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PubMed1988

Muscle strength and muscle endurance of middle-aged women and men associated to type, duration and intensity of muscular load at work.

Muscle strength and muscle endurance in groups with different occupational muscular load was studied among 60 women and 69 men. The mean age of the subjects was 52.0 +/- 3.4 years. Isometric grip and trunk strength were measured on dynamometers, and dynamic muscle endurance by sit-ups. A job analysis was done with the AET method including the assessment of intensity, duration and type of muscular work of each subject. According to the job analysis, the subjects were classified into groups with low or high muscular load at work. The maximal isometric hand grip strength of women with a load classified as long duration of static or dynamic load on the hands at work was 86 and 88%, respectively of the strength of those with a load of short duration. The women with high intensity in static work had a grip strength of 86% of those with low intensity. These differences in strength among women between the high and low load groups were statistically significant (P less than 0.05). No other statistically significant differences in muscle strength or muscle endurance between the high and low work load groups were found, although the high work load group had systematically the lowest muscle strength and muscle endurance in almost all comparisons. Muscle strength and muscle endurance was, however, not a discriminating factor between the group classifications of static and dynamic work. The results indicated that the muscle strength and muscle endurance of middle-aged employees was systematically lower among those with high muscular load compared to those with low load at work.

Female↗
PubMed1991

Identification of and pattern of transitions of cardiac, adult slow and slow skeletal muscle-like embryonic isoforms of troponin T in developing rat and human skeletal muscles.

Using a monoclonal antibody (CDC4) that recognizes both the cardiac and slow skeletal isoforms of troponin T in an immunoblotting procedure, the composition of troponin T isoforms in adult and developing skeletal muscles of the rat and human were studied. Two major isoforms of slow troponin T (HS1 and HS2) were detected in all the adult human skeletal muscles investigated. Significant amounts of another isoform (HS3) in addition to HS1 and HS2 were also detectable in a subgroup of these muscles. All the human fetal skeletal muscles at 20 weeks of gestation expressed HS1 and HS2 isoforms but not HS3. The fetal skeletal muscles, also expressed cardiac troponin T in addition. Unlike the human skeletal muscles, only a single isoform of slow troponin T was detected by antibody CDC4 in both the adult and neonatal rat skeletal muscles. The investigation of fetal rat skeletal muscles using the same antibody, however, detected the presence of not only the embryonic cardiac and adult slow skeletal isoforms but also five additional not previously described isoforms (Es1-Es5) of troponin T. These embryonic isoforms, Es1-Es5, were undetectable in the postnatal skeletal muscles although their small amounts could be detected in the neonatal rat hearts. The analysis of individual skeletal muscles from different parts of the body at different stages of fetal development showed marked variations in both the composition of troponin T isoforms and the time sequence of their transitions in each muscle.

Animals↗
PubMed1977

In vitro studies of skeletal muscle membranes. Adenylate cyclase of fast and slow twitch muscle and the effects of denervation.

Sarcolemmal membranes were prepared from slow-twitch (red) and fast-twitch (white) skeletal muscle of the rat. A sensitive adenylate cyclase assay was used and basal, fluoride- and catecholamine-stimulated activities measured. The greater in vivo sensitivity of red muscle to the effects of catecholamines correlates, in the present study, with approximately a twofold stimulation of its sarcolemmal adenylate cyclase with isoproterenol (10 micronm). The white muscle enzyme, on the other hand, is only minimally stimulated (20%) at the same concentration of beta-adrenergic agonist. Fast-twitch muscle is known to be physiologically insensitive to catecholamine in vivo. A course of sciatic nerve denervation was followed to further distinguish these two metabolic types of skeletal muscle and their respective adenylate cyclases. The slow-twitch muscle enzyme activities were completely and permanently lost on denervation. The white muscle enzyme, however, recovered almost completely after an initial reduction in specific activity the first week. Interestingly, the NaF-stimulated activity lagged behind both the basal and hormone-stimulated activities of the white muscle enzyme, in returning to control levels. The activities of cyclic nucleotide phosphodiesterase were evaluated in homogenates of the two muscle types in innervated rats and following denervation, in order to further define the neural influence on skeletal muscle cyclic nucleotide metabolism. The results suggest that the motor nerve may regulate some of the metabolic properties of slow-twitch muscle (which may involve cyclic AMP) by controlling the responsiveness of its sarcolemmal-bound adenylate cyclase system.

