Detection and relative quantitation of mRNA for creatine kinase isoenzymes in mRNA from myogenic cell cultures and embryonic chicken tissues

Transferrin as a muscle trophic factor

Muscle cells grow by proliferation and protein accumulation. During the initial stages of development the participation of nerves is not always required. Myoblasts and satellite cells proliferate, fusing to form myotubes which further differentiate to muscle fibers. Myotubes and muscle fibers grow by protein accumulation and fusion with other myogenic cells. Muscle fibers finally reach a quasi-steady state which is then maintained for a long period. The mechanism of maintenance is not well understood. However, it is clear that protein metabolism plays a paramount role. The role played by satellite cells in the maintenance of muscle fibers is not known. Growth and maintenance of muscle cells are under the influence of various tissues and substances. Among them are Tf and the motor nerve, the former being the main object of this review and essential for both DNA and protein synthesis. Two sources of Tf have been proposed, i.e., the motor nerve and the tissue fluid. The first proposal is that the nervous trophic influence on muscle cells is mediated by Tf which is released from the nerve terminals. In this model, the sole source of Tf which is donated to muscle cells should be the nerve, and Tf should not be provided for muscle fiber at sites other than the synaptic region; otherwise, denervation atrophy would not occur, since Tf provided from TfR located at another site would cancel the effect of denervation. The second proposal is that Tf is provided from tissue fluid. This implies that an adequate amount of Tf is transferred from serum to tissue fluid; in this case TfR may be distributed over the entire surface of the cells. The trophic effects of the motor neuron have been studied in vivo, but its effects of myoblast proliferation have not been determined. There are few experiments on its effects on myotubes. Most work has been made on muscle fibers, where innervation is absolutely required for their maintenance. Without it, muscle fibers atrophy, although they do not degenerate. In contrast, almost all the work on Tf has been performed in vitro. Its effects on myoblast proliferation and myotube growth and maintenance have been established; myotubes degenerate following Tf removal. But its effects on mature muscle fibers in vivo are not well understood. Muscle fibers possess TfR all over on their cell surface and contain a variety of Fe-binding proteins, such as myoglobin. It is entirely plausible that muscle fibers require an amount of Tf, and that this is provided by TfR scattered on the cell surface.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of chronic denervation and denervation-reinnervation on cytoplasmic creatine kinase transcript accumulation

The extensor digitorum longus (EDL) and soleus muscles of adult mice were chronically denervated or denervated and allowed to reinnervate. Muscles were evaluated 1, 5, 14, 21, and 52 days after sciaticectomy. In terms of weight loss, myofiber atrophy, degeneration, and fibrosis, the soleus muscle was more affected than the EDL by chronic denervation. Fifty-two days after chronic denervation, the number of molecules of MCK/ng total RNA in both muscles (determined with competitive PCR) decreased, with the soleus muscle being more affected. At that stage, BCK mRNA levels in the denervated soleus were unchanged, but they were increased (>50%) in the EDL. Reinnervation restored MCK transcript accumulation in the EDL, whereas, in the soleus MCK, transcripts exceeded control values by 57%, approaching levels in the reinnervated EDL. Despite restoration of MCK mRNA levels, the number of molecules of BCK mRNA/ng total RNA was four- to fivefold higher in reinnervated versus control muscles, suggesting that the genes encoding the CK mRNAs are not coordinately regulated in adult muscle. The role of denervation induced, fiber type changes in regulating CK mRNA accumulation has been evaluated. Electron microscopic analyses have established that fibrosis is not a factor that determines BCK mRNA levels in the chronically denervated or denervated-reinnervated muscles. CK isozyme analyses support the hypothesis that a greater proportion of BCK mRNA found in 52 day chronically denervated and denervated-reinnervated muscles is produced in myofibers vs. nonmuscle cells than in control muscles.

