Experiments were performed on the stage of a microscope and cell viability was monitored using fluorescent markers for apoptotic and necrotic cell death. Hypoxia did not lead to significant cell death over a 22 h period. By contrast, compression led to immediate cell death that increased with time. No additional effect of hypoxia on cell death was observed. These data show that contrary to existing theories, compression can cause development of muscle damage and that hypoxia does not contribute to cell death development within 22 h in engineered muscle.

Animals↗
PubMed1994

Substructure of cytoplasmic dense bodies and changes in distribution of desmin and alpha-actinin in developing smooth muscle cells.

The substructure of assembling cytoplasmic dense bodies (CDBs) and changes in the distribution of desmin and alpha-actinin during development of smooth muscle were studied in gizzard samples from 10- and 16-day embryos and from 1- and 7-day post-hatch chickens. CDBs in these cells lack the density of CDBs in mature or adult smooth muscle cells and, thus, allow observations of the changes inside CDBs. The random filament orientation seen in younger embryonic cells is first modified to include relatively small patches of IFs that are somewhat straighter and are approaching a side-by-side arrangement. As development proceeds, the IFs in these arrays become straighter, are parallel over longer lengths of the IFs and later acquire the density characteristic of mature CDBs. Anti-desmin labeling in embryonic 10- and 16-day cells showed that desmin intermediate filaments (IFs) were located in the myofilament compartment but were concentrated in or near assembling CDBs. Anti-desmin labeling shifted to the perimeter of CDBs after hatching. Cross sections, longitudinal sections, and stereo pairs all show that IF profiles are present inside unlabeled assembling CDBs. Anti-alpha-actinin labeling was directly on CDBs and was often associated with the cross-connecting filaments (CCFs) (average diameter of 2-3nm) inside CDBs. We propose, based on these data, that desmin IFs, alpha-actinin-containing CCFs, and actin filaments are the principal components of the substructure of assembling CDBs. We also present a proposed model for CDB assembly.

Actinin↗
PubMed1995

Cytoskeletal features in longitudinal and circular smooth muscles during development of the rat portal vein.

Immunohistochemistry of alpha-smooth muscle actin and desmin, two markers of smooth muscle cell differentiation, and electron-microscopic observation of thick filaments of myosin were performed on the media of the developing rat hepatic portal vein to gain insights into the chronology of differentiation of its longitudinal and circular smooth muscles. In accordance with the ultrastructural distribution of thin filaments, staining of alpha-smooth muscle actin is lightly positive in the myoblasts at postnatal day 1 and then extends in probably all muscle cells of the developing vessel. Desmin, which appears later than alpha-smooth muscle actin in the two muscles, is distributed throughout the longitudinal layer at day 8, whereas the first arrangements of thick filaments are detectable in most longitudinal muscle cells; at this stage, desmin and thick filaments are absent from the poorly differentiated circular muscle cells. The longitudinal muscle cells differentiate in a strikingly synchronized way from day 8 onwards, conferring a homogeneous structure to the developing and mature longitudinal layer. Several desmin-positive cells and a heterogeneous distribution of thick filaments occur in the circular muscle at day 14; the subsequent extension of these filaments in this layer results in a persisting heterogeneous distribution in the young 7-week-old adult. Many features of the mature smooth muscle cells are established within the third week in the longitudinal muscle, approximately one week before those of the circular layer. These results are consistent with the function of the longitudinal muscle as a spontaneously contractile smooth muscle unit, and emphasize the need for its fast maturation to fulfil its major role in the control of portal blood flow.

Actins↗
PubMed1982

Acyl-CoA synthase and acyltransferase activity in developing skeletal muscle membranes.

