Search PubMed⌕ Search

Biomedical subjects

T Braun

Publications and source records attributed to T Braun.

At least 55 records · Page 3Linked to original sources
PubMed2000

The 6.9-A structure of GlpF: a basis for homology modeling of the glycerol channel from Escherichia coli.

The three-dimensional structure of GlpF, the glycerol facilitator of Escherichia coli, was determined by cryo-electron microscopy. The 6.9-A density map calculated from images of two-dimensional crystals shows the GlpF helices to be similar to those of AQP1, the erythrocyte water channel. While the helix arrangement of GlpF does not reflect the larger pore diameter as seen in the projection map, additional peripheral densities observed in GlpF are compatible with the 31 additional residues in loops C and E, which accordingly do not interfere with the inner channel construction. Therefore, the atomic structure of AQP1 was used as a basis for homology modeling of the GlpF channel, which is predicted to be free of bends, wider, and more vertically oriented than the AQP1 channel. Furthermore, the residues facing the GlpF channel exhibit an amphiphilic nature, being hydrophobic on one side and hydrophilic on the other side. This property may partially explain the contradiction of glycerol diffusion but limited water permeation capacity.

Aquaporin 1↗
PubMed2000

Genetics of muscle determination and development.

Skeletal muscles in vertebrates develop from somites as the result of patterning and cell type specification events. Here, we review the current knowledge of genes and signals implicated in these processes. We discuss in particular the role of the myogenic determination genes as deduced from targeted gene disruptions in mice and how their expression may be controlled. We also refer to other transcription factors which collaborate with the myogenic regulators in positive or negative ways to control myogenesis. Moreover, we review experiments that demonstrate the influence of tissues surrounding the somites on the process of muscle formation and provide model views on the underlying mechanisms. Finally, we present recent evidence on genes that play a role in regeneration of muscle in adult organisms.

Animals↗
PubMed2000

Myristoylation-dependent N-terminal cleavage of the myristoylated alanine-rich C kinase substrate (MARCKS) by cellular extracts.

The myristoylated alanine-rich C kinase substrate (MARCKS) has been proposed to regulate the plasticity of the actin cytoskeleton at its site of attachment to membranes. In macrophages, MARCKS is implicated in various cellular events including motility, adhesion and phagocytosis. In this report we show that macrophage extracts contain a protease which specifically cleaves human MARCKS, expressed in a cell-free system or in E. coli, between Lys-6 and Thr-7. Cleavage of MARCKS decreases its affinity for macrophage membranes by ca. one order of magnitude, highlighting the contribution of the myristoyl moiety of MARCKS to membrane binding. Importantly, cleavage requires myristoylation of MARCKS. Furthermore, MARCKS-related protein (MRP), the second member of the MARCKS family, is not digested. Since Thr-7 is lacking in MRP this suggests that Thr-7 at the P1 position is important for the recognition of lipid-modified substrates. A different product is observed when MARCKS is incubated with a calf brain cytosolic extract. This product can be remyristoylated in the presence of myristoyl-CoA and N-myristoyl transferase, demonstrating that cycles of myristoylation/demyristoylation of MARCKS can be achieved in vitro. Although the physiological relevance of these enzymes still needs to be demonstrated, our results reveal the presence of a new class of cleaving enzymes recognizing lipid-modified protein substrates.

Amino Acid Sequence↗
PubMed2000

Inner ear and lateral line expression of a zebrafish Nkx5-1 gene and its downregulation in the ears of FGF8 mutant, ace.

An orthologue of the mouse homeobox gene Nkx5-1 was cloned and characterized in the zebrafish. As in the mouse and chick, the zebrafish Nkx5-1 gene is expressed in the ear placode and vesicle and in cells forming the vestibulo-acoustic ganglion. In addition, a novel expression domain, the lateral line, appears in the zebrafish, supporting a common precursor hypothesis for these two organs. In the FGF8 zebrafish mutant ace, expression of Nkx5-1 in the otic structures is diminished. The most significant reduction of zfNkx5-1 expression was observed in cells of the vestibulo-acoustic ganglion.