Creatine kinase transcript accumulation: effect of nerve during muscle development

To determine the role of the nerve in regulating the accumulation of cytoplasmic creatine kinase (CK) mRNAs in hindleg muscles of the developing mouse, the lumbosacral spinal cords of 14-day gestation mice (E14) were laser ablated, and the accumulation of muscle CK (MCK) and brain CK (BCK) mRNAs was evaluated just prior to birth with in situ hybridization. Numbers of molecules of each of these transcripts/ng total RNA in the soleus and extensor digitorum longus (EDL) muscles were determined with competitive PCR and compared to transcripts found in innervated crural muscles. Data suggest that: 1) the level of BCK mRNA accumulation in innervated hindlimb muscles peaks at E16.5 and remains at fetal levels until the second month postnatal, when it falls to the level found in the adult. Given that MCK transcripts meet or exceed adult levels by day 28 postnatal, the "down-regulation" of the BCK gene and the "up-regulation" of the MCK gene are not tightly coupled; 2) the developmental switch from BCK to MCK, as the dominant cytoplasmic CK mRNA, occurs in innervated and aneural leg muscles between E14 and E16.5, indicating this switch is not nerve dependent; 3) the absence of innervation has no effect on BCK mRNA accumulation. MCK transcripts/ng total RNA continue to increase in aneural muscle throughout the late fetal period, but from E16.5-E19.5 the MCK transcript levels in aneural muscles become progressively lower than in age-matched innervated muscles. Thus, the accumulation of the muscle specific cytoplasmic CK, but not BCK, transcripts is affected by the absence of innervation during the fetal period. Dev Dyn 1999;215:285-296.

Use of gene targeting for compromising energy homeostasis in neuro-muscular tissues: the role of sarcomeric mitochondrial creatine kinase

We have introduced a single knock-out mutation in the mitochondrial creatine kinase gene (ScCKmit) in the mouse germ line via targeted mutagenesis in mouse embryonic stem (ES) cells. Surprisingly, ScCKmit -/- muscles, unlike muscles of mice with a deficiency of cytosolic M-type creatine kinase (M-CK -/-; Van Deursen et al. (1993) Cell 74, 621-631), display no altered morphology, performance or oxidative phosphorylation capacity. Also, the levels of high energy phosphate metabolites were essentially unaltered in ScCKmit mutants. Our results challenge some of the present concepts about the strict coupling between CKmit function and aerobic respiration.

Overexpression of myotonic dystrophy kinase in BC3H1 cells induces the skeletal muscle phenotype

Myotonic muscular dystrophy is an autosomal dominant defect that produces muscle wasting, myotonia, and cardiac conduction abnormalities. The myotonic dystrophy locus codes for a putative serine-threonine protein kinase of unknown function. We report that overexpression of human myotonic dystrophy protein kinase induces the expression of skeletal muscle-specific genes in undifferentiated BC3H1 muscle cells. BC3H1 clones expressing myotonic dystrophy kinase appear equivalent to differentiated cells with respect to expression of myogenin, retinoblastoma tumor supressor gene, M creatine kinase, beta-tropomyosin, and vimentin. In addition, differential display analysis demonstrates that the pattern of gene expression exhibited by myotonic dystrophy kinase-expressing cells is essentially identical to that of differentiated BC3H1 muscle cells. These observations suggest that myotonic dystrophy kinase may function in the myogenic pathway.

Ultrastructure of developing muscle in the upper limbs of the human embryo and fetus

BACKGROUND

The ultrastructure of the myogenesis, which proceeds along with the appearance of muscle-specific proteins and isozymes, has not been fully described in the upper limb of staged human embryos.

METHODS

Eight human embryos (Carnegie stage 14-22) and two fetuses (11 and 12 weeks of gestation) were fixed with 5% glutaraldehyde, 4% paraformaldehyde, and 0.2% picric acid in 0.1 M phosphate buffer, pH 7.2. The upper limbs were dissected out and processed for transmission electron microscopy, and sections of the biceps brachii muscle were cut and examined.

RESULTS

At stage 14, the myoblasts were loosely scattered in the ventral proximal region of the upper limb bud and had a small amount of cytoplasm with a few intracellular organelles. At stage 16, the myoblasts were spindle shaped and oriented parallel to the axis of the upper limb bud. These cells had irregularly shaped nuclei with prominent nucleoli, rough endoplasmic reticulum (ER), and mitochondria, but no myofilaments were observed. At stages 17-19, rough ER, free ribosomes, and mitochondria increased in number and thick and thin filaments with faint Z-lines appeared in the peripheral cytoplasm of the myotube. The plasma membranes of some neighboring myotubes were continuous, suggesting that these cells were in the initial stages of the fusion process. At stage 22, the striated pattern of the myofilaments became evident and tubular structures appeared around them and near the plasma membrane. In the fetus at the 11th week, the basal lamina began to surround the myotubes, and T-tubules with sarcoplasmic reticulum were observed. Dyads and triads were observed in the myotube of the 12th week fetus.

