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PubMed1984

Effect of maternal alcohol consumption on pre- and post-natal muscle development of mice.

The effect of maternal alcohol consumption during pregnancy on muscle development of the offspring was investigated in 28 mice (14 males, 14 females) at 12 weeks of age. Both the control and alcohol-fed groups received food ad-libitum throughout the period of study. The control group received water ad-libitum also throughout the period of study. The alcohol-fed group, on the other hand, received only water up to six weeks of age. Subsequently, between 6 and 8 weeks of age they received 10% ethanol (v/v) in water and 20% ethanol (v/v) from 8 to 11 weeks age. Both groups were bred at 11 weeks of age. Following diagnosis of pregnancy, the alcohol-fed group received 30% ethanol (v/v) till delivery. The off-spring of both groups were fed water and food ad-libitum throughout the period of study. Each of the off-spring was killed at 12 weeks of age. Body weight, as well as weights of soleus, biceps brachii, long digital extensor and cranial tibial muscles were significantly smaller in off-spring of the alcohol-fed group indicating that maternal consumption of alcohol during pregnancy retards growth, as well as "catch-up growth" in both body weights and muscle mass. The smaller muscle mass, as observed from analyses of soleus muscle, resulted from retardation of muscle growth pre-natally by suppression of normal hyperplasia of muscle fibres during myogenesis and postnatally by suppression of normal hypertrophy of muscle fibres.

Animals↗
PubMed2002

Integrin expression patterns during early limb muscle development in the mouse.

Cell-extracellular matrix interactions play crucial roles in limb muscle development but practically nothing is known on what integrins are involved before the differentiation of muscle precursor cells (MPCs) in the limb muscle masses. In this study we determine the expression patterns of integrins during early forelimb muscle development in the mouse. alpha6beta1 integrin is downregulated in the lateral dermomyotome when delamination of MPCs occurs. In late E9.5 embryos, alpha1beta1 and alpha5beta1 are expressed in a pattern very similar to pax3, which marks MPCs migrating to the limb bud. After myf5 upregulation in the limb bud, alpha1beta1 and alpha5beta1 expression is maintained and the alpha4beta1 integrin starts being expressed.

Animals↗
PubMed2003

Recapitulation of fast skeletal muscle development in zebrafish by transgenic expression of GFP under the mylz2 promoter.

A 1,934-bp muscle-specific promoter from the zebrafish mylz2 gene was isolated and characterized by transgenic analysis. By using a series of 5' promoter deletions linked to the green fluorescent protein (gfp) reporter gene, transient transgenic analysis indicated that the strength of promoter activity appeared to correlate to the number of muscle cis-elements in the promoter and that a minimal -77-bp region was sufficient for a relatively strong promoter activity in muscle cells. Stable transgenic lines were obtained from several mylz2-gfp constructs. GFP expression in the 1,934-bp promoter transgenic lines mimicked well the expression pattern of endogenous mylz2 mRNA in both somitic muscle and nonsomitic muscles, including fin, eye, jaw, and gill muscles. An identical pattern of GFP expression, although at a much lower level, was observed from a transgenic line with a shorter 871-bp promoter. Our observation indicates that there is no distinct cis-element for activation of mylz2 in different skeletal muscles. Furthermore, RNA encoding a dominant negative form of cAMP-dependent protein kinase A was injected into mylz2-gfp transgenic embryos and GFP expression was significantly reduced due to an expanded slow muscle development at the expense of GFP-expressing fast muscle. The mylz2-gfp transgene was also transferred into two zebrafish mutants, spadetail and chordino, and several novel phenotypes in muscle development in these mutants were discovered.

Animals↗
PubMed2003

Breast muscle development in commercial broiler chickens.

Genetic and gender-related variations in breast muscle yield of broiler chickens may be attributed to differences in number and size of muscle cells (myofibers). In this study, male and female broilers from eight commercial strain crosses (SC) were compared for body and breast muscle weight with adjustment of the Gompertz function. Additionally, breast fillet dimensions (length, width, and depth) and myofiber density (myofiber number/area; MFD) were assessed. Live weight and breast muscle development was determined to 56 d of age at weekly intervals. MFD was assessed at 8 d of age. As expected, SC differed in BW, breast weight and yield, and breast fillet dimensions and had variations in growth curves. Maximal growth rate for breast weight was reached approximately 4 d after that of BW. Males and females showed different growth curves, with males having slower growth rate maturity parameter and reaching the maximal growth rate later than females for BW and breast weight. Breast depth was the breast measure with highest positive correlation to breast yield. SC differences could not be explained by MFD, but males had higher MFD density than females. The possible relationship of the MFD observations to total myofiber number is discussed.

