THE SARCOTUBULAR SYSTEM OF FROG SKELETAL MUSCLE : A Morphological and Biochemical Study

In the frog skeletal muscle cell a well defined and highly organized system of tubular elements is located in the sarcoplasm between the myofibrils. The sarcoplasmic component is called the sarcotubular system. By means of differential centrifugation it has been possible to isolate from the frog muscle homogenate a fraction composed of small vesicles, tubules, and particles. This fraction is without cytochrome oxidase activity, which is localized in the mitochondrial membranes. This indicates that the structural components of this fraction do not derive from the mitochondrial fragmentation, but probably from the sarcotubular system. This fraction, called sarcotubular fraction, has a Mg⁺⁺-stimulated ATPase activity which differs from that of muscle mitochondria in that it is 3 to 4 times higher on the protein basis as compared with the mitochondrial ATPase, and is inhibited by Ca⁺⁺ and by deoxycholate like the Kielley and Meyerhof ATPase. We therefore conclude that the "granules" of the Kielley and Meyerhof ATPase, which were shown to have a relaxing effect, are fragments of the sarcotubular system. The isolated sarcotubular fraction has a high RNA content and demonstrable activity in incorporating labeled amino acids, even in the absence of added supernatant.     

Biochemical and serological evidence for an RNase E-like activity in halophilic Archaea.

Endoribonuclease RNase E appears to control the rate-limiting step that mediates the degradation of many mRNA species in bacteria. In this work, an RNase E-like activity in Archaea is described. An endoribonucleolytic activity from the extreme halophile Haloarcula marismortui showed the same RNA substrate specificity as the Escherichia coli RNase E and cross-reacted with a monoclonal antibody raised against E. coli RNase E. The archaeal RNase E activity was partially purified from the extreme halophilic cells and shown, contrary to the E. coli enzyme, to require a high salt concentration for cleavage specificity and stability. These data indicate that a halophilic RNA processing enzyme can specifically recognize and cleave mRNA from E. coli in an extremely salty environment (3 M KCI). Having recently been shown in mammalian cells (A. Wennborg, B. Sohlberg, D. Angerer, G. Klein, and A. von Gabain, Proc. Natl. Acad. Sci. USA 92:7322-7326, 1995), RNase E-like activity has now been identified in all three evolutionary domains: Archaea, Bacteria, and Eukarya. This strongly suggests that mRNA decay mechanisms are highly conserved despite quite different environmental conditions.     

Closed-Cell Stent-Assisted Coiling of Intracranial Aneurysms: Evaluation of Changes in Vascular Geometry Using Digital Subtraction Angiography

BackgroundStent-assisted coil embolization (SACE) plays an important role in the treatment of intracranial aneurysms. The purpose of this study was to investigate geometrical changes caused by closed-cell design stents in bifurcation and sidewall aneurysms.Methods31 patients with 34 aneurysms underwent SACE with closed-cell design stents. Inflow angle α, determined by aneurysm neck and afferent vessel, and angle between afferent and efferent vessel close to (δ₁), respectively, more remote from the aneurysm neck (δ₂) were graphically determined in 2D angiography projections.ResultsStent assisted coiling resulted in a significant increase of all three angles from a mean value (±SEM) of α = 119° (±6.5°) pretreatment to 130° (±6.6°) posttreatment (P ≤ .001), δ₁ = 129° (±6.4°) to 139° (±6.1°), (P ≤ .001) and δ₂ = 115° (±8.4°) to 126° (±7.5°), (P ≤ .01). Angular change of δ₁ in AcomA aneurysms was significant greater compared to sidewall aneurysms (26°±4.9° versus 8°± 2.3°, P ≤ .05). The initial angle of δ₁ and δ₂ revealed a significantly inverse relationship to the angle increase (δ₁: r = -0.41, P ≤ .05 and δ₂: r = -0.47, P ≤ .01). Moreover, angle δ₁ was significantly higher in unruptured compared to ruptured aneurysms (135°±7.1° versus 103°±10.8°, P ≤ .05).ConclusionStent deployment modulates the geometry of the aneurysm-vessel complex, which may lead to favorable hemodynamic changes more similar to unruptured than to ruptured aneurysms. Our findings also suggest that the more acute-angled aneurysm-vessel anatomy, the larger the angular change. Further studies are needed to investigate whether these changes improve the clinical outcome.     

Angiogenic synergism,vascular stability and improvement of hind-limb ischemia by a combination of PDGF-BB and FGF-2

The establishment of functional and stable vascular networks is essential for angiogenic therapy. Here we report that a combination of two angiogenic factors, platelet-derived growth factor (PDGF)-BB and fibroblast growth factor (FGF)-2, synergistically induces vascular networks, which remain stable for more than a year even after depletion of angiogenic factors. In both rat and rabbit ischemic hind limb models, PDGF-BB and FGF-2 together markedly stimulated collateral arteriogenesis after ligation of the femoral artery, with a significant increase in vascularization and improvement in paw blood flow. A possible mechanism of angiogenic synergism between PDGF-BB and FGF-2 involves upregulation of the expression of PDGF receptor (PDGFR)-alpha and PDGFR-beta by FGF-2 in newly formed blood vessels. Our data show that a specific combination of angiogenic factors establishes functional and stable vascular networks, and provides guidance for the ongoing clinical trials of angiogenic factors for the treatment of ischemic diseases.     

