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PubMed1992

Muscle fiber pattern is independent of cell lineage in postnatal rodent development.

Muscle fibers specialized for fast or slow contraction are arrayed in characteristic patterns within developing limbs. Clones of myoblasts analyzed in vitro express fast and slow myosin isoforms typical of the muscle from which they derive. As a result, it has been suggested that distinct myoblast lineages generate and maintain muscle fiber pattern. We tested this hypothesis in vivo by using a retrovirus to label myoblasts genetically so that the fate of individual clones could be monitored. Both myoblast clones labeled in muscle in situ and clones labeled in tissue culture and then injected into various muscles contribute progeny to all fiber types encountered. Thus, extrinsic signals override the intrinsic commitment of myoblast nuclei to particular programs of gene expression. We conclude that in postnatal development, pattern is not dictated by myoblast lineage.

Animals↗
PubMed1990

Development and innervation of the abdominal muscle in embryonic Xenopus laevis.

The morphogenesis and innervation of the ventral abdominal musculature in Xenopus embryos was examined using microscopic techniques. Muscle development begins at Nieuwkoop and Faber Stage 31, when aggregates of undifferentiated cells form on the ventrolateral margins of rostral trunk myotomes. During subsequent stages, aggregates form and detach from progressively more caudal myotomes to form a series of seven discrete cell clusters (anlagen). The anlagen migrate ventrally in a cell-free space between the epidermis and a subepidermal layer of pigment cells. Extracellular aggregates of 30-nm granules are evident transiently between the migrating anlagen and the epidermis. During stages 39 and 40, each anlage transforms into a sheet of myotubes which attaches rostrally and caudally to adjacent sheets to form a seven-segmented muscle. The series of broad segments, approximately one fiber thick, extends from the pericardium to the level of the proctodeum. The embryonic muscle is innervated by the ventral rami of spinal nerves 2 to 9. The major nerve trunks to the muscle develop between stages 35/36 and 40. Axons initially grow ventrally along the paths taken by the muscle anlagen. When the anlagen become muscle segments, the nerves are deep to the narrow boundaries between the segments. Spinal nerve 2 ramifies in the first muscle segment and sends fibers rostrally to the geniohyoid muscle. The findings represent the first description of the development of this muscle in Xenopus and the first account of the development of the abdominal motor nerves in an amphibian embryo.

Abdominal Muscles↗
PubMed1992

Association of titin and myosin heavy chain in developing skeletal muscle.

To understand molecular interactions that organize developing myofibrils, we examined the biosynthesis and interaction of titin and myosin heavy chain in cultures of developing muscle. Use of pulse-labeling, immunoprecipitation, and a reversible cross-linking procedure demonstrates that within minutes of synthesis, titin and myosin heavy chain can be chemically cross-linked into very large, detergent-resistant complexes retaining many features of intact myotubes. These complexes, predominantly of titin and myosin, occur very early in myofibrillogenesis as well as later. These data suggest that synthesis and assembly of titin and myosin are temporally and spatially coordinated in nascent myofibrils and support the hypothesis that titin molecules help to organize sarcomere formation.

Animals↗
PubMed1975

Sodium and calcium components of the action potential in a developing skeletal muscle cell line.

1. Developmental changes in action potential properties were studied in a clonal rat skeletal muscle cell line. 2. Small action potentials were evoked in mononucleate myoblasts. No spike was seen in Na-free saline. A similar spike was evoked in a medium where all NaCl was replaced by LiCl. No spike was evoked when NaCl was replaced by CsCl. 3. Action potentials overshot zero membrane potential in multinucleate myotubes. The action potential was composed of two components, an initial fast spike and a hump on the falling phase or in some cases a distinct second peak. 4. Teh overshoot of the initial fast spike decreased when the external Na concentration was decreased. 5. In saline with 10 mM-Ca the second component often formed a distinct peak following the initial fast spike. A slow regenerative potential was evoked in Na-free media with a depolarizing current pulse. 6. In saline containing BaCl-2 instead of CaCl-2 there was always a second peak, the overshoot of which changed with external Ba concentration. A slow regenerative potential was evoked in Na-free, Ba-saline. The membrane conductance at the peak of the Ba-action potential was larger than in the resting state. 7. In adult rat skeletal muscle, the shape of the action potential was not changed when Ca was replaced by Ba. No action potential was evoked in Na-free Ba-saline or Ba-saline with tetrodotoxin (3 times 10-7 M). 8. The significance of the Ca component in the developing muscle is discussed.

