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PubMed2004

Skeletal muscle development in normal and double-muscled cattle.

This study examined the effect of genotype on prenatal muscle development in both normal-muscled (NM) animals and in double-muscled (DM) animals harboring a mutation in the gene for myostatin that results in the production of a functionally inactive protein. The following muscle development parameters were analyzed at four gestational ages: muscle weight, fiber type, by both enzyme histochemistry and myosin heavy-chain (MHC) immunocytochemistry, and average fiber area. The weights of both M. vastus lateralis and M. vastus medialis were greater throughout prenatal development in the DM animals compared to NM. The percentage of type 1 muscle fibers initially declined with gestational age and subsequently increased in both NM and DM. The percentage of type 1 fibers was consistently lower in DM than in NM. A pattern of MHC isoform localization was shown in DM muscle that is indicative of a delay in muscle development relative to NM. Muscle fiber size was differentially regulated in NM and DM, depending on fiber type. Type 1 fibers were smaller in DM than NM in late gestation, while type 2 fibers were smaller throughout gestation. This study suggests that the inactivating myostatin mutation in DM animals may be associated with changes in both skeletal muscle fiber type and fiber size during bovine muscle development.

Animals↗
PubMed1998

Myosin heavy chain isoform expression in rat smooth muscle development.

Smooth muscle myosin heavy chains (MHCs), the motor proteins that power smooth muscle contraction, are produced by alternative splicing from a single gene. The smooth muscle MHC gene is capable of producing four isoforms by utilizing alternative splice sites located at the regions encoding the carboxy terminus and the junction of the 25- and 50-kDa tryptic peptides. These four isoforms, SM1A, SM1B, SM2A, and SM2B, are a combination of one of two heavy chains containing different carboxy-terminal tails (1 or 2) without (A) or with (B) an additional motif in the myosin head. In the present study, using RNA analysis and isoform-specific antibodies, we demonstrate the expression patterns of MHC isoforms during development in rat smooth muscle tissues. RNase protection analysis indicates that the mRNAs for SMA and SMB isoforms, which differ by a 21-nucleotide insertion in the region encoding the S1 head region of the myosin molecule, are differentially expressed during development in a highly tissue-specific manner. Smooth muscle MHC transcripts are first detectable in developing rat smooth muscle tissues at 17 days of fetal development. The SMB mRNA is shown to be expressed in smooth muscle from fetal bladder, intestine, and stomach and from neonatal aorta; however, it is not expressed in cultured smooth muscle cells from rat aorta. The SMA mRNA is also present at all stages of development in the smooth muscles examined; however, it is much less abundant than SMB mRNA in most fetal smooth muscles. We show here that the SMB isoform, which contains a unique seven-amino acid insertion at the junction of the 25- and 50-kDa tryptic peptides, is present in conjunction with SM1 and SM2 tails on immunoblots of smooth muscle from stomach, intestine, bladder, and uterus and is expressed during development in a pattern distinct from that of the SM1 and SM2 tail isoforms.

Aging↗
PubMed1995

Muscle development. Making Drosophila muscle.

Analysis of flies with mutations in the gene encoding the D-mef2 transcription factor identifies it as a controller of differentiation in multiple muscle cell types; it is the first such gene to be described.

Animals↗
PubMedDate not supplied

[Constructive synergism of regulatory genes expressed in the course of the eye and muscle development and regeneration].

The expression patterns of regulatory genes involved in the formation of the eye in Drosophila and vertebrates during early development were analyzed comparatively. The results demonstrated that, although the compound eyes of invertebrates and the camera eyes of vertebrates markedly differ in their structure and development, they exhibit a striking similarity at the molecular level. This similarity manifests itself in the fact that the homologous regulatory genes ey/Pax, eya/Eya, dac/Dac, and so/Six, which control the early stages of eye development, are expressed in both groups. Not only was synergism shown in the expression of early regulatory genes, but direct interactions of ey/Pax- and so/Six-encoded transcription factors with DNA and protein-protein interactions between nuclear transcription factors encoded by eya/Eya and dac/Dac were also revealed. Transcription factors produced by expressing gene cascades--ey/eya/dac/so in invertebrates and Pax/Eya/Dac/Six in vertebrates--from the transcription complexes that control eye morphogenesis. Paradoxically, the development of muscles in vertebrates proved to involve the expression of genes homologous to the same regulatory genes that control eye morphogenesis in invertebrates and vertebrates. In the developing muscles, regulatory genes also produce transcription factors that form transcription complexes with the mechanism of action based on protein-DNA and protein-protein interactions. The processes of regeneration in the eye and skeletal muscles are controlled by the homologues of the same regulatory genes. Thus, the Pax/Eya/Dac/Six regulatory network is a general system involved in regeneration as well as in development.

