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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The specificity of highly differentiated tissues is largely achieved through the action of cell- and stage-restricted transcription factors. The basic events in skeletal muscle development are triggered by a unique family of myogenic basic helix-loop-helix proteins - MyoD, Myf-5, myogenin and MRF-4. Binding sites for these factors are found in the promoter regions of many genes whose expression is restricted to muscle cells, but the tight regulation of gene expression is dependent on the interaction of different factors. In this respect zinc finger proteins seem to play an important role, not only in the establishment of muscle cells but also in the maintenance of muscle function. This review discusses several zinc finger proteins that have been characterized as regulators of muscle development and muscle-specific gene expression.
Mol Gen Genet 1999 Mar
PMID:Zinc finger proteins: watchdogs in muscle development. 1010 54

Primary transcripts encoding the MADS box superfamily of proteins, such as MEF2 in animals and ZEMa in plants, are alternatively spliced, producing several isoformic species. We show here that murine serum response factor (SRF) primary RNA transcripts are alternatively spliced at the fifth exon, deleting approximately one-third of the C-terminal activation domain. Among the different muscle types examined, visceral smooth muscles have a very low ratio of SRFDelta5 to SRF. Increased levels of SRFDelta5 correlates well with reduced smooth muscle contractile gene activity within the elastic aortic arch, suggesting important biological roles for differential expression of SRFDelta5 variant relative to wild-type SRF. SRFDelta5 forms DNA binding-competent homodimers and heterodimers. SRFDelta5 acts as a naturally occurring dominant negative regulatory mutant that blocks SRF-dependent skeletal alpha-actin, cardiac alpha-actin, smooth alpha-actin, SM22alpha, and SRF promoter-luciferase reporter activities. Expression of SRFDelta5 interferes with differentiation of myogenic C2C12 cells and the appearance of skeletal alpha-actin and myogenin mRNAs. SRFDelta5 repressed the serum-induced activity of the c-fos serum response element. SRFDelta5 fused to the yeast Gal4 DNA binding domain displayed low transcriptional activity, which was complemented by overexpression of the coactivator ATF6. These results indicate that the absence of exon 5 might be bypassed through recruitment of transcription factors that interact with extra-exon 5 regions in the transcriptional activating domain. The novel alternatively spliced isoform of SRF, SRFDelta5, may play an important regulatory role in modulating SRF-dependent gene expression.
Mol Cell Biol 1999 Jul
PMID:Dominant negative murine serum response factor: alternative splicing within the activation domain inhibits transactivation of serum response factor binding targets. 1037 7

The alpha-striated tropomyosin 3' untranslated region (TM UTR) promotes differentiation of fibroblasts into cells resembling skeletal muscle. To investigate the mechanism of this observation, RNA harvested from transfected primary fibroblasts was used for semiquantitative RT-PCR with primers specific for muscle transcription factors, showing that myoD and myogenin transcripts are detected in these cells, but that differentiation after TM UTR expression is independent of a detectable increase in these transcripts. Double immunofluorescent staining with antibodies to myoD family members and to titin confirms that muscle differentiation in TM UTR-transfected fibroblasts is independent of production of any transcription factor in this family. In contrast, the muscle transcription factor myocyte enhancer factor 2 (mef-2) is strongly expressed after transfection of fibroblasts with the TM UTR. The increase in mef-2 protein is due to an increase in the steady-state level of its mRNA, as shown by Northern analysis. The expression of p21 ordinarily observed in skeletal myogenesis before the expression of muscle-specific proteins is not seen in fibroblasts induced to differentiate by the TM UTR. These results demonstrate that post-transcriptional regulation of myoD family members is seen in fibroblasts, and that the TM UTR induces muscle differentiation independent of the myoD transcription factors and without expressing proteins characteristic of terminal withdrawal from the cell cycle. Finally, an increase in the steady-state level of mef-2 transcripts appears in the proximal pathway of myogenic activation in response to expression of the TM UTR. These results imply that fibroblasts can utilize an additional differentiation route upon TM UTR expression resulting in mature muscle other than that requiring myoD family members.
Mol Genet Metab 1999 Jul
PMID:Muscle-specific transcription factors in fibroblasts expressing the alpha-striated tropomyosin 3' untranslated region. 1038 29