Enzymes participating in the activation and esterification of fatty acids for complex lipid biosynthesis were characterized in neonatal and adult rabbit skeletal muscle membranes. The activity of acyl-CoA synthase was 1.4-1.6-fold greater in neonatal vs. adult sarcoplasmic reticulum for the fatty acid substrates linoleic (2.6 vs. 1.61 nmol 18:2-CoA/min per mg), stearic (0.94 vs. 0.66 nmol 18:0-CoA/min per mg) and palmitic (2.43 vs. 1.51 nmol 16:0-CoA/min per mg) acids. Enzyme activity was identical between neonate and adult for coenzyme A, ATP and linoleic acid concentration dependence. Glycerol-3-phosphate acyltransferase activity was 6-fold greater in neonatal than adult sarcoplasmic reticulum for both linoleoyl-CoA (1.4 vs. 0.22 nmol 18:2/min per mg) and stearoyl-CoA (1.1 vs. 0.13 nmol 18:0/min per mg) donor substrates, whereas lysophosphatidylcholine acyltransferase activity was similar. Enriched fractions of sarcolemmal membranes possessed the highest activity for lysophosphatidylcholine acyltransferase activity, being 2-4-fold greater than sarcoplasmic reticulum. In contrast to sarcoplasmic reticulum, lysophosphatidylcholine acyltransferase activity was 2-3-fold greater in neonatal compared to adult sarcolemma for lineoleic (18.9 vs. 8.5 nmol 18:2/min per mg) and the stearic (2.8 vs. 0.68 nmol 18:0/min per mg) acid incorporation. The greater capacity of neonatal membranes for acylation by the de novo pathway is in accord with the requirements for neonatal muscle to effect high rates of triacylglycerol and phospholipid synthesis essential for oxidative metabolism and membrane synthesis during postnatal development and growth.

Acyl Coenzyme A↗
PubMed2000

Ciliary neurotrophic factor increases muscle fiber number in the developing levator ani muscle of female rats.

In addition to its well characterized neurotrophic properties, ciliary neurotrophic factor (CNTF) also has myotrophic effects in several experimental paradigms. We have previously observed that the volume of the levator ani (LA) muscle is increased in female rats treated with CNTF during the perinatal period. In order to determine the cellular basis for the effect of CNTF on LA muscle volume, female rat pups were given daily perineal injections of CNTF or a control solution from postnatal day 1 through 6. Mean cross-sectional area of LA muscle fibers and LA fiber number were assessed on postnatal day 7. CNTF treatment increased LA muscle fiber number more than 300% while having no effect on LA fiber size. We conclude that CNTF prevents muscle fiber degeneration and/or increases myogenesis in the developing LA muscle.

Animals↗
PubMed1991

Structure and developmental expression of troponin I isoforms. cDNA clone analysis of avian cardiac troponin I mRNA.

We isolated avian (chicken and quail) cardiac troponin I (TnIcardiac) cDNA clones for studies of Tn-Icardiac protein structure/evolution and developmental gene regulation. Comparison of the cDNA-predicted avian TnIcardiac amino acid sequences with known TnI sequences indicated 1) that the presence of an N-terminal extension sequence carrying a dual protein kinase A phosphorylation target site and an adjacent proline-rich segment is an ancient cardiac-specific feature of TnI which has been conserved since the bird/mammal divergence, 2) that features of the near-N-terminal troponin C (TnC)-binding site sequence suggest isoform-specific adaptation of TnI and TnC, and 3) that the avian TnIcardiac internal actin/TnC-binding, actomyosin-inhibitory, domain shows significant sequence divergence from mammalian TnIcardiac sequences, including the absence of a protein kinase C target site which is a cardiac-specific feature of TnI in mammals. Use of the cDNA clones to probe TnIcardiac mRNA expression during striated muscle development showed active expression in cardiac muscle from early developmental times (day 4 in ovo), but not in embryonic or adult skeletal muscle or in embryonic skeletal muscle cell cultures. Transcriptional run-on analysis showed that the heart-specific expression of TnIcardiac mRNA in embryonic striated muscle reflects transcriptional control of TnIcardiac gene expression. In many other contractile protein gene families, genes encoding cardiac isoforms are expressed early in skeletal muscle development and are later repressed. Thus, the restriction of active TnIcardiac gene expression to the cardiac muscle cell lineage is an unusual expression pattern for cardiac contractile protein genes and indicates that diverse gene regulatory mechanisms direct the differential expression of cardiac and skeletal muscle isoforms in different muscle gene families.

Amino Acid Sequence↗
PubMed1983

Formation of dolichol-linked sugar intermediates during the postnatal development of skeletal muscle.