Amino Acid Sequence↗
PubMed2000

Heterozygous myogenic factor 6 mutation associated with myopathy and severe course of Becker muscular dystrophy.

Myogenic factors (MYF) belong to the basic helix-loop-helix (bHLH) transcription factor family and regulate myogenesis and muscle regeneration. The physiological importance of both functions was demonstrated in homozygous Myf knockout mice and mdx mice. Myf5 and Myod are predominantly expressed in proliferating myoblasts while Myf4 and Myf6 are involved in differentiation of myotubes. In a boy with myopathy and an increase of muscle fibres with central nuclei we detected a heterozygous 387G-->T nucleotide transversion in the MYF6 gene (MIM*159991). Protein-protein interaction of mutant MYF6 was reduced, and DNA-binding potential and transactivation capacity were abolished, thus demonstrating MYF6 haploinsufficiency. The boy's father carried the identical mutation and, in addition, an in-frame deletion of exons 45-47 in his dystrophin gene. This mutation is normally associated with a mild to moderate course of Becker muscular dystrophy but the father suffered from a severe course of Becker muscular dystrophy suggesting MYF6 as a modifier.

Adult↗
PubMed2000

A revisited auditing of the analytical abstracts database

This paper is a follow-up of a previous one dealing with the "Image of Analytical Chemistry as Reflected in the Analytical Abstracts Database: Journal Coverage, Concentration and Dispersion of the Analytical Literature" (J. Chem. Inf. Comput. Sci. 1993, 33, 164-173). It deals with revisiting these topics. The results have shown that the database has substantially improved its coverage by editorial reorganizations in 1994. The only open problem which has been revealed is a somewhat excessive emphasis given to the coverage of the journals on the lower tail of the journal distribution. The suggestion is made to reduce this emphasis in favor of an even more complete coverage of some "titled" analytical journals.

Journal Article↗
PubMed2000

Fullerene data mining using bibliometrics and database tomography

Database tomography (DT) is a textual database analysis system consisting of two major components: (1) algorithms for extracting multiword phrase frequencies and phrase proximities (physical closeness of the multiword technical phrases) from any type of large textual database, to augment (2) interpretative capabilities of the expert human analyst. DT was used to derive technical intelligence from a fullerenes database derived from the Science Citation Index and the Engineering Compendex. Phrase frequency analysis by the technical domain experts provided the pervasive technical themes of the fullerenes database, and phrase proximity analysis provided the relationships among the pervasive technical themes. Bibliometric analysis of the fullerenes literature supplemented the DT results with author/journal/institution publication and citation data. Comparisons of fullerenes results with past analyses of similarly structured near-earth space, chemistry, hypersonic/supersonic flow, aircraft, and ship hydrodynamics databases are made. One important finding is that many of the normalized bibliometric distribution functions are extremely consistent across these diverse technical domains and could reasonably be expected to apply to broader chemical topics than fullerenes that span multiple structural classes. Finally, lessons learned about integrating the technical domain experts with the data mining tools are presented.

Journal Article↗
PubMed2000

The 3.7 A projection map of the glycerol facilitator GlpF: a variant of the aquaporin tetramer.

GlpF, the glycerol facilitator protein of Escherichia coli, is an archetypal member of the aquaporin superfamily. To assess its structure, recombinant histidine-tagged protein was overexpressed, solubilized in octylglucoside and purified to homogeneity. Negative stain electron microscopy of solubilized GlpF protein revealed a tetrameric structure of approximately 80 A side length. Scanning transmission electron microscopy yielded a mass of 170 kDa, corroborating the tetrameric nature of GlpF. Reconstitution of GlpF in the presence of lipids produced highly ordered two-dimensional crystals, which diffracted electrons to 3.6 A resolution. Cryoelectron microscopy provided a 3.7 A projection map exhibiting a unit cell comprised of two tetramers. In projection, GlpF is similar to AQP1, the erythrocyte water channel. However, the major density minimum within each monomer is distinctly larger in GlpF than in AQP1.

