Biochemical studies on the developing thoracic muscles of the tobacco horn worm. II. Phospholipid composition in mitochondria during development.
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Uncoupling protein-3 gene expression in skeletal muscle during development is regulated by nutritional factors that alter circulating non-esterified fatty acids.
Uncoupling protein-3 gene expression in skeletal muscle is up-regulated during postnatal development of mice. A high-carbohydrate diet at weaning induces a decrease in uncoupling protein-3 mRNA levels that does not occur when mice were weaned onto a high-fat diet. Uncoupling protein-3 mRNA levels do not increase in response to fasting in young pups. Only after day 15 of life, when fasting increases serum non-esterified fatty acids, uncoupling protein-3 mRNA is up-regulated by starvation. Over-nutrition or under-nutrition during lactation increases or decreases, respectively, uncoupling protein-3 mRNA expression in skeletal muscle. Regulation of uncoupling protein-3 gene expression in skeletal muscle during development is mediated by ontogenic and nutritional factors determining changes in circulating non-esterified fatty acids.
Age Factors↗
Knowing chops from chuck: roasting myoD redundancy.
The myf5 and myoD genes are implicated in the specification of vertebrate skeletal muscle. These genes have been thought to be functionally redundant because neonatal mice bearing homozygous null mutations in either gene show grossly normal muscle development. By analyzing the early embryonic development of the mutants, Michael Rudnicki and coworkers show that trunk muscle development is retarded in embryos bearing myf5 null mutations, while early limb and branchial arch muscle development is retarded by myoD null mutations. These results indicate that the myoD and myf5 genes are not redundant but that each controls the early specification of distinct muscle cell lineages.
Animals↗
Development of human fetal muscles: a comparative histochemical analysis of the psoas and the quadriceps muscles.
The development of human muscle can be divided into three distinct phases on the basis of the enzyme histochemistry (Dubowitz 1965). On the other hand, muscles can be classified into trunk muscles innervated by the motoneurons in the anteromedial nucleus of the anterior horn and limb muscles innervated by those of the lateral nucleus. We compared histochemically the development of the psoas muscle as a trunk muscle with the quadriceps. Four legally aborted fetuses and sixteen autopsied preterm or full-term infants with conceptional ages ranging from sixteen to fourty-two weeks, served as subjects. Serial crossly cut frozen sections of the psoas and the quadriceps were stained with HE, modified Gomori-trichrome, NADH-TR, myofibrillar ATPase (routine, preincubation at pH 4.6, 4.3), and analyzed quantitatively. In the psoas and the quadriceps, all muscles consisted of undifferentiated type IIC fibers before the eighteenth week of gestation. Type I fiber began to appear around the eighteenth week in both muscles. Before the thirtieth week, both muscles comprised a great number of smaller type IIC fibers and scattered large type I fibers. The psoas had already a little more type I fibers than the quadriceps in this phase. After the thirtieth week, the percentage of type I fibers increased greatly to about 50% at term in the psoas, gradually to 20-23% at term in the quadriceps. Type IIA and IIB fibers appeared suddenly around the thirty-seventh week. Total percentage of these two type fibers increased at term to about 50% and 70% in the psoas and the quadriceps, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Adenosine Triphosphatases↗
Expression of the Fgf6 gene is restricted to developing skeletal muscle in the mouse embryo.
Fgf6, a member of the Fibroblast Growth Factor (FGF) family, is developmentally regulated and its expression is highly restricted in the adult. To gain further insight into the role of Fgf6, we studied its expression during embryogenesis using RNA in situ hybridization. Fgf6 expression is restricted to developing skeletal muscle. Fgf6 transcripts are first detected in the somites at 9.5 days post-conceptus, and expression continues in developing skeletal muscles up to at least 16.5 days post-conceptus. Fgfr4 is a putative receptor for FGF6. Its pattern of expression during myogenesis overlaps that of Fgf6, but both genes are not expressed in exactly the same population of cells. In addition, recombinant FGF6 protein is able to repress the terminal differentiation of myoblasts in culture, providing additional support to the concept that FGF6 plays an important role in myogenesis.
Animals↗
Curare-induced transformation of myosin pattern in developing skeletal muscle fibers.
