Chemical labels differ between two closely related shearwater taxa

Chemical signals may be the basis of interspecific recognition and speciation in many animals. To test whether a chemical label allowing recognition between closely related species exists in seabirds, we investigated two closely related taxa breeding sympatrically at some localities: Cory's and Scopoli's shearwaters. Procellariiform seabirds are ideal for this study because they have a well‐developed olfactory system and unequalled associated capabilities among birds. We analysed and compared the relative volatile compounds composition of the uropygial gland secretions of Cory's and Scopoli's shearwaters. As the volatile components from uropygial secretions might also provide some critical eco‐chemical information about population origin and sex, we also examined variations in the volatile compounds between populations and sexes in Cory's shearwater. The chemical data were obtained using gas chromatography–mass spectrometry techniques looking for the presence of these three particular labels: species, population and gender. We found diagnostic differences in uropygial secretions between the two species of shearwaters and smaller but significant variation between populations of Cory's shearwater in the Atlantic. No significant differences were observed between males and females. Individuals might thus use the chemical variation between species to recognize and mate with conspecifics, especially at localities where both species breed sympatrically. Geographical variation in chemical composition of uropygial secretions suggests that selective forces might vary according to locality, and might represent a key in the species recognition. Further behavioural bioassays are needed to determine whether or not these species labels are signals allowing reproductive isolation between these two taxa. Finally, one of the aims of our study was to test easier methods than freezing for storing uropygial gland secretions in the field. We describe here a new possibility for the storage of uropygial secretion samples at ambient temperature in the field, providing an alternative, simple protocol for the sampling of avian chemosignals.     

Stalked Bacteria: Properties of Deoxriybonucleic Acid Bacteriophage φCbK

The Caulobacter crescentus bacteriophage phiCbK was studied with respect to the physical and chemical properties of both the phage and its deoxyribonucleic acid (DNA). Electron micrographs reveal the phage to be among the largest DNA bacteriophages reported, with head dimensions of 64 by 195 nm and a flexible tail 275 nm in length. The phage is composed of 57% DNA. This DNA is double-stranded as indicated by (i) the sharp increase in extinction coefficient over a narrow range of temperature increase, (ii) an increase in density in CsCl upon thermal denaturation, and (iii) the equivalence of guanine and cytosine as well as adenine and thymine, determined by chemical analysis. phiCbK DNA cosediments with Escherichia coli phage T2 DNA and has therefore been assigned an S(20,w) value of 63.5S. The size of the phage and its DNA and the percentage of DNA indicate that the phiCbK phage head is relatively loosely packed. The properties of the DNA from bacteriophage phiCbK are similar to those of host C. crescentus DNA with respect to buoyant density, thermal transition point, and guanine plus cytosine content.     

Deoxyribonucleic Acid-Dependent Ribonucleic Acid Polymerase of Caulobacter crescentus

Deoxyribonucleic acid-dependent ribonucleic acid (RNA) polymerase (EC 2.7.7.6) was purified from the dimorphic bacterium Caulobacter crescentus at three stages in development. Enzyme from pure populations of stalked cells, as well as populations enriched in swarmer and predivisional cells, appeared identical in subunit structure and template requirements. The molecular weights of the enzyme subunits were 165,000, 155,000, 101,000, and 44,000, respectively. By analogy with RNA polymerase from other bacterial sources, they are considered to be components of the C. crescentus holoenzyme, beta', beta, sigma, and alpha, respectively. The C. crescentus enzyme appeared similar to the Pseudomonas aeruginosa enzyme and unlike the Escherichia coli enzyme with respect to subunit molecular weights and failure to separate into core and sigma components upon phosphocellulose chromatography. In addition, the effects of ionic strength on the time course of polymerization varied both with the sources of bacterial polymerase and bacteriophage DNA.     