Action Potentials↗
PubMed1989

A variant beta-tubulin isoform of Drosophila melanogaster (beta 3) is expressed primarily in tissues of mesodermal origin in embryos and pupae, and is utilized in populations of transient microtubules.

The beta 3-tubulin gene of Drosophila melanogaster codes for a variant tubulin isoform which is expressed at two distinct times during development: (1) during midembryogenesis from 8-16 hr postfertilization, and (2) during the 4 days of pupal development. We have determined the spatial pattern of beta 3-tubulin expression by localizing the beta 3 mRNA in paraffin sections using a 3' message-specific RNA probe and by localizing the beta 3 protein using a polyclonal antibody specific for Drosophila beta 3-tubulin. During embryogenesis beta 3 is restricted to and is expressed in all of the developing muscles. During pupal development beta 3 is also expressed at high levels in developing adult muscles. In addition, early in pupal development beta 3 is expressed in the imaginal discs, while at later times beta 3 is expressed in the epidermal cells of the wing blade, the optic lobe, the ovaries, and the testes. The expression of beta 3 tubulin ceases by the end of pupal development in all of these tissues except the ovaries and testes where expression persists into the adult. In both developing muscles and wings our results indicate that beta 3-tubulin is utilized in populations of specialized but transient cytoskeletal microtubules which are involved in establishing the final form of the tissue.

Animals↗
PubMed1988

Identification and changes in the pattern of expression of slow-skeletal-muscle-like myosin heavy chains in a developing fast muscle.

Immunochemical studies of chicken pectoralis major, a fast muscle, have demonstrated large amounts of myosin heavy chains (MHCs) of the slow-skeletal-muscle type during early stages of embryonic development. A large majority of the myotubes present in early embryonic muscle stained for this class of MHC. As development progressed, its synthesis was suppressed in most of the muscle, except in the deeper presumptive red-strip region. The level of this MHC in the embryonic muscle appeared to be reduced by its suppression in a proportion of the existing cells, by the addition of many presumptive fast cells that never expressed this MHC, and by atrophy or degeneration of a small proportion of the slow MHC-positive cells. Further suppression of this MHC in a proportion of the histochemically typed slow cells present in the red-strip region did not occur until quite late in the post-hatch period.

Animals↗
PubMed1976

Postnatal cytochemical development of muscle fibers in segmental tail muscles of the rat.

Postnatal development of extrafusal and intrafusal muscle fibers was examined histochemically in segmental tail muscles of the rat. At birth all fibers show a strong reaction for myosin ATPase, uniformity in diameter, and homogeneity in staining intensity. During the first postnatal week, the muscle fibers undergo gradual hypertrophy and hyperplasia but they all maintain the same intense homogeneous staining pattern for the enzyme. By day 9, further differentiation of the muscle fibers results in the formation of a second intrafusal fiber type while the extrafusal fibers are still relatively homogeneous. Finally, two kinds of extrafusal fiber and a third type of intrafusal fiber can be distinguished by day 21. This histochemical fiber pattern is essentially maintained in the adult. These findings show that fiber type development in rat tail muscles lags behind the usual time course of myogenesis known to occur in more rostral regions of the animal. It also indicates that histochemical differentiation of intrafusal fibers in these muscles does not parallel that which occurs in extrafusal fibers. It is likely that arrival and initial contact of sensory nerve terminals on developing intrafusal fibers at day 7 directly influences their relatively early histochemical heterogeneity.

