Isolation of skeletal muscle nuclei

Indirect Measurement of CRAC Channel Activity Using NFAT Nuclear Translocation by Flow Cytometry in Jurkat Cells

Flow cytometry is a powerful technology to assess the presence of NFAT in the nuclei after CRAC channel activation. Here we described a simplified procedure for the analysis of CRAC channel activity using NFAT nuclear translocation by flow cytometry, based on the isolation of Jurkat E6-1 cell nuclei.

Differential effects of methimazole and dexamethasone in avian muscular dystrophy

We showed previously that thyroid antagonists and glucocorticoids partially alleviated the impaired righting ability and abnormally high levels of plasma creatine kinase activity in genetically dystrophic chicks. The goals of the present study were: (1) to ascertain whether the beneficial effects of methimazole (MMI; thyroid antagonist) on muscle function and plasma creatine kinase (CK) activity in dystrophic chickens are correlated with significant reduction in plasma triiodothyronine (T3) and thyroxine (T4); (2) to assess whether the MMI-induced thyroid changes are accompanied by increased plasma corticosterone level and/or changes in muscle glucocorticoid receptors which might account partially for the beneficial effects of MMI; and (3) to determine if plasma T3 and T4 are reduced in dexamethasone (DEX) treated dystrophic chickens which might account at least partially for the beneficial effects of DEX (a potent glucocorticoid) on avian dystrophy. The data show that beneficial effects of MMI are associated with reduced plasma levels of thyroid hormones and increased circulating levels of corticosterone. In addition, DEX actually increases plasma T3 levels. These differential effects indicate that reduced plasma thyroid hormone levels do not represent a common mechanism of beneficial drug effects in avian muscular dystrophy. On the other hand, elevated plasma glucocorticoid levels accompany the beneficial effects of both severe hypothyroidism and DEX treatment. The data also show that MMI induces down-regulation of muscle cytosolic glucocorticoid receptors which are higher than normal in dystrophic muscles.

Nuclear location of phosphoglycerate mutase BB isozyme in rat tissues

We have previously reported (Ureña et al. Eur. J. Cell Biol. 1990) that in skeletal muscle, type MM phosphoglycerate mutase isozyme is present in the nucleus as well as in the cytosol. To determine whether type BB phosphoglycerate mutase isozyme is also present in nucleus, the subcellular location of this isozyme was studied in different rat tissues by cell fractionation and immunogold techniques. With the aid of high affinity-purified anti-phosphoglycerate mutase BB isozyme antibodies, the isozyme was located in the nucleus of neuronal, astroglial and liver cells but not in the nucleus of oligodendroglial and endothelial cells. Biochemical studies on purified nuclear fractions also demonstrated the presence of phosphoglycerate mutase activity in the nucleus. Both immunocytochemical and biochemical techniques showed that nuclear phosphoglycerate mutase-specific activity depended on the type of cell.

RNA polymerase II-directed gene transcription by rat skeletal muscle nuclear extracts

A cell-free transcription system was developed using nuclear extracts of rat skeletal muscle to examine the transcription of specific genes involved in ribosome biogenesis and histone synthesis. Isolation and purification of muscle tissue nuclei were required prior to obtaining a transcriptionally active extract. The transcriptional abilities of myoblast, myotube, and muscle tissue nuclear extracts were then compared using the adenovirus major late promoter as a reporter gene. Transcription of r-protein L32 and histone H4 gene templates remained high in all extracts while histone H3 gene transcription was reduced in both myotube and muscle tissue extracts. These data indicate that transcription of these genes in myotubes and muscle tissue nuclear extracts is similar. Therefore, the L6 myoblast system accurately reflects the ability of intact muscle tissue to transcribe the genes concerned with histone production and ribosome biogenesis.

Nuclear glucocorticoid receptor binding in L6 skeletal muscle cells in culture

Mechanisms underlying glucocorticoid hormone actions on skeletal muscle remain incompletely understood. This problem may be amenable to solution with a simple cell culture system in which the hormonal environment can be controlled. In this report, we demonstrate that the L6 muscle cell line may provide such a system. These cells, which possess many morphological and functional characteristics of skeletal muscle, originate as mononuclear myoblasts, which fuse to form multinucleated myotubes. L6 myoblasts and myotubes contain an intracellular glucocorticoid receptor that has binding parameters and ligand specificity similar to those of glucocorticoid receptors of classical glucocorticoid target tissues. A major advantage of the use of cultured cells is ease of isolation of myonuclei that display specific glucocorticoid receptor binding. L6 muscle cells should provide a valuable model system for further studies of the mechanisms of glucocorticoid hormone actions on muscle.

Oestrogen specific binding sites in bovine muscle nuclei

A method for preparation of purified bovine diaphragm nuclei was developed and the presence of specific oestradiol binding sites was demonstrated in salt extracts of such muscle nuclei by kinetic, equilibrium and competition studies. Scatchard analysis of [3H]zeranol binding also indicated the presence of high-affinity binding sites in nuclei from female animals (heifers) for this synthetic oestrogenic anabolic agent. Measured levels of specific [3H]oestradiol binding were higher in zeranol-treated steer than in untreated heifer, or steer diaphragm nuclei. A second, lower-affinity oestrogen-binding component was identified using [3H]oestradiol at concentrations greater than 8 nM in all three types of animals. The data suggest that gonadal oestrogens or related anabolic agents might have direct effects on muscle through receptor-like macromolecules.

