Big flies, small repeats: the "Thr-Gly" region of the period gene in Diptera

The region of the clock gene period (per) that encodes a repetitive tract of threonine-glycine (Thr-Gly) pairs has been compared between Dipteran species both within and outside the Drosophilidae. All the non- Drosophilidae sequences in this region are short and present a remarkably stable picture compared to the Drosophilidae, in which the region is much larger and extremely variable, both in size and composition. The accelerated evolution in the repetitive region of the Drosophilidae appears to be mainly due to an expansion of two ancestral repeats, one encoding a Thr-Gly dipeptide and the other a pentapeptide rich in serine, glycine, and asparagine or threonine. In some drosophilids the expansion involves a duplication of the pentapeptide sequence, but in Drosophila pseudoobscura both the dipeptide and the pentapeptide repeats are present in larger numbers. In the nondrosophilids, however, the pentapeptide sequence is represented by one copy and the dipeptide by two copies. These observations fulfill some of the predictions of recent theoretical models that have simulated the evolution of repetitive sequences.      

Prostaglandin F2 alpha increases responsiveness of pulmonary airways in dogs

We studied the effect of prostaglandin F2 alpha (PGF2 alpha) on the responsiveness of pulmonary airways in dogs. Airway responsiveness was assessed by determining the bronchoconstrictor response to increasing concentrations of acetylcholine aerosol delivered to the airways. In each of five dogs, we determined responsiveness during treatment with physiologic saline, histamine, or PGF2 alpha aerosols. The doses of histamine and PGF2 alpha were determined by establishing the largest dose of each which could be given to the dog without causing bronchoconstriction (subthreshold doses). We found that airway responsiveness was not significantly different during histamine treatment than after saline, however, responsiveness increased during treatment with PGF2 alpha. In addition, the hyperresponsiveness induced by PGF2 alpha was prevented by pretreatment with the ganglion blocking drug hexamethonium (5 mg/kg given intravenously). The results show that PGF2 alpha specifically increases the responsiveness of pulmonary airways in doses that do not cause bronchoconstriction, and suggest that the hyperresponsiveness involves a neural mechanism such as increased responsiveness of airway sensory nerves.     

Eosinophilopoiesis in a murine model of allergic airway eosinophilia: involvement of bone marrow IL-5 and IL-5 receptor alpha

The airway inflammation in asthma is dominated by eosinophils. The aim of this study was to elucidate the contribution of newly produced eosinophils in airway allergic inflammation and to determine mechanisms of any enhanced eosinophilopoiesis. OVA-sensitized BALB/c mice were repeatedly exposed to allergen via airway route. Newly produced cells were identified using a thymidine analog, 5-bromo-2'-deoxyuridine, which is incorporated into DNA during mitosis. Identification of IL-5-producing cells in the bone marrow was performed using FACS. Bone marrow CD3+ cells were enriched to evaluate IL-5-protein release in vitro. Anti-IL-5-treatment (TRFK-5) was given either systemically or directly to the airways. IL-5R-bearing cells were localized by immunocytochemistry. Repeated airway allergen exposure caused prominent airway eosinophilia after three to five exposures, and increased the number of immature eosinophils in the bone marrow. Up to 78% of bronchoalveolar lavage (BAL) granulocytes were 5-bromo-2'-deoxyuridine positive. After three allergen exposures, both CD3+ and non-CD3 cells acquired from the bone marrow expressed and released IL-5-protein. Anti-IL-5 given i.p. inhibited both bone marrow and airway eosinophilia. Intranasal administration of anti-IL-5 also reduced BAL eosinophilia, partly via local effects in the airways. Bone marrow cells, but not BAL eosinophils, displayed stainable amounts of the IL-5R alpha-chain. We conclude that the bone marrow is activated by airway allergen exposure, and that newly produced eosinophils contribute to a substantial degree to the airway eosinophilia induced by allergen. Airway allergen exposure increases the number of cells expressing IL-5-protein in the bone marrow. The bone marrow, as well as the lung, are possible targets for anti-IL-5-treatment.     