CONCLUSION

These findings suggest that rapid myogenesis occurs during the late embryonic period in human upper limbs and that the ultrastructural characteristics of mature myotubes are established during the early fetal period.

The muscle-specific phosphoglycerate mutase gene is specifically expressed in testis during spermatogenesis

Spermatogenesis is a dramatic differentiation process which involves very selective but poorly characterized gene-expression patterns. To gain insight into this process, we have investigated the expression during spermatogenesis of the genes that encode phosphoglycerate mutase, an essential glycolytic enzyme for the spermatozoa energy supply. By using cDNA and genomic probes we demonstrate the presence in testis of a mRNA corresponding to the muscle-specific phosphoglycerate mutase which shows a longer poly(A) tail. This muscle-specific gene is submitted to developmental regulation during testis maturation and begins to be expressed at postnatal day 22, when germ cells start to enter into meiosis. Northern blot and in situ hybridization experiments show that in contrast to what happens during skeletal-muscle differentiation, PGAM-M gene expression during spermatogenesis is not coupled to constitutive phosphoglycerate mutase (PGAM-B) gene repression. Thus, the muscle-specific PGAM-M gene constitutes a meiotic gene and therefore represents a very interesting model to study differential tissue-specific gene expression.

Expression of creatine kinase M and B mRNAs in treadmill trained rat skeletal muscle

Gastrocnemius muscle from treadmill trained rats was analyzed for creatine kinase (CK) isoenzyme activities by agarose electrophoresis and M and B CK mRNA levels by Northern blot analysis. Total CK activity in exercise-trained (143 (SD 15) U/g) and control (154 (SD 16) U/g) muscles did not differ. CK-MB increased 220% in exercised-trained muscle compared to controls. CK-B subunit mRNA increased 40%, while CK-M subunit mRNA decreased 42% in exercised-trained muscle compared to control. Thus, gene expression of CK isoenzymes appears to be partially controlled at the level of transcription following exercise training.

Structural changes in the C-terminal region of human brain creatine kinase studied with monoclonal antibodies

Epitopes on human brain creatine kinase (B-CK) recognized by three monoclonal antibodies have been located by chemical cleavage methods, followed by peptide synthesis or analysis of specificity for natural variants (isoforms). One antibody, CK-HTB, recognizes a conformational, or assembled, surface epitope on native CK which is also present on partially unfolded forms. It requires an Asn residue at position 300 in the amino acid sequence and will not recognize variants with Lys or His in this position. This results in a striking specificity of the antibody, which binds to B-CK only in chicken and man, but to muscle-form (M-CK) only in the rat. The results suggest that Asn-300 is exposed on the enzyme surface as part of a relatively denaturation-resistant region. Two monoclonal antibodies, CK-END1 and CK-END2, recognise epitopes within 53 amino acids of the C-terminus and bind to a synthetic hexapeptide representing the last six amino acids of human B-CK (Leu-375-Lys-380). The two antibodies show overlapping, but distinct, specificities in their binding to CK variants. CK-END1 requires Met-376 and will not tolerate Ile in this position, whereas CK-END2 requires Leu-375 and will not tolerate Met. Neither antibody binds to native CK, though both will bind to a folding intermediate and to partially unfolded states. This shows that the C-terminus of CK becomes inaccessible to the antibodies during those later stages of protein folding associated with recovery of enzyme activity and suggests that the protein may 'tuck in its tail' during one of the final steps.

Opposite regulation of the mRNAs for parvalbumin and p19/6.8 in myotonic mouse muscle

The gene mutation in the mouse, 'arrested development of righting response', adr, causes a defect of chloride conductance of the muscle fibre membrane leading to the symptoms of myotonia [Mehrke, G., Brinkmeier, H. and Jockusch, H. (1988) Muscle & Nerve 11, 440-446]. In fast muscle, the myotonic phenotype is accompanied by a drastic reduction of the Ca2+-binding protein, parvalbumin. Messenger RNA levels in organs of myotonic (ADR) mice were analysed. In fast muscles of the mutant, in-vitro-translatable parvalbumin mRNA was strongly reduced, whereas the mRNA for the slow-muscle-specific protein, p19/6.8, was increased. In contrast, the parvalbumin mRNA in the cerebellum was not affected by the adr mutation. A reduction of the two parvalbumin mRNA species (700 and 1100 nucleotides) in ADR fast muscle and unaltered parvalbumin mRNA levels in mutant cerebella were demonstrated by cDNA/mRNA hybridisation, using a rat parvalbumin cDNA as a probe. The mRNA level for another Ca2+-binding protein, calmodulin, was low in muscle and high in the central nervous system but was unaffected by the mutation. When adr/adr mice were fed a diet containing the membrane-stabilising drug, tocainide, the levels in muscle of the mRNAs for parvalbumin and p19/6.8 were partially normalised.

