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T Braun

Publications and source records attributed to T Braun.

At least 91 records · Page 5Linked to original sources
PubMed1992

Inactivation of MyoD in mice leads to up-regulation of the myogenic HLH gene Myf-5 and results in apparently normal muscle development.

The myogenic basic HLH transcription factor family of genes, composed of MyoD, myogenin, Myf-5, and Myf-6, are thought to regulate skeletal muscle differentiation. To understand the role of MyoD in myogenesis, we have introduced a null mutation of MyoD into the germline of mice. Surprisingly, mice lacking MyoD are viable and fertile. Histological examination of skeletal muscle failed to reveal any morphological abnormalities in these mice. Furthermore, Northern analysis revealed normal levels of skeletal muscle-specific mRNAs. Significantly, Myf-5 mRNA levels are elevated in postnatal mutant mice. Normally, Myf-5 expression becomes markedly reduced at day 12 of gestation when MyoD mRNA first appears. This suggests that Myf-5 expression is repressed by MyoD. Our results indicate that MyoD is dispensable for skeletal muscle development in mice, revealing some degree of functional redundancy in the control of the skeletal myogenic developmental program.

Animals↗
PubMed1992

Calculating the prevalence of cancer.

Incidence, prevalence and mortality are commonly used measures to assess the impact of disease on human populations. Prevalence, although regularly assessed for a number of different diseases, has only had recent use to measure the impact of cancer. The calculation of the prevalence of cancer presents several difficulties since there is no reporting mechanism established to measure the proportion of the community that has the disease. In the absence of such a mechanism, mortality data linked to incidence data from cancer registries have been used. The assumption is made that once diagnosed with cancer an individual remains a prevalent case until death. In this paper we present alternatives to this assumption and use them to produce estimates of cancer prevalence. We illustrate the effect of these assumptions on the calculated prevalence of cancer using data from the British Columbia Cancer Registry.

Algorithms↗
PubMed1992

Co-operativity of functional domains in the muscle-specific transcription factor Myf-5.

Myf-5 is a member of a family of muscle-specific transcription factors that activate myogenesis in 10T1/2 fibroblasts. Here we report the analysis of Myf-5 structural domains that are responsible for its biological activity. Site-directed mutagenesis revealed that two clusters of basic amino acids within a conserved basic region and two amphipathic helices within the adjacent HLH domain are essential for sequence-specific DNA binding and hetero-oligomerization, respectively. Transcriptional activation by Myf-5 requires two additional domains located in the amino- and carboxyl-termini. The two domains apparently co-operate since deletion of either one results in inactivation. Chimeric proteins between DNA binding domain of the yeast transcription factor GAL4 and the separate Myf-5 transactivator domains exhibit activity that is enhanced when both regions are combined. Dimerization of Myf-5 with the ubiquitously expressed bHLH protein E12 not only increases the affinity for DNA but also stimulates transactivation independently of DNA binding. The Myf-5 transactivator domains are dependent for activity on a specific amino acid sequence motif within the basic region when Myf-5 activity is mediated through the E-box DNA recognition sequence but not when DNA binding occurs through the GAL4 DNA binding domain. This demonstrates that muscle-specific transactivation by Myf-5 requires the collaboration of two activation domains and the DNA binding region in addition to sequence-specific DNA binding. Transcriptional activation and interaction with DNA are executed by separable domains; however, transactivation is influenced by the basic region in a manner distinguishable from DNA binding.

Amino Acid Sequence↗
PubMed1992

Cytokines, receptors, and inhibitors.

Cytokines are endogenous mediators in inflammatory and immunologic host defense reactions. In various diseases cytokines produced in excess cause systemic or local toxic effects. Cytokines therefore are tightly controlled by regulation of their biosynthesis and release and by counteracting mechanisms which limit their activities. Two new cytokine inhibitory mechanisms have recently been discovered. First, the generation of soluble receptors which compete with cellular receptors for cytokine binding has been recognized as a general phenomenon. Second, a receptor antagonist polypeptide binding to the receptor but not eliciting biological activity has been discovered in the IL-1 system. These polypeptides, when expressed in various recombinant forms, are not only research tools but may find also direct clinical use.