Activation of p38 MAP kinase by asbestos in rat mesothelial cells is mediated by oxidative stress

Asbestos fibers are biopersistent particles that are capable of stimulating chronic inflammatory responses in the pleura of exposed individuals. Exposure of pleural mesothelial cells, the progenitor cell of malignant mesothelioma, to asbestos induces an array of cellular responses. The present studies investigated whether the p38 mitogen-activated protein kinase cascade was induced under asbestos-exposed conditions. p38 plays a vital role in the response to stressful stimuli and enables the cell to enter an inflammatory state characterized by cytokine production. Western blot and in vitro kinase assays showed increases in dual phosphorylation and actual activity of p38 after exposure to fibrous and nonfibrous (milled) crocidolite; in contrast, polystyrene beads and iron (III) oxide had no such effects. In common with other asbestos-induced events, this was shown to be an oxidative stress-sensitive effect, inasmuch as preincubation with N-acetyl-L-cysteine or -tocopherol (vitamin E) ameliorated the effect. The present studies show that p38 activity is important for crocidolite-induced activator protein-1 DNA binding, inasmuch as an inhibitor of p38, SB-203580, reduced this activity. Crocidolite-induced cytotoxicity was also reduced with SB-203580, indicating a role for p38 in asbestos-mediated cell death. Our studies suggest that p38 activity could be a crucial factor in the chronic immune response elicited by asbestos and may represent a target for future pharmacological intervention.     

Retinol-binding protein-deficient mice: biochemical basis for impaired vision

We reported previously that mice lacking plasma retinol-binding protein (RBP) are phenotypically normal except that they display impaired vision at the time of weaning. This visual defect is associated with greatly diminished eyecup levels of retinaldehyde and is reversible if the mutants are maintained for several months on a vitamin A-sufficient diet. Here we provide a biochemical basis for the visual phenotype of RBP-deficient mice. This phenotype does not result from inadequate milk total retinol levels since these are not different for RBP-deficient and wild-type mice. The eye, unlike all other tissues that have been examined, takes up dietary retinol very poorly. Moreover, compared to other tissues, the eye displays a strong preference for retinol uptake when retinol is delivered bound to RBP. The poor uptake of dietary retinol by the eye coupled with its marked ability to take up retinol from RBP, we propose, provides a basis for the impaired vision observed in weanling RBP-deficient mice. Further study of the mutants suggests that the impaired vision is reversible because the eyes of mutant mice slowly acquire sufficient retinol from the low levels of retinol present in their circulation either bound to albumin or present in lipoprotein fractions. Thus, the eye is unlike other tissues in the body in that it shows a very marked preference for acquiring retinol needed to support vision from the retinol-RBP complex and is unable to meet adequately its retinol need through uptake of recently absorbed dietary retinol. This provides an explanation for the impaired vision phenotype of RBP-deficient mice.     

Rapid inactivation of the Escherichia coli Kdp K+ uptake system by high potassium concentrations

The Kdp K+ uptake system of Escherichia coli is induced by limitation for K+ and/or high osmolarity. In the present study, the regulation of the activity of the Kdp system has been investigated in E. coli mutants possessing only the Kdp system as the mechanism of K+ accumulation. Cells grown in the presence of low K+ (0.1-1 mM) exhibit normal growth. However, growth inhibition results from exposure of cells to moderate levels of external K+ (> 5 mM). Measurement of the cytoplasmic pH, of K+ pools and of transport via the Kdp system demonstrates that the Kdp system is rapidly and irreversibly inhibited by moderate external K+. Concentrations of K+ greater than 2 mM are sufficient to cause inhibition of Kdp. At pH 6, this results in rapid lowering of the capacity for pH homeostasis, but at pH 7 the intracellular pH is unaffected. Parallel analysis of the expression of the Kdp system in a Kdp+/kdpFABC-lacZ strain shows that levels of K+ that are sufficient to inhibit Kdp activity also repress expression. As a result, growth inhibition of strains solely possessing Kdp arises jointly from inhibition of Kdp activity and repression of Kdp gene expression. These data identify an important aspect of the regulation of potassium transport via the Kdp system and also provide support for a model of regulation of Kdp expression via at least two mechanisms: sensing of both turgor and external K+ concentration.     

Taurine-induced attenuation of MPP+ neurotoxicity in vitro: a possible role for the GABA(A) subclass of GABA receptors

Taurine is a sulphur-containing beta-amino acid found in high (millimolar) concentrations in excitable tissues such as brain and heart. Its suggested roles include osmoregulator, thermoregulator, neuromodulator, and potential neurotransmitter. This amino acid has also been shown to be released in large concentrations during ischaemia and excitotoxin-induced neuronal damage. Here we report a protective effect of taurine against MPP(+)-induced neurotoxicity in coronal slices from rat brain. Significant protective effects were observed at taurine concentrations of 20 and 1 mM, suggesting a potential role for taurine in cases of neuronal insult. Studies with the synthetic taurine analogues taurine phosphonate, guanidinoethane sulphonate, and trimethyltaurine suggested the observed effect to be mediated via an extracellular mechanism. The use of GABA receptor ligands muscimol and bicuculline indicated the effect to be mediated through activation of GABA(A) receptors.