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PubMed1989

Insulin-like growth factors (IGF) in muscle development. Expression of IGF-I, the IGF-I receptor, and an IGF binding protein during myoblast differentiation.

The insulin-like growth factors (IGFs) I and II exert pleiotropic effects on diverse cell types through interaction with specific high affinity cell surface receptors and with locally produced binding proteins. In skeletal muscle and in myoblast cell lines, the functions of IGF-I and -II are complex. Both growth factors appear capable of stimulating cellular proliferation and differentiation, as well as exerting insulin-like effects on intermediary metabolism. We have demonstrated recently that the expression of IGF-II and its receptor is induced during the terminal differentiation of the myoblast cell line, C2, and have suggested that IGF-II may be an autocrine growth factor in these cells (Tollefsen, S.E., Sadow, J.L., and Rotwein, P. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 1543-1547). We now have examined this cell line for expression of other components involved in IGF signaling. The synthesis of IGF-I is low during myoblast proliferation; IGF-I mRNA can be detected only through use of a sensitive solution hybridization assay. Typical IGF-I receptors can be measured in myoblasts, whereas IGF binding proteins cannot be detected in proliferating cells or in conditioned culture medium. During myogenic differentiation, IGF-I mRNA levels increase transiently by 6-10-fold within 48-72 h. The expression of IGF-I mRNA is accompanied by a 2.5-fold accumulation of IGF-I in the culture medium. IGF-I receptors also increase transiently, doubling by 48 h after the onset of differentiation. By contrast, secretion of a Mr 29,000 IGF binding protein is induced 30-fold to 100 ng/ml within 16 h and continues to increase throughout differentiation. These studies demonstrate that several components critical to IGF action are produced in a fusing skeletal muscle cell line in a differentiation-dependent manner and suggest that both IGF-I and IGF-II may be autocrine factors for muscle.

Amino Acid Sequence↗
PubMed1985

Human glyceraldehyde-3-phosphate dehydrogenase: mRNA levels and enzyme activity in developing muscle.

Analysis of human glyceraldehyde-3-phosphate dehydrogenase mRNA revealed that levels in adult skeletal muscle are 12-fold greater per microgram of polyadenylated RNA than in fetal skeletal muscle, whereas in cardiac muscle RNA levels were about equal in fetal and adult tissue. The mRNA levels correlate well with glyceraldehyde 3-phosphate dehydrogenase enzyme activities. There was no evidence for fetus- or tissue-specific forms.

Adult↗
PubMed1998

Distinct molecular phenotypes in murine cardiac muscle development, growth, and hypertrophy.

The onset of cardiac hypertrophy is associated with characteristic changes in myocardial gene expression that are thought to recapitulate a developmental gene program. We report here the first gene expression profile of the murine myocardium, using a rapid method of quantitative expression analysis based on real-time analytical RT-PCR. This assay was used to measure expression levels of 29 genes in (1) late stage development as represented by day 1 neonatal ventricles, (2) normal cardiac growth in 3 and 18 month old mice, and (3) cardiac hypertrophy following pressure overload by aortic constriction. For males and females normal growth is not associated with differential expression although there is elevated expression of skeletal and smooth muscle actin mRNA's in males compared to females. Using normal adult ventricles as a reference, there are many qualitative and quantitative differences between the day 1 neonatal myocardium and experimental cardiac hypertrophy. These data suggest that the response to POL involves a subset of re-expressed developmental genes together with altered expression of genes not necessarily associated with cardiac development.

Animals↗
PubMed1993

Ultrastructure of the developing muscle and enteric nervous system in the small intestine of human fetus.

The ultrastructural organization and some histochemical characteristics of the enteric nervous system (ENS) were investigated in 10- and 18-week-old human fetuses. In the 10-week-old human fetus immature myoblasts, and mostly neuroblasts were found in the ganglia. Simple, undifferentiated neuropil was observed among neuronal cells. The neuropil generally did not contain synapses; however axosomatic synapse was registered rarely on the surface of certain neurons. Neuromuscular junctions were common, both axons and neurons were in close contact with the sarcolemma. In the 18-week-old human fetus the fine-structural characteristics of the intestinal smooth muscle cells were the same as in the adult. Nerve profiles were frequently found among the muscle cells. NADH-diaphorase histochemistry revealed the presence of numerous ganglia but solitary neurons still occurred. Differentiated neurons and neuroblasts could be distinguished in the myenteric ganglia. Synapses were often detected in the neuropil. Thick nerve plexuses were frequently found in the proximity of smooth muscle cells, forming "distant" and "close" myoneural contacts. Well-defined fluorescent network and several fluorescent nerve cell bodies were demonstrated by glyoxylic acid. The above organization may provide a satisfactory basis for an integrated peristaltic movement in the gut of the 18-week-old human fetus.