Animals↗
PubMed2000

The distribution of stanniocalcin 1 protein in fetal mouse tissues suggests a role in bone and muscle development.

We previously isolated a mammalian gene STC1 that encodes a glycoprotein related to stanniocalcin (STC), a fish hormone that plays a major role in calcium homeostasis. However, the mammalian STC1 gene is expressed in a variety of adult tissues in contrast to fish where STC is expressed only in one unique gland, the corpuscles of Stannius. This suggested that STC1 may have wider autocrine/paracrine functions in mammals. In the present study, using immunocytochemistry, we showed that STC1 protein is localized in the developing bone and muscle of the mouse fetus. During endochondral bone formation, STC1 is found principally in prechondrocytes and prehypertrophic chondrocytes. During intramembranous bone formation STC1 is present in the mesenchyme that is about to undergo ossification. STC1 is also found in the myocardiocytes of the developing heart and at all stages of differentiation from myoblasts to myotube formation in developing skeletal muscle. The specific localization of STC1 to chondrocytes and muscle cells suggests a role for this protein in chondrogenic and myogenic differentiation.

Animals↗
PubMed2004

Basic principles of muscle development and growth in meat-producing mammals as affected by the insulin-like growth factor (IGF) system.

This presentation aims to describe how the basic events in prenatal muscle development and postnatal muscle growth are controlled by the insulin-like growth factor system (IGF). The prenatal events (myogenesis) cover the rate of proliferation, the rate and extent of fusion, and the differentiation of three myoblast populations, giving rise to primary fibers, secondary fibers, and a satellite cell population, respectively. The number of muscle fibers, a key determinant of the postnatal growth rate, is fixed late in gestation. The postnatal events contributing to myofiber hypertrophy comprise satellite cell proliferation and differentiation, and protein turnover. Muscle cell cultures produce IGFs and IGF binding proteins (IGFBPs) in various degrees depending on the origin (species, muscle type) and state of development of these cells, suggesting an autocrine/paracrine mode of action of IGF-related factors. In vivo studies and results based on cell lines or primary cell cultures show that IGF-I and IGF-II stimulate both proliferation and differentiation of myoblasts and satellite cells in a time and concentration-dependent way, via interaction with type I IGF receptors. However, IGF binding proteins (IGFBP) may either inhibit or potentiate the stimulating effects of IGFs on proliferation or differentiation. During postnatal growth in vivo or in fully differentiated muscle cells in culture, IGF-I stimulates the rate of protein synthesis and inhibits the rate of protein degradation, thereby enhancing myofiber hypertrophy. The possible roles and actions of the IGF system in regulating and determining muscle growth as affected by developmental stage and age, muscle type, feeding levels, treatment with growth hormone and selection for growth performance are discussed.

Animal Husbandry↗
PubMed1985

Monoclonal antibodies to desmin: evidence for stage-dependent intermediate filament immunoreactivity during cardiac and skeletal muscle development.

Monoclonal antibodies reactive with desmin (D3 and D76) have been generated and their specificities validated by immunoblots, RIAs, and immunocytochemistry. No cross-reaction with other IFPs has been observed. The McAbs recognized different epitopes but both reside in the amino-terminal rod domain of desmin. Whereas McAb D3 produces a staining pattern characteristic of desmin throughout the development of cardiac and skeletal muscles, McAb D76 was selectively unreactive with certain regions of early (three days in ovo) embryonic cardiac anlage, with cultured cardiac myocytes derived from 7-day-old embryos, and with skeletal myotubes in early stages of myogenesis in vitro. Positive reactivity of D76 was seen at stages of myofibrillogenesis when the sarcomeres assume lateral alignment. Evidence was presented that differential reactivity of D76 did not result from the biosynthesis of a new desmin isoform or the post-translational modification of an existing protein. We suggest that the appearance of D76 immunoreactivity during striated muscle development represents an unmasking of the epitope by some IF-associated protein. Since this transition during skeletal muscle differentiation occurs during lateral alignment of the myofibrils, this antibody may serve as a useful probe for exploring this reorganization of the contractile apparatus during myogenesis and muscle regeneration.