Cytokines↗
PubMed1992

Inhibition of muscle differentiation by the adenovirus E1a protein: repression of the transcriptional activating function of the HLH protein Myf-5.

Myogenic differentiation can be inhibited by the adenovirus E1a protein in the rat L6 muscle cell line. The present investigation provides evidence that E1a interferes with the expression of myogenin and the activity of Myf-5, the two myogenic helix-loop-helix (HLH) proteins that are expressed in L6 muscle cells. In nuclei of E1a-expressing L6 cells, Myf-5 protein accumulates to normal or even elevated levels and shows no alterations of its ability to bind to the DNA-binding site (CANNTG). However, trans-activation of muscle-specific reporter genes by Myf-5 is strongly inhibited. The same inhibition by E1a can be shown for the other myogenic HLH proteins, MyoD, myogenin, and MRF4/Myf-6, that have been expressed in 10T1/2 fibroblasts. In contrast to the normal level of Myf-5 expression, synthesis of myogenin is entirely abolished in the differentiation-defective L6-E1a cells. Here, we demonstrate that the carboxy-terminal trans-activator domain and probably the basic-HLH (bHLH) region of Myf-5 constitute targets for the inhibition by E1a. The effect of E1a depends on its intact transforming regions but not on the transcriptional activator domain. Our data suggest that activation of myogenin gene expression and the establishment of the differentiated phenotype may require functional Myf-5. Expression of the Myf-5 gene, however, is apparently independent of auto- or cross-regulation by the myogenic HLH proteins.

Adenovirus Early Proteins↗
PubMed1992

Regulation of myogenin expression in normal and transformed myogenic cell lines.

The control of myogenin (Myf-4), one of the muscle-specific regulatory proteins, is particularly interesting since its expression appears obligatory in myoblasts at the onset of differentiation. We isolated the human Myf-4 (myogenin) gene and determined promoter elements which direct cell type-specific expression and are subject to transactivation by the muscle transcription factors Myf-5 and MyoD1 in fibroblasts. Extrinsic signals such as serum components and purified growth factors or potential intracellular signals such as cAMP down-regulate transcription of the myogenin gene. Constitutive expression of the catalytic subunit of PKA completely suppresses transactivation of the myogenin promoter by Myf-5 or MyoD1 suggesting that cAMP may act via phosphorylation by PKA. In contrast to normal myogenic cell lines in which differentiation and myogenin expression can be induced by the removal of serum components, retinoic acid (RA) is required for differentiation in the rat rhabdomyosarcoma cell line BA-Han-1C. This model system was utilized to investigate factors which influence the balance between the transformed state and differentiation. Administration of retinoic acid to BA-Han-1C cells leads to the accumulation of myogenin mRNA approximately 48 h after the addition of RA. This late induction requires ongoing protein- and DNA-synthesis suggesting that trans- and cis-acting factors may be involved in the control. The critical involvement of myogenin in the process of terminal muscle differentiation was also demonstrated in the rat L6 muscle cell line which has been blocked for differentiation by the transforming protein E1a of Ad5 adenovirus. In cells which stably express E1a, myogenin expression is completely suppressed while Myf-5 continues to be synthesized normally. However, E1a inhibits the transactivator function of Myf-5, as demonstrated on GAL4-Myf5 chimeric proteins. A possible interpretation of this result is that Myf-5 or factors activated by Myf-5 are required for the expression of myogenin and myogenin itself is necessary for the terminal differentiation of myoblasts.

Blood↗
PubMed1991

The four human muscle regulatory helix-loop-helix proteins Myf3-Myf6 exhibit similar hetero-dimerization and DNA binding properties.