Aquaporins↗
PubMed1999

PTSD among bereaved parents following the violent deaths of their 12- to 28-year-old children: a longitudinal prospective analysis.

This study examined the prevalence of posttraumatic stress disorder (PTSD) among parents bereaved by the violent deaths of their 12- to 28-year-old children. A community-based sample of 171 bereaved mothers and 90 fathers was recruited by a review of Medical Examiner records and followed for 2 years. Four important findings emerged: Both parents' gender and children's causes of death significantly affected the prevalence of PTSD symptoms. Twice as many mothers and fathers whose children were murdered met PTSD caseness (full diagnostic) criteria compared with accident and suicide bereavement. Symptoms in the reexperiencing domain were the most commonly reported. PTSD symptoms persisted over time, with 21% of the mothers and 14% of the fathers who provided longitudinal data still meeting caseness criteria 2 years after the deaths. Parents who met caseness criteria for PTSD, compared with those who did not, were significantly different on multiple study variables. Both theoretical and clinical implications for the findings are discussed.

Adaptation, Psychological↗
PubMed1999

Early specification of limb muscle precursor cells by the homeobox gene Lbx1h.

During vertebrate embryogenesis, myogenic precursor cells of limb muscles delaminate from the ventro-lateral edge of the somitic dermomyotome and migrate to the limb buds, where they congregate into dorsal and ventral muscle masses. It has been proposed that the surrounding connective tissue controls muscle pattern formation in limbs. Regulatory molecules such as receptor tyrosine kinases like c-Met ( ref. 6) and those encoded by homeobox-containing genes, including c-Met (ref. 6), Tbx1 (ref. 7), Mox2 (ref. 8), Six1 and Six2 (ref. 9), Pitx2, Pax3 (refs 10,11) and Lbx1h (refs 12,13), are expressed in migrating limb precursor cells. The role of these genes in the patterning of limb muscles is unknown, although mutation of Pax3 or Met causes disruption of limb muscle development at an initial step, disturbing the epithelial-to-mesenchymal transition of the somitic epithelium. No limb muscle cells form in these mutants, and the early loss of myogenic precursor cells prevented an analysis of later functions of these genes during limb muscle development. Based on quail-chick chimaera studies, it was assumed that a cell-autonomous contribution of myogenic cells to the formation of individual limb muscles is negligible, and that an instructive role of limb mesenchyme is critical in this process. Here we show that Lbx1h determines migratory routes of muscle precursor cells in a cell-autonomous manner, thereby leading to the formation of distinct limb muscle patterns. Inactivation of Lbx1h, which is specifically expressed in migrating muscle precursor cells, led to a lack of extensor muscles in forelimbs and an absence of muscles in hindlimbs. The defect was caused by the failure of all muscle precursor cells of hindlimbs and of precursor cells of extensor muscles of forelimbs to migrate to their corresponding muscle anlagen. Our results demonstrate that Lbx1h is a key regulator of muscle precursor cell migration and is required for the acquisition of dorsal identities of forelimb muscles.

Animals↗
PubMed1998

Role of the proteasome in membrane extraction of a short-lived ER-transmembrane protein.

Selective degradation of proteins at the endoplasmic reticulum (ER-associated degradation) is thought to proceed largely via the cytosolic ubiquitin-proteasome pathway. Recent data have indicated that the dislocation of short-lived integral-membrane proteins to the cytosolic proteolytic system may require components of the Sec61 translocon. Here we show that the proteasome itself can participate in the extraction of an ER-membrane protein from the lipid bilayer. In yeast mutants expressing functionally attenuated proteasomes, degradation of a short-lived doubly membrane-spanning protein proceeds rapidly through the N-terminal cytosolic domain of the substrate, but slows down considerably when continued degradation of the molecule requires membrane extraction. Thus, proteasomes engaged in ER degradation can directly process transmembrane proteins through a mechanism in which the dislocation of the substrate and its proteolysis are coupled. We therefore propose that the retrograde transport of short-lived substrates may be driven through the activity of the proteasome.