Adenylyl Cyclases↗
PubMed1993

Respiratory muscle stiffness is age- and muscle-specific.

We investigated the possible contribution of respiratory muscles to the well documented increase in chest wall stiffness with age. Diaphragm and internal intercostal muscle strips were dissected from male Fischer 344 rats of 3, 6, 12, and 24 months of age. Muscles were subjected, in vitro, to stress-strain and yield point tests. Passive tension data from these tests were normalized to a reference length (Lr), which was defined in terms of absolute stress, 700 Pascals. In general, Lr of diaphragm was found to be 90% of the length (Lo) required for maximal tetanic tension. Within a range of stretch between Lr and 130% Lr, diaphragm muscles from adult rats (6-12 month) were more compliant than those of either young (3 month) or old (24 month) animals. In contrast, intercostal muscles from old rats were stiffer than those of young or adult rats. Yield strength of both muscles was constant with age, but diaphragm muscles were found to have a higher yield strength than intercostal muscles from any age. Thus, only some passive mechanical properties of respiratory muscles vary with age, and this variation in muscle-specific. A surprising finding of this study was that diaphragm muscles of adult animals were more compliant than those of either young or old rats.

Aging↗
PubMed2006

Course of the innervation supply of medial head of triceps muscle and anconeus muscle at the posterior aspect of humerus (anatomical study).

INTRODUCTION: In elbow surgery; posterior side of joint has been described as the front door for accessing the elbow pathologies. Triceps splitting, triceps reflection, posterolateral Kocher, posteromedial Bryan-Morrey, modified MacAusland transolecranon approaches are the well known posterior surgical approaches. In the English literature, release and transposition of ulnar nerve on the medial side was fully described in posterior approaches. We believe that there was a need to identify the structures at the lateral aspect of the elbow while an iatrogenic injury may inversely effect an excellent radiological result. Therefore, we exposed the detailed innervation supply to the anconeus muscle and medial head of triceps muscle and tried to show possible denervation sites of these two structures during posterior approaches. MATERIALS AND METHODS: This study was performed on 14 elbows in formalin-preserved 7 cadavers. We exposed the course of the innervation supply to the medial head of triceps muscle and anconeus muscle and tried to show possible denervation sites of these two structures during posterior approaches. The branching pattern of radial nerve innervating anconeus muscle and its deriving level from radial nerve was identified. Distance from a vertical line which is passing through lateral epicondyle to branching point was measured. RESULTS: The mean distance of the branching point of the nerve to medial head of triceps muscle and anconeus was 168.3 mm (range 130.36-185.4). The nerve to anconeus muscle ran along the posterior aspect of the humerus from the horizontal line passing through lateral epicondyle at a distance of 142.20 mm (range 153.72-136.41) medial to olecranon and at a distance of 47.45 mm (range 77.13-30.14) lateral to olecranon. CONCLUSION: Although splitting the fibers of triceps proximaly increases the exposure of the posterior humerus, innervation of the lateral portion of the medial head of triceps muscle and anconeus muscle may be jeoparadized. Therefore, surgeons who have interest in elbow surgery; (1) should revise the course of the nerve to medial head of triceps and anconeus muscle, (2) be aware of possible iatrogenic injury of the extensor muscles of the elbow via transtricipital approaches, (3) try to choose a more conservative posterior surgical approach.

Elbow↗
PubMed2000

Experimental muscle pain modulates muscle activity and work performance differently during high and low precision use of a computer mouse.

