On the cellular regulation of growth and development in skeletal muscle

Cellular development in muscle differs between Angus steers from low and high muscle score selection lines1

This study assessed cellular characteristics of longissimus lumborum (LL) and semitendinosus (ST) muscles in steers genetically selected for low (Low) or high (High) muscling using live muscle scoring, and High steers with 1 copy of the loss-of-function 821 del11 MSTN allele (HighHet). We hypothesized High and HighHet have altered muscle cellular characteristics and mechanisms influencing muscling compared with Low steers. Angus steers 25 mo old comprising 14 High, 19 Low, and 11 HighHet were backgrounded to 20 mo of age, grain finished for 150 d, and then slaughtered. Body and carcass weights did not differ due to muscling line (P = 0.46). Weight of LL was 16% greater (P = 0.004) and total protein in LL was 18% greater (P = 0.012) in HighHet than Low steers. ST weight in HighHet was 10% and 13% greater than in High and Low steers (P = 0.007), respectively, and of total ST protein 12% and 17% greater in HighHet than High or Low (P = 0.002). Cross-sectional area (CSA) of LL was greater in HighHet than in High and greater in High than in Low (85.0 vs. 77.0 vs. 70.4 cm2, P < 0.001). Apparent number of myofibers and myofibers per unit CSA did not differ between the muscling lines in LL (P = 0.14) or ST (P = 0.47). Myofiber CSA was greater in the ST of Low than of High and HighHet for type 1 (36% and 31% respectively, P = 0.005) and 2A (22% and 25%, P < 0.001). HighHet steers had greater area of glycolytic (type 2X) relative to more oxidative myofiber types within LL (P = 0.02; 11% and 43% more than High and Low, respectively) and ST (P < 0.001; 27% and 75%). Concentration of RNA in LL was 13% and 10% greater (P = 0.005) in High than in Low and HighHet, respectively, and total amount of RNA in LL was 22% greater in High and 20% greater in HighHet than in Low (P < 0.001). The LL of High steers had less protein to RNA (P = 0.03; 57.4 vs. 65.6) and more RNA to DNA (P = 0.007; 9.03 vs. 7.83) than Low. HighHet steers had 11% more DNA in ST than High (P = 0.04) and 19% more RNA in ST than Low (P = 0.012). The shift towards glycolytic myofibers was consistent with loadings in a principal component that explained 39% of the variation in LL and 38% in ST. Overall, these findings show that selection for increased muscling using live cattle muscle scoring, and 1 copy of the 821 del11 MSTN allele, results in more glycolytic muscle. They also suggest that increased muscling of the High compared with Low steers may be associated with increased translational capacity in the LL.

Indices of cellular development in muscles of lambs are influenced by sire estimated breeding values and pastoral nutritional system

This study examined influences of sire (n = 9) estimated breeding values (EBVs), sire-group (Muscle, Growth, and Control), and nutrition (low and high quality and availability pasture) from birth to slaughter at ~8 months of age on indices of muscle cellularity and transcriptional and translational capacity in 56 castrate lambs. Effects of nutritional systems to 8 months of age were greater, overall, than those due to EBVs or sire-group. Amount of DNA increased with increasing EBV for post-weaning eye muscle depth (PEMD or Muscle EBV) in longissimus but not in semimembranosus and semitendinosus muscles, while Muscle EBV also had an inverse association with concentration of DNA. Protein to DNA and RNA to DNA were related positively to Muscle EBV, the associations being strongest for the semitendinosus muscle. Post-weaning weight (PWWT or Growth) EBV correlated positively with the RNA to DNA ratio and, among high but not low nutrition lambs, was inversely related to concentration of muscle DNA, whereas post-weaning fat depth (PFAT or Fat) EBV was correlated positively with RNA concentration. Overall, the magnitude of effects of sire-group was less than for sire EBVs, presumably due to differing selection pressures for muscling, fatness, and growth. High nutrition lambs had more protein to DNA than low nutrition lambs in the longissimus and semitendinosus muscles, but not in the semimembranosus muscle. In low compared with high nutrition lambs, concentration of DNA was greater in the longissimus and semitendinosus muscles. Total amount of DNA was reduced by more in low compared with high nutrition in the longissimus and semimembranosus than in the semitendinosus, and amount of protein was reduced by more in low compared with high nutrition in the longissimus than in the other two muscles. We conclude that genetic selection for eye muscle depth in sheep has differing effects on cellular characteristics of the longissimus, semimembranosus, and semitendinosus muscles, and has greater effects on muscle cellular characteristics than genetic selection for post-weaning weight or fat depth.