Axons↗
PubMed1996

Specific localization of zebrafish hsp90 alpha mRNA to myoD-expressing cells suggests a role for hsp90 alpha during normal muscle development.

Members of the eukaryotic hsp90 family function as important molecular chaperones in the assembly, folding and activation of a select group of cellular signalling molecules and transcription factors. Several of the molecules with which hsp90 interacts, such as the bHLH transcription factor myoD, are known to be important regulators of developmental events in vertebrates. However, little information is available in support of any specific role for hsp90 in developing embryos in vivo. In this study, we provide the first in vivo evidence that the hsp90 alpha gene may play a role in the process of myogenesis. We show that constitutive hsp90 alpha mRNA in zebrafish embryos is restricted primarily to a subset of cells within the somites and pectoral fin buds which also express myoD. Furthermore, expression of the hsp90 alpha gene is down-regulated along with myoD in differentiated muscles of the trunk at a time when levels of mRNA encoding the muscle structural protein alpha-tropomyosin remain high. No hsp90 alpha mRNA is detectable within the CNS at control temperatures. In contrast, heat shock-induced expression of the hsp90 alpha gene occurs throughout the embryo at all stages of development examined. The expression patterns strongly suggest that the hsp90 alpha gene plays a specific role in the normal process of myogenesis in addition to providing protection to all cells of the embryo during periods of environmental stress.

Animals↗
PubMed1998

Integrins during muscle development and in muscular dystrophies.

Cellular interactions with the extracellular matrix (ECM) have been shown to be important for a number of developmental events from the time of fertilization up till the maturation of the organism. In the following review we will discuss what is currently known about these interactions with special emphasis on the role of integrins during the formation of skeletal muscle. The importance of cell-ECM interactions will also be illustrated by a discussion of what happens when these interactions go awry, as happens in muscular dystrophies.

Animals↗
PubMed1992

Actions of thrombin and thrombin receptor peptide analogues in gastric and aortic smooth muscle: development of bioassays for structure-activity studies.

We have examined the biological activities of thrombin and the thrombin-receptor-related polypeptides, S42FLLRNPNDKYEPF55(TRP42-55), S42FLLRNPND50(TRP42-50), and A42FLLRNPND50(A42-TRP42-50) as well as an arginine-containing basic peptide beginning with the SF motif (SFRGHITR), in rat aortic (RA) rings and in a gastric guinea pig longitudinal (LM) smooth muscle preparation. In the RA preparation, thrombin, as well as the three receptor-related peptides caused a relaxation in tissue that was precontracted with noradrenaline; the basic peptide, SFRGHITR, was inactive either as an agonist or as an antagonist to TRP42-55. In the LM bioassay, which unlike the RA preparation did not persistently desensitize in response to thrombin, all three receptor-related peptides, like thrombin, caused a prompt phasic reproducible contraction. The basic peptide, SFRGHITR, was inactive. In the LM assay, TRP42-55, TRP42-50 and A42-TRP42-55 all caused comparable contractile responses. We conclude that the gastric LM smooth muscle possesses a thrombin receptor and provides a convenient and reliable assay for the activities of thrombin receptor-related peptides. Our data also demonstrated that neither the C-terminal hirudin-related pentapeptide nor the N-terminal serine hydroxyl group are required for the biological activity of the thrombin receptor-derived peptide previously described (TRP42-55). Based on our findings we suggest that only a small portion of the N-terminal sequence of TRP42-55 may be required for thrombin-like biological activity.

Amino Acid Sequence↗
PubMed1999

Cardiac and skeletal muscle development in P19 embryonal carcinoma cells.

Mouse P19 embryonal carcinoma cells are pluripotent stem cells that can be maintained in culture in an undifferentiated state or can be induced to differentiate in vitro into multiple cell types. P19 cells aggregated in the presence of dimethylsulfoxide differentiate into spontaneously beating cardiomyocytes and bipolar skeletal myocytes that exhibit the biochemical and physiologic properties of their embryonic equivalents. P19 cells can be readily manipulated genetically, resulting in the loss or over-expression of a gene of interest. Because of this versatility, the P19 system is suited for examining the molecular mechanisms controlling the developmental decisions of stem cells differentiating into the skeletal or cardiac muscle lineage.