Animals↗
PubMed1998

Age-related changes and location of type I, III and IV collagens during skeletal muscle development of double-muscled and normal bovine foetuses.

The aim of this study was to investigate age-related changes in collagen content in muscles of normal and double-muscled (DM) bovine foetuses. Psoas major (PM) and triceps brachii (TB) muscles were collected from foetuses at 110 to 260 days post-conception (p.c.), frozen and powdered. Cyanogen bromide (CNBr) digestion and hydroxyproline measurements were carried out on the powder. CNBr peptides underwent SDS-polyacrylamide gel electrophoresis, and type I and III collagen relative variations were measured by densitometric analysis. Type I and III procollagen mRNA were located by in situ hybridization and types I, III and IV collagen located by indirect immunofluorescence. Although there was no significant difference between normal and DM animals in the amounts of collagen (except in PM muscle at 180 and 230 days p.c.), there was nevertheless a tendency to lower collagen content in muscles of DM animals. Amounts of hydroxyproline in PM and TB muscles from 110 to 230 days p.c. increased two- and threefold to 8.5 micrograms per mg of dry matter (d.m.) and 12 micrograms per mg d.m., respectively, and then decreased up to 260 days p.c., when they were twice as high in TB muscle (9.1 micrograms per mg d.m.) as in PM (4.5 micrograms per mg d.m.). The same difference in hydroxyproline levels was observed between normal adult PM and TB muscles. These variations were explained, mainly, by those of type I. In foetal muscle, in both genotypes and as in adult muscle, perimysium was types I and III, and endomysium type I, III and IV. Procollagen type I and III mRNA were located in perimysium. In conclusion, this study emphasizes that at the end of foetal life, collagen content is representative of what it will be in adult in muscle of both normal and DM animals.

Aging↗
PubMedDate not supplied

Insulin-like growth factor II (IGF-II) mRNA expression during skeletal muscle development of double-muscled and normal bovine foetuses.

We investigated the IGF-II gene expression in developing Semitendinosus muscle in foetal normal and double-muscled cattle. Samples from normal and double-muscled foetuses ranging from 90 to 210 d post-conception were collected and total RNA extracted. Northern blot analysis was performed using the human IGF-II cDNA probe. Five IGF-II transcripts, 5.1, 4.4, 3.7, 2.6 and 1.7 kb, were detected in muscle samples. Throughout gestation, all transcripts, except for the 5.1 kb one, decreased similarly in both genetic types. In double-muscled foetuses, the amount of the 5.1 kb transcript was higher than those of the other transcripts and its expression remained stable throughout the gestational stages analysed. These results indicated that the regulation of IGF-II gene transcription was distinct in both genetic types. The IGF-II foetal plasma concentrations increased throughout gestation. In bovine foetuses, the first muscle cell differentiation was concomitant with a high autocrine IGF-II mRNA expression and low plasma IGF-II levels in both genetic types. The second step of muscle cell differentiation was associated with high IGF-II plasma concentrations and the autocrine expression of IGF-II was reduced.

Actins↗
PubMed1993

Vimentin mRNA location changes during muscle development.

The mRNAs for some cytoskeletal proteins are localized, suggesting that mRNA for these proteins may concentrate at sites appropriate for assembly. To test this hypothesis, we observed vimentin mRNA in developing chicken muscle cultures by in situ hybridization with a digoxigenin-labeled DNA probe to vimentin, detected by confocal microscopy using fluorescent anti-digoxigenin antibody. This method has submicrometer resolution. In developing muscle, vimentin mRNA was bipolar in young myoblasts, somewhat perinuclear in elongated myoblasts and spread fibroblasts, and diffuse in young and developing myotubes. In mature myotubes, vimentin mRNA occurred at costameres with vimentin protein. Localization of mRNA may prove important for assembling and maintaining differentiated cytoskeletal structures, as it is for organizing the embryo.

Animals↗
PubMed1990

Striated muscle tropomyosin-enriched microfilaments of developing muscles of chicken embryos.