Yeast mitochondrial dynamics: fusion, division, segregation, and shape

Mitochondria are essential organelles found in virtually all eukaryotic cells that play key roles in a variety of cellular processes. Mitochondria show a striking heterogeneity in their number, location, and shape in many different cell types. Although the dynamic nature of mitochondria has been known for decades, the molecules and mechanisms that mediate these processes are largely unknown. Recently, several laboratories have isolated and analyzed mutants in the yeast Saccharomyces cerevisiae defective in mitochondrial fusion and division, in the segregation of mitochondria to daughter cells, and in the establishment and maintenance of mitochondrial shape. These studies have identified several proteins that appear to mediate different aspects of mitochondrial morphogenesis. Although it is clear that many additional components have yet to be identified, some of the newly discovered proteins raise intriguing possibilities for how the processes of mitochondrial division, fusion, and segregation occur. Below we summarize our current understanding of the molecules known to be required for yeast mitochondrial dynamics.

Conditions for the culture of bovine embryonic myogenic cells

The objective of this experiment was to determine the growth characteristics of bovine embryonic muscle cells and to optimize the growth conditions for these cells using commercially-prepared media and sera. In the first study, the growth of muscle cells isolated from the hindlimb was determined by measuring DNA content. The DNA concentration was lowest (P < 0.001) at 24 h post-plating and increased to a maximum at approximately 60 h. The slopes of creatine kinase activity and fusion index curves were similar to the DNA; however, the creatine kinase activity achieved a maximum at 140 h post-plating, while the fusion index reached maximum at 120 h. In the second study, cells were cultured on different substrata, either plastic, gelatin, or collagen. There were no differences (P > 0.05) in the cell growth rates for any of the three substrata. In the third study, cells were grown in 10% fetal bovine serum (FBS) and either a balanced salt solution (BSS; 30 mM Hepes, 10 mM glucose, 120 mM NaCl, 2.5 mM Na2HPO4, and 3 mM KCl), McCoy's 5A, Dulbecco's Minimal Essential Medium/Ham's F12 (DMEM/F12), or 70% DMEM/20% M-199. Cell numbers adhering to the plate at 26 h post-plating were different (P > 0.001) between each medium (DMEM/M-199 > McCoy's 5A > DMEM/F12 > BSS). Cell proliferation rates for each treatment medium were greatest for DMEM/M-199, followed by McCoy's 5A, DMEM/F12, and BSS. Cell differentiation was highest (P < 0.05) in the DMEM/F12, followed by McCoy's 5A, DMEM/M-199, and BSS. In the final study, the cells were treated with different sources of serum added at 10% to DMEM/M-199. The sera consisted of FBS, newborn calf serum (NCS), horse serum (HS) and iron-supplemented calf serum (Fe(2+)-CS). The cells were added to each well at 10(4) cells. At 24 h post-plating, the serum-free, NCS, and FBS-treated cell numbers were greater (P < 0.05) than the cells treated with HS or Fe(2+)-CS, which may reflect the efficient adherence to the surface or faster adaptation to the serum by the cells. The proliferation rate was greatest (P < 0.001) for the cells treated with Fe(2+)-CS, followed by FBS = NCS, HS, and no serum. Therefore, the muscle cells obtained from bovine embryos grow and differentiate similar to muscle cells from other species. The optimal growth medium for growing these cells in vitro is DMEM/M-199 plus 10% Fe(2+)-CS, while the optimal differentiation medium is McCoy's 5A.

Enzyme activities of the mitochondrial energy generating system in skeletal muscle tissue of preterm and fullterm neonates

Quadriceps muscle specimens from autopsy of 28 neonates (gestational age 25-42 weeks) were investigated to determine pyruvate and malate oxidation rates and several enzymes of the mitochondrial oxidative process. In general, the levels of all mitochondrial parameters measured, including carnitine levels, were lower in the neonates who died within the first week of life than those in the control group (age > 5 years). Pyruvate and malate oxidation rates (P < 0.05), activities of pyruvate dehydrogenase complex (P < 0.10) and succinate: cytochrome c oxidoreductase (P < 0.05) increased significantly with gestational age. Pyruvate oxidation rates (P < 0.05) as well as activities of citrate synthase (P < 0.05) and NADH:Q1 oxidoreductase (P < 0.05) were significantly lower in the group of very preterm infants at an age of 1-7 days compared with very preterm infants at an age between 3-8 weeks. We conclude from our study that special reference values are necessary for a correct biochemical diagnosis of mitochondrial encephalomyopathies in the neonatal period. Differences between preterm and fullterm children of the same age (1 week) indicate a maturational process in human muscle tissue during gestation. Comparison of two different age groups within the very preterm neonates point to a postnatal maturation of the mitochondrial energy metabolism, at least in preterm neonates.