Accumulation of CK-MM is impaired in innervated and contracting cultured muscle fibers of Duchenne muscular dystrophy patients

No specific abnormalities have been reproducibly manifested in aneurally cultured muscle of Duchenne muscular dystrophy (DMD) patients. We now report that the accumulation of the muscle-"specific" isozyme of creatine kinase (CK-MM) was significantly and preferentially impaired in long-term innervated contracting muscle fibers cultured from 4 DMD patients (DMD-InnCMFs) compared to: i) their noninnervated sister-cultured muscle fibers, and ii) innervated contracting control cultured human muscle fibers (Control-InnCHMFs). Accumulation of other muscle-"specific" isozymes (MSIs), viz. glycogen phosphorylase, phosphoglycerate mutase, and lactic dehydrogenase, was not significantly impaired. We have not observed preferentially-impaired CK-MM accumulation in any Control-InnCHMFs from 22 patients (children and adults) with a variety of neuromuscular diseases. There was no apparent difference between DMD-InnCMFs and Control InnCHMFs regarding: acceptance of innervation; neuronally-driven, virtually continuous muscle-fiber contractions; characteristic myofiber organization by phase-contrast microscopy, and increased longevity of the innervated fibers.

Heart C-protein is transiently expressed during skeletal muscle development in the embryo, but persists in cultured myogenic cells

The expression of cardiac and white skeletal C-protein isoforms was analyzed in developing chicken embryos and in primary skeletal muscle cell cultures by immunoblot and immunofluorescence staining using polyclonal antibodies specific for both of the two different proteins. In the embryo, cardiac C-protein was detected in the developing heart from very early stages through adulthood. In skeletal muscle, cardiac C-protein is shown to be transiently expressed between Days 3 and 15 during development. In contrast, the expression of white skeletal C-protein is gradual and progressive starting approximately from Day 15 on in development. In primary cell cultures of skeletal muscle, however, cardiac C-protein remained expressed throughout prolonged culture time, this in conjunction with white skeletal C-protein. Thus the down regulation of cardiac C-protein and the transition from cardiac C-protein to adult skeletal (white) C-protein which was observed during skeletal muscle development in vivo, does not seem to go to completion in the in vitro system.

Molecular and cell isoforms during development

Development proceeds by way of a discrete yet overlapping series of biosynthetic and restructuring events that result in the continued molding of tissues and organs into highly restricted and specialized states required for adult function. Individual molecules and cells are replaced by molecular and cellular variants, called isoforms; these arise and function during embryonic development or later life. Isoforms, whether molecular or cellular, have been identified by their structural differences, which allow separation and characterization of each variant. These isoforms play a central and controlling role in the continued and dynamic remodeling that takes place during development. Descriptions of the individual phases of the orderly replacement of one isoform for another provides an experimental context in which the process of development can be better understood.

Isoenzyme-specific localization of M-line bound creatine kinase in myogenic cells

Experiments using isolated fibre bundles or myofibrils of chicken skeletal muscle have shown that a relatively small portion of the muscle-specific MM-type of creatine kinase (CK) (EC 2.7.3.2) is specifically bound to the M-line and yet greatly contributes to the electron-dense M-line structure. Here we demonstrate the presence of M-line bound CK in cultured myogenic cells by removing the unbound sarcoplasmic CK through permeabilization with Triton X-100 and extensive washing of the cells prior to immunofluorescence staining. When stained with antibodies specific for M-CK subunits these cells exhibit bright fluorescence within the M-line region of myofibrils. Occasionally this cross-striated pattern is also observed in mononucleated presumably postmitotic myoblasts. Anti-B-CK incubation, in contrast, results in a weak, diffuse fluorescence at the Z-band. Even though these cells contain appreciable amounts of B-type CK, specific fluorescence at the M-line is never observed with anti-B-CK antibody thus ruling out the presence of BB-type or MB-type CK at this location. Therefore the presence of CK within the M-line structure of myogenic cells which contain all three CK isoenzymes seems to be restricted to the MM-type isoenzyme.