The muscle regulatory proteins Myf3, Myf4, Myf5, and Myf6 share a highly conserved DNA binding and dimerization domain consisting of a cluster of basic amino acids and a potential helix-loop-helix structure. Here we demonstrate that the four human muscle-specific HLH proteins have similar DNA binding and dimerization properties. The members of this family form protein complexes of comparable stability with the ubiquitously expressed HLH proteins E12, E2-2, and E2-5 and bind to the conserved DNA sequence CANNTG designated as E-box with similar efficiency in vitro. The binding affinities of the various complexes are greatly influenced by the variable internal and flanking nucleotides of the consensus motif. Combinations of Myf proteins with one another and with lyl-1, and HLH protein from human T cells, do not bind to DNA in vitro. Our results suggest that combinatorial associations of the various tissue-specific and more widely expressed HLH factors do not result in differential recognition of DNA sequences by Myf proteins.

Base Sequence↗
PubMed1991

Baculovirus-expressed myogenic determination factors require E12 complex formation for binding to the myosin-light-chain enhancer.

Two recombinant baculoviruses BcV-myf4 and BcV-myf5 have been constructed to synthesize the human myogenic determination factors myogenin (myf4) and myf5 in eucaryotic cells. Both recombinant proteins are localized to the nucleus of virus-infected Spodoroptera frugiperda (sf) insect cells and can be recovered as soluble factors. The virus-produced proteins exhibit high-affinity binding to a muscle-specific DNA sequence in the presence of the ubiquitous helix-loop-helix (HLH) protein E12, but only marginal binding in unsupplemented sf nuclear extracts. Both baculovirus-encoded myogenic factors are able to heterooligomerize with E12 in the absence of DNA-binding sites. We conclude from our results that these muscle-specific HLH proteins produced in eucaryotic cells largely depend on dimerization with E12 or similar HLH proteins to recognize the myosin-light-chain-enhancer-MEF-1-binding site. We have no evidence for intracellular protein modifications exerting major effects on the interaction between these factors and DNA.

Baculoviridae↗
PubMed1991

Amino-terminal leucine-rich repeats in gonadotropin receptors determine hormone selectivity.

Recombinant expression of truncated receptors for luteinizing hormone/chorionic gonadotropin (LH/CG) revealed that the amino-terminal leucine-rich repeats 1-8 of the extracellular receptor domain bind human chorionic gonadotropin (hCG) with an affinity (Kd = 0.72 +/- 0.2 nM) similar to that of the native LH/CG receptor (Kd = 0.48 +/- 0.05 nM). LH/CG receptor leucine-rich repeats 1-8 were used to replace homologous sequences in the closely related receptor for follicle stimulating hormone (FSH). Cells expressing such chimeric LH/CG-FSH receptors bind hCG and show elevated cylic AMP levels when stimulated by hCG but not by recombinant human FSH (rhFSH). Similarly, a chimeric LH/CG receptor in which leucine-rich repeats 1-11 originated from the FSH receptor is activated by rhFSH but not by hCG. For this chimera, no residual [125I] hCG binding was observed in a range of 2 pM to 10 nM. Our results demonstrate that specificity of gonadotropin receptors is determined by a high affinity hormone binding site formed by the amino-terminal leucine-rich receptor repeats.

Base Sequence↗
PubMed1991

Temporomandibular joint dysfunction syndrome: a close association with systemic joint laxity (the hypermobile joint syndrome)

