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At least 19 recordsLinked to original sources
PubMed1978

Biochemical aspects of cardiac muscle differentiation.

Experiments were designed to determine whether DNA synthesis ceases in terminally differentiating cardiac muscle of the rat because the activity of the putative replicative DNA polymerase (DNA polymerase alpha) is lost or whether the activity of this enzyme is lost because DNA synthesis ceases. DNA-template availability and 3'-hydroxyl termini in nuclei and chromatin, isolated from cardiac muscle at various times during the developmental period in which DNA synthesis and the activity of DNA polymerase alpha are decreasing, were measured by using Escherichia coli DNA polymerase I, Micrococcus luteus DNA polymerase and DNA polymerase alpha under optimal conditions. Density-shift experiments with bromodeoxyuridine triphosphate and isopycnic analysis indicate that DNA chains being replicated semi-conservatively in vivo continue to be elongated in isolated nuclei by exogenous DNA polymerases. DNA template and 3'-hydroxyl termini available to exogenously added DNA polymerases do not change as cardiac muscle differentiates and the rate of DNA synthesis decreases and ceases in vivo. Template availability and 3'-hydroxyl termini are also not changed in nuclei isolated from cardiac muscle in which DNA synthesis had been inhibited by administration of isoproterenol and theophylline to newborn rats. DNA-template availability and 3'-hydroxyl termini, however, were substantially increased in nuclei and chromatin from cardiac muscle of adult rats. This increase is not due to elevated deoxyribonuclease activity in nuclei and chromatin of the adult. Electron microscopy indicates that this increase is also not due to dispersal of the chromatin or disruption of nuclear morphology. Density-shift experiments and isopycnic analysis of DNA from cardiac muscle of the adult show that it is more fragmented than DNA from cardiac-muscle cells that are, or have recently ceased, dividing. These studies indicate that DNA synthesis ceases in terminally differentiating cardiac muscle because the activity of a replicative DNA polymerase is lost, rather than the activity of this enzyme being lost because DNA synthesis ceases.

Animals↗
PubMed1975

Biochemical aspects of cardiac muscle differentiation. Deoxyribonucleic acid synthesis and nuclear and cytoplasmic deoxyribonucleic acid polymerase activity.

DNA synthesis and DNA polymerase activity have been measured in terminally differentiating cardiac muscle of the rat. Incorporation of [3H]thymidine into DNA essentially ceases by the 17th day of postnatal development. Cardiac muscle of neonatal rats contains at least two molecular species of DNA polymerase: a 3.5 S DNA polymerase that can be extracted from nuclei with 0.2 m potassium phosphate and a 6 to 8 S soluble cytoplasmic DNA polymerase. The nuclear DNA polymerase in crude extracts has a pH optimum of 9.0 and is more active with native DNA than with denatured DNA as the primer-template. The cytoplasmic DNA polymerase in crude extracts has a pH optimum of 7.5 and is more active with denatured DNA. The activity of the 6 to 8 S cytoplasmic DNA polymerase decreases 80-fold from day 1 to day 17 after birth, which correlates temporally with the reduced rate of DNA synthesis. The activity of the 3.5 S nuclear DNA polymerase remains relatively constant throughout postnatal development. Mixing experiments (assay of neonatal enzyme extracts with adult enzyme extracts) gave additive results, suggesting that the decline in 6 to 8 S DNA polymerase activity apparently is not due to the presence of absence of soluble activators or inhibitors at different times during development. These studies may provide a system which can be used to investigate the control of DNA synthesis and cellular proliferation during the terminal stages of cardiac muscle differentiation.

Aging↗
PubMed1975

Effect of oncogenic virus on muscle differentiation.

Chick muscle cultures infected with wild-type Rous sarcoma virus form myotubes, but these myotubes vacuolate and by day 6 most have degenerated, leaving only large numbers of transformed mononucleated, replicating cells. Muscle cultures infected with a temperature-sensitive mutant (TS) at permissive temperatures behave as cells infected with wild-type Rous sarcoma virus. TS-infected cells reared for 8 days at nonpermissive temperature form contracting myotubes, plus large numbers of fibroblastic cells. If these cultures are lowered to permissive temperature, within 72 hr the myotubes vacuolate and degenerate, whereas the mononucleated cells transform. If replicating TS-transformed cells after 8 days at permissive temperature are shifted to nonpermissive temperature, within 72 hr many cells fuse and form contracting, post-mitotic myotubes. Creatine kinase (ATP:creatine N-phosphotransferase, EC 2.7.3.2) levels parallel the formation and degeneration of myotubes during these temperature shifts. If the viral transforming gene is expressed in the post-mitotic myotubes it is lethal, whereas it is not lethal if expressed in replicating percursor myogenic cells. The viral gene expression at permissive temperature blocks further myogenesis depending on the position of the cells in the myogenic program. The virus does not cancel the replicating, transformed myogenic cells' commitment to, or position in, the myogenic lineage. When the transforming action of the virus is suppressed, the normal myogenic program resumes.