Beta-adrenergic agonists and hypertrophy of skeletal muscles

Chronic administration of some beta-adrenergic agonists markedly stimulates hypertrophy of skeletal muscles. It appears that type II fibers are more responsive to beta-adrenergic agonists than type I fibers. The hypertrophic effect of beta-adrenergic agonists is transient, with the effect diminishing during prolonged treatment. Similarly, some cellular responses including the increase in RNA concentration and the decrease in calpain I activity are also short-lived. Recent evidence suggests that the temporal response is associated with decreased beta-adrenoceptor density. Both increased rate of protein synthesis and/or decreased protein degradation have been suggested as the mechanism of action of these compounds on hypertrophy of skeletal muscles. It is important to consider the temporal nature of cellular responses to chronic treatment of beta-adrenergic agonists as well as the differential effects of these compounds on protein metabolism among skeletal muscle fiber types when investigating the mechanism(s) of action of these compounds.

Relationships between muscle fibre characteristics and physical performance capacity in trained athletic boys

The relationships between muscle fibre characteristics and the physical performance capacity of trained athletic boys (aged 11-13 years) were studied over 2 days. The subjects were divided into two groups according to muscle fibre distribution. The 'fast' group (FG) comprised 10 subjects (sprinters, weightlifters, tennis players) with more than 50% fast-twitch fibres (type II), and the 'slow' group (SG) comprised 8 subjects (endurance runners, tennis players, one weightlifter) with more than 50% slow-twitch fibres (type I) in their vastus lateralis muscle. The 'fast' group had 59.2 +/- 6.3% and the 'slow' group had 39.4 +/- 9.8% type II fibres. Other clear differences (P less than 0.05-0.01) between the groups were observed as regards reaction time, rate of force development and rise of the body's centre of gravity in the squatting jump. For these variables, the 'fast' group was superior to the 'slow' group. Muscle fibre distribution (% type II) correlated (P less than 0.05-0.01) negatively with reaction time. Muscle fibre area (% type II) correlated negatively with reaction time (P less than 0.05-0.001) and positively with chronological age (P less than 0.05) height (P less than 0.05), mass (P less than 0.001), serum testosterone (P less than 0.05), force production (P less than 0.05-0.01) and blood lactate (P less than 0.05) in the 60-s maximal anaerobic test. There were no significant correlations between muscle fibre characteristics and maximal oxygen uptake. The present study assumes that heredity partly affects the selection of sporting event. Growth, development and training are associated with muscle fibre area, which affects the physical performance capacity of the neuromuscular system in trained young boys.

Glycogen accumulation in normal and irradiated minced muscle autografts on frog gastrocnemius

Alterations induced in glycogen content and phosphorylase activity have been studied in normal and irradiated minced muscle autografts on frog gastrocnemius at days 1, 3, 5, 7, 10, 15 and 30 postgrafting. The changes observed in the glycogen content and phosphorylase activity conform to the degeneration and regeneration phases of muscle repair. An attempt has been made to explain the altered glycogen utilizing capacities of the frog skeletal muscle during its repair and regeneration.

Glucose-6-phosphatase activity in normal and denervated developing chick gastrocnemii: reappraisal of glycogenolytic and glycolytic metabolism in skeletal muscle

Biochemical changes in glycogen content and activity levels of phosphorylase (EC 2.4.1.1), glucose-6-phosphatase (EC 3.1.3.9), phosphohexose isomerase (EC 5.3.1.9) and aldolase (EC 4.1.2.13) have been studied in normal and denervated whole gastrocnemius muscle and its three fasciculi, viz., pars externus, medius and internus up to 9 weeks in chicks. Glycogen content as well as phosphorylase, phosphohexose isomerase and aldolase decrease in normal muscle with advancement of postembryonic growth whereas transiently increased glucose-6-phosphatase reveals an inverse relationship with these parameters. Denervated muscles demonstrate loss of glycogen and related enzymes owing to ablation of neural supply during the initial 4 weeks. Denervation results in a delayed stimulation of glycogenolysis and glycolysis which seems to be governed by decreasing activity of glucose-6-phosphatase. The significance of glucose-6-phosphatase in the regulation of glycogenolysis and glycolytic metabolism of normal and denervated skeletal muscle is discussed.