The aim was to investigate the influence of experimental muscle pain on performance and upper extremity muscle activity during occupational work requiring different levels of precision. Experimental muscle pain was induced by infusing hypertonic saline (0.3 ml, 5% NaCl) into the extensor carpi ulnaris (ECU) muscle. The same amount of isotonic saline was infused on a separate day to act as a control. Tasks requiring use of a computer mouse with high and low levels of precision were performed during the two sessions. Electromyographic (EMG) activity was measured from the ECU, the flexor carpi radialis (FCR) and the trapezius muscles. A group of 13 men participated in the study. Performance measured as work cycle time, cursor movements on the screen, and velocity of cursor movement were unaffected by muscle pain. The ECU muscle pain did not modulate EMG profiles of either the trapezius or FCR muscles either during high or during low precision work. During the low precision work the painful ECU muscle showed lower EMG activity in specific phases of the work cycle (highest activity phases) compared to the control session (P<0.05), whereas during the high precision work, experimental pain had no effect on the activity of the ECU muscle. In conclusion experimental muscle pain seems to modulate motor control differently depending on the precision level of the task. This may be of importance for our understanding of why some tasks lead to chronic musculoskeletal disorders.

Adult↗
PubMed1985

Topographic studies relating distribution of Ia- and gamma-fibres in spinal cord and position of muscle spindles in cat tibialis anterior muscle.

The segmental distribution of 115 Ia- and 115 paired gamma-fibres of the tibialis anterior muscle was studied in anaesthetized cats. All Ia-fibres recorded were found in the lumbar segments L6 and L7, from caudal L6 to middle L7. The paired gamma-axons were also mainly found in these parts of the spinal cord, only 7 gamma-fibres were localized in caudal L7. A total of 70% of all fibres was found in L7. Of the fibres constituting 'muscle spindle units' of the tibialis anterior 92.2% enter the same segment (a 'muscle spindle unit' is here defined as a muscle spindle with its Ia-fibres and one gamma-fibre innervating it). More than that, 88% of the afferent and efferent fibres of muscle spindle units were found in the same part of the segment. For the first time, the position of the muscle spindles was related to the location of their Ia- and gamma-fibres in the spinal cord. In general, the muscle spindles located in the proximal muscle region project to the more cranial part of the spinal cord and the muscle spindles localized distally in the muscle project to the more caudal part of the spinal cord. The topographic pattern of the muscle spindle units is discussed with respect to the topographically arranged monosynaptic reflex loop.

Animals↗
PubMed1985

Muscle development in the grasshopper embryo. II. Syncytial origin of the extensor tibiae muscle pioneers.

The extensor tibiae muscle (ETi) in the metathoracic leg of the grasshopper, which powers the jump, is among the most studied insect muscles. In contrast to many insect muscles which are simple (consisting of only a single bundle of muscle fibers), the ETi is a complex muscle which consists of an array of bundles of muscle fibers, each with a separate site of insertion on the body wall ectoderm and on the ETi apodeme ectoderm. Here we describe the embryonic development of this complex muscle. The ETi muscle develops from a single muscle pioneer (MP) which connects the initial invagination of the ETi apodeme to the wall of the femur. This MP then dramatically expands around the developing apodeme to form a large horseshoe-shaped, multinucleate cell, called the supramuscle pioneer (supra-MP); the number of nuclei in the supra-MP increases by cell fusion rather than by nuclear division. The arms of the supra-MP grow steadily longer and their outer edges begin to appear scalloped, certain areas remaining tightly apposed to the ectoderm of the wall of the leg while adjacent areas lose their adhesion and are pulled away. By about 50% of embryonic development the ETi supra-MP consists of a periodic series of bridges (cytoplasmic extensions) connecting the leg wall ectoderm with the apodeme, and linked into a giant syncytium near their inner, apodeme surface by a thin layer of cytoplasm containing hundreds of nuclei. Each bridge is surrounded by a cluster of many smaller mesoderm cells. Next the syncytium begins to divide such that by 60% the periodic bridges of the supra-MP have lost syncytial contact with each other and now themselves form an array of smaller, individual, multinucleate MPs connecting the body wall to the apodeme, each surrounded by a mass of undifferentiated mesoderm cells. This initial cycle of fusion and division is followed by a second similar cycle in which the individual mesoderm cells surrounding each MP fuse with the MP. At the same time, the MP divides into the initial bundle of smaller muscle fibers. Coincident with this division into muscle fibers is the further development of thick and thin filaments and the T-tubule system.