Comparative Pathogenicity of Actinomyces naeslundii and Actinomyces israelii

Typical actinomycosis has been produced in mice following single intraperitoneal injections of saline suspensions of Actinomyces israelii and A. naeslundii. A. israelii produced infections in 95.8% of the animals inoculated. A. naeslundii, generally considered to be a saprophytic organism, produced lesions in 89.7% of the inoculated animals. The finding that A. naeslundii produced lesions in mice similar to those produced by A. israelii suggests that A. naeslundii has similar pathogenic potential for man. The isolation of A. naeslundii from suppurative lesions of man also supports this conclusion.     

The effect of variable magnesium intake on potential factors influencing endurance capacity

Rats fed a magnesium (MG) deficient diet have a lower endurance capacity than rats fed Mg adequate diets. The current study evaluates the effects of marginal, moderate, and severe Mg deficiencies on physiological and biochemical changes that may contribute to the reduced endurance capacity of Mg deficient rats. Variable levels of dietary Mg (400, 200, 100, 50 μg/g) were fed for 23 d to 5-wk-old male Osborne-Mendel rats. Indirect blood pressure and heart rate were measured during dietary treatment. Forty-eight hours after an endurance test, rats were killed and sampled for plasma glucose, insulin, and triglyceride levels. Organ weights, mineral and trace element concentrations, and carcass composition were determined. Blood pressure was lower in rats fed 50 and 100 ppm Mg during the first half of the study than in controls (400 ppm Mg). There were no significant differences in blood pressure among groups at the end of the study. Heart rate was not affected by dietary Mg intake. Plasma insulin was lowered by decreasing dietary Mg; however, plasma glucose and triglyceride concentrations were not affected by dietary Mg intake. Rats fed 100 and 50 ppm Mg diets had significantly higher calcium concentrations in plasma and gastrocnemius muscle than controls. Dietary Mg variably affected tissue trace element (iron, zinc, copper, and manganese) concentrations but did not affect Mg concentrations in any organ studied. Body composition was significantly altered by dietary Mg intake. In conclusion, variable Mg intake differentially affects the parameters evaluated. Thus, the decreased endurance capacity of the Mg deficient rat is apparently not the result of a single biochemical lesion but is likely to be multifactorial.     

Three-dimensional reconstruction of the flagellar hook from Caulobacter crescentus

The structure of the bacterial flagellar hook produced by a mutant of Caulobacter crescentus was studied by electron microscopy, optical diffraction, and digital image processing techniques. The helical surface lattice of the hook is defined by a single, right-handed genetic helix having a pitch of about 23 Å, an axial rise per subunit of 4 Å and an azimuthal angle between subunits of 64·5 °. The lattice is also characterized by intersecting families of 5-start, 6-start and long-pitch 11-start helices. These helical parameters are remarkably similar to those determined for the flagellar filaments from several strains of gram-negative bacteria. The technique of three-dimensional image reconstruction (DeRosier & Klug, 1968) was applied to nine of the better preserved specimens and the diffraction data from five of these were correlated and averaged and used to generate an average three-dimensional model of the hook. The pattern of density modulations in the three-dimensional model is suggestive of an elongated, curved shape for the hook subunit (100 Å × 25 Å × 25 Å). The subunits are situated in the lattice of the polyhook such that their long axes are tilted about 45 ° with respect to the hook axis. The subunits appear to make contact with each other along the 6-start helices at a radius of 80 Å and also along the 11-start helices at a radius of 65 Å. Few structural features are revealed at radii between 15 å and 45 Å and, therefore, we are unable to decide to what extent the hook subunits extend into this region. The most striking characteristic of the model is the presence of deep, broad, continuous 6-start helical grooves extending from an inner radius of about 50 Å to the perimeter of the particle at 105 Å radius. Normal hooks usually appear curved in electron micrographs and sometimes so are the mutant hooks; the prominent 6-start grooves appear to allow for bending with minimal distortion of matter in the outer regions of the hook. A round stain-filled channel about 25 Å in diameter runs down the center of the polyhook. Such a channel supports a model for flagellar assembly in which flagellin subunits travel through the interior of the flagellum to the growing distal end of the filament.     