The striated muscle tropomyosin-enriched microfilaments were isolated from developing muscles in ovo by the previously described method with a monoclonal antibody against striated muscle isoforms of tropomyosin (Lin & Lin, 1986). Two-dimensional gel analysis of the isolated microfilaments from developing heart, thigh and breast muscles revealed the coexistence of non-muscle isoforms of tropomyosin and actin throughout all stages of embryogenesis. A small but significant amount of skeletal muscle isoforms (alpha, beta) of tropomyosins and their phosphorylated forms was detected in the microfilaments isolated from hearts of 6-15-day-old embryos. These skeletal isoforms of tropomyosins disappeared after this stage of embryogenesis. In addition, we also detected both embryonic and adult isoforms of troponin T in early developing hearts. In developing thigh and breast muscles, the presence of non-muscle tropomyosin isoforms 2, 3a and 3b in the isolated microfilaments was apparent. The contents of tropomyosin isoform 2 were decreased with development and this non-muscle isoform completely disappeared at the 15th day of embryogenesis. On the other hand, the non-muscle tropomyosin isoforms 3a and 3b were present throughout all stages of development. Double-label immunofluorescence microscopy with monoclonal CH1 (anti-striated muscle isoforms of tropomyosin) and CG beta 6 (anti-non-muscle isoforms of tropomyosin) on the isolated, glycerinated skeletal and cardiac muscle cells of 10-day-old or 13-day-old embryos confirmed the colocalization of muscle and non-muscle isoforms of tropomyosins within the same cells. These results suggest that different isoforms of actin and tropomyosin can assemble into a class of microfilaments (i.e. striated muscle tropomyosin-enriched microfilaments) in ovo, which may transform into the thin filaments of mature muscle cells.

Actin Cytoskeleton↗
PubMed2002

The cell adhesion molecule M-cadherin is not essential for muscle development and regeneration.

M-cadherin is a classical calcium-dependent cell adhesion molecule that is highly expressed in developing skeletal muscle, satellite cells, and cerebellum. Based on its expression pattern and observations in cell culture, it has been postulated that M-cadherin may be important for the fusion of myoblasts to form myotubes, the correct localization and function of satellite cells during muscle regeneration, and the specialized architecture of adhering junctions in granule cells of cerebellar glomeruli. In order to investigate the potential roles of M-cadherin in vivo, we generated a null mutation in mice. Mutant mice were viable and fertile and showed no gross developmental defects. In particular, the skeletal musculature appeared essentially normal. Moreover, muscle lesions induced by necrosis were efficiently repaired in mutant mice, suggesting that satellite cells are present, can be activated, and are able to form new myofibers. This was also confirmed by normal growth and fusion potential of mutant satellite cells cultured in vitro. In the cerebellum of M-cadherin-lacking mutants, typical contactus adherens junctions were present and similar in size and numbers to the equivalent junctions in wild-type animals. However, the adhesion plaques in the cerebellum of these mutants appeared to contain elevated levels of N-cadherin compared to wild-type animals. Taken together, these observations suggest that M-cadherin in the mouse serves no absolutely required function during muscle development and regeneration and is not essential for the formation of specialized cell contacts in the cerebellum. It seems that N-cadherin or other cadherins can largely compensate for the lack of M-cadherin.

Adherens Junctions↗
PubMed1984

Genesis of oestrogenic inhibition of soleus muscle development in female mice.

The mechanism by which oestrogen inhibits development of muscle mass was investigated in the soleus muscle of 20 sexually immature female mice. Half of the population were injected weekly (from one to nine weeks old) with a physiological dose of 0.01 mg stilboestrol dipropionate (synthetic oestrogen). After each mouse was killed at 10 weeks old, the weight and muscle index was determined for each muscle. The number of muscle fibres was counted in each soleus muscle. The muscle fibre size for each muscle was determined by measuring the greatest diameter of at least 100 fibres. The number of muscle fibres was similar in both normal and oestrogen treated animals but the individual muscle fibre sizes were significantly smaller in oestrogen treated animals. These observations indicated, therefore, that oestrogen inhibits development of muscle mass in females by limiting the size of individual muscle fibres and not by inhibiting the multiplication of muscle fibres.

Animals↗
PubMed2003

mef2c is activated directly by myogenic basic helix-loop-helix proteins during skeletal muscle development in vivo.