Adenosine Triphosphatases↗
PubMed1989

Myosin light chain gene expression in developing and denervated fetal muscle in the mouse.

We have investigated the accumulation of mRNA transcripts of the atrial (or embryonic) myosin light chain MLC1A (MLC1emb), and the two adult fast muscle myosin light chains (MLC1F and MLC3F) during fetal skeletal muscle development in the mouse. In 15-day fetal muscle, MLC1A is the predominant mRNA detectable, by 18 days MLC1F has become the major transcript and MLC3F mRNA is detectable for the first time. By 12 days after birth, MLC1A transcripts are undetectable and MLC1F and MLC3F are similar in abundance. In fetuses treated with beta-bungarotoxin and which therefore develop in the absence of functional nerve, MLC1A and MLC1F undergo normal transitions but MLC3F mRNA accumulation is significantly retarded. This demonstrates that these myosin light chain mRNAs accumulate with differing kinetics, and that MLC3F mRNA accumulation is nerve-dependent during fetal development. The results are discussed in terms of secondary muscle fibre formation, and in relation to the independent regulation of MLC1F and MLC3F mRNAs which are transcribed from the same gene.

Animals↗
PubMed1989

Axonal guidance and the development of muscle fiber-specific innervation in Drosophila embryos.

The outgrowth of peripheral nerves and the development of muscle fiber-specific neuromuscular junctions were examined in Drosophila embryos using immunocytochemistry and computer-enhanced digital optical microscopy. We find that the pioneering of the peripheral nerves and the formation of the neuromuscular junctions occur through a precisely orchestrated sequence of stereotyped axonal trajectories, mediated by the selective growth cone choices of pioneer motoneurons. We have also examined the establishment of the embryonic muscle fibers and, using intracellular dye fills, have identified cells that are putative muscle pioneers. The muscle fibers of the bodywall have completed their morphogenesis prior to the initiation of synaptic contacts, and owing to the timing of neurite outgrowth from the CNS, synaptogenesis is synchronous at muscle fibers throughout the bodywall. At each muscle fiber the innervating axons make their initial contacts on a characteristic surface domain of the target cell's membrane. Through stereotyped growth cone-mediated trajectories the motoneurons actively establish the basic anatomical features of the mature neuromuscular junction, including the stereotyped, muscle fiber-specific branch anatomy. These events occur without significant process pruning or apparent synapse elimination. Our results suggest that the basic elements of the mature neuromuscular innervation, including the details of the ending trajectory on the target cell's surface, are formed by the precise navigation and presumed recognition by the motoneuron growth cones of muscle membrane surface features.

Animals↗
PubMedDate not supplied

[Myosin isoforms of the developing skeletal muscles in the loach].

Changes in the myosin isozyme spectrum were studied in the loach developing skeletal muscle. It was shown using disk-electrophoresis in polyacrylamide gel and peptide mapping that light and heavy myosin chains from the larval muscles, as well as from the red and white muscle of adult fish differ from each other. Forms of myosin light and heavy chains were found which were characteristic of the larval muscle only.

Animals↗
PubMed1990

Effects of easily chewable diet and unilateral extraction of upper molars on the masseter muscle in developing mice.

The effects of easily chewable diets and unilateral extraction of upper molars on the masseter muscle were studied in developing mice. A liquid diet requiring no mastication suppressed the development of the masseter muscles more than a fine-grained diet, and extraction of unilateral upper molars also caused inhibition of muscle development. Moreover, both unilateral extraction of upper molars and a liquid diet had an additive effect on the suppression of the postnatal development of the masseter muscle, and bilateral suppression of the development of the masseter muscle was induced following unilateral extraction of upper molars. These findings suggest that the sensory input from the sensory endings in the periodontal ligament may also play an important role in the postnatal development of the masseter muscle and that there may be some crossing pathways to convey the sensory input coming from the side of the extracted upper molars to the contralateral motor neurons via the interneuronal circuits.

Animals↗
PubMed1987

Primary, secondary and tertiary myotubes in developing skeletal muscle: a new approach to the analysis of human myogenesis.