The postnatal development of skeletal muscle is characterized by changes in membrane function associated with N-linked glycoproteins. In the present study, early reactions involved in the synthesis of the dolichol-linked core oligosaccharide were examined in neonatal and adult rabbit skeletal muscle sarcoplasmic reticulum membranes. The initial rate of N-acetylglucosamine incorporation in the presence of exogenous dolichol phosphate was similar between neonate and adult (3.5-4.1 pmol of GlcNAc/min/mg). The Km values for UDP-GlcNAc and exogenous dolichol phosphate were similar. Tunicamycin (0.04-0.08 micrograms/ml) inhibited N-acetylglucosamine incorporation by 50%. UDP-GlcNAc pyrophosphatase activity was greater in neonatal membranes than adult (840 versus 350 pmol of GlcNAc-1-P/min/mg), explaining, in part, the greater enhancement of neonatal GlcNAc incorporation by pyrophosphatase inhibitors. Nucleotide-sugar pyrophosphatase inhibitors (alpha, beta-methylene ATP and dimercaptopropanol) increased the capacity of neonatal activity 4-fold and adult enzyme 2-fold. Analysis of dolichol-linked products by mild acid hydrolysis however, revealed that neonate had higher capacity for N,N'-diacetylchitobiosyl(pyro)phosphoryldolichol synthesis than adult. Mannosyltransferase and glucosyltransferase were elevated 6- and 5-fold in neonate compared to adult membranes. Neonate exhibited 4-fold greater GDP-Man pyrophosphatase activity than adult (500 versus 125 pmol of Man-1-P/min/mg). The Km for GDP-Man increased in the presence of exogenous dolichol phosphate. Increasing concentrations of exogenous dolichol phosphate did not equalize neonate and adult mannosyltransferase activity, indicating that the decline in activity during development was not due to a decrease in a pool of dolichol phosphate accessible to mannosyltransferase. Glucosyltransferase for the synthesis of glucosylphosphoryldolichol was also elevated 5-fold in neonatal compared to adult sarcoplasmic reticulum (7 versus 1.4 pmol of Glc/min/mg). In a previous study, it was reported that glycoprotein sialyltransferase activity decreased by a factor of 6.5 during the postnatal maturation and that total membrane hexose content of sarcoplasmic reticulum decreased by a factor of 8. Together, these results suggest that the postnatal development of skeletal muscle is characterized by coordinated changes in the expression of enzymes involved in both the "early" and "late" reactions of N-linked oligosaccharide biosynthesis.

Acetylglucosamine↗
PubMed1984

Analysis of chromatin of skeletal muscle of developing rats using micrococcal nuclease and DNase I.

Conformational changes in the chromatin of skeletal muscle of 3-, 14- and 30 day-old developing rats have been studied using DNase I and micrococcal nuclease (MCN). Purified nuclei were digested separately by MCN and DNase I. The rate and extent of digestion by MCN decreases gradually as development proceeds. The electrophoretic pattern of MCN digested DNA, however, shows no change. The kinetics of digestion of nuclei by DNase I show no change with development. However, the electrophoretic pattern of DNase I digested DNA shows a gradual decrease in the amount of 10-30 bp fragments with progressive development. These studies show that the chromatin of the skeletal muscle undergoes certain conformational changes during postnatal development, and such changes in chromatin may be necessary for terminal differentiation of this tissue.

Age Factors↗
PubMed2000

Beta1 integrin expression during normal and low score normal avian myogenesis.

Skeletal muscle development is, in part, regulated by myoblast-extracellular matrix interactions mediated by the transmembrane integrin family of heterodimeric receptors. The avian genetic muscle weakness, low score normal (LSN), exhibits modified myotube and sarcomere structure that may be associated with altered integrin expression. Protein expression of the beta1 integrin subunit was measured during normal and LSN Pectoralis major muscle development at 14, 16, and 18 d of embryonic development, and 1 d and 1 and 6 wk posthatch. During embryonic development, integrin expression was downregulated. However, by 1 wk posthatch, integrin levels were upregulated and remained elevated through 6 wk posthatch. This pattern was observed in both normal and LSN muscle development. Overall, beta1 integrin levels were lower in the LSN P. major muscle. In normal and LSN satellite cell cultures, beta1 integrin expression was low during proliferation. In early differentiation, beta1 integrin expression increased and was then downregulated. As observed in the muscle extracts, LSN beta1 integrin expression was significantly lower during differentiation. These results suggest that the regulation of beta1 integrin expression is critical to the progression of myogenesis, and, during LSN myogenesis, decreased expression of beta1 integrin may be associated with modifications in muscle structure.