Animals↗
PubMed1999

Genetic models for the study of insulin-like growth factors (IGF) and muscle development in birds compared to mammals.

IGFs are important positive modulators of overall body and muscle growth in different species. Genetic variation in IGF-I gene expression exists as shown by the possibility of genetic selection for high or low circulating IGF-I concentrations in mice and the associated variations in growth potential. Targeted over-expression of IGF-I in transgenic mice results in muscle hypertrophy, but it is yet unknown whether genetic variability in muscle IGF-I gene expression exists. Much less data are available in birds. This review is focussed on the potential role of IGFs on chicken muscle development. Apart from the absence of a type 2 IGF receptor (IGF-II receptor), the general characteristics of the chicken IGF system seem to be similar to mammalian species. In different genetic models with altered growth rates or body composition, differences in the IGF system are observed suggesting its importance in regulating body growth in those species. The components for a paracrine action of IGF are also present in chicken muscle but it has not yet been demonstrated if they contribute to differences in muscle development.

Animals↗
PubMed2004

Calcineurin signaling and NFAT activation in cardiovascular and skeletal muscle development.

Calcineurin signaling has been implicated in a broad spectrum of developmental processes in a variety of organ systems. Calcineurin is a calmodulin-dependent, calcium-activated protein phosphatase composed of catalytic and regulatory subunits. The serine/threonine-specific phosphatase functions within a signal transduction pathway that regulates gene expression and biological responses in many developmentally important cell types. Calcineurin signaling was first defined in T lymphocytes as a regulator of nuclear factor of activated T cells (NFAT) transcription factor nuclear translocation and activation. Recent studies have demonstrated the vital nature of calcium/calcineurin/NFAT signaling in cardiovascular and skeletal muscle development in vertebrates. Inhibition, mutation, or forced expression of calcineurin pathway genes result in defects or alterations in cardiomyocyte maturation, heart valve formation, vascular development, skeletal muscle differentiation and fiber-type switching, and cardiac and skeletal muscle hypertrophy. Conserved calcineurin genes are found in invertebrates such as Drosophila and Caenorhabditis elegans, and genetic studies have demonstrated specific myogenic functions for the phosphatase in their development. The ability to investigate calcineurin signaling pathways in vertebrates and model genetic organisms provides a great potential to more fully comprehend the functions of calcineurin and its interacting genes in heart, blood vessel, and muscle development.

Animals↗
PubMed1993

Localisation of transforming growth factor beta 1 in developing muscles: implications for connective tissue and fiber type pattern formation.

Skeletal muscles are highly ordered mixtures of cell types, with each muscle having its own characteristic pattern of fiber types, connective tissues, and vasculature. The precursors of the myogenic and connective elements of a muscle are initially intermixed and are proliferating and differentiating together in a manner that generates an ordered array of mature cells. The molecular basis of myogenesis is unknown, although in vitro studies have revealed numerous putative regulators. The results obtained from in vitro studies are not easily related to in vivo myogenesis because of a lack of information about the localisation of the putative regulators in developing muscles. The objective of this paper was therefore to describe the spatial and temporal distribution of transforming growth factor beta 1 (TGF-beta 1), a small peptide that affects cultured fibroblasts, myoblasts, and vascular endothelial cells. TGF-beta 1-immunoreactivity was associated with the epimysia, perimysia, and vasculature of the developing muscles. The expression of TGF-beta 1 within developing muscles had a distinct spatial and temporal pattern that correlated with the fate of adjacent myotubes. Myotubes which formed prior to the expression of TGF-beta 1 developed into slow fibers whereas those which formed adjacent to TGF-beta 1-containing connective tissue matured into fast fibers. The possibility that TGF-beta 1 is involved in the generation of the pattern of epi- and perimysia and/or fiber types is discussed.

Animals↗
PubMed2004

The nuclear orphan receptor COUP-TFII is required for limb and skeletal muscle development.