Monoclonal antibodies to myosins have been used to describe and define the appearance and maturation of 3 different classes of myotube in developing human quadriceps muscle. Five monoclonal antibodies were used: (i) MAb A against human slow myosin heavy chain; (ii) MAb B against a myosin heavy chain present in most adult Type 2 fibres; (iii) MAb C against myosin heavy chain present in all mature and immature Type 2 fibres; (iv) MAb D, with similar reactivity to MAb C; (v) MAb E against human embryonic myosin. The combined use of two of these antibodies (A and B) enables the confident early identification of each of 3 classes (primary, secondary, tertiary) of myotubes, which appear sequentially during myogenesis. Our results show that induction of slow myosin heavy chain synthesis is a biphasic phenomenon in developing human skeletal muscle. Slow myosin heavy chain was present in all the earliest (9 weeks gestation) primary myotubes, but was not detected in secondary or tertiary myotubes until about 29 weeks gestation. Each stage of fetal muscle development has a characteristic immunocytochemical pattern which reveals cellular heterogeneity not evident on myosin ATPase histochemistry. Myosin immunocytochemistry may usefully be applied to assess the gestational age of fetuses. A new interpretation of human skeletal muscle development is proposed, based on the separate programming of 3 different kinds of myotube. This may be important in the analysis of diseased muscle in which developmental abnormalities or regeneration are present.

Antibodies, Monoclonal↗
PubMed1991

Reinnervation of developing rat muscle by non-axotomized motoneurons.

To study the ability of developing motoneurons to reinnervate their denervated muscle, axotomized motoneurons in rat neonates and pups were retrogradely labeled with two fluorescent tracers. Fluorogold (FG), a long-lasting fluorescent dye, was injected into intercostal muscle T8 to retrogradely label the motoneurons that innervated it. Two days later intercostal nerves T7-T9 were cut. The intercostal muscle denervated at birth was reinnervated within 10-20 days, as evidenced by nerve-evoked muscle contraction. Three weeks following axotomy, tetramethylrhodamine isothiocyanate (TRITC) was injected into the same muscle to label the motoneurons that reinnervated it. The motoneurons double-labeled with FG and TRITC were, therefore, axotomized motoneurons that regenerated to reinnervate T8. In neonates, axotomy resulted in a significant reduction in the number of FG-labeled motoneurons, which suggests that axon transection at early postnatal days causes a massive motoneuron death. The percentage of double-labeled motoneurons was significantly smaller than that in non-axotomized rats. TRITC-labeled motoneurons constituted the majority of stained motoneurons; these were located in different nuclei than the intercostal motoneurons. These findings suggest that muscle reinnervation is, at least in part, by motoneurons which originally did not innervate intercostal muscle T8. Unlike axotomy at birth, axotomy performed 2-3 weeks after birth did not result in a significant motoneuron loss. The number of stained motoneurons labeled with both FG and TRITC was significantly smaller, however, than in non-axotomized spinal cords. Our data indicate that in pups only a small percentage of axotomized motoneurons reinnervated the denervated muscle.

Animals↗
PubMed1976

Adult motor patterns produced by moth pupae during development.

Muscle potentials were recorded extracellularly from developing pupae and adults of the saturniid moths Antheraea polyphemus and A. pernyi and the sphingid moth Manduca sexta. During the week prior to the terminal ecdysis, developing moths still enclosed within the pupal cuticle produced motor patterns similar to those recorded from adults during flight and shivering. The pupal patterns had a longer cycle time and were more variable than the adult motor patterns. Characteristic inter-family differences in adult motor patterns were apparent in pupal motor patterns. Development of motor patterns was followed over several days by observing individuals with chronically implanted leads. Early in the pupal period potentials were small and infrequent. The amount of activity gradually increased and became more patterned. As development proceeded adult patterns were produced for increasing lengths of time, although the patterns changed quickly and spontaneously. Restricting the wing movements of A. polyphemus adults increased the cycle time, increased the number of spikes per burst in muscles opposing the restraint, and did not alter the interspike interval within a burst. The flight patterns produced by pharate moths, in which the wings are also immobile, also have a longer cycle time than that of adult flight, but the number of spikes per burst the same and the interspike interval is longer than in adult flight. These observations suggest that the differences between pupal and adult patterns are not necessarily due to the confinement of the wings by the pupal cuticle.