The effects of neuromuscular block on the pattern of distribution of myosin isozymes in developing skeletal muscle fibers was examined by immunocytochemistry. The homogeneous population of fibers in the anterior latissimus dorsi (ALD) of the 18-day chick embryo was converted by curare to a mosaic of at least two categories of fibers. Normally all fibers in this slow muscle reacted with antibodies against slow myosin (anti-ALD). They also reacted with an antibody specific for the alkali 1 light chain (anti-delta 1) but not the alkali 2 light chain (anti-delta 2) of fast myosin. After treatment with curare, which inhibits neuronal cell death and increases the number of axonal endings, ALD muscle fibers continued to react with anti-delta 1, but many now reacted with anti-delta 2 as well. The same fibers failed to react with anti-ALD. From this it can be concluded that the myosin in this population was converted to a type not normally present. The changes, therefore, are not merely a result of the preferential loss of a slow type of fiber, nor are they a result of delayed maturation. In contrast, curare had no apparent effect on the fast posterior latissimus dorsi (PLD). As in the normal muscle at 18 days, all fibers reacted strongly with anti-delta 1 and to variable degrees with anti-delta 2, and very few fibers reacted with anti-ALD. Our observations suggest that the dual response to antibodies against fast and slow myosin during development is not a necessary consequence of multiple axon terminals. We present evidence that curare induces the expression of a different myosin in the embryonic ALD, and we suggest that the selective transformation of the fiber population may be a manifestation of a change in composition of the motoneuron pool.
Animals↗
A reappraisal of the origin of human extraocular muscles.
It has previously been suggested that extraocular muscles develop from mesoderm surrounding the head cavities and grow anteriorly into the orbit. A reappraisal of 54 specimens ranging in size from 8 mms to term indicates that human extraocular muscles develop from the mesoderm within the orbit and that these muscles do not develop from the apex of the orbit and grow anteriorly. Furthermore, the origin, belly, and insertion of the extraocular muscles develop contemporaneously, and each individual muscle develops at the same time. The morphogenesis of extraocular muscles includes the stages of mesenchymal cell, early myoblasts cells, myoblast cell, fusion of myoblast cell, myotube cell, and mature muscle cell.
Humans↗
Myofibrillar M-band proteins in rat skeletal muscles during development.
The distribution of three myofibrillar M-band proteins, myomesin, M-protein and the muscle isoform of creatine kinase, was investigated with immunocytochemical techniques in skeletal muscles of embryonic, fetal, newborn and four-week-old rats. Furthermore, muscles of newborn rats were denervated and examined at four weeks of age. In embryos, myomesin was present in all myotome muscle fibres of the somites, whereas M-protein was detected only in a small proportion of the myotome muscle fibres and muscle creatine kinase was not detected at all. In fetal and newborn muscles, all fibres contained all three M-band proteins. At four weeks of age, when fibre types (type 1 or slow twitch fibres and type 2 or fast twitch fibres) were clearly discernable, the pattern was changed. Myomesin and muscle creatine kinase were still observed in all fibres, whereas M-protein was present only in type 2 fibres. On the other hand, in muscle fibres denervated at birth all three M-band proteins were still detected. Our results suggest 1) that during the initial stages of myofibrillogenesis expression and incorporation of myomesin into the M-band precede that of M-protein and muscle creatine kinase; 2) that expression and incorporation of all three M-band proteins during fetal development is nerve independent and non coordinated to the expression of different forms of myosin heavy chains, and 3) that the suppression of M-protein synthesis during postnatal development is nerve dependent and reflects the maturation of slow twitch motor units.
Adenosine Triphosphatases↗
Myogenesis in primary cell cultures from Drosophila melanogaster: protein synthesis and actin heterogeneity during development.
Muscle cell cultures from Drosophila melanogaster were obtained by plating dissociated gastrula stage embryo cells on protamine-treated culture dishes. They myogenic cells in these cultures fuse to form multinucleated pulsating cells by 15 hr after plating. An analysis of protein synthesis during myogenesis in these cultures, as measured by the incorporation of 35S-methionine and analyzed by two-dimensional polyacrylamide gel electrophoresis, showed profound changes in the pattern of protein synthesis. This analysis enabled us to identify three distinct classes of proteins. Class A proteins, the most abundant, are synthesized continuously throughout myogenesis, class B proteins are those proteins whose synthesis is initiated during myogenesis and continued throughout development; class C proteins are those synthesized at specific times during development. In addition, three forms of actin have been identified in these cultures. Actin I, which shows increased synthesis concomitant with the myogenic development in these cultures, is apparently a muscle-specific form of actin. Actin II, the predominant "cytoplasmic" form of actin in the nonmuscle Schneider cell line 2, is also the major form in the gastrula cultures before differentiation begins. Synthesis of this actin continues in the myogenic cultures. Actin III is a rapidly turning over form of actin which does not accumulate in either the Schneider cells or the myogenic cultures.
Actins↗
Collagen synthesis in the muscle of developing chick embryos.