Skeletal muscle development requires the coordinated expression of numerous transcription factors to control the specification of mesodermal progenitor cells to a muscle fate and the differentiation of those committed myoblasts into functional, contractile muscle. Two families of transcription factors play key roles in these processes. The myogenic basic helix-loop-helix (bHLH) proteins, MyoD and Myf5, are required for myoblast specification, while two members of the same family, myogenin and MRF4, play key roles in myoblast differentiation in vivo. All four members of the myogenic bHLH family are sufficient to dominantly induce myogenesis when introduced into a variety of non-muscle cells in culture, however this function requires the activity of a second family of transcriptional regulators, the myocyte enhancer factor 2 (MEF2) family. MEF2 factors are essential for muscle differentiation, and previous studies have shown that MyoD and MEF2 family members function combinatorially to activate transcription and myogenesis. Consistent with these observations, the majority of skeletal muscle genes require both MyoD and MEF2 family members to activate their transcription. A possible exception to this combinatorial model for activation is suggested by the observation that myogenic bHLH factors may be able to independently activate the expression of MEF2. This raises the question as to how mef2 gene transcription is induced by MyoD factors without cooperative activation by MEF2. During skeletal muscle development, mef2c is the first member of the MEF2 family to be expressed. In this study, we have investigated the regulation of a skeletal muscle-specific enhancer from the mouse mef2c gene using a transgenic approach. We show that mef2c is a direct transcriptional target of the MyoD family in vivo via an essential E box in the skeletal muscle enhancer of mef2c, and we show that mef2c is not a direct target for autoregulation by MEF2.

Animals↗
PubMed1992

Cell culture as a tool for the study of poultry skeletal muscle development.

Postnatal development of skeletal muscle is the responsibility of the myogenic satellite cells. Satellite cells, isolated from the pectoralis major muscle of young growing tom turkeys, have been cultured in vitro to provide a system for studying cellular and hormonal aspects of poultry skeletal muscle development. Satellite cell clones derived from primary cultures have been developed so that in vitro observations would not be confounded by the presence of nonmyogenic cells. Likewise, a serum-free medium that promotes proliferation of the turkey satellite cell has been developed to provide a hormonally controlled environment for in vitro developmental studies. These two techniques have enabled us to examine the following: 1) factors that influence satellite cell proliferation and differentiation, 2) the interaction of hormones with cellular receptors, 3) secretion of biologically important proteins from cells and 4) the expression of genes important to muscle development.

Animals↗
PubMed2002

Effect of selection for growth rate on embryonic breast muscle development in turkeys.

Muscle development at 20 and 25 d of incubation was studied in a randombred control line (RBC2), a subline (F) of RBC2 selected only for increased 16-wk BW, a commercial sire line (B), and reciprocal crosses of the F and B lines. Muscle samples from three males and three females of each genetic group were collected in such a manner to avoid contraction. After fixing, the muscles were stained with hematoxylin and eosin, measurements of muscle fiber width, muscle fiber bundle length and width, number of fibers within a 15.6 microm2 area, and extracellular matrix perimysial (PW) and endomysial (EW) width were taken with an Olympus XI 70 microscope equipped with an Olympus Magna Fire digital camera linked to Image Pro software. From each slide, 20 measurements were taken for each characteristic analyzed. In most of the muscle traits measured, additive genetic variation, as indicated by line differences, occurred when the RBC2 line was included in the comparison of pure lines. However, when only the B and F lines were compared, line differences were less frequent. In comparisons of the B and F lines and their reciprocal crosses, heterosis, as measured by contrasts of the average of the pure lines and the average of the reciprocal crosses, was an important source of variation for individual fiber measurements (negative) and extracellular space (positive) at 20 d of incubation but was less important at 25 d of incubation. No significant interactions between genetic group and sex were noted at 20 d of incubation, but such interactions were frequent at 25 d of incubation. These results suggest that muscle organizational differences between the two sexes begin to occur between these two ages and are not the same for different genetic groups.

Animals↗
PubMed1999

Growth factors controlling muscle development.

The enlarged muscles of certain breeds of cattle, such as the Belgian Blue, have been shown to result from a marked increase in the number of normal sized muscle fibers. Originally insulin-like growth factors (IGFs) were implicated in this myofiber hyperplasia, as IGFs have been shown to stimulate myoblast proliferation as well as maintain fiber differentiation. Recently it has been reported that mice lacking a myostatin gene, a member of the TGFbeta superfamily, have enhanced skeletal mass resulting from increased muscle fiber number and size. Mutations in this gene have been found in double-muscled cattle, indicating that myostatin is an inhibitor of muscle growth. Myostatin is expressed early in gestation and then maintained to adulthood in certain muscles. Myostatin expression in bovine muscle is highest during gestation when muscle fibers are forming and some of the myogenic regulatory factors have elevated expression over the same period as myostatin. Molecular expression of the IGF axis does not differ between Belgian Blue and normal muscled cattle, and IGF-II mRNA is increased throughout formation of secondary fibers in both breeds. However, myostatin and MyoD expression in muscle differ between normal and hypertrophied muscle cattle breeds. This evidence strongly suggests that lack of myostatin is associated with an increase in fiber number which then results in a marked increase in potential muscle mass in double-muscled cattle.