Animals↗
PubMed1979

Elevated levels of a calcium-activated muscle protease in rapidly atrophying muscles from vitamin E-deficient rabbits.

A Ca2+-activated proteolytic enzyme that partially degrades myofibrils was isolated from hind limb muscles of normal rabbits and rabbits undergoing rapid muscle atrophy as a result of vitamin E deficiency. Extractable Ca2+-activated protease activity was 3.6 times higher in muscle tissue from vitamin E-deficient rabbits than from muscle tissue of control rabbits. Ultrastructural studies of muscle from vitamin E-deficient rabbits showed that the Z disk was the first myofibrillar structure to show degradative changes in atrophying muscle. Myofibrils prepared from muscles from vitamin E-deficient rabbits showed partial or complete loss of Z-disk density. Sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that the amount of troponin-T (37 000 daltons) and alpha-actinin (96 000 daltons) was reduced in myofibrils from atrophying muscle as compared to myofibrils prepared from control muscle. In vitro treatment of purified myofibrils with purified Ca2+-activated proteolytic enzyme produced alterations in myofibrillar ultrastructure that were identical to the initial alterations occurring in myofibrils from atrophying muscle (i.e. weakening and subsequent removal of Z disks). Additonally the electrophoretic banding pattern of Ca2+-activated proteolytic enzyme-treated myofibrils is very similar to that of myofibrils prepared from muscles atrophying as a result of nutritional vitamin E deficiency. The possible role of Ca2+-activated proteolytic enzyme in disassembly and degradation of the myofibril is discussed.

Animals↗
PubMed1994

Insulin-like growth factor-II expression in developing skeletal muscle of double muscled and normal cattle.

Double muscled (DM) cattle possess nearly 40% more muscle fibers than normal muscled (NM) beef or dairy cattle. Previous work showed that serum from DM fetuses stimulated proliferation of L6 myoblasts to a greater extent than serum from NM fetuses. Although the exact role of insulin-like growth factor-II (IGF-II) in the regulation of fetal myogenesis is unknown, it has been shown to serve as a autocrine-acting growth factor during terminal differentiation of myoblasts in mitogen-depleted culture media. Delay of IGF-II expression may alter the ultimate number of muscle fibers formed during fetal development. To investigate this, forty-seven skeletal muscle and twenty-nine liver samples were collected from NM fetuses representing fetuses grouped by crown-rump lengths (CRL) of < 20, 21-30, 31-40, 41-50, 51-60, 61-70 or > 70 cm. Twelve DM fetuses representing 20, 40, 50, and 85 cm were compared to NM groups with the same CRL. Total RNA preparations from these samples were subjected to northern and dot blot analysis using rat IGF-II and beta actin cDNAs and a human 28S rRNA oligomer. IGF-II transcripts of 4.5, 3.6, 2.75, 2.5, and 1.15 kilobases (kb) were detected in liver and muscle RNA from both DM and NM fetuses. Liver IGF-II expression increased (P < 0.05) in both DM and NM fetuses with CRL. Mean concentrations of muscle IGF-II mRNA initially increased (P < 0.05), then decreased (P < 0.05) with CRL in DM and NM fetuses. Muscle IGF-II mRNA was greater (P < 0.05) for NM fetuses compared to DM fetuses at 20 cm CRL, whereas at 53 cm CRL, DM muscle IGF-II was greater (P < 0.05) than that of NM fetuses. These results show that the maximum expression of muscle IGF-II is delayed in DM fetuses compared to NM fetuses. This delayed expression may play an explicit role in controlling myogenesis in the development of double muscle cattle.

Analysis of Variance↗
PubMed2006

Muscle specificity in tests of cervical flexor muscle performance.