Cysteine Endopeptidases↗
PubMed1998

Pax-3 is necessary but not sufficient for lbx1 expression in myogenic precursor cells of the limb.

In vertebrates all skeletal muscles of trunk and limbs are derived from condensations of the paraxial mesoderm, the somites. Limb muscle precursor cells migrate during embryogenesis from somites to limb buds where migration stops and differentiation occurs. We have characterized lbx1 homeobox genes in chicken and mice and found them to be expressed in migrating limb muscle precursor cells in both species. Analysis of splotch mutant mice showed that lbx1 and c-met are differently affected by the lack of Pax-3. Limb buds of splotch (Pax-3 mutant) mice were devoid of lbx1 transcripts, while expression of c-met was still detectable at a low level. The presence of c-met-positive cells in splotch mice entering the limbs indicates that migration of cells from somites to limbs is not entirely dependent on Pax-3. We show that induction of epithelial to mesenchymal transition of Pax-3-positive cells by SF/HGF was not sufficient to induce ectopic lbx-1 expression at the inter-limb level, while ectopic limb formation was able to activate lbx1 expression. We postulate that Pax-3 is necessary for lbx1 expression in the lateral tips of somites but additional, yet unknown signals derived from limb buds are needed to initiate lbx1 expression. The role of limb bud-derived signals involved in targeted muscle precursor cell migration, and lbx1 activation was further confirmed by analysis of explanted somite/limb bud co-cultures in collagen gels.

Amino Acid Sequence↗
PubMed1998

Nkx5-1 controls semicircular canal formation in the mouse inner ear.

The inner ear develops from the otic vesicle, a one-cell-thick epithelium, which eventually transforms into highly complex structures including the sensory organs for balance (vestibulum) and hearing (cochlea). Several mouse inner ear mutations with hearing and balance defects have been described but for most the underlying genes have not been identified, for example, the genes controlling the development of the vestibular organs. Here, we report the inactivation of the homeobox gene, Nkx5-1, by homologous recombination in mice. This gene is expressed in vestibular structures throughout inner ear development. Mice carrying the Nkx5-1 null mutation exhibit behavioural abnormalities that resemble the typical hyperactivity and circling movements of the shaker/waltzer type mutants. The balance defect correlates with severe malformations of the vestibular organ in Nkx5-1(-/-) mutants, which fail to develop the semicircular canals. Nkx5-1 is the first ear-specific molecule identified to play a crucial role in the formation of the mammalian vestibular system.

Animals↗
PubMed1997

Faithful expression of the Myf-5 gene during mouse myogenesis requires distant control regions: a transgene approach using yeast artificial chromosomes.

Myf-5, a member of the family of four muscle-specific basic helix-loop-helix (bHLH) transcription factors is the first to be expressed in somites, branchial arches, and limb buds during prenatal mouse development. However, little is known about control mechanisms which actually regulate Myf-5 gene activity within these various muscle-forming domains. To identify control regions that contribute to the correct spatiotemporal activity pattern of the Myf-5 gene during mouse embryogenesis, here we report the characterization of yeast artificial chromosomes (YACs) which faithfully direct muscle-specific expression of the gene in chimeric mouse embryos. Forty-five kilobases of sequence 5' to the Myf-5 gene together with 500 kb of 3' flanking DNA drives the correct Myf-5 expression in the mesenchyme of the visceral arches and in somites but not in the hypaxial muscles of limb buds. An additional 50 kb of DNA at the 5' end is required to activate Myf-5 gene expression in developing limbs. These results demonstrate for the first time that unexpectedly distant regions of the Myf-5 gene are necessary to recapitulate its precise developmental expression pattern. We also show that Myf-5 expression in hypaxial muscles and in somites and visceral arches is regulated by separate and distinct far upstream regions. The identification of these remote regulatory elements on YACs carrying the mouse Myf-5 gene constitutes the first important step toward further dissection of the complex mechanisms by which cell-autonomous and external cues control Myf-5 expression during skeletal muscle formation in the mouse embryo.