Amino Acid Sequence↗
PubMed1996

Muscle organizers in Drosophila: the role of persistent larval fibers in adult flight muscle development.

In many organisms muscle formation depends on specialized cells that prefigure the pattern of the musculature and serve as templates for myoblast organization and fusion. These include muscle pioneers in insects and muscle organizing cells in leech. In Drosophila, muscle founder cells have been proposed to play a similar role in organizing larval muscle development during embryogenesis. During metamorphosis in Drosophila, following histolysis of most of the larval musculature, there is a second round of myogenesis that gives rise to the adult muscles. It is not known whether muscle founder cells organize the development of these muscles. However, in the thorax specific larval muscle fibers do not histolyze at the onset of metamorphosis, but instead serve as templates for the formation of a subset of adult muscles, the dorsal longitudinal flight muscles (DLMs). Because these persistent larval muscle fibers appear to be functioning in many respects like muscle founder cells, we investigated whether they were necessary for DLM development by using a microbeam laser to ablate them singly and in combination. We found that, in the absence of the larval muscle fibers, DLMs nonetheless develop. Our results show that the persistent larval muscle fibers are not required to initiate myoblast fusion, to determine DLM identity, to locate the DLMs in the thorax, or to specify the total DLM fiber volume. However, they are required to regulate the number of DLM fibers generated. Thus, while the persistent larval muscle fibers are not obligatory for DLM fiber formation and differentiation, they are necessary to ensure the development of the correct number of fibers.

Actins↗
PubMed1985

Muscle development in the grasshopper embryo. I. Muscles, nerves, and apodemes in the metathoracic leg.

Much is known about the development of nerve pathways in the metathoracic limb bud of the grasshopper embryo. In this series of three papers, we report on the development of muscles in the same embryonic appendage. In a fourth paper (E. E. Ball, R. K. Ho, and C. S. Goodman, 1985, J. Neurosci, in press) we examine the development of specific neuromuscular connections for one of these muscles (coxal muscle 133a). In this first paper, we present an overview of the development of muscles, nerves, and apodemes (tendons). We previously reported on a class of large mesodermal cells, called muscle pioneers (MPs), that arises early in development and appears to act as a scaffold for developing muscles and guidance cue for motoneuron growth cones (R. K. Ho, E. E. Ball, and C. S. Goodman, 1983, Nature (London) 301, 66-69). We have used the I-5 monoclonal antibody (which specifically labels the MPs as well as the nerve pathways), HRP immunocytochemistry, and Normarski optics to visualize muscle, nerve, and apodeme development in the embryonic metathoracic limb bud from 27.5% (before the appearance of the MPs) to 55% (after the muscles have attained their basic adult pattern). Cell fusions, cell migration, and cell death all appear to play important roles in the development of MPs. The patterns of muscle development vary greatly, ranging from (i) single MPs for simple muscles (which in the adult have only one bundle of muscle fibers, e.g., coxal muscle 133a), to (ii) arrays of MPs for complex muscles [which in the adult have many bundles of muscle fibers each with separate sites of insertion, e.g., the extensor tibiae (ETi) and flexor tibiae (FlTi) muscles in the femur].

Animals↗
PubMed2006

Decreased expression of myogenic transcription factors and myosin heavy chains in Caenorhabditis elegans muscles developed during spaceflight.

The molecular mechanisms underlying muscle atrophy during spaceflight are not well understood. We have analyzed the effects of a 10-day spaceflight on Caenorhabditis elegans muscle development. DNA microarray, real-time quantitative PCR, and quantitative western blot analyses revealed that the amount of MHC in both body-wall and pharyngeal muscle decrease in response to spaceflight. Decreased transcription of the body-wall myogenic transcription factor HLH-1 (CeMyoD) and of the three pharyngeal myogenic transcription factors, PEB-1, CEH-22 and PHA-4 were also observed. Upon return to Earth animals displayed reduced rates of movement, indicating a functional defect. These results demonstrate that C. elegans muscle development is altered in response to spaceflight. This altered development occurs at the level of gene transcription and was observed in the presence of innervation, not simply in isolated cells. This important finding coupled with past observations of decreased levels of the same myogenic transcription factions in vertebrates after spaceflight raises the possibility that altered muscle development is a contributing factor to spaceflight-induced muscle atrophy in vertebrates.

Animals↗