The deep cervical flexor (DCF) muscles are considered to be of substantial clinical importance in the management of neck pain. While conventional cervical flexion (CF) dynamometry methods have been used frequently to assess the capacity of the cervical flexor muscles, it has been suggested that cranio-cervical flexion (CCF) methods may provide a more specific test of DCF muscle performance. This study compared the activation of the deep and superficial cervical flexor muscles between tests of isometric cranio-cervical flexion (CCF) and conventional cervical flexion (CF) dynamometry. Normalised root-mean-square values were recorded for the deep cervical flexor (DCF), sternocleidomastoid (SCM), anterior scalene (AS), and sternohyoid (SH) muscles during isometric CCF and CF tests at maximal voluntary contraction (MVC), 50% MVC, and 20% MVC in ten healthy volunteers. The results demonstrated significantly greater electromyography (EMG) amplitude for the SCM (P<.001-.002) and AS (P<.001-.001) muscles in the CF test conditions (MVC, 20%MVC, and 50%MVC) compared to CCF test conditions. Moreover, the SH muscle demonstrated significantly greater EMG amplitude during CF compared to CCF but only in the 50% MVC and 20% MVC conditions (P=.007 and .02 respectively). These results demonstrate that dynamometry tests of CF result in greater activity of the superficial cervical flexor muscles compared to tests of CCF. As a result, CCF dynamometry may provide a more specific method to assess and retrain DCF muscle performance, compared to conventional CF in which superficial muscle activity may mask impaired performance of the DCF muscles.

Adult↗
PubMed2006

ASIC3 in muscle mediates mechanical, but not heat, hyperalgesia associated with muscle inflammation.

Peripheral initiators of muscle pain are virtually unknown, but likely key to development of chronic pain after muscle insult. The current study tested the hypothesis that ASIC3 in muscle is necessary for development of cutaneous mechanical, but not heat, hyperalgesia induced by muscle inflammation. Using mechanical and heat stimuli, we assessed behavioral responses in ASIC3-/- and ASIC3+/+ mice after induction of carrageenan muscle inflammation. ASIC3-/- mice did not develop cutaneous mechanical hyperalgesia after muscle inflammation when compared to ASIC3+/+ mice; heat hyperalgesia developed similarly between groups. We then tested if the phenotype could be rescued in ASIC3-/- mice by using a recombinant herpes virus vector to express ASIC3 in skin (where testing occurred) or muscle (where inflammation occurred). Infection of mouse DRG neurons with ASIC3-encoding virus resulted in functional expression of ASICs. Injection of ASIC3-encoding virus into muscle or skin of ASIC3-/- mice resulted in ASIC3 mRNA in DRG and protein expression in DRG and the peripheral injection site. Injection of ASIC3-encoding virus into muscle, but not skin, resulted in development of mechanical hyperalgesia similar to that observed in ASIC3+/+ mice. Thus, ASIC3 in primary afferent fibers innervating muscle is critical to development of hyperalgesia that results from muscle insult.

Acid Sensing Ion Channels↗
PubMed1997

An anatomical study of a muscle bundle separated from the medial pterygoid muscle.

When mandibular dentures are fabricated, marginal sealing should be taken into consideration for the stability of the denture. We selected specimens of the medial pterygoid muscle showing insertion of an independent small muscle bundle at its insertion site, and evaluated the anatomical relationship between the morphology of the insertion site and the denture. The insertion of the pterygoid muscle was classified according to the insertion morphology of the independent small muscle bundle into three types using the retromolar pad as a reference: Type I, insertion of the independent muscle bundle posterior to the retromolar pad; Type II, insertion immediately below the retromolar pad; and Type III, insertion into the fascia of the mylohyoid muscle. Types II and III muscles seem to affect the denture because of their closeness to the mandibular denture. In the oral cavity, the independent small muscle bundle studied appeared as a streak-like structure. When such a structure is detected during examination for denture fabrication, the following consideration is necessary. Since the medial pterygoid muscle is a mouth-closing muscle, this independent small muscle bundle may contract during mouth closing, appearing more markedly in the oral cavity. Therefore, examination should be performed not only with the mouth closed but also with assumed centric occlusion.

Aged↗
PubMed1994

Assembly of body wall muscle and muscle cell attachment structures in Caenorhabditis elegans.