Animals↗
PubMed1997

A role for FGF-6 in skeletal muscle regeneration.

Fibroblast growth factor-6 (FGF-6) belongs to a family of cytokines that control cell proliferation, cell differentiation, and morphogenetic events. Individual FGFs are either expressed widely or in a restricted pattern during embryonic, fetal, and adult life. FGF-6 exhibits a restricted expression profile predominantly in the myogenic lineage. Important functions in wound healing and tissue regeneration have been proposed for various FGFs in the past, although data from knockout mice have not supported this view. We have inactivated the FGF-6 gene in mice to investigate the role of FGF-6 in skeletal muscle development and regeneration. Wild-type mice up-regulate FGF-6 after skeletal muscle injuries and completely restore experimentally damaged skeletal muscle. In contrast, FGF-6(-/-) mutant mice show a severe regeneration defect with fibrosis and myotube degeneration. The number of MyoD- and Myogenin-expressing activated satellite cells after injury were significantly reduced in mutants. This reduction was not caused by a reduced pool of quiescent satellite cells but presumably by a lack of activation or proliferation. Interbreeding of FGF-6(-/-) mutants with mdx mice leads to striking dystrophic changes in skeletal muscles of double homozygous mice characterized by myotube degeneration, the presence of large amounts of mononuclear cells, and deposition of collagen. RNA analysis revealed an up-regulation of MyoD mRNA in mdx but not in FGF-6(-/-)/mdx double mutant mice. We conclude that FGF-6 is a critical component of the muscle regeneration machinery in mammals, possibly by stimulating or activating satellite cells.

Animals↗
PubMed1997

Value of a supervised exercise program for the therapy of arterial claudication.

PURPOSE: This study was performed to test the effectiveness of a formal supervised exercise program against a home-based exercise program for both walking ability and quality of life endpoints. METHODS: Patients with arterial claudication were randomized to either a 12-week supervised exercise program (SUPEX) with weekly lectures relating to peripheral vascular disease or to a home exercise group (HOMEX) who attended an identical lecture program and received weekly exercise instruction. The study population included 29 men and 26 women, with a mean age of 69.1 +/- 8.1 years. Forty-seven patients completed the 12-week program, 46 were available for testing at completion, and 38 for 6-month testing. Claudication pain time (CPT) and maximum walking time (MWT) on a progressive treadmill exercise test were assessed at baseline, program completion, and 6 months. The Medical Outcomes Study Short Form-36 (SF-36) was administered at these intervals to assess effects on quality of life. RESULTS: Each group improved (p < 0.001) in both CPT and MWT at the completion of the 12-week program, which was sustained at the 6-month follow-up. Increase in HOMEX CPT from baseline (3.6 +/- 2.73 minutes) to 6-month follow-up (6.6 +/- 3.17 minutes) was less than for the SUPEX group (3.8 +/- 2.74 to 11.2 +/- 4.02 minutes, respectively); similar results were obtained for MWT. At both completion and 6 months, there was a significant intergroup difference for CPT and MWT (p < 0.004) favoring SUPEX. For both groups, measures of health perception based on the SF-36 demonstrated improvement (p < 0.002) in Physical Function Subscale, Bodily Pain Subscale, and Physical Composite Score. There were no between-group differences on the subsets of the SF-36 at the three assessment intervals. CONCLUSIONS: Supervised exercise programs provide superior increased walking ability in the noninterventional therapy of arterial claudication, and both supervised and home based exercise therapy result in improved SF-36 functional measures. The lack of intergroup differences in these measures may be a result of the high degree of interaction with healthcare providers in the HOMEX group. Although a supervised program results in optimal walking benefits, a highly structured home-based program provides similar functional improvement and may be a satisfactory alternative for patients with lesser walking requirements.

Aged↗