Radioactive protein was prepared from the leg muscle of chick embryos, 11, 14, 16 and 17 days old, each injected with radioactive proline and incubated for 30, 60 or 90 min afterwards. The radioactive protein was incubated with collagenase purified by chromatography on a Sephadex G-100 column. Under this condition, only collagen is digested into products soluble in trichloroacetic acid. The relative rate of collagen synthesis was determined by comparing the amount of radioactivity released into the supernatant fraction and that in the residue, by the method of Diegelmann & Peterkofsky [(1972) Dev. Biol. 28, 443--453]. The results show that the rate of collagen synthesis remains at approx. 10% of the rate of synthesis of other non-collagenous proteins during the development of chick embryonic muscle from 11 to 17 days. This suggests that the synthesis of collagen and that of other proteins are co-ordinately regulated at these stages of development.
Animals↗
A strong constant magnetic field affects muscle tension development in bullfrog neuromuscular preparations.
Effects of a constant magnetic field (CMF) of 0.65 T on muscle tension over 9 h were studied in the neuromuscular preparation of the bullfrog sartorius muscle. Tension was developed every 30 min by stimulation of the sciatic nerve (nerve stimulation) or of the sartorius muscle itself (muscle stimulation). In sciatic nerve stimulation, tension decreased rapidly for the first 3-4 h at a similar rate in both test (exposed to CMF) and control muscles. However, the rate of decrease became smaller and almost leveled off after 3-4 h in the test muscles, whereas tension continued to decrease monotonically in control muscles. The slope of the decrease for these later periods was significantly different between the test and the control conditions. Accordingly, tension was larger in test than in control muscles. In muscle stimulation, tension decreased monotonically from the start of experiments in control muscles, while tension in test muscles maintained their initial values for almost 3 h. Thereafter they started to decrease with a similar rate to the control. Hence, tension was always larger in test than in control muscles. A similar pattern of temporal change was observed for the rate of rise of the maximum tension for nerve or muscle stimulation. However, a significant difference was detected only in the case of muscle stimulation. The present results showed that a strong CMF of 0.65 T had biological effects on tension development of the bullfrog sartorius muscle by stimulation of the sciatic nerve as well as by stimulation of muscle itself. The presence of a small AC magnetic field component leaves open the possibility of an AC, rather than a CMF effect.
Animals↗
Expression of neuronal acetylcholine receptor genes in vertebrate skeletal muscle during development.
Of the 15 nicotinic ACh receptor genes identified in vertebrates, only four (alpha 1, beta 1, gamma, and delta) have been shown to be expressed in embryonic skeletal muscle at early times. In mammalian muscle a fifth gene (epsilon) replaces the gamma gene in expression at later times. The remaining 10 nicotinic receptor genes identified to date (alpha 2-alpha 8, beta 2-beta 4) are expressed in the nervous system and are considered neuronal genes. Using RNase protection assays, we show here that four of the neuronal-type genes (alpha 4, alpha 5, alpha 7, and beta 4) are expressed in developing chick skeletal muscle. Two of them (alpha 4 and alpha 7) decline substantially in transcript abundance between embryonic days 11 and 17, as does alpha 1, while the other two (alpha 5 and beta 4) show only moderate decreases over the same time period. At embryonic day 8, alpha 7 transcripts are nearly 20% as abundant as alpha 1 transcripts. In situ hybridizations confirm the presence of alpha 7 transcripts in muscle cells both in cell culture and in embryonic tissue. No evidence was found for expression of the alpha 2, alpha 3, alpha 8, or beta 3 genes in muscle. Immunoprecipitations and immunoblot analysis using subunit-specific monoclonal antibodies reveal alpha 7 protein in muscle, and the amount of protein rises and declines with the amount of alpha 7 mRNA during development. Sucrose gradient analysis demonstrates that the alpha 7 protein is present in muscle as a species of 10S, the size expected for a nicotinic receptor. The alpha 7 species in muscle binds alpha-bungarotoxin but does not contain alpha 1 subunits, indicating that the two kinds of alpha-type gene products segregate during assembly. The results suggest that neuronal AChRs may play a role in early muscle development.
Animals↗
Denervated skeletal muscle fibers develop discrete patches of high acetylcholine receptor density.
Denervated skeletal muscle fibers of mice develop discrete patches of high acetylcholine receptor density. The patches vary in size from less than 1 micrometer up to 30 micrometers, depending on the muscle and the period of denervation. Within the patches the acetylcholine receptor density is some 20 times greater than elsewhere along the muscle fiber and probably approaches that in the subsynaptic membrane.
Acetylcholine↗
Developmental changes of cardiac and slow skeletal muscle troponin T expression in chicken cardiac and skeletal muscles.