Animals↗
PubMed1988

Contractile properties of chick embryo muscles in development.

In this paper we report on the observation of two parameters of embryonic muscles which show the functional activity of myofibrillar ATPase activity of embryonic muscles and superprecipitation (SP) of natural actomyosin. Our results indicate that, during the embryonic period, the myofibrillar ATPase activity and the SP of actomyosin significantly increased, the rate of this increase being different for leg and breast muscles.

Animals↗
PubMed2004

In ovo temperature manipulation influences post-hatch muscle growth in the turkey.

1. The effect of manipulating egg incubation temperature for short periods on turkey muscle development was determined using the M. semitendinosus, a thigh muscle, as the model. 2. Experiment 1. Eggs were incubated at a control temperature of 37.5 degrees C. For a 4-d period of 0 to 4, 5 to 8, 9 to 12, 13 to 16, 17 to 20 or 21 to 24 embryonic days (ED) eggs were transferred to either 38.5 or 35.5 degrees C. A regime of 38.5 degrees C at 5 to 8 and 9 to 12 ED caused an increased myonuclei number and muscle fibre number, respectively. 3. Experiment 2. Eggs were incubated at a control temperature of 37.5 degrees C. At 5 to 8 ED eggs were transferred to 38.5 or 35.5 degrees C. Temperature-manipulated embryos showed a delay in differentiation (myogenin expression) of the semitendinosus muscle compared to controls. 4. Manipulating the incubation temperature for 4 d in early incubation alters muscle development in the turkey with no observation of deformities or reduction in hatchability. We speculate that this increase in temperature may result in an improved muscle growth in the post-hatch bird.

Animal Husbandry↗
PubMed1985

The early development of head control in preterm infants.

This study documents the longitudinal development of head control in 104 infants born at 25-33 weeks gestation. Protective side turning of the head was found to have a developmental sequence of reducing spinal extension. In the 93 infants with normal motor outcome, individual differences in the rate of development correlated with caudo-cephalic muscle development (P less than 0.001, r = 0.5) but not with the length of extra-uterine experience. As a group, the 11 infants with later motor handicap showed a persistence of the early form of movement at 35-39 weeks post-menstrual age, without a significant correlation with the ratio of upper-lower limb muscle development. Head control, supine to sitting, in the infants with normal motor outcome showed variations in the rate of preterm development. The infants born at less than 31 weeks showed significantly higher scores at 33-35 weeks post-menstrual age than those born at 31-33 weeks (P less than 0.01). There was no difference at later ages. The spinal extension movement accompanying protective side turning of the head is age specific to the preterm infant. Individual rates of normal preterm development can be evaluated by longitudinal standardised examination. As a group, the infants with subsequent abnormal motor development showed delay at preterm age but this was not individually significant.

Cerebral Palsy↗
PubMed1984

Muscle fiber type differentiation and satellite cell populations in normally grown and neonatally denervated muscles in the rat.

To examine the neural influence upon fiber type differentiation in developing muscles, newborn rats were subjected to sciatic nerve dissection, and the denervated extensor digitorum longus (EDL) (white) and soleus (red) muscles were examined in chronologic sequence by means of histochemistry and electron microscopy. The skeletal muscles in the newborn rats were undifferentiated (type 2C fibers seen on ATPase staining) and contained numerous myotubes. In the controls, the type 2C fibers started to differentiate at around 5 days and had almost completed type differentiation by 30 days in EDL and by 90 days in soleus muscles. On the other hand, none of the fibers in the neonatally denervated muscles developed into well differentiated type 1 and 2 A fibers, but both the EDL and soleus showed long-lasting type 2C and 2B populations. The satellite cells in the denervated EDL and soleus muscles decreased in number at the same rate as in the control muscles with maturation. The absence of a neural supply in the developing muscles induced a delay in muscle fiber type differentiation but did not influence the satellite cell populations in either EDL or soleus muscles.

Animals↗
PubMed1994

A central role for epidermal segment border cells in the induction of muscle patterning in the Drosophila embryo.

