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At least 775 records · Page 43Linked to original sources
PubMed1980

Selective elimination of motor nerve terminals in the rat soleus muscle during development.

1. The pattern of innervation and either frequency of miniature end-plate potentials (m.e.p.p.s) or acetylcholine (ACh) sensitivity was examined in individual fibres of the soleus muscle in new-born rats to elucidate the mechanism of elimination of motor nerve terminals. 2. the number of motor nerve terminals innervating a muscle fibre was judged by the difference in latencies of end-plate potentials evoked by stimulation of the ventral roots L4 and L5. 3. At early developmental stages, about 50% of soleus muscle fibres were usually singly innervated by the L5 ventral root and this nerve to fibre relation did not change throughout the developmental days. In contrast to the L5 root, the L4 root innervated all the muscle fibres polyneuronally at day 6. In day 16 or older animals, the remaining half of the fibres were singly innervated by the L4 ventral nerves. Therefore, it is concluded that the elimination of motor nerve terminals in the soleus muscle occurs selectively only for the L4 ventral nerves. 4. The number of polyneuronally innervated fibres was increased, to some extent, within 2 days after transection of the spinal cord at day 12. It is suggested that the increased polyneuronal innervation following the inactivity produced by cordotomy may reflect the recovery of terminals which had lost function only a short time previously during elimination. 5. Though frequency of m.e.p.p.s increased from day 6 to adult age as previously reported, there was no significant difference in the frequencies between singly and polyneuronally innervated fibres at any age. Cord transection at day 12 caused no change in the frequency. 6. ACh sensitivity observed in singly innervated fibres was similar to that in polyneuronally innervated fibres. Furthermore, cordotomy on day 12 did not induce an increase in ACh sensitivity around the end-plate. It is concluded that the elimination of terminals is not causally related to changes in ACh sensitivity. 7. The possible mechanisms of selective elimination of terminals and the process of elimination are discussed.

Acetylcholine↗
PubMed2002

Chiton myogenesis: perspectives for the development and evolution of larval and adult muscle systems in molluscs.

We investigated muscle development in two chiton species, Mopalia muscosa and Chiton olivaceus, from embryo hatching until 10 days after metamorphosis. The anlagen of the dorsal longitudinal rectus muscle and a larval prototroch muscle ring are the first detectable muscle structures in the early trochophore-like larva. Slightly later, a ventrolaterally situated pair of longitudinal muscles appears, which persists through metamorphosis. In addition, the anlagen of the putative dorsoventral shell musculature and the first fibers of a muscular grid, which is restricted to the pretrochal region and consists of outer ring and inner diagonal muscle fibers, are generated. Subsequently, transversal muscle fibers form underneath each future shell plate and the ventrolateral enrolling muscle is established. At metamorphic competence, the dorsoventral shell musculature consists of numerous serially repeated, intercrossing muscle fibers. Their concentration into seven (and later eight) functional shell plate muscle bundles starts after the completion of metamorphosis. The larval prototroch ring and the pretrochal muscle grid are lost at metamorphosis. The structure of the apical grid and its atrophy during metamorphosis suggests ontogenetic repetition of (parts of) the original body-wall musculature of a proposed worm-shaped molluscan ancestor. Moreover, our data show that the "segmented" character of the polyplacophoran shell musculature is a secondary condition, thus contradicting earlier theories that regarded the Polyplacophora (and thus the entire phylum Mollusca) as primarily eumetameric (annelid-like). Instead, we propose an unsegmented trochozoan ancestor at the base of molluscan evolution.

Actin Cytoskeleton↗
PubMed1981

Chemical changes in human skeletal muscle during fetal development.