C. Elegans has four muscle quadrants that are used for locomotion. Contraction is converted to locomotion because muscle cells are anchored to the cuticle (the outer covering of the worm) by a specialized basement membrane and hemidesmosome structures in the hypodermis (a cellular syncytium that covers the worm and secretes the cuticle). To study muscle assembly, we have used antibodies to determine the spatial and temporal distribution of muscle and attachment structure components in wild-type and mutant C. elegans embryos. Myofibrillar components are first observed diffusely distributed in the muscle cells, and are expressed in some dividing cells. Later, the components accumulate at the membrane adjacent to the hypodermis where the sarcomeres will form, showing that the cells have become polarized. Assembly of muscle attachment structures is spatially and temporally coordinated with muscle assembly suggesting that important developmental signals may be passed between muscle and hypodermal cells. Analysis of embryos homozygous for mutations that affect muscle assembly show that muscle components closer to the membrane than the affected protein assemble quite well, while those further from the membrane do not. Our results suggest a model where lattice assembly is initiated at the membrane and the spatial organization of the structural elements of the muscle is dictated by membrane proximal events, not by the filament components themselves.

Animals↗
PubMed1999

Expression of the primary coxsackie and adenovirus receptor is downregulated during skeletal muscle maturation and limits the efficacy of adenovirus-mediated gene delivery to muscle cells.

Skeletal muscle fibers are infected efficiently by adenoviral vectors only in neonatal animals. This lack of tropism for mature skeletal muscle may be partly due to inefficient binding of adenoviral particles to the cell surface. We evaluated in developing mouse muscle the expression levels of two high-affinity receptors for adenovirus, MHC class I and the coxsackie and adenovirus receptor (CAR). The moderate levels of MHC class I transcripts that were detected in quadriceps, gastrocnemius, and heart muscle did not vary between postnatal day 3 and day 60 adult tissue. A low level of CAR expression was detected on postnatal day 3 in quadriceps and gastrocnemius muscles, but CAR expression was barely detectable in adult skeletal muscle even by reverse transcriptase-polymerase chain reaction. In contrast, CAR transcripts were moderately abundant at all stages of heart muscle development. Ectopic expression of CAR in C2C12 mouse myoblast cells increased their transducibility by adenovirus at all multiplicities of infection (MOIs) tested as measured by lacZ reporter gene activity following AVCMVlacZ infection, with an 80-fold difference between CAR-expressing cells and control C2C12 cells at an MOI of 50. Primary myoblasts ectopically expressing CAR were injected into muscles of syngeneic hosts; following incorporation of the exogenous myoblasts into host myofibers, an increased transducibility of adult muscle fibers by AVCMVlacZ was observed in the host. Expression of the lacZ reporter gene in host myofibers coincided with CAR immunoreactivity. Furthermore, sarcolemmal CAR expression was markedly increased in regenerating muscle fibers of the dystrophic mdx mouse, fibers that are susceptible to adenovirus transduction. These analyses show that CAR expression by skeletal muscle correlates with its susceptibility to adenovirus transduction, and that forced CAR expression in mature myofibers dramatically increases their susceptibility to adenovirus transduction.

Adenoviridae↗
PubMed1999

Fast skeletal muscle-specific expression of a zebrafish myosin light chain 2 gene and characterization of its promoter by direct injection into skeletal muscle.