Sixty-two patients admitted for elective reconstructive surgery of the temporomandibular joint (TMJ) and eight seen as outpatients with a chief complaint of TMJ dysfunction during the same time interval were evaluated for possible etiologic factors contributing to the disease. All hospitalized patients had severe, end-stage degenerative changes within the TMJ, whereas outpatients had less severe disease and did not require surgery. TMJ dysfunction in some patients was said to be a result of established causes including bruxism, malocclusion, and trauma. No patient in this series had evidence of a systemic inflammatory polyarthritis. Of the 70 patients, 38 (54%) met criteria, based on those of Carter and Wilkinson, as modified by Beighton et al., sufficient to warrant a diagnosis of the hypermobile joint syndrome. Five patients had classic Ehlers-Danlos syndrome and therefore were not patients with "benign hypermobility," and an additional two cases were described as "marfanoid" and as possible Ehlers-Danlos syndrome, respectively. Radiographs showed TMJ hyperextensibility in four hypermobile patients. Long-term surgical outcome was identical in the hypermobile and nonhypermobile groups. The incidence of hypermobility in this series is strikingly higher than the expected incidence in an otherwise population. Magnetic resonance images of the TMJs on separate groups of asymptomatic normal and hypermobile women identified excessive anterior movement in the hypermobile group, together with abnormal anterior disk position in some. We hypothesize that hypermobility within the TMJ may cause accelerated disk destruction and degenerative disease.

Adolescent↗
PubMed1991

Expression of members of the myf gene family in human rhabdomyosarcomas.

Northern analysis of tumour RNA has been used to examine the expression of members of the myf family of muscle determining genes (myf3, myf4, myf5 and myf6) in a series of 20 rhabdomyosarcomas. A 2.0 kb myf3 transcript was observed in 85% of tumours, a 1.8 kb myf4 transcript was detected in 70% of tumours and a 1.7 kb myf5 transcript was observed in 55% of tumours. Transcription of myf6 occurred in 28% of tumours, but there were several transcript sizes (1.2, 1.5, 2.0 and 3.5 kb) and in some individual tumours two or more transcripts were observed. Only two rhabdomyosarcomas, one classified as embryonal and one as pleomorphic, failed to exhibit transcription of members of the myf gene family. We were unable to detect transcription of myf genes in neuroblastomas, Wilms' tumours, hepatoblastomas, paediatric non-Hodgkin's lymphoma and leiomyosarcomas. When considered together these observations suggest that expression of myf genes could provide an extremely useful marker in the diagnosis of rhabdomyosarcoma.

Adolescent↗
PubMed1991

The muscle regulatory gene, Myf-6, has a biphasic pattern of expression during early mouse development.

The spatial and temporal expression pattern of the muscle regulatory gene Myf-6 (MRF4/herculin) has been investigated by in situ hybridization during embryonic and fetal mouse development. Here, we report that the Myf-6 gene shows a biphasic pattern of expression. Myf-6 transcripts are first detected in the most rostral somites of the mouse embryo at 9 d of gestation and accumulate progressively in myotomal cells along the rostro-caudal axis. This expression is transient and Myf-6 mRNA can no longer be detected in myotomal cells after day 12 post coitum (p.c.). In contrast to other muscle determination genes (MyoD1, myogenin, Myf-5), Myf-6 mRNA is not detected in limb buds or visceral arches and skeletal muscle of the mouse embryo (day 8-15 p.c.). In fetal mice, Myf-6 transcripts appear at day 16 p.c. in all skeletal muscles, and the gene continues to be expressed at a high level after birth. These results suggest that early Myf-6 expression may be restricted to a population of myogenic cells that does not contribute to the embryonic muscle masses in limb buds and visceral arches. The reappearance of Myf-6 mRNA in fetal skeletal muscle coincides approximately with secondary muscle fiber formation and the onset of innervation.

Base Sequence↗
PubMed1991

Transcription of the muscle regulatory gene Myf4 is regulated by serum components, peptide growth factors and signaling pathways involving G proteins.