Skeletal muscle samples obtained from 6 nonmacerated stillborn fetuses and 18 liveborn neonates who died within 24 h of birth were analyzed. Gestational age ranged from 19 to 44 weeks. 17 neonates were normally grown (NG) and 7 were intrauterine growth retarded (IGR). Chemical components were expressed in milliliters or grams per 100 g of tissue. As gestation progressed, total water (TW) and extracellular water (ECW) contents decreased, intracellular water (ICW) content and nitrogen content remained stable, and intracellular/total water ratio (ICW/TW) increased. Fat content was negligible throughout gestation. Compared to their NG peers, IGR neonates had muscle with decreased ECW and increased ICW/TX, whereas TW, ICW and nitrogen contents were similar. These preliminary data provide a basis for further studies of muscle composition and for discussion of existing hypotheses on the effect of fetal growth retardation upon body composition.

Body Composition↗
PubMed1988

Early and late influences of testosterone on acetylcholinesterase activity of skeletal muscles from developing rats.

1. The influence of perinatal and pubertal gonadal androgens on acetylcholinesterase (AChE) activity was studied in the hormone-sensitive levator ani (LA) and extensor digitorum longus (EDL) muscles of adult male rats (105 days). 2. The hormone was withdrawn by gonadectomy at various ages and the effects on AChE and weight were compared with those induced by chronic denervation of both muscles from adult rats. 3. Gonadectomy of infantile (2-30 days) rats prevented LA muscle growth, and reduced total AChE activity to values similar to those found in denervated muscles (15% of control). The EDL muscles were slightly affected and only in rats castrated on the 2nd postnatal day. 4. When the rats were castrated at puberty (45 days), LA muscle weight and total AChE activity were reduced to 20% and 18% of control values, respectively. 5. Gonadectomy of adult (60 and 75 days) rats led to atrophy of the LA muscle (to 29% of control) and reduced the total AChE activity (to 40% of control). 6. AChE activity per unit weight was reduced by 30% in rats castrated from 5 to 20 days of age, and increased by 30% in both LA and EDL muscles from rats castrated in adulthood. Gonadectomy before puberty prevented total AChE in the LA from increasing above the levels detected in chronically denervated muscles. 7. Gonadectomy after puberty reduced total AChE of the LA but never to the extent caused by muscle denervation. 8. It is concluded that testosterone regulates AChE in the LA by early priming of the motoneuron and by pubertal stimulation of enzyme synthesis, the synthesis being dependent on intact innervation.

Acetylcholinesterase↗
PubMed1986

The skeletal and cardiac alpha-actin genes are coexpressed in early embryonic striated muscle.

The relative steady-state abundance of cardiac and skeletal alpha-actin mRNAs at different stages of embryonic skeletal and cardiac (striated) muscle development was determined by a reverse transcriptase extension assay employing an single oligonucleotide primer complementary to a perfectly conserved region near the 5' end of both mRNAs. Both mRNAs were found to be present at every stage of embryonic striated muscle development tested, including the earliest assayable stages of limb muscle and cardiac muscle development. At early stages of skeletal muscle development the two mRNAs are present at similar levels while at later stages the abundance of the skeletal alpha-actin mRNA far exceeds that of the cardiac alpha-actin mRNA. Both mRNAs are also present at similar levels throughout embryonic cardiac muscle development while in adult cardiac muscle the cardiac alpha-actin mRNA predominates over the skeletal alpha-actin mRNA. These results for early embryonic striated muscle, in combination with previous results with late embryonic and adult striated muscle, indicate that both genes are coexpressed throughout striated muscle ontogeny. These two genes may not, therefore, be regulated under unique tissue-specific regulatory programs but each may have acquired regulatory elements which confer important quantitative differences in their level of expression in mature striated muscle cells.

Actins↗
PubMed1976

Mechanics and electrolyte composition of arterial smooth muscle in developing dogs.