Drosophila sine oculis and eyes absent genes synergize in compound-eye formation. The murine homologues of these genes, Six and Eya, respectively, show overlapping expression patterns during development. We hypothesized that Six and Eya proteins cooperate to regulate their target genes. Cotransfection assays were performed with various combinations of Six and Eya to assess their effects on a potential natural target, myogenin promoter, and on a synthetic promoter, the thymidine kinase gene promoter fused to multimerized Six4 binding sites. A clear synergistic activation of these promoters was observed in certain combinations of Six and Eya. To investigate the molecular basis for the cooperation, we first examined the intracellular distribution of Six and Eya proteins in transfected COS7 cells. Coexpression of Six2, Six4, or Six5 induced nuclear translocation of Eya1, Eya2, and Eya3, which were otherwise distributed in the cytoplasm. In contrast, coexpression of Six3 did not result in nuclear localization of any Eya proteins. Six and Eya proteins were coimmunoprecipitated from nuclear extracts prepared from cotransfected COS7 cells and from rat liver. Six domain and homeodomain, two evolutionarily conserved domains among various Six proteins, were necessary and sufficient for the nuclear translocation of Eya. In contrast, the Eya domain, a conserved domain among Eya proteins, was not sufficient for the translocation. A specific interaction between the Six domain and homeodomain of Six4 and Eya2 was observed by yeast two-hybrid analysis. Our results suggest that transcription regulation of certain target genes by Six proteins requires cooperative interaction with Eya proteins: complex formation through direct interaction and nuclear translocation of Eya proteins. This implies that the synergistic action of Six and Eya is conserved in the mouse and is mediated through cooperative activation of their target genes.
Mol Cell Biol 1999 Oct
PMID:Cooperation of six and eya in activation of their target genes through nuclear translocation of Eya. 1049 Jun 20

Rho family GTPases have been implicated in the regulation of the actin cytoskeleton in response to extracellular cues and in the transduction of signals from the membrane to the nucleus. Their role in development and cell differentiation, however, is little understood. Here we show that the transient expression of constitutively active Rac1 and Cdc42 in unestablished avian myoblasts is sufficient to cause inhibition of myogenin expression and block of the transition to the myocyte compartment, whereas activated RhoA affects myogenic differentiation only marginally. Activation of c-Jun N-terminal kinase (JNK) appears not to be essential for block of differentiation because, although Rac1 and Cdc42 GTPases modestly activate JNK in quail myoblasts, a Rac1 mutant defective for JNK activation can still inhibit myogenic differentiation. Stable expression of active Rac1, attained by infection with a recombinant retrovirus, is permissive for terminal differentiation, but the resulting myotubes accumulate severely reduced levels of muscle-specific proteins. This inhibition is the consequence of posttranscriptional events and suggests the presence of a novel level of regulation of myogenesis. We also show that myotubes expressing constitutively active Rac1 fail to assemble ordered sarcomeres. Conversely, a dominant-negative Rac1 variant accelerates sarcomere maturation and inhibits v-Src-induced selective disassembly of I-Z-I complexes. Collectively, our findings provide a role for Rac1 during skeletal muscle differentiation and strongly suggest that Rac1 is required downstream of v-Src in the signaling pathways responsible for the dismantling of tissue-specific supramolecular structures.
Mol Biol Cell 1999 Oct
PMID:Distinct effects of Rac1 on differentiation of primary avian myoblasts. 1051 56

Myogenic cell differentiation is induced by Arg(8)-vasopressin, whereas high cAMP levels and protein kinase A (PKA) activity inhibit myogenesis. We investigated the role of type 4 phosphodiesterase (PDE4) during L6-C5 myoblast differentiation. Selective PDE4 inhibition resulted in suppression of differentiation induced by vasopressin. PDE4 inhibition prevented vasopressin-induced nuclear translocation of the muscle-specific transcription factor myogenin without affecting its overall expression level. The effects of PDE4 inhibition could be attributed to an increase of cAMP levels and PKA activity. RNase protection, reverse transcriptase PCR, immunoprecipitation, Western blot, and enzyme activity assays demonstrated that the PDE4D3 isoform is the major PDE4 expressed in L6-C5 myoblasts and myotubes, accounting for 75% of total cAMP-hydrolyzing activity. Vasopressin cell stimulation caused a biphasic increase of PDE4 activity, which peaked at 2 and 15 min and remained elevated for 48 h. In the continuous presence of vasopressin, cAMP levels and PKA activity were lowered. PDE4D3 overexpression increased spontaneous and vasopressin-dependent differentiation of L6-C5 cells. These results show that PDE4D3 plays a key role in the control of cAMP levels and differentiation of L6-C5 cells. Through the modulation of PDE4 activity, vasopressin inhibits the cAMP signal transduction pathway, which regulates myogenesis possibly by controlling the subcellular localization of myogenin.
Mol Biol Cell 1999 Dec
PMID:Involvement of type 4 cAMP-phosphodiesterase in the myogenic differentiation of L6 cells. 1058 63

Muscle formation and postnatal growth is under the control of the muscle regulatory factors (MRF) gene family, consisting of four genes: MyoD1, myogenin, myf-5, and myf-6. Muscle mass is also known to be affected by specific drugs, like glucocorticoids. Glucocorticoids have also been characterized as muscle atrophying agents. However, glucocorticoids are also the only drugs reported to have a beneficial effect on the treatment of muscle degenerative disorders. Since muscle mass relates to gender, this may be partially caused by gender. The aim of this study is to investigate gender-related basal and dexamethasone-induced expression of the MRF genes. Gender-specific MRF mRNA levels were investigated in anterior tibial muscles of the rat. Myogenin, myf-5, and myf-6 mRNA level was significantly higher in female rats than in male rats. Since muscle mass is usually higher in males, we conclude that the development of gender-related differences in muscle mass is not primarily under the control of the mRNA levels of the MRF genes. Male rats treated with dexamethasone for 14 days (1 mg per kg body weight) showed increased levels of MyoD1, myogenin and myf-5 compared to control male rats. Female rats treated with dexamethasone showed decreased expression of myf-6 compared to control female rats. These results suggest that dexamethasone increase satellite cell-specific MRF activity in male muscle tissue, which is suggested to be associated with muscle hypertrophy, while maintenance of muscle tissue is affected in female muscle tissue. Therefore, we conclude that both basal and dexamethasone-induced MRF gene mRNA levels are regulated gender-specific.
Mol Biol Rep 1999 Dec
PMID:Gender related and dexamethasone induced differences in the mRNA levels of the MRF genes in rat anterior tibial skeletal muscle. 1063 11