Cross-regulation among disparate antibiotic biosynthetic pathways of Streptomyces coelicolor

A complex programme of regulation governs gene expression during development of the morphologically and biochemically complex eubacterial genus Streptomyces. Earlier work has suggested a model in which 'higher level' pleiotropic regulators activate 'pathway-specific' regulators located within chromosomal gene clusters encoding biosynthesis of individual antibiotics. We used mutational analysis and adventitious overexpression of key Streptomyces coelicolor regulators to investigate functional interactions among them. We report here that cluster-situated regulators (CSRs) thought to be pathway-specific can also control other antibiotic biosynthetic gene clusters, and thus have pleiotropic actions. Surprisingly, we also find that CSRs exhibit growth-phase-dependent control over afsR2/afsS, a 'higher level' pleiotropic regulatory locus not located within any of the chromosomal gene clusters it targets, and further demonstrate that cross-regulation by CSRs is modulated globally and differentially during the S. coelicolor growth cycle by the RNaseIII homologue AbsB. Our results, which reveal a network of functional interactions among regulators that govern production of antibiotics and other secondary metabolites in S. coelicolor, suggest that revision of the currently prevalent view of higher-level versus pathway-specific regulation of secondary metabolism in Streptomyces species is warranted.     

Composite organization of the cobalamin binding and cubilin recognition sites of intrinsic factor

Intrinsic factor (IF(50)) is a cobalamin (Cbl)-transporting protein of 50 kDa, which can be cleaved into two fragments: the 30 kDa N-terminal peptide IF(30) and the 20 kDa C-terminal glycopeptide IF(20). Experiments on binding of Cbl to IF(30), IF(20), and IF(50) revealed comparable association rate constants (k(+)(Cbl) = 4 x 10(6), 14 x 10(6), and 26 x 10(6) M(-1) s(-1), respectively), but the equilibrium dissociation constants were essentially different (K(Cbl) = 200 microM, 0.2 microM, and 相似文献   

The impact of asymptomatic helminth co-infection in patients with newly diagnosed tuberculosis in north-west ethiopia

Background

Areas endemic of helminth infection, tuberculosis (TB) and HIV are to a large extent overlapping. The aim of this study was to assess the impact of asymptomatic helminth infection on the immunological response among TB patients with and without HIV, their house hold contacts and community controls.

Methodology

Consecutive smear positive TB patients (n = 112), their household contacts (n = 71) and community controls (n = 112) were recruited in Gondar town, Ethiopia. Stool microscopy, HIV serology, serum IgE level, eosinophil and CD4 counts were performed and tuberculosis patients were followed up for 3 months after initiation of anti-TB treatment.

Results

Helminth co-infection rate was 29% in TB patients and 21% in both community control and household contacts (p = 0.3) where Ascaris lumbricoides was the most prevalent parasite. In TB patients the seroprevalence of HIV was 47% (53/112). Eosinophilia and elevated IgE level were significantly associated with asymptomatic helminth infection. During TB treatment, the worm infection rate of HIV+/TB patients declined from 31% (10/32) at week 0 to 9% (3/32) at week 2 of TB treatment, whereas HIV−/TB patients showed no change from baseline to week 2, 29% (13/45) vs. 22.2% (10/45). This trend was stable at week 8 and 12 as well.

Conclusion

One third of smear positive TB patients were infected with helminths. Eosinophilia and elevated IgE level correlated with asymptomatic worm infection, indicating an effect on host immunity. The rate of worm infection declined during TB treatment in HIV+/TB co-infected patients whereas no decline was seen in HIV−/TB group.     

A spatially dynamic cohort of regulatory genes in the endomesodermal gene network of the sea urchin embryo

A gene regulatory network subcircuit comprising the otx, wnt8, and blimp1 genes accounts for a moving torus of gene expression that sweeps concentrically across the vegetal domain of the sea urchin embryo. Here we confirm by mutation the inputs into the blimp1cis-regulatory module predicted by network analysis. Its essential design feature is that it includes both activation and autorepression sites. The wnt8 gene is functionally linked into the subcircuit in that cells receiving this ligand generate a β-catenin/Tcf input required for blimp1 expression, while the wnt8 gene in turn requires a Blimp1 input. Their torus-like spatial expression patterns and gene regulatory analysis indicate that the genes even-skipped and hox11/13b are also entrained by this subcircuit. We verify the cis-regulatory inputs of even-skipped predicted by network analysis. These include activation by β-catenin/Tcf and Blimp1, repression within the torus by Hox11/13b, and repression outside the torus by Tcf in the absence of Wnt8 signal input. Thus even-skipped and hox11/13b, along with blimp1 and wnt8, are members of a cohort of torus genes with similar regulatory inputs and similar, though slightly out-of-phase, expression patterns, which reflect differences in cis-regulatory design.