The effects of age on arterial smooth muscles (SM) mechanics and electrolyte composition were studied during growth and development in six litters of puppies and their mothers from isolated segments of carotid, renal, mesenteric, and iliac arteries. An increase in the maximum wall stress following both norepinephrine (NE) and potassium (K) was found with age at all sites. The ratio of the stress response for K/NE was found to decrease with age. The maximum stress response for both NE and K shifted to lower values of wall strain with age in the same manner that passive stress-strain curves were shifted. The maximum diameter re3 (3 SM activator to SM activator were not significantly altered with age, but they were better maintained at higher transmural pressure in older animals. Chemical analysis indicated "cell" water, Mg, and K contents decreased with age, as did extracellular water, Na, and Cl. Na anhe suggest that changes in SM excitation-contraction coupling occur with age. Passive wall elements appear to interact with the contractile elements in determining wall responses to SM activation.

Aging↗
PubMed1992

Intramembrane charge movement in developing skeletal muscle cells from fetal mice.

The development of intramembrane charge movement was studied in freshly isolated skeletal muscle cells from 13- to 19-day-old mouse fetuses. Charge movement was present in myotubes from 13-day-old fetuses. The relationship between charge movement and membrane potential could be described by a two-state Boltzmann equation. The amount of maximum charge movement (Qmax) increased substantially with the age of the fetuses from 2.84 +/- 0.39 nC/microF (n = 10) at day 13 to 10.01 +/- 0.97 nC/microF (n = 15) at day 19. Nifedipine (1 microM) consistently reduced Qmax by 33 +/- 2% (n = 37) of the control value at each age studied. Increasing the concentration of nifedipine to 20 microM had no further effect, suggesting that the charge movement in developing myotubes consists of at least two components: a nifedipine-sensitive charge movement (Qns) and a nifedipine-resistant one (Qnr). Both Qns and Qnr increased exponentially with a distinct enhancement of rate at day 16.

Animals↗
PubMed1996

Neural cell adhesion molecule (NCAM) expression in nerves and muscle of developing human large bowel.

Most studies of neural cell adhesion molecule (NCAM) in human musculature are devoted to either developing or adult skeletal and cardiac muscle. The aim of this study was to determine the pattern of NCAM expression in the intestinal musculature of the developing human large bowel. In specimens of large bowel from foetuses (gestational age 8-20 weeks), we examined the immunohistochemical localisation of NCAM in parallel to those of alpha-smooth muscle actin and desmin. Within the developing neural complex, NCAM was expressed at all stages investigated. In intestinal muscle at 8 weeks, immunoreactivity for all antisera was restricted to the muscularis propria. The differentiating muscularis mucosae was demonstrated first at 15 weeks by immunostaining for alpha-smooth muscle actin, and this expression was followed by that of NCAM and desmin at 17 and 19 weeks, respectively. At 20 weeks, NCAM immunoreactivity in the external muscle was intense at the inner border of the circular muscle, with its concentration decreasing towards the outer margin of the muscular wall, whereas alpha-smooth muscle actin and desmin were uniformly distributed in all muscle layers. NCAM is expressed by nerves and muscle of developing human large intestine. Its appearance follows a predetermined pattern, which implies its relevance to the differentiation of intestinal muscle layers.

Actins↗
PubMed2001

Altered primary myogenesis in NFATC3(-/-) mice leads to decreased muscle size in the adult.

Signal transduction pathways involving calcineurin and its downstream effector NFAT have been implicated in regulating myogenesis. Several isoforms of NFAT exist that may differentially contribute to regulating skeletal muscle physiology. The purpose of this study was to determine the role of the NFATC3 isoform in skeletal muscle development. Adult mice lacking NFATC3 have reduced muscle mass compared to control mice. The smaller size of the muscles is not due to atrophy or blunted myofiber growth, but rather to a reduced number of myofibers. This reduction in myofiber number is not limited to a specific fiber type nor are the proportions of fiber types altered. The lower fiber number found in the adult NFATC3(-/-) mice is a consequence of impaired muscle development during embryogenesis. Immunohistochemical studies of E15 EDL muscles indicate that the total number of primary myofibers is decreased in NFATC3(-/-) embryos. At E17.5 no further decrease in primary myofiber number occurs; the size and organization of the myofibers are unaltered, and secondary myogenesis proceeds normally, suggesting a role for NFATC3 during early events in primary myogenesis. These results suggest a heretofore unknown role for the transcription factor NFAT in early skeletal muscle development.