Cytoplasmic activation of human nuclear genes in stable heterocaryons

We have induced the stable expression of muscle-specific genes in human nonmuscle cells. Normal diploid human amniocytes were fused with differentiated mouse muscle cells by using polyethylene glycol. The fusion product, a stable heterocaryon in which the parental cell nuclei remained distinct, did not undergo division and retained a full complement of chromosomes. This is in contrast with typical interspecific hybrids (syncaryons), in which the parental nuclei are combined and chromosomes are progressively lost during cell division. The human muscle proteins, myosin light chains 1 and 2, MB and MM creatine kinase and a functional mouse-human hybrid MM enzyme molecule were detected in the heterocaryons. Synthesis of these proteins was evident 24 hr after fusion and increased in a time-dependent manner thereafter. Our results indicate that differentiated mouse muscle nuclei can activate human muscle genes in the nuclei of a cell type in which they are not normally expressed, and that this activation occurs via the cytoplasm. The activators are still present in cells which have already initiated differentiation, are recognized by nuclei of another species, and do not diffuse between unfused cells. The reprogrammed amniocyte nuclei of stable heterocaryons provide a unique system in which to study the mechanisms regulating gene expression during cell specialization.

In vitro translation of canine mitochondrial creatine kinase messenger RNA

The cell-free translation products of mRNA from canine myocardium were immunoprecipitated using antiserum specific for either the MM or mitochondrial creatine kinase subunit. The two subunits were shown to be encoded by the nuclear genome and translated from separate mRNAs. The mitochondrial subunit was translated as a polypeptide with a molecular weight approximately 6,000 greater than the mature form of the enzyme. In contrast, the M-subunit was translated as a polypeptide having a molecular weight identical to that of the mature cytosolic M-subunit. It is assumed that the mitochondrial subunit precursor must be proteolytically processed during translocation from the cytoplasm into mitochondria.

Creatine kinase activity in normal and Duchenne muscular dystrophy fibroblasts

Cultured human skin fibroblasts from 9 patients with Duchenne muscular dystrophy (DMD) and 8 normal age- and sex-matched controls were examined for creatine kinase (CK) activity. Both the normal and the DMD fibroblasts were found to have significant levels of CK activity (approximately 10 x 10(-3) IU per milligram of fibroblast protein). The control cells had slightly higher CK activity than the DMD lines, but this difference was not significant (0.2 less than P less than 0.1). The MM (muscle) isozyme, the BB (brain) isozyme, and the MB (hybrid) isozyme, of CK were found to be present in fibroblasts. The isozymes were separated by electrophoresis and the relative amount of each was determined for both normal and DMD cells. In normal fibroblasts, approximately 48% of the total CK activity was of the MM type, 40% was of the BB type, and 12% was of the MB type with no significant differences apparent between normal and DMD groups. The presence in human fibroblasts of significant levels of CK activity with a characteristic isozyme profile is an important consideration for studies of this "marker" enzyme in the pseudohypertrophic muscle of DMD.

Occurrence of heterogenous forms of the subunits of creatine kinase in various muscle and nonmuscle tissues and their behaviour during myogenesis

Purified, homodimeric creatine kinases from chicken were subjected to two-dimensional gel analysis under dissociating conditions. Each of the subunits M-creatine kinase and B-creatine kinase was resolved into a basic and an acidic subspecies with very similar mobilities in the sodium dodecylsulfate dimension. The M-creatine kinase subspecies were found in myogenic cells, fast muscle, slow muscle and the B-creatine kinase subspecies were present in heart, gizzard and brain. The creatine kinase subunits were identified in these tissues by a variety of methods like immunoreplicas of two-dimensional gels, immunoprecipitations, or coelectrophoresis with purified creatine kinase and all gave the same results. In the course of myogenic development in vitro the subspecies were synthesized coordinately and no indication was found for a differential regulation of any of the subspecies of the creatine kinase subunits. No radioactive phosphorus was incorporated into either one of the subspecies, hence phosphorylation could be ruled out as the source of heterogeneity. Furthermore, peptide mapping analysis of partial proteolytic digests did not reveal differences among the subspecies of the same subunit. Not only chicken but also rat creatine kinase displayed this type of heterogeneity. All subspecies were observed after translation of chicken RNA in a cell-free protein-synthesizing system. The heterogeneity probably might best be explained by the existence of multiple, but closely related genes for the creatine kinase subunits.