Eosinophils preserve parasitic nematode larvae by regulating local immunity

Eosinophils play important roles in regulation of cellular responses under conditions of homeostasis or infection. Intestinal infection with the parasitic nematode, Trichinella spiralis, induces a pronounced eosinophilia that coincides with establishment of larval stages in skeletal muscle. We have shown previously that in mouse strains in which the eosinophil lineage is ablated, large numbers of T. spiralis larvae are killed by NO, implicating the eosinophil as an immune regulator. In this report, we show that parasite death in eosinophil-ablated mice correlates with reduced recruitment of IL-4(+) T cells and enhanced recruitment of inducible NO synthase (iNOS)-producing neutrophils to infected muscle, as well as increased iNOS in local F4/80(+)CD11b(+)Ly6C(+) macrophages. Actively growing T. spiralis larvae were susceptible to killing by NO in vitro, whereas mature larvae were highly resistant. Growth of larvae was impaired in eosinophil-ablated mice, potentially extending the period of susceptibility to the effects of NO and enhancing parasite clearance. Transfer of eosinophils into eosinophil-ablated ΔdblGATA mice restored larval growth and survival. Regulation of immunity was not dependent upon eosinophil peroxidase or major basic protein 1 and did not correlate with activity of the IDO pathway. Our results suggest that eosinophils support parasite growth and survival by promoting accumulation of Th2 cells and preventing induction of iNOS in macrophages and neutrophils. These findings begin to define the cellular interactions that occur at an extraintestinal site of nematode infection in which the eosinophil functions as a pivotal regulator of immunity.     

Humanized beta-thalassemia mouse model containing the common IVSI-110 splicing mutation

Splicing mutations are common causes of beta-thalassemia. Some splicing mutations permit normal splicing as well as aberrant splicing, which can give a reduced level of normal beta-globin synthesis causing mild disease (thalassemia intermedia). For other mutations, normal splicing is reduced to low levels, and patients are transfusion-dependent when homozygous for the disease. The development of therapies for beta-thalassemia will require suitable mouse models for preclinical studies. In this study, we report the generation of a humanized mouse model carrying the common IVSI-110 splicing mutation on a BAC including the human beta-globin ((hu)beta-globin) locus. We examined heterozygous murine beta-globin knock-out mice ((mu)beta(th-3/+)) carrying either the IVSI-110 or the normal (hu)beta-globin locus. Our results show a 90% decrease in (hu)beta-globin chain synthesis in the IVSI-110 mouse model compared with the mouse model carrying the normal (hu)beta-globin locus. This notable difference is attributed to aberrant splicing. The humanized IVSI-110 mouse model accurately recapitulates the splicing defect found in comparable beta-thalassemia patients. This mouse model is available as a platform for testing strategies for the restoration of normal splicing.     

Site-specific 3D imaging of cells and tissues with a dual beam microscope

Current approaches to 3D imaging at subcellular resolution using confocal microscopy and electron tomography, while powerful, are limited to relatively thin and transparent specimens. Here we report on the use of a new generation of dual beam electron microscopes capable of site-specific imaging of the interior of cellular and tissue specimens at spatial resolutions about an order of magnitude better than those currently achieved with optical microscopy. The principle of imaging is based on using a focused ion beam to create a cut at a designated site in the specimen, followed by viewing the newly generated surface with a scanning electron beam. Iteration of these two steps several times thus results in the generation of a series of surface maps of the specimen at regularly spaced intervals, which can be converted into a three-dimensional map of the specimen. We have explored the potential of this sequential "slice-and-view" strategy for site-specific 3D imaging of frozen yeast cells and tumor tissue, and establish that this approach can identify the locations of intracellular features such as the 100 nm-wide yeast nuclear pore complex. We also show that 200 nm thick sections can be generated in situ by "milling" of resin-embedded specimens using the ion beam, providing a valuable alternative to manual sectioning of cells and tissues using an ultramicrotome. Our results demonstrate that dual beam imaging is a powerful new tool for cellular and subcellular imaging in 3D for both basic biomedical and clinical applications.