Numerous troponin T (TnT) isoforms are produced by alternative splicing from three genes characteristic of cardiac, fast skeletal, and slow skeletal muscles. Apart from the developmental transition of fast skeletal muscle TnT isoforms, switching of TnT expression during muscle development is poorly understood. In this study, we investigated precisely and comprehensively developmental changes in chicken cardiac and slow skeletal muscle TnT isoforms by two-dimensional gel electrophoresis and immunoblotting with specific antisera. Four major isoforms composed of two each of higher and lower molecular weights were found in cardiac TnT (cTnT). Expression of cTnT changed from high- to low-molecular-weight isoforms during cardiac muscle development. On the other hand, such a transition was not found and only high-molecular-weight isoforms were expressed in the early stages of chicken skeletal muscle development. Two major and three minor isoforms of slow skeletal muscle TnT (sTnT), three of which were newly found in this study, were expressed in chicken skeletal muscles. The major sTnT isoforms were commonly detected throughout development in slow and mixed skeletal muscles, and at developmental stages until hatching-out in fast skeletal muscles. The expression of minor sTnT isoforms varied from muscle to muscle and during development.
Animals↗
Temperature dependence of contraction characteristics in developing rat muscles.
Contractions of rat extensor digitorum longus (EDL, a fast muscle) and soleus (SOL, a slow muscle) muscles of different ages (1-4 weeks) were recorded in vitro with direct stimulation and at different temperatures (range 35-10 degrees C). Twitch tension in 4-week-old EDL muscle increased in cooling from 35 to 20 degrees C (cooling potentiation); the tension decreased in further cooling below 20 degrees C. This pattern of temperature dependence of twitch tension was seen in fast muscles of all ages (1-4 weeks). Twitch tension in 4-week-old SOL muscle decreased monotonically in cooling from 35 to 10 degrees C (cooling depression). This pattern of cooling depression was not clearly evident in younger SOL muscles. There was a marked hysteresis in the temperature dependence of twitch tension in the 1-week-old SOL muscles. Tetanic tension was depressed by low temperature in both EDL and SOL muscles at 1 week and at 4 weeks of age. Results show that the processes concerned with contractile activation are nearly fully developed in the fast muscle fibers at an early age (1 week), whereas they develop later in the slow muscle fibers.
Animals↗
Changes in myosin heavy chain stoichiometry in pig tracheal smooth muscle during development.
The stoichiometry of the myosin heavy chains (MHCs) has been measured in the tracheal smooth muscle of the pig after electrophoresis on SDS 4% polyacrylamide gel. The ratio of slower migrating MHC to the faster migrating MHC was 2.1 neonates, 1.5 in young and 0.95 in old pigs (P less than 0.01) showing that MHC composition changes with development. The unequal proportion of MHCs was not compatible with a heterodimeric arrangement of the MHCs in the native molecule as proposed earlier by Rovner et al. [(1986) Am. J. Physiol. 250, C861-870] and it is suggested that native molecules may be composed of homodimer heavy chains.
Animals↗
Selective innervation of types of fibres in developing rat muscle.
The technique of glycogen depletion has been used to identify the types of muscle fibres innervated by individual motor neurones in the neonatal rat. This analysis shows that neonatal motor units are highly biased in their fibre type composition, even at times when the fibres receive extensive polyneuronal innervation. This finding suggests that the innervation of muscle fibres is somehow sorted according to type during early development. This sorting does not appear to occur during the removal of the polyneuronal innervation because little, if any, increase in the bias of unit compositions occurs as the number of synapses present in the muscle is reduced 2- to 3-fold. To determine whether the sorted innervation might be explained by a selective synaptogenesis, a study was made of the type compositions of units formed by reinnervation of neonatal soleus muscle. Glycogen depletion of single units 2 weeks following crush of the soleus nerve at postnatal day 2 showed that most of them (10/12) had biased type compositions which could not be explained by a random reinnervation. The location of fibres in the reinnervated motor units suggests that the regenerating axons innervated a novel set of fibres. The differentiation of fibres into types was apparently not changed during their reinnervation. These results imply that regenerating motor neurones in the neonatal rat selectively reinnervate muscle fibre types. These and other studies further imply that the organization of fibres into motor units during normal development does not occur, as is widely believed, by a random innervation of naive fibres and their subsequent differentiation under the influence of innervation.
Animals↗
Identification of decorin and chondroitin sulfate proteoglycans in turkey skeletal muscle.
Turkey pectoral muscles were examined at 15 through 25 d of embryonic age in order to delineate the developmental pattern of proteoglycan expression during skeletal muscle development. Glycosaminoglycan concentration, decorin, and muscle chondroitin sulfate proteoglycan (M-CSPG) levels were measured at each developmental age. Glycosaminoglycan levels rose during the developmental period studied, whereas decorin and M-CSPG levels were initially high at Day 15 and then decreased. The results from this study demonstrate the presence of both decorin and M-CSPG during turkey skeletal muscle development.
Animals↗