Nuclear localization of a lactic dehydrogenase with single-stranded DNA-binding properties

In the preceding article [1] we identified the 34 kD single-stranded DNA-binding (ssb) protein, whose synthesis is inhibited in PC12 cells concomitantly with nerve growth factor (NGF)-induced mitotic arrest, with the enzyme lactic dehydrogenase (LDH-ssb protein). Localization studies performed with antibodies raised against the LDH-ssb protein demonstrate the presence of a pool of this protein in the nucleus of several cell types. The nuclear association of this protein is sensitive to DNase treatment of the cells and quantitative electron microscopy confirms that the LDH-ssb protein is located close to chromatin structures. These results point to a possible involvement of the LDH-ssb protein in some nuclear function(s).

Concentrations of high-mobility-group proteins in the nucleus and cytoplasm of several rat tissues

Nuclear and cytoplasmic fractions were isolated from various tissues of the rat by a nonaqueous technique. The high-mobility-group (HMG) proteins were extracted from these fractions with acid and separated by one- and two-dimensional PAGE. The concentrations of high-mobility-group proteins HMG1, HMG2, and HMG17 in the nucleus and cytoplasm were then estimated from the staining intensities of the electrophoretic bands. The cytoplasmic concentrations of these proteins were very low--usually less than 1/30 of those present in the corresponding nuclear fractions. For the tissues studied (liver, kidney, heart, and lung), the concentrations of HMG proteins in the nucleus did not differ significantly from one tissue to another. Averaged over the four tissues investigated, there were 0.28 molecule of HMG1, 0.18 molecule of HMG2, and 0.46 molecule of HMG17 per nucleosome. These values are considerably higher than those that have been reported previously.

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.

Heterogeneous binding of high mobility group chromosomal proteins to nuclei

A dramatic difference is observed in the intracellular distribution of the high mobility group (HMG) proteins when chicken embryo fibroblasts are fractionated into nucleus and cytoplasm by either mass enucleation of cytochalasin-B-treated cells or by differential centrifugation of mechanically disrupted cells. Nuclei (karyoplasts) obtained by cytochalasin B treatment of cells contain more than 90 percent of the HMG 1, while enucleated cytoplasts contain the remainder. A similar distribution between karyoplasts and cytoplasts is observed for the H1 histones and the nucleosomal core histones as anticipated. The presence of these proteins, in low amounts, in the cytoplast preparation can be accounted for by the small percentage of unenucleated cells present. In contrast, the nuclei isolated from mechanically disrupted cells contain only 30-40 percent of the total HMGs 1 and 2, the remainder being recovered in the cytosol fraction. No histone is observed in the cytosol fraction. Unike the higher molecular weight HMGs, most of the HMGs 14 and 17 sediment with the nuclei after cell lysis by mechanical disruption. The distribution of HMGs is unaffected by incubating cells with cytochalasin B and mechanically fractionating rather than enucleating them. Therefore, the dramatic difference in HMG 1 distribution observed using the two fractionation techniques cannot be explained by a cytochalasin-B-induced redistribution. On reextraction and sedimentation of isolated nuclei obtained by mechanical cell disruption, only 8 percent of the HMG 1 is released to the supernate. Thus, the majority of the HMG 1 originally isolated with these nuclei, representing 35 percent of the total HMG 1, is stably bound, as is all the HMGs 14 and 17. The remaining 65 percent of the HMGs 1 and 2 is unstably bound and leaks to the cytosol fraction under the conditions of mechanical disruption. It is suggested that the unstably bound HMGs form a protein pool capable of equilibrating between cytoplasm and stably bound HMGs.

Actomyosin ATPase. I. Quantitative measurement of activity in cryostat sections

A method for the quantitative study of the actomyosin ATPase activity (Ca,MG-ATPase) in thin sections cut in a cryostat is presented. This method is based on the liberation of 32P from [gamma 32P]ATP or 45Ca phosphate precipitation. The advantage of this method lies in the requirement for only a small muscle sample and the availability of serially cut sections for other assays including Ca uptake by sarcoplasmic retciulum and histochemical tests for oxidative and glycolytic enzymes. The actomyosin ATPase activity for various types of muscles determined by this method showed the same sequence found in isolated protein, that is, fast-twitch skeletal greater than slow-twitch skeletal greater than cardiac. The Ca,Mg-ATPase of cryostat sections showed Ca sensitivity. The fact that the sections retained Ca sensitivity at 37 degrees C, in contrast to myofibrils, which have been reported to lose Ca sensitivity at this temperature, indicates that the structural integrity of the contractile and regulatory apparatus is preserved to a higher degree in sections than in isolated myofibrils.

Studies of nuclear proteins in the skeletal muscle of the cardiomyopathic Syrian hamster

Nonhistone nuclear proteins (NHNP) were isolated from the skeletal muscle of dystrophic hamsters and their respective paired controls. These proteins were extracted with phenol and fractionated by polyacrylamide gel electrophoresis. One-dimensional gel electrophoresis using either sodium-dodecylsulfate or isoelectrofocusing revealed quantitative changes between the two groups. An improved resolution using a two-dimensional system showed both quantitative and very limited qualitative differences. There are differences in proteins focusing at pH 5.0, molecular weight 55,000, in the dystrophic tissue. In addition proteins from dystrophic muscle focusing between pH 5.0 and 7.0, molecular weight 45,000, and proteins focusing between pH 7.0 and 9.0, molecular weights 35,000--45,000 and 60,000--70,000 were reduced as compared to the controls. There were no detectable differences in the electrophoretic patterns between the two groups of proteins derived from skeletal muscle homogenates. The differences in NHNP appear to be reflections of alterations in the nuclear composition of the dystrophic muscle cell. Some of these differences may represent changes secondary to the muscle disease. However, if NHNP interacting with DNA play a major role in the control of genetic expression, some of the manifestations of hamster dystrophy could be due to a different constitution of NHNP in the skeletal muscle.