The muscle regulatory protein myogenin accumulates in differentiating muscle cells when the culture medium is depleted for serum. To investigate the regulation of myogenin gene expression, we have isolated and characterized the Myf4 gene which encodes the human homologue of murine myogenin. Serum components, basic FGF (b-FGF), transforming growth factor beta (TGF-beta), and EGF, agents which suppress differentiation of muscle cells in vitro, down-regulate the activity of the Myf4 gene, suggesting that it constitutes a nuclear target for the negative control exerted by these factors. The 5' upstream region containing the Myf4 promoter confers activity to a CAT reporter plasmid in C2C12 myotubes but not in fibroblasts and undifferentiated myoblasts. Unidirectional 5' deletions of the promoter sequence reveal that integral of 200 nucleotides upstream of the transcriptional start site are sufficient for cell type-specific expression. The forced expression of the muscle determining factors, MyoD1, Myf5, and Myf6 and to a lesser degree Myf4, results in the transactivation of the Myf4 promoter in C3H mouse 10T1/2 fibroblasts. Pathways potentially involved in conveying signals from the cell-surface receptors to the Myf4 gene were probed with pertussis- and cholera toxin, forskolin, and cAMP. Dibutyryl-cAMP and compounds that stimulate adenylate cyclase inhibit the endogenous Myf4 gene and the Myf4 promoter in CAT and LacZ reporter constructs. Conversely, pertussis toxin which modifies Gi protein stimulates Myf4 gene expression. In summary, our data provide evidence that the muscle-specific expression of the Myf4 gene is subject to negative control by serum components, growth factors and a cAMP-dependent intracellular mechanism. Positive control is exerted by a pertussis toxin-sensitive pathway that presumably involves G proteins.

Adenylate Cyclase Toxin↗
PubMed1991

[Side effects of the immunsuppressive cyclosporin A in dentistry].

31 renal transplant patients with Cyclosporin-A-Medication were dental discussed. Half of the patients showed gingival hyperplasia in the anterior region of the maxilla after different time of medication. A relation between gingival hyperplasia, age and sex could'nt be seen. Two stomatitis were presented. The oral hygiene and the parodontal statement before the transplantation influenced the formation of gingival hyperplasia. At time it seems, that Nifedipin has no influence on the formation of gingival hyperplasia. We recommend a extensive research with a long list of patients. A patient with a voluminous hyperplasia was discussed.

Adult↗
PubMed1990

A highly conserved enhancer downstream of the human MLC1/3 locus is a target for multiple myogenic determination factors.

A potent muscle-specific enhancer element, originally described in the rat myosin light chain (MLC) 1/3 locus located downstream of the coding region, is found in an analogous position in the human MLC1/3 gene. When linked to a CAT reporter gene and transfected into muscle or non-muscle cells, the human MLC enhancer directs high levels of muscle-specific gene expression from homologous or heterologous promoters, irrespective of position or orientation relative to the CAT transcription unit. A significant degree of sequence homology (over 85%) in the 3'-flanking regions of the two MLC genes is restricted to a 200 bp sequence which lies approximately 1.5 kb downstream of the polyadenylation site in both species. The human enhancer sequence includes binding sites for human myogenic determination factors containing a common basic helix-loop-helix motif, and it can be trans-activated to varying degrees in non-muscle cells by these factors. This study establishes the MLC enhancer as an evolutionarily conserved, integral component of the MLC1/3 locus which constitutes a novel target for the action of myogenic determination factors.

Animals↗
PubMed1990

Transcriptional activation domain of the muscle-specific gene-regulatory protein myf5.

The human muscle determination factor myf5, like MyoD and other members of the family of skeletal muscle-specific regulatory proteins, contains a highly conserved putative helix-loop-helix domain. In MyoD this motif is required for the initiation of myogenesis in C3H mouse 10T1/2 fibroblasts and other non-muscle cells as well as for transcriptional activation of muscle genes. High affinity DNA binding of MyoD to regulatory DNA elements in muscle genes requires the formation of heterodimers with ubiquitous helix-loop-helix proteins such as E12 or E47. To investigate the potential of myf5 as a transcription factor, we have fused the GAL4 DNA-binding domain to various parts of the myf5 protein and analysed the transactivation of a GAL4 reporter plasmid. Here we report that myf5 contains an intrinsic transcriptional activation domain which is distinct from the helix-loop-helix motif. The predominant transactivating effect is associated with the C-terminal half of the myf5 molecule. High-affinity sequence-specific DNA binding of myf5 also requires hetero-oligomeric association with the enhancer-binding protein E12 to confer muscle-specific transactivation.

Animals↗