Although fetal breathing movements are required for normal lung development, there is uncertainty concerning the specific effect of absent fetal breathing movements on pulmonary cell maturation. We set out to evaluate pulmonary development in a genetically defined mouse model, the myogenin null mouse, in which there is a lack of normal skeletal muscle fibers and thus skeletal muscle movements are absent in utero. Significant decreases were observed in lung:body weight ratio and lung total DNA at embryonic days (E)14, E17, and E20. Reverse transcriptase/polymerase chain reaction, in situ immunofluorescence, and electron microscopy revealed early lung cell differentiation in both null and wild-type lungs as early as E14. However at E14, myogenin null lungs had decreased 5'-bromo-2-deoxyuridine incorporation compared with that of wild-type littermates, whereas at E17 and E20, increased Bax immunolabeling and terminal deoxyribonucleotidyl transferase-mediated dUTP-biotin nick-end labeling staining were detected in the myogenin null mice but not in the wild-type littermates. These observations highlight the importance of skeletal muscle contractile activity in utero for normal lung organogenesis. Null mice lacking the muscle-specific transcription factor myogenin exhibit a secondary effect on lung development such that decreased lung cell proliferation and increased programmed cell death are associated with lung hypoplasia.
Am J Respir Cell Mol Biol 2000 Mar
PMID:Pulmonary hypoplasia in the myogenin null mouse embryo. 1069 67

The Rho family of GTP-binding proteins plays a critical role in a variety of cellular processes, including cytoskeletal reorganization and activation of kinases such as p38 and C-jun N-terminal kinase (JNK) MAPKs. We report here that dominant negative forms of Rac1 and Cdc42Hs inhibit the expression of the muscle-specific genes myogenin, troponin T, and myosin heavy chain in L6 and C2 myoblasts. Such inhibition correlates with decreased p38 activity. Active RhoA, RhoG, Rac1, and Cdc42Hs also prevent myoblast-to-myotube transition but affect distinct stages: RhoG, Rac1, and Cdc42Hs inhibit the expression of all muscle-specific genes analyzed, whereas active RhoA potentiates their expression but prevents the myoblast fusion process. We further show by two different approaches that the inhibitory effects of active Rac1 and Cdc42Hs are independent of their morphogenic activities. Rather, myogenesis inhibition is mediated by the JNK pathway, which also leads to a cytoplasmic redistribution of Myf5. We propose that although Rho proteins are required for the commitment of myogenesis, they differentially influence this process, positively for RhoA and Rac1/Cdc42Hs through the activation of the SRF and p38 pathways, respectively, and negatively for Rac1/Cdc42Hs through the activation of the JNK pathway.
Mol Biol Cell 2000 Aug
PMID:Critical activities of Rac1 and Cdc42Hs in skeletal myogenesis: antagonistic effects of JNK and p38 pathways. 1093 Apr 50

The muscle regulatory factors (MRF) gene family regulate muscle fibre development. Several hormones and drugs also affect muscle development. Glucocorticoids are the only drugs reported to have a beneficial effect on muscle degenerative disorders. We investigated the glucocorticoid-related effects on C2C12 myoblast proliferation rate, morphological differentiation, and subsequent mRNA expression patterns of the MRF genes. C2C12 cells were incubated with the glucocorticoids dexamethasone or alpha-methyl-prednisolone. Both glucocorticoids showed comparable effects. Glucocorticoid treatment of C2C12 cells during the proliferative phase reduced the proliferation rate of the cells dose dependently, especially during the third and fourth day of culture, increased MyoD1, myf-5, and MRF4 mRNA levels, and reduced myogenin mRNA level, compared to untreated control cells. Thus, the mRNA level of proliferation-specific MyoD1 and myf-5 expression does not seem to associate with C2C12 myoblast proliferation rate. Glucocorticoid treatment of C2C12 cells during differentiation reduced the differentiation capacity dose dependently, which is accompanied by a dose dependent reduction of myogenin mRNA level, and increased MyoD1, myf-5, and MRF4 mRNA levels compared to untreated control cells. Therefore, we conclude that glucocorticoid treatment reduces differentiation of C2C12 myoblasts probably through reduction of differentiation-specific myogenin mRNA level, while inducing higher mRNA levels of proliferation-associated MRF genes.
Mol Biol Rep 2000 Jun
PMID:Glucocorticoid inhibition of C2C12 proliferation rate and differentiation capacity in relation to mRNA levels of the MRF gene family. 1109 55


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