Skeletal muscle metabolism in mice bearing adenocarcinoma. I. Histochemical alterations in glycogenolytic, glycolytic, lipolytic and oxidative metabolism

Metabolism of triceps, pectoralis (in the vicinity of tumor) and gastrocnemius (away from the tumor) muscles in Swiss albino mice bearing adenocarcinoma has been studied histochemically with regard to content of glycogen, lipids, phosphorylase, aldolase, lipase, succinate dehydrogenase and cytochrome oxidase in the constituent fibres. At 9-10 weeks after transplantation of adenocarcinoma, a negligible glycogen content and decreased phosphorylase and aldolase activities are observed in the white, intermediate and red fibre types in the three muscles. Hypertrophy of fibres and occurrence of targetoid fibres is distinct in the muscles of tumor-bearing mice. The red fibres demonstrate a general loss of lipids, lipase, succinate dehydrogenase and cytochrome oxidase whereas the hypertrophied fibres reveal intense localization of these parameters in their central zones. The results indicate that a decline in glycogenolysis, glycolysis, lipolysis and oxidative metabolism in the various fibre types may contribute to the muscle weakness and muscle wasting in the adenocarcinoma-bearing mice.

Enhancement of human muscle growth in diffusion chambers by bone marrow cells

Samples of minced human muscle were cultured in millipore diffusion chambers incubated in the peritoneal cavities of mice. In about half the chambers the minced muscle samples were mixed with autogenous bone marrow cells which lead to improved myogenic growth. A similar but less marked effect was produced by mononuclear cells from the patients' blood. No growth enhancement occurred when the muscle and marrow cells were separated by a filter in double chambers. In addition to accelerated myogenesis, the chambers with added bone marrow cells had a much lower incidence of infection. This work may have practical clinical implications for the treatment of muscle injuries. Local implantation of autogenous marrow cells (+/- minced muscle) may prove useful in improving myogenic regeneration.

Postnatal development of palmitate oxidation and mitochondrial enzyme activities in rat cardiac and skeletal muscle

1. The palmitate oxidation rate was measured in intact diaphragm and m. flexor digitorum brevis and in whole homogenates of heart, diaphragm and m. quadriceps of developing rats between late foetal life and maturity. Activities of the mitochondrial enzymes cytochrome c oxidase and citrate synthase were also determined. 2. Immediately after birth the palmitate oxidation rate increases markedly in both intact diaphragm and m. flexor digitorum brevis and falls gradually after day 1 to adult values which are about 35% of those at birth. 3. The oxidation capacities of diaphragm and m. quadriceps, but especially of heart, increase steadily during development, starting before birth and reaching adult values at 15-20 days postnatally. The activities of the mitochondrial enzymes show a similar developmental pattern. 4. In heart the increase of oxidative capacity is the result of an increase of both mitochondrial content and mitochondrial activity. The mitochondrial contents of diaphragm and m. quadriceps, on the other hand, decrease with age and the increase of their oxidative capacities is due to a large rise of the mitochondrial activity.

An ultrastructural study of the differentiation of skeletal muscle in the bovine fetus

The differentiation of skeletal muscle was studied by electron microscopy in bovine fetuses from 47 days gestation to neonatal calves 3 days of age. Initially, the muscle was composed of clusters of myotubes with mononucleated myoblasts between them. In 2-month-old fetuses these myoblasts became apposed to the differentiating muscle cells and were enclosed within the rudimentary basal lamina of the myotubes. At this stage the clusters of myotubes consisted of central, larger diameter, more differentiated myotubes and also the mononucleated satellite cells. The differentiated myotubes separated from the clusters accompanied by satellite cells which continued proliferating and fused together to form new generations of satellite myotubes. In this manner new clusters of myotubes were formed. By 4-5 months some of the separating myotubes began to form individual myotubes and independent myofibers were prominent in fetuses of 5-8 months of age. The myofibers in the 8-month-old fetuses showed diversification into fiber types by differences in the thickness of the Z-line, the prominence of the sarcotubular system, the amount of glycogen and lipid droplets and also the number of mitochondria.

Effect of zinc deficiency on the weight, cellularity and zinc concentration of different skeletal muscles in the post-weanling rat

Zinc-deficient (ZD), weight-restricted (WR), pair-fed (PF) andad lib.-fed (AL) Sprague-Dawley male rats were killed after feeding the respective Zn-deficient and Zn-supplemented diets from 3 to 8 weeks of age. Animals killed at the start of the experiment served as a baseline control (BC).

Four different skeletal muscles – biceps brachii, soleus, plantaris and extensor digitorum longus (EDL) – were studied for changes in weight, the number and diameter of muscle fibres and Zn concentration.