Animals↗
PubMed1998

Thrombospondins in early Xenopus embryos: dynamic patterns of expression suggest diverse roles in nervous system, notochord, and muscle development.

The thrombospondins (TSPs) are a family of extracellular matrix (ECM) glycoproteins that modulate many cell behaviors including adhesion, migration, and proliferation. Here we report the molecular cloning of the Xenopus homologs of TSP-1 and TSP-3, and the developmental patterns of expression of Xenopus TSP-1, TSP-3, and TSP-4 mRNAs. Xenopus TSP-1 and TSP-3 protein sequences each share approximately 80% amino acid identity with their mammalian counterparts. TSP-1 mRNAs are detectable at low levels in fertilized eggs indicating that this TSP is a maternally deposited transcript. Zygotic expression of TSP-1, TSP-3, and TSP-4 begins at the end of gastrulation and transcripts encoding each protein accumulate through the tadpole stages of development. Whole mount in situ hybridizations reveal that each TSP mRNA is localized in the embryo with distinct, developmentally regulated patterns of expression. TSP-1 mRNAs are detected in a wide range of tissues including the floor plate of the neural tube, epidermis, somites, notochord and, most notably, alternating rhombomeres. Transcripts encoding TSP-3 are expressed in the notochord, floor plate, sensorial layer of the epidermis and sensory epithelia. TSP-4 mRNAs are restricted to somitic mesoderm and skeletal muscle. These data suggest that the TSPs represent a functionally diverse family of ECM proteins with tissue-specific functions during embryogenesis.

Amino Acid Sequence↗
PubMed1998

Sexual dimorphism in broiler chick embryos and embryonic muscle development in late incubation.

Studies were conducted to compare the weights and the characteristics of the Pectoralis superficialis, Semimembranosus, and Gastrocnemius of male and female chicken embryos at 16 and 20 d of incubation. Male embryos were significantly heavier than females at 16 d of incubation, but not at 20 d. The cross-sectional area of myofibers in the P. superficialis of 20-d-old female embryos was greater than that of males and the area of Semimembranosus myofibers was greater at 16 and 20 d. The Semimembranosus apparent myofiber number of 16-d-old male embryos was greater than of females (P = 0.002). There was a significant increase in apparent myofiber number in this muscle between 16 and 20 d of incubation but there was no sex difference at 20 d. The number of Type I myofibers per 30,000 microm2 area of the Gastrocnemius of 20-d-old male embryos was greater than that in females (P = 0.06). There were no significant sex differences in the protein concentration, DNA concentration, or protein:DNA ratio in the muscles at either age when data were pooled across the whole population. There were significant differences in these characteristics between sire families and in some sire families significant sex differences were noted. The protein:DNA ratio of the muscles increased between 16 and 20 d of incubation and the mitotic index decreased. These data suggest that the muscles of male embryos have more but smaller, myofibers than females, which may be responsible for the sex difference in embryo weight and provide the framework for the greater posthatching muscle growth.

Animals↗
PubMed1985

Enzyme histochemical studies in an ontogeny study of muscle development in Ossabaw and decapitated fetuses: cellular reactions.

Fetuses were decapitated in one uterine horn in each of 14 sows at 45 d of gestation. Control (C) and decapitated (D) fetuses were removed by Caesarean section from three sows at 65 d of gestation (total of 10 D and 10 C fetuses), two sows at 85 d (six D and six C fetuses) and nine sows at 110 d (nine C and nine D fetuses) of gestation (Exp. 1). In Exp. 2, four to six fetuses were removed from each of two Ossabaw (O) gilts and three crossbred (C, Landrace X Yorkshire) gilts at 70 d of gestation, from three C and O gilts at 90 d of gestation and from three C and two O gilts at 110 d of gestation. In Exp. 1, one semitendinosis muscle was removed for histochemistry, whereas the contralateral muscle was removed and weighed. A medial portion of biceps femoris muscle was removed and used for histochemistry in Exp. 2. In both experiments, transverse sections (cryostat) of muscle were stained for lipid, glycogen (PAS) and the following enzymes: acid ATPase, NADH-TR, NADPH-TR, malate dehydrogenase (NAD- and NADP-dependent reactions; MDH), succinate dehydrogenase (SDH), alpha-glycerol phosphate dehydrogenase (with and without NAD; alpha-GPDH), isocitrate dehydrogenase (NAD dependent; ICDH), esterase, lipoprotein lipase and lipase. In Exp. 1, body and muscle weights of the two groups were not significantly different (P greater than .05) at 65 d of gestation, whereas D fetuses were smaller and had lighter weight muscles (P less than .05) at 85 d of gestation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