The nuclear orphan receptor COUP-TFII is widely expressed in multiple tissues and organs throughout embryonic development, suggesting that COUP-TFII is involved in multiple aspects of embryogenesis. Because of the early embryonic lethality of COUP-TFII knockout mice, the role of COUP-TFII during limb development has not been determined. COUP-TFII is expressed in lateral plate mesoderm of the early embryo prior to limb bud formation. In addition, COUP-TFII is also expressed in the somites and skeletal muscle precursors of the limbs. Therefore, in order to study the potential role of COUP-TFII in limb and skeletal muscle development, we bypassed the early embryonic lethality of the COUP-TFII mutant by using two methods. First, embryonic chimera analysis has revealed an obligatory role for COUP-TFII in limb bud outgrowth since mutant cells are unable to contribute to the distally growing limb mesenchyme. Second, we used a conditional-knockout approach to ablate COUP-TFII specifically in the limbs. Loss of COUP-TFII in the limbs leads to hypoplastic skeletal muscle development, as well as shorter limbs. Taken together, our results demonstrate that COUP-TFII plays an early role in limb bud outgrowth but not limb bud initiation. Also, COUP-TFII is required for appropriate development of the skeletal musculature of developing limbs.

Animals↗
PubMed1992

Differential regulation of the atrial isoforms of the myosin light chains during striated muscle development.

We have isolated a cDNA that encodes the human regulatory myosin light chain isoform predominant in adult atrial muscle. The cDNA contains an open reading frame of 175 amino acids and encodes a hydrophilic protein of a largely helical structure with two potential phosphorylation sites. The protein is different from any other regulatory myosin light chain so far described and is the product of a previously uncharacterized single copy gene. An isoform-specific probe was used to analyze the expression of this isoform in adult muscle and in cardiac and skeletal muscle development in vivo and in vitro. Parallel analysis of the corresponding human alkali myosin light chain (predominant in adult atrium) showed that both isoforms are expressed in early heart development, in both atrium and ventricle. Although the atrial alkali light chain is expressed throughout embryonic striated muscle development, the regulatory myosin light chain was not detected in skeletal myogenesis in vivo or in vitro. Thus the atrial isoforms are not universally or exclusively "paired" and can be independently regulated. We propose that the manner in which these particular isoforms fulfill the functional requirements of the muscle at different developmental times may have direct impact on their regulation.

Adult↗
PubMed2007

MicroRNAs regulate the expression of the alternative splicing factor nPTB during muscle development.

Alternative pre-mRNA splicing determines many changes in gene expression during development. Two regulators known to control splicing patterns during neuron and muscle differentiation are the polypyrimidine tract-binding protein (PTB) and its neuronal homolog nPTB. These proteins repress certain exons in early myoblasts, but upon differentiation of mature myotubes PTB/nPTB expression is reduced, leading to increased inclusion of their target exons. We show here that the repression of nPTB expression during myoblast differentiation results from its targeting by the muscle-restricted microRNA miR-133. During differentiation of C2C12 myoblasts, nPTB protein but not mRNA expression is strongly reduced, concurrent with the up-regulation of miR-133 and the induction of splicing for several PTB-repressed exons. Introduction of synthetic miR-133 into undifferentiated C2C12 cells leads to a decrease in endogenous nPTB expression. Both the miR-133 and the coexpressed miR-1/206 microRNAs are extremely conserved across animal species, and PTB proteins are predicted targets for these miRNAs in Drosophila, mice, and humans. There are two potential miR-133-responsive elements (MRE) within the nPTB 3' untranslated region (UTR), and a luciferase reporter carrying this 3' UTR is repressed by miR-133 in an MRE-dependent manner. Transfection of locked nucleic acid (LNA) oligonucleotides designed to block the function of miR-133 and miR-1/206 increases expression of nPTB and decreases the inclusion of PTB dependent exons. These results indicate that miR-133 directly down-regulates a key splicing factor during muscle development and establishes a role for microRNAs in the control of a developmentally dynamic splicing program.

3' Untranslated Regions↗
PubMed1989

Genetic analysis of muscle development in Drosophila melanogaster.

The different thoracic muscles of Drosophila are affected specifically in the mutants: stripe (sr), erect wing (ewg), vertical wings (vtw), and nonjumper (nj). We have tested the extent of this specificity by means of a genetic analysis of these loci, multiple mutant combinations, and gene dosage experiments. A quantitative, rather than a qualitative, specificity is found in the mutant phenotypes. All muscles are altered by mutations in any given gene, but the severity of these alterations is muscle specific. The locus stripe seems to have a polar organization where different allelic combinations show quantitative specificity in the muscle affected. In addition to the muscle phenotypes, neural alterations are detected in these mutants. The synergism found between ewg, vtw and ewg, sr as well as the dosage effect of the distal end of the X chromosome upon the expression of ewg and sr suggests the existence of functional relationships among the loci analyzed.