Animals↗
PubMed1976

Biochemical aspects of cardiac muscle differentiation. Possible control of deoxyribonucleic acid synthesis and cell differentiation by adrenergic innervation and cyclic adenosine 3':5'-monophosphate.

A single injection of either isoproternol or N6, O2'-dibutyryl adenosine 3':5'-monophosphate (dibutyryl cyclic AMP) results in an inhibition in the rate of [3H]thymidine incorporation into DNA of differentiating cardiac muscle of the neonatal rat. This inhibition is not due to substantially altered cellular uptake or catabolism of [3H]thymidine. Inhibition of [3H]thymidine incorporation by isoproterenol or dibutyryl cyclic AMP is potentiated by theophylline. Maximal inhibition (95%) is observed 24 h after administration of isoproterenol, and the rate of incorporation returns to a value 80% of control by 72 h. Norepinephrine also inhibits [3H]thymidine incorporation whereas cyclic GMP, N2, 02-Dibutyryl guanosine 3':5'-monophosphate (dibutyryl cyclic GMP), and phenylephrine have little effect. Equilibrium sedimentation analysis of cardiac muscle DNA in neutral and alkaline cesium chloride gradients using bromodeoxyuridine as a density label indicate that isoproterenol and dibutyryl cyclic AMP inhibit [3H]thymidine incorporation into DNA that is replicating semiconservatively. Administration of isoproterenol or dibutyryl cyclic AMP to neonatal rats inhibits by approximately 60% the incorporation of [3H]thymidine into DNA of tissue slices of cardiac muscle prepared 16 h later. [3H]Thymidine incorporation into DNA of tissue slices is into chains that were growing in vivo. This incorporation is linear for at least 4 h of incubation and is inhibited by isoproterenol and dibutyryl cyclic AMP. Inhibition is not due to altered cellular uptake of [3H]thymidine nor is it due to a cytotoxic action. Several other compounds which elevate intracellular levels of cyclic AMP (epinephrine, norepinephrine, glucagon, and prostaglandin E1) also inhibit [3H]thymidine incorporation into DNA or cardiac muscle tissue slices. Cyclic GMP, dibutyryl cyclic GMP, sodium butyrate, and phenylephrine have little effect. Isoproterenol administered together with theophylline to neonatal rats signficantly stimulates the in corporation of [3H]phenylalanine into total cardiac muscle protein and into myosin. This enhanced incorporation may be due in part to an increase in the cellular uptake of [3H]phenylalanine. DNA synthesis decreases progressively in differentiating cardiac muscle of the rat during postnatal development and essentially ceases by the middle of the third week (Claycomb, W. C. (1975) J. Biol. Chem. 250, 3229-3235). In reviewing the literature it was found that this decline in synthetic activity correlates temporally with a progressive increase in tissue concentrations of norepinephrine and cyclic AMP and with the anatomical and physiological development of the adrenergic nerves in this tissue. Because of these facts and data presented in this report it is proposed that cell proliferation and cell differentiation in cardiac muscle may be controlled by adrenergic innervation with norepinephrine and cyclic AMP serving as chemical mediators.

Aging↗
PubMed1979

Biochemical aspects of muscle differentiation as analyzed by in vitro cultivation techniques.

Myoblasts cultivated in vitro will undergo terminal differentiation to form muscle fibres. Teratoma derived mouse cell lines, a pluripotent primitive line, and a muscle cell line, provide a possibility for comparing RNA populations in an early precursor cell with those in committed myoblasts and differentiated myotubes. Molecular hybridization analyses led to the conclusion that new RNA sequences appear in the cytoplasm during muscle differentiation. Such muscle specific sequences are not detectable in the nuclear RNA of myoblasts or primitive cells. Studies of protein synthesis during terminal myogenesis indicate co-ordinate expression of the muscle contractile proteins. These represent distinct isozymes, distinguishable from the contractile proteins of other cell types. In the case of myosin light chains isozymic transitions between different muscle forms have been identified during early development.

Animals↗
PubMed1979

A transient increase in amino acid transport modulated by insulin in differentiating muscle cells.

During synchronous differentiation of embryonic chick muscle cells in cultures, the Na-dependent uptake of an amino acid analog, alpha-amino isobutyric acid (AIB) undergoes in abrupt, transient increase. The increase in AIB uptake is concomitant with the rapid fusion of mononucleated myoblasts, and precedes the accumulation of muscle-specific proteins. Subsequently, Na-dependent AIB transport diminishes markedly during postfusional differentiation of myotubes. The rate of AIB uptake is increased by insulin both before and after myoblast fusion. This stimulation by insulin is restricted to the Na-dependent component of total AIB uptake but is apparently not the result of insulin-mediated increase in the trans-membrane Na gradient.