The soleus muscle had the highest concentration of Zn. It was the only muscle to reduce its Zn concentration due to Zn deficiency.

There was a loss of muscle fibres during normal growth (groups BCv.AL) in the soleus muscle (P< 0.05). The estimated length of muscle and the diameter of the muscle fibres in all four muscles increased significantly (P< 0.001). Therefore postweanling growth appears to occur as a result of longitudinal and transverse increases in the dimensions of these muscles.

The reduction in muscle fibre number in ZD rats compared to BC animals may occur within the range of expected fibre loss during normal growth. Fibre loss in ZD rats may be more affected by feeding-pattern-dependent metabolic changes than by a deficiency of Zn per se (groups ZDv.WR). Soleus fibre loss in ZD rats may be related to the high Zn concentration in this muscle.

The effect of Zn deficiency per se on muscle fibre diameter may be inaccurately interpreted by comparing the ZD animals with their PF and AL controls. There was no significant difference in fibre diameter in any of the four muscles when ZD and WF rats were compared.

The kinetics of myofibrillar protein breakdown in perfused rat skeletal muscle

Nt-Methylhistidine, a non-reutilised amino acid present in some myofibrillar proteins, was radioactively labelled in vivo with [Me-3H]methionine. The specific radioactivities of protein-bound methylhistidine and free methylhistidine in perfusate after perfusion of rat hind limbs taken from prelabelled rats was determined. The decrease in urinary methylhistidine activity with time was determined for rats similarly labelled. Comparison of the specific activities of free and bound methylhistidine and the non-linear semilogarithmic plot of urinary methylhistidine activity suggest that the myofibrillar protein catabolism, as indicated by methylhistidine release, may not be a simple exponential process. The possibility of non-random decay is discussed and an alternative model proposed.

[The regulation of protein synthesis in heart muscle. Biochemical data, stimulative and inhibitory factors and their clinical significance (author's transl)]

The regulation of protein synthesis in heart muscle has been investigated by many authors under both normal and pathological conditions. This review summarizes the evidence for the dependence of normal heart protein synthesis from normal serum levels of insulin, amino acids, fatty acids and glucose. A decreased serum concentration of these substances causes an inhibition of heart muscle protein synthesis by 30--60%. Various drugs and other chemical lead to similar impairments of heat muscle protein synthesis. The resulting imbalance between synthesis and degradation of myocardial proteins with their half-times of 5--12 days gradually leads to a decrease in their myocellular concentration with a consequent impairment of myocardial function. Finally, the biochemial sequences are described which represent the important pathogenetic mechanisms in the development of heart muscle hypertrophy and in the adriamycin-induced cardiomyopathy.

Growth metabolism of diaphragm in Swiss albino mice

During the postnatal growth of diaphragm in swiss albino mice, a continuous decline in glycogen content reciprocates with the increasing SDH-activity and protein accumulation. An inverse relationship between DNA-contents and the basic protein levels points towards the regulatory behaviour of the latter during protein synthesis. While the variations in the contents of DNA and RNA speak of a feedback mechanism operative between the 2 nucleic acids during the postnatal growth, the fluctuations in RNA appear to be significant in determining the amount of acidic proteins, in this muscle.

Tongue muscle regeneration, Gold marker studies following cold injury

Rat's tongues were injured by cold and the reactive processes were observed by light and electron microscopy. Injured animals and untreated controls were injected with aurothiomalate and the cells in tongue muscles which contained gold were observed after increasing injection-sacrifice time intervals. In the very rapid regeneration, gold-containing macrophage-like cells fused with each other and with well preserved parts of myofibers. The selectivity of gold localization suggested, at least morphologically, a macrophage to myoblast development. The possible factors affecting the rate of muscle regeneration have been discussed with special reference to the nature of the injurious stimulus and the type of cellular response.

Research on variation in dental occlusion. A "state of the art" workshop conducted by the Craniofacial Anomalies Program, the National Institute of Dental Research

The following report on assessing research on variation in dental occlusion was based in part on a workshop conducted by the National Institute of Dental Research at the initiative of Richard L. Christiansen, Chief, Craniofacial Anomalies Program. The meeting was planned and developed by Robert J. Isaacson, Chairman, Touro M. Graber, Richard A. Riedel, and Richard L. Christiansen. This report is designed to provide a review of the achievements, directions, and needs of research concerning variations in dental occlusion. The workshop was held at the National Institutes of Health, Bethesda, Maryland, on Nov 22 and 23, 1972. The material presented by the workshop participants has been summarized and incorporated in this report. The subject of research related to the field of malocclusion was discussed in an article published in the American Journal of Orthodontics in January, 1971.