Alleles↗
PubMed1995

Mutations in a novel gene, myoblast city, provide evidence in support of the founder cell hypothesis for Drosophila muscle development.

We have used mutations in the newly identified gene myoblast city to investigate the founder cell hypothesis of muscle development in Drosophila melanogaster. In embryos mutant for myoblast city the fusion of myoblasts into multinucleate muscles is virtually abolished. Nevertheless, a subset of the myoblasts develop specific muscle-like characteristics, including gene expression appropriate to particular muscles, migration to the appropriate part of the segment, correct position and orientation, and contact by motor neurons. We suggest that this subset of myoblasts represents the proposed muscle founder cells and we draw an analogy between these founder cells and the muscle pioneers described for grasshopper muscle development.

Animals↗
PubMed1995

Inactivation of Myf-6 and Myf-5 genes in mice leads to alterations in skeletal muscle development.

Myf-6, alternatively called MRF4 or herculin, is a member of a group of muscle-specific transcription factors which also comprises Myf-5, myogenin and MyoD. All family members show distinct expression patterns during skeletal muscle development and can convert a variety of cell lines to myocytes. We disrupted the Myf-6 gene in mice to investigate its functional role in the network of regulatory factors controlling myogenesis. Homozygous mice carrying the disrupted Myf-6 gene show pronounced down-regulation of Myf-5 transcription for reasons presently unknown. Consequently, these mice represent a double knock-out model for Myf-6 and Myf-5. The mutants resemble most of the Myf-5 phenotype with aberrant and delayed early myotome formation and lack of distal rib structures. In addition, we find a reduction in the size of axial muscles in the back. Apart from changes in the pattern of some contractile protein isoforms, the existing myofibers appear fairly normal. This suggests that Myf-6 has no major role in the maturation of myotubes, as previously proposed. Our results provide evidence that skeletal myogenesis can proceed in the absence of two myogenic factors, Myf-5 and Myf-6, therefore they must exert largely non-redundant functions in vivo.

Animals↗
PubMed1999

Laminins during muscle development and in muscular dystrophies.

Cellular interactions with the extracellular matrix during muscle formation and in muscular dystrophy have received increased interest during the past years. Laminins constitute a growing family of proteins with complex expression patterns in forming basement membranes during muscle development. In skeletal muscle, laminins constitute major ligands for cell surface receptors involved in the transmission of force from the cell interior, but laminins might also influence signal transmission events during muscle formation and in muscle regeneration. During myogenesis the laminin alpha1 chain is present around the epithelial somite; but later, in forming muscle, the laminin alpha1 chain is restricted to the myotendinous junction. The laminin alpha2, alpha4 and alpha5 chains are major laminin chains in the muscle basement membrane during muscle formation, but laminin alpha4 and alpha5 chains are absent in adult muscle. The importance of laminins for muscle integrity is manifested in congenital muscular dystrophies with defects in the laminin alpha2 chain. There is no good evidence for the presence of laminin alpha1 chain in dystrophic muscle, but some other fetal muscle laminins can be detected in dystrophic muscle. Characterization of laminin expression patterns in muscular dystrophies might be of diagnostic and therapeutic value. In this paper, we review the recent publications on the biological functions of muscle laminins and discuss their roles in skeletal muscle.

Animals↗
PubMed1988

Myosin ATPase activity during avian cardiac and skeletal muscle development.

The myosin ATPase activity and myosin light chain composition in developing chick heart and skeletal muscles were studied and compared. Embryonic myosin was purified and characterized from day 7 to day 19 of embryogenesis. Embryonic cardiac myosin generally showed the same Ca2+-activated myosin ATPase activity level as the adult value. In comparison, pooled pectoralis and hindlimb skeletal muscles from day 10 through day 19 showed myosin ATPase activities that were all significantly less than the adult counterpart. The myosin light chain pattern of embryonic cardiac myosin remained relatively constant like the myosin ATPase activity, whereas developmental changes were observed in skeletal myosin light chains.

Animals↗