Aminoisobutyric Acids↗
PubMed1978

Sythesis of tropomyosin in cultures of differentiating muscle cells.

The accumulation of tropomyosin in cultures of differentiating muscle cells was quantitatively measured. Tropomyosin was isolated from cultured cells during and after myoblast fusion; both alpha- and beta-subunits were present in myotube cultures. During fusion small amounts of tropomyosin were detectable, but, as fusion approached a maximum, tropomyosin accumulation began to increase. The increased synthesis of tropomyosin after the initiation of muscle cell fusion is consistent with the increased synthesis of other proteins characteristic of muscle, including myosin.

Animals↗
PubMed1979

Cell surface changes during muscle differentiation in vitro: a study with the probe 2,4,6-trinitrobenzene sulphonate.

Cell surface changes during muscle differentiation in vitro, were investigated using the non permeant probe 2,4,6-trinitrobenzene sulphonate (TNBS) in order to label the aminogroups of proteins exposed on the outer surface of the plasma membrane. Surface proteins of chick myotubes and 'mature' unfused myoblasts (myoblasts grown for 7 days in a calcium-depleted medium) were found to bind an equal amount of probe, which is twice the amount bound by surface proteins in 'immature' myoblasts (1--2 days of culture) and fibroblasts. This indicates that a 'remodelling' of the plasma membrane outer surface takes place in the course of muscle cell differentiation even in the absence of cell fusion. Moreover, the total amount of TNBS bound to the surface was 4--5 times greater in myotubes than in unfused myoblasts. This appears to result from the surface expansion which occurs in myotubes during the development of the T tubule system.

Animals↗
PubMed1979

Expression of single copy DNA sequences in nuclear RNA from undifferentiated mouse embryonal carcinoma and differentiated muscle cell line.

Nuclear RNA from an undifferentiated mouse embryonal carcionma (EC) cell line and a differentiated muscle (Mt) cell line from similar origin has been analysed with respect to base sequence complexity and frequency distribution with different probes. With the single copy component of mouse genomic DNA it is shown that total EC nuclear RNA and Mt nuclear RNA have respectively base sequence complexities of 100 Kb and 140 Kb corresponding to 6% and 8% of one strand of DNA. It is shown by hybridization with a purified DNA component complementary to total nuclear RNA that nuclear poly A+RNA in both cell types has only one fifth of total nuclear RNA complexity (as has polysomal RNA), but still contains all poly A+RNA present in polysomal poly A+RNA. Polysomal poly A+ sequences in total and poly A+ nuclear RNA are present in a restricted range of frequency distribution in contrast to the situation observed at the polysomal level. The implication of these results in terms of transcriptional and post-transcriptional control is discussed.

Animals↗
PubMed2026

miR-191 affects skeletal muscle differentiation by regulating Wwp1 in mouse myoblasts.

Skeletal muscle atrophy is a key complication of various diseases, such as chronic obstructive pulmonary disease (COPD) and cancer. The mechanisms by which these diseases affect skeletal muscle metabolism need to be deeply explored. By analyzing the miRNA expression profiles in the plasma of patients with COPD, we found that miR-191 expression was significantly altered and it may influence skeletal muscle metabolism by regulating ubiquitination and the mTOR pathway. Using a mouse model of skeletal muscle injury induced by cardiotoxin, we found that miR-191 and Wwp1 showed a dynamic negative correlation in injury repair. Transfection with miR-191 mimics significantly inhibited the expression of myogenic regulatory factor Myog and differentiation markers Myh1/7/8, while downregulating key genes in the mTOR pathway. Molecular mechanism studies showed that miR-191 could directly act on the 3' untranslated region of the Wwp1 gene to inhibit its expression. This study reveals the important role of the miR-191/Wwp1 axis in skeletal muscle differentiation and provides a novel theoretical basis for research on muscle atrophy induced by COPD, cancer cachexia, and other diseases.

Animals↗
PubMed1977

Neurotrophic control of cyclic nucleotide levels during muscle differentiation in cell culture.

The effects of chick brain-spinal cord extract on morphological development and cyclic nucleotide levels of cultured chick embryo skeletal muscle cells were determined. It had previously been shown that the extract stimulated morphological differentiation, protein synthesis, and choliniesterase activity of muscle cells. Myoblasts fused earlier and an increase in number as well as diameter of myotubes were seen in the extract treated cultures. Cyclic nucleotides levels were higher (almost twice the controls for both adenosine 3',5'-cyclic monophosphate and guanosine 3',5'-cyclic monophosphate) and preceded their occurrence in the control cultures. It was suggested that factor(s) in the extract interact with membrane receptor(s) to alter nucleotide levels which, in turn, allow the effects to be expressed.