Action Potentials↗
PubMed1979

Ultrastructure of human intramuscular blood vessels in development.

Muscles from human foetuses of nine weeks to nine months development were examined by electron microscopy. Capillaries, arteries and veins are frequent in the human foetal muscle at all stages of development. At nine weeks the vessels have the appearance of capillaries and basement membrane lies around the endothelial cells forming them. The capillaries are of continuous type which do not have apertures in their walls. Tight junctions are seen at some zones of adjacent endothelial cells of the capillaries. Sometimes, pericytes are also seen. At sixteen weeks vessels having the features of veins and of arteries can be identified between the muscle cells. Regarding the arteries, some of the endothelial cells are united to the smooth muscle cells and the intimal elastic lamina is interrupted where these cells approximate. The significance of this junction may be to anchor the intima to the media.

Arteries↗
PubMed1991

Changes in the protein kinase C activity or rat sternomastoid muscle during development and after denervation.

The relationship between the activity of protein kinase C (PKC) and muscle innervation was explored in the rat sternomastoid muscle (SM) from day 18 of gestation (E18) to adult age. Between E18 and birth, PKC activity rose 5-fold, and during the day after birth, diminished to a level characteristic of the mature muscle. The rise chiefly occurred in the neural part of the muscle, in both the membrane and the cytosol fractions. Between E18 and day 5 after birth, the ratios of membrane to cytosol PKC activity rose from 0.5 to 10 and 3 respectively in the neural and aneural parts of the muscle. Denervation of adult SM reduced PKC activity by half in the membrane fraction of the neural part but did not significantly change it in the membrane or cytosol fractions of the aneural parts. These results suggest that innervation plays an important part in determining the level of PKC activity in muscle.

Aging↗
PubMed1990

[Effects of denervation of the masseter nerve and bite raising on the masseter muscle of developing rats].

The effects of masseteric denervation and bite raising on muscle fiber type differentiation were examined in the masseteric muscle of developing rats by histological and histochemical studies. Three-week-old Wistar rats had of their masseteric nerve at right side dissected, and a part of them were bite raised at anterior region one week after denervation for three weeks. The unoperated side and number of sham animals served as control. The animals were killed 3, 7, 10, 14, 21, 28, 35, 49 days later and then their masseter muscles were removed wholly and weighed them. After freezing of superficial and deep masseter muscles serial sections were made and HE staining carried out, ATPase staining and NADH-TR staining. On the photographs of the HE stained specimens, I measured the diameter of the muscle fibers. Gross findings on the denervated group, revealed the lower incisors shifted to unoperated side and on with the bite raising group, it shifted to the operated side. In denervated animals, the wet weight of the masseter muscle had decreased significantly. The masseteric muscle fibers in three-old-week control rats were undifferentiated on ATPase staining, but it became well differentiated on and after four-old-week. The superficial masseter of control mainly composed of type 2B fibers. In the deep masseter, about 10% type 1 and 2C fibers were found in limited area around the muscle spindles, and surrounded with type 2A and 2B fibers. In superficial masseter muscle of the denervated group, the percentage of type 2A fibers increased, and that of type 2B fibers decreased. The type 2C fibers were found from the 21st days after denervation. In deep masseter muscles, the percentage of type 1 and 2A fibers decreased, and that of type 2B and 2C fibers increased. In the denervated bite raising group, the composition of the muscle fiber type approached the control group. These results as above suggested, masseteric denervation causes degeneration of muscle fiber composition, and the possibility that early preventive treatment like bite raising may recover the muscle fiber composition normally.

Animals↗