Animals↗
PubMed2001

Sonic hedgehog is a survival factor for hypaxial muscles during mouse development.

Sonic hedgehog (Shh) has been proposed to function as an inductive and trophic signal that controls development of epaxial musculature in vertebrate embryos. In contrast, development of hypaxial muscles was assumed to occur independently of Shh. We here show that formation of limb muscles was severely affected in two different mouse strains with inactivating mutations of the Shh gene. The limb muscle defect became apparent relatively late and initial stages of hypaxial muscle development were unaffected or only slightly delayed. Micromass cultures and cultures of tissue fragments derived from limbs under different conditions with or without the overlaying ectoderm indicated that Shh is required for the maintenance of the expression of myogenic regulatory factors (MRFs) and, consecutively, for the formation of differentiated limb muscle myotubes. We propose that Shh acts as a survival and proliferation factor for myogenic precursor cells during hypaxial muscle development. Detection of a reduced but significant level of Myf5 expression in the epaxial compartment of somites of Shh homozygous mutant embryos at E9.5 indicated that Shh might be dispensable for the initiation of myogenesis both in hypaxial and epaxial muscles. Our data suggest that Shh acts similarly in both somitic compartments as a survival and proliferation factor and not as a primary inducer of myogenesis.

Adaptor Proteins, Signal Transducing↗
PubMed1988

Relationship between the tyrosination state of tubulin and the activities of tubulin:tyrosine ligase and tubulin carboxypeptidase in rat muscle during development.

Tubulin can be post-translationally modified by the incorporation or the release of a tyrosine residue at the COOH-terminus of the alpha subunit. The present study demonstrates that rat muscle soluble preparations contain tubulin carboxypeptidase besides tubulin:tyrosine ligase. The state of tyrosination of tubulin and the activities of both the ligase and the carboxypeptidase were examined in rat muscle during development. The proportion of tyrosinated tubulin with respect to tyrosinable tubulin (tyrosinated plus detyrosinated tubulin) decreased from 83% (new-born rats) to 28% (adult rats) with the corresponding increase in detyrosinated tubulin. The activities of the enzymes decreased continuously and in a near parallel fashion during development. These results indicate that the changes in the tyrosination state of tubulin can not be explained merely by changes in the enzyme activities. We also compared the ability of rat muscle and brain [14C]tyrosinated tubulin to act as substrate of the carboxypeptidase. Muscle tubulin was found to be a less efficient substrate than brain tubulin.

Aging↗
PubMed1977

Indirect fluorescence of primary and secondary myofibers in developing porcine muscle.

Cytochemical differentiation of two populations of developing skeletal myofibers has been demonstrated in fetal muscle with metachromatic fluorescence of ribonucleic acid and deoxyribonucleic acid by staining fresh frozed cryostat sections of developing porcine skeletal muscle with acridine orange (CL. 46005). Evidence is presented that supports the hypothesis that first-formed myofibers (primary myofibers) serve as a structural framework upon which myoblasts proliferate, fuse in linear sequence and give rise to a second population (secondary myofibers) of myofibers.

Animals↗
PubMed1980

Human ontogenesis. I. Ultrastructural characteristics of developing human muscle.

Muscle cells of 25 humans fetuses 7, 9, 10, 14, 17, 20, and 24 weeks old were examined by electron microscopy to determine the structural characteristics of developing muscle. Three structurally different levels of maturation of muscle cells, the primitive myotube, the mature myotube, and the immature muscle fibers, have been observed in the process of human ontogenesis. The sequence of morphological changes and the timing of transformation of one form of fetal muscle into a more mature form are presented.

Arm↗