The correct patterning of muscles in the Drosophila embryo depends on the migration of developing muscles over the ectoderm and on the attachment of these muscles to specific attachment sites. We investigate the mechanisms that are involved in this process and describe experiments that allow a genetic dissection of the role of the ectoderm in muscle migration and attachment. We show that cells along the segmental border in the ectoderm are used by the developing muscles to reach their attachment sites. These segment border cells are recognized by dissociated myotubes in single suspensions in culture. Thus, developing muscles have properties that allow the specific recognition of the segment border cells and migrate to attach to these cells. The segment border cells are absent in the mutant wingless and naked. In these mutants, the muscles are severely disorganized. We show that this is not a mere consequence of disruption of the epidermis, since, in the mutant patched, where segmental patterning is affected, the segment border cells are present near their normal position; the muscles in this mutant are relatively organized. Similarly, in the mutant lines where ectopic segment border cells are present, the observed muscle derangement correlates well with the ectopic attachment sites that are present. Finally, we have analyzed mutants at the stripe locus and have shown that lethal alleles disrupt muscle organization during embryogenesis. Enhancer-trap alleles of stripe that we have analyzed show reporter gene expression in the segment border cells. Our results indicate a role for the segment border cells in guidance of migrating muscle fibers to their attachment sites.

Animals↗
PubMed1975

The formation of synapses in amphibian striated muscle during development.

1. A study has been made of the formation of synapses in developing reinnervated and cross-reinnervated amphibian twitch muscles which receive either a focal (iliofibularis) or a distributed (sartorius) innervation from 'en plaque' nerve terminals using histological, ultrastructural and electrophysiological techniques. 2. During the development of the tadpole through metamorphosis to the adult frog, the sartorius myofibres increased in length at about twice the rate of the iliofibularis myofibres, due to a fast rate of growth at their insertions on to the pelvic tendon. 3. The short iliofibularis and sartorius myofibres of young tadpoles (800 mum long) possessed only a single synapse and the iliofibularis myofibres did not receive any further innervation during development. However the sartorius myofibres received further transient innervation on the new muscle laid down during development at the fast growing pelvic insertion, until the distance between the original synapse formed on the myofibres and the synapse at the pelvic end of the muscle was about 12 mm. 4. During development synapses possessed either skewed, multimodal, or unimodal m.e.p.p. amplitude-frequency distributions; the intervals between m.e.p.p.s. were not distributed randomly according to a Poisson process, as m.e.p.p.s. of similar amplitudes tended to be separated by very short intervals; the unit-size e.p.p. had a similar amplitude-frequency distribution as the m.e.p.p.s. if these had a unimodal distribution. 5. Reinnervation or cross-reinnervation of the sartorius and the iliofibularis muscles in adults or at a late stage of development simply reconstituted the normal focal and distributed innervation patterns of the muscles, as found in the control muscles of the contralateral and unoperated legs. 6. These observations on synapse formation in amphibia are consistent with the hypothesis that during development the axon making the initial synaptic contact on the muscle cells induces a property over a length of muscle membrane adjacent to this site which makes it refractory to synapse formation; thus during reinnervation or cross-reinnervation of adult muscles this refractory property constrains synapse formation to these sites.

Amphibians↗
PubMed2006

MicroRNAs in muscle differentiation: lessons from Drosophila and beyond.

The mesoderm- and muscle-specific expression of microRNAs observed in a wide range of organisms suggests that post-transcriptional regulation by microRNAs can contribute significantly to the regulation of muscle development and physiology. One of these microRNAs, miR-1, is among the most widely conserved microRNAs during evolution. Genetic inactivation of miR-1 in Drosophila has shown that miR-1 is essential for maintaining the development and integrity of body wall muscles during phases of rapid growth, whereas it is not needed for normal mesoderm patterning and muscle specification. Expression analysis of a large set of potential miR-1 target mRNAs has revealed that these mRNAs tend to be expressed in non-muscle tissues, in patterns that are mutually exclusive with miR-1. Together, these findings lend support to the hypothesis that miR-1 exerts 'quality control' during muscle development by blocking detrimental mRNAs that are promiscuously expressed. Other miRNAs might promote specific developmental switches during the development and regeneration of muscles.

Animals↗