A zebrafish myosin light chain 2 cDNA clone was isolated and characterized. Sequence analysis of the clone revealed a high homology with the mammalian and avian genes encoding the fast skeletal muscle isoform, MLC2f. In situ hybridization and Northern blot hybridization analyses indicated that the zebrafish MLC2f mRNA is expressed exclusively in the fast skeletal muscle. Ontogenetically, the MLC2f mRNA appears around 16 hours postfertilization (hpf) in the first few well-formed anterior somites. At later stages, the MLC2f mRNA can also be detected in fin buds, eye muscles, and jaw muscles. To develop a useful model system for analyzing muscle gene regulation, the promoter of the zebrafish MLC2f gene was isolated and linked to the chloramphenicol acetyltransferase (CAT) reporter gene. The MLC2f/CAT chimeric constructs were analyzed by direct injection into the zebrafish skeletal muscle, and significant CAT activity was observed; in contrast, little or no CAT activity was generated from a similarly injected prolactin gene promoter/CAT gene construct. Within the 1 kb of the MLC2f promoter region, several MEF2-binding sites and E-boxes were identified, suggesting that MLC2f can be regulated by muscle transcription factors MEF2 and myogenic bHLH proteins. A 5' deletion analysis indicated that the proximal 79 nucleotides from the transcription start site, which contains a single MEF2-binding site, is sufficient to drive a high level of CAT activity in injected muscle. Internal deletion of the MEF2 element in the -79-bp construct caused an 80% decrease in CAT activity, whereas internal deletion of the same MEF2 element in a -1044-bp construct had no effect on induced CAT activity. These observations suggest that an MEF2 element is important to activate the MLC2f gene in muscle cells, and the effect of loss of the proximal MEF2 element can be compensated for by the presence of the upstream MEF2 elements. This study also demonstrated that direct injection of DNA into skeletal muscle is a valid and valuable approach to analyze muscle gene promoters in the zebrafish.

Amino Acid Sequence↗
PubMed2005

Zebrafish as a model for caveolin-associated muscle disease; caveolin-3 is required for myofibril organization and muscle cell patterning.

Caveolae are an abundant feature of many animal cells. However, the exact function of caveolae remains unclear. We have used the zebrafish, Danio rerio, as a system to understand caveolae function focusing on the muscle-specific caveolar protein, caveolin-3 (Cav3). We have identified caveolin-1 (alpha and beta), caveolin-2 and Cav3 in the zebrafish. Zebrafish Cav3 has 72% identity to human CAV3, and the amino acids altered in human muscle diseases are conserved in the zebrafish protein. During embryonic development, cav3 expression is apparent by early segmentation stages in the first differentiating muscle precursors, the adaxial cells and slightly later in the notochord. cav3 expression appears in the somites during mid-segmentation stages and then later in the pectoral fins and facial muscles. Cav3 and caveolae are located along the entire sarcolemma of late stage embryonic muscle fibers, whereas beta-dystroglycan is restricted to the muscle fiber ends. Down-regulation of Cav3 expression causes gross muscle abnormalities and uncoordinated movement. Ultrastructural analysis of isolated muscle fibers reveals defects in myoblast fusion and disorganized myofibril and membrane systems. Expression of the zebrafish equivalent to a human muscular dystrophy mutant, CAV3P104L, causes severe disruption of muscle differentiation. In addition, knockdown of Cav3 resulted in a dramatic up-regulation of eng1a expression resulting in an increase in the number of muscle pioneer-like cells adjacent to the notochord. These studies provide new insights into the role of Cav3 in muscle development and demonstrate its requirement for correct intracellular organization and myoblast fusion.

Amino Acid Sequence↗
PubMed1995

Visualization of dystrophic muscle fibers in mdx mouse by vital staining with Evans blue: evidence of apoptosis in dystrophin-deficient muscle.

Degenerating muscle fibers in the skeletal muscle of mdx mice were visualized by vital staining with Evans blue. Evans blue injected intravenously stained only degenerating muscle fibers which were visible as blue fibers macroscopically and could also be seen as red fluorescent fibers microscopically. Evans blue-stained muscle fibers were either hypercontracted or degrading. Intact or regenerating muscle fibers in mdx mice and muscle fibers in B10 control mice were not stained with the dye. DNA isolated from Evans blue-stained fibers exhibited fragmentation to approximately 180 base pairs on agarose gel electrophoresis. Such DNA fragmentation was not found in DNA from unstained muscle fibers in mdx or B10 mice. Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling (TUNEL)-positive myonuclei were also found in Evans blue-stained muscle fibers but not in unstained ones. These results indicate that degenerating muscle fibers in the mdx mouse show an increase in membrane permeability and undergo apoptosis. Vital staining with Evans blue is useful not only for distinguishing degenerating muscle fibers, but also for studying the degeneration process biochemically in dystrophin-deficient muscle. This method may also be useful for evaluating the therapeutic effects of drug administration, gene transfer, and myoblast transfer in the mdx mouse.

Animals↗