Animals↗
PubMed1978

Disparity of motoneurone and muscle differentiation following spinal transection in the kitten.

1. The spinal cord of kittens, 3--5 days of age, was transected at the lower thoracic level. Isometric contractions of the medial gastrocnemius and soleus muscles as well as intracellular potentials of their motoneurones were recorded after varying post-operative periods of up to 110 days. Similar observations were made 52--59 days after cord transection in adult cats. 2. In cord-transected kittens, contraction time of the gastrocnemius muscle showed normal development, whereas the soleus muscle failed to maintain slow contraction. In adult cats, cord transection increased the speed of contraction in the soleus muscle without significant changes in contraction times of the gastrocnemius muscle. 3. Soleus motoneurones showed a normal post-natal increase in the duration of afterhyperpolarization (a.h.p.) up to a certain stage (61--71 days in age) following cord transection. However, the subsequent increase in the duration of a.h.p. of soleus motoneurones observed in normal kittens was lacking in cord-transected kittens. It is suggested that soleus motoneurones show two stages of differentiation in terms of the duration of a.h.p. 4. In adult cats, cord transection caused a decrease in the duration of a.h.p. of soleus motoneurones approximately to the value observed at the end of the first stage of differentiation in kittens. 5. The duration of a.h.p. of gastrocnemius motoneurones remained virtually unchanged follwoing cord transection in both kittens and adult cats. 6. The positive correlation between the duration of a.h.p. of soleus motoneurones and contraction time of the innervated muscle fibres normally observed in kittens and adult cats was absent following cord transection. 7. It was assumed that alteration s in contraction time of the muscle following cord transection are due to virtual elimination of motoneurone discharge and that the duration of a.h.p. reflects the discharge pattern of motoneurones under normal conditions. Based on these assumptions, a possible process for normal post-natal differentiation of motoneurone and muscle is proposed.

Age Factors↗
PubMed1978

Replication of animal viruses in differentiating muscle cells: vaccinia and herpes simplex virus type 1.

Cells cultured from the breast muscles of 11 to 12-day-old chick embryos were infected in the undifferentiated mitotic myoblast stage or in the terminally differentiated non-mitotic myotube stage with one of two DNA viruses, vaccinia and herpes simplex virus type 1 (HSV-1). DNA synthesis was measured and production ov virus-specific DNA detected in cells infected as myoblasts or myotubes by isotope labelling, autoradiographic and buoyant density centrifugation techniques. Furthermore, fully fused myotubes resemble myoblasts in their ability to support productive infection by these DNA viruses although DNA replication and nuclear division have ceased in myotubes and only minimum levels of host-cell DNA polymerase activity are present.

Animals↗
PubMed1977

Replication of animal viruses in differentiating muscle cells: influenza virus A.

Cells were cultured from the breast muscle of 11- to 12-day-old chick embryos and were grown under conditions optimal for the development of the cells into terminally differentiated, fused myotubes. Myotubes were infected with influenza virus A/Ann Arbor/6/60(H2N2) at high multiplicity, and synthesis of virus-specific proteins and RNAs was detected by haemadsorption, fluorescence microscopy and/or isotope labelling and electrophoresis techniques. Provided that myotubes were maintained at temperatures below 39 degrees C after infection, production of virus components and yield of infectious virus in these cells was similar to those observed in infected chick kidney cells. However, if cells were maintained at temperatures of 39 degrees to 40 degrees C after infection, virus nucleoprotein was prominent in the nuclei, and synthesis of virus-specific polypeptides and of plus-strand RNA was reduced about fourfold to 20-fold compared to that detected at lower temperatures. Moreover, infectious virus was not produced when temperatures of 39 to 40 degrees C were used during virus replication. The results demonstrate that under suitable conditions avian myotubes formed in culture resemble epithelioid cells in their ability to support the productive replication of influenza virus.

Animals↗
PubMed1977

[Changes in the characteristics of several carbohydrate metabolism enzymes during differentiation of loach skeletal muscle].

The gradual change of enzymes of glycogen metabolism proceeds during the skeletal muscle differentiation in the loach. The portion of the muscle type phosphorylase in the skeletal muscles of the embryo at the stage of the beginning of movement amounts to 30% and that at the stage of hatching to slightly over 50%. At the stage of yolk resorption, the skeletal muscles contain the muscle type phosphorylase only. At the same time the value of KM(UDPG) for glycogen synthetase gradually increases from 0,1 X 10(-3) up to 0,57 X 10(-3) M. The activity of alpha-glycerophosphate dehydrogenase increases more than 70 times.

Animals↗