Sexual dimorphism in the visual system of flies: The divided brain of male Bibionidae (Diptera)

Summary The mapping of the compound eyes onto the visual neuropils and the cell types in the lamina and the lobula complex of Bibionidae (Diptera) were studied by means of extracellular cobalt injections and Golgi impregnations. Dorsal and ventral eyes in males map into separate dorsal-and ventral neuropils up to the level of the lobula complex. The dorsal-eye lamina is unilayered, while the ventral-eye lamina in males and the lamina in females are multilayered: layers A and C are invaded by en-passant terminals of long visual fibres, layer B by the terminals of short visual fibres. Long visual fibres have a short and a long terminal in the ventral medulla with terminal specialisations in three distinct layers. Only one type of receptor ending exists in the dorsal medulla, the terminal branches of which are restricted to one layer only. Arrays of contralateral neurones are found in the medial part of the dorsal lobula, which receives input from the zone of binocular vision of the ipsilateral dorsal eye, and in the posterior dorsal lobula and lobula plate. The dorsal lobula plate contains large tangential neurones, the dendritic arborisations of which are revealed by cobalt injection into the thoracic ganglia. The divided brain of male bibionids offers the opportunity to investigate separately the nervous systems involved in sex-specific visually guided flight behaviour and in general visually guided flight control.     

Mechanisms of cell differentiation: Affinity of a morphogenetic factor to DNA

Summary A morphogenetic factor which induces inTriturus gastrula ectoderm tissues which are derived from mesoderm and endoderm has been extracted from chicken and amphibian embryos. The factor which is protein in nature has been obtained from chicken embryos in a highly purified state.The biological activity of the chicken factor is partially inhibited when the factor is combined with chicken DNA or sonicated chicken DNA.When the 3H-labelled factor is combined with sonicated DNA and then centrifuged on a sucrose gradient the factor migrates in part with the DNA. This indicates that the factor is bound to DNA.The inferences from these results are discussed with regard to the possible mechanism of action of the factor and the molecular mechanism of differentiation.     

Kinetics of insulin internalization and processing in adipocytes: effects of insulin concentration

We have studied the effect of insulin concentration on the kinetics of insulin internalization and efflux in isolated rat adipocytes. To determine internalization rates adipocytes were incubated with 125I-insulin at 37 degrees C; and at frequent, early time points surface-bound and intracellular insulin were quantitated. Surface-bound and intracellular insulin were discriminated by the sensitivity of the former to rapid dissociation by a pH 3.0 buffer at 4 degrees C. From this data the endocytotic (internalization) rate constant (ke) was calculated for six insulin concentrations ranging from 0.3 to 100 ng/ml. Ke was found to decrease in an insulin concentration-dependent manner (P less than .001). Thus, values for ke were 0.121 +/- 0.006 min-1 versus 0.074 +/- 0.011 min-1 at 0.3 ng/ml and 100 ng/ml, respectively. The decrease in ke did not parallel insulin concentration-dependent changes in insulin receptor affinity indicating it was not the result of an inability of low affinity receptors to be internalized. The kinetics of insulin efflux were determined by loading various concentrations of 125I-insulin into the adipocyte interior, washing away surface-bound and extracellular insulin, and then monitoring the subsequent efflux of pre-loaded insulin into medium that contained the same concentration of insulin used in the loading step. The overall rate of efflux was independent of insulin concentration. In summary, these results show that at high insulin concentrations the efficiency of insulin internalization is impaired. In contrast, the rate of insulin efflux is unaffected.     

Comparative study of methodologies for obtaining β-glucosidase immobilized on dextran-modified silica

In this study, two procedures for the immobilization of β-glucosidase on silica are compared. The first approach comprises a preliminary stabilization of β-glucosidase by coupling with dextran dialdehyde and subsequent immobilization of the obtained β-glucosidase dextran dialdehyde with aminopropylsilica. In the second approach, β-glucosidase is immobilized on silica modified with a dextran-dialdehyde coating. Enzyme immobilized via coupling with dextran dialdehyde and subsequent attachment with aminopropylsilica show a remarkably enhanced thermostability. Enzyme immobilized by the alternative approach demonstrated an inferior thermoresistance. The difference in behavior of the immobilized enzyme obtained via these two methods can be explained considering the number of links between the enzyme and carrier. Enzyme immobilized on dextran dialdehydecoated silica is fixed via a limited number of links. On the other hand, with soluble β-glucosidase-dextran conjugates, the enzyme configuration is already stabilized via a high number of links with the dextran backbone. It is clear from this study that the sequence of reactions in immobilizing enzymes on silica support via a dextran-dialdehyde linker has a significant effect on the final properties.     

Plant regeneration from ryegrass ovules cultivated on endosperm-derived feeder cells

An efficient method for the regeneration of zygote-derived plants via ovule culture is desirable for overcoming postzygotic cross incompatibility as well as for the development of certain methods for genetic manipulation. High-frequency plantlet regeneration from ovules of Italian ryegrass (Lolium multiflorum Lam.) and a hybrid Italian/perennial ryegrass excised 1 to 4 days post pollination was obtained by culture on endosperm-derived feeder cells. Ovules excised 3 or 4 days after anthesis and grown on feeder cells generally regenerated about twice as frequently as ovules grown directly on nutrient medium. In one of the genotypes tested, ovules excised 1, 2 and 3 days post pollination developed into plantlets at percentages of 38.1, 52.0 and 52.8, respectively, using the feeder-cell system.Abbreviations EM endosperm multiplications - OC ovule culture - R regeneration - 2,4-d 2,4-dichlorophenoxyacetic acid     

In vitro susceptibility ofPityrosporum ovale (Malassezia furfur) to human androgenic steroids

Cells ofPityrosporum ovale that colonize human pilosebaceous units are constantly exposed to cutaneous androgenic steroids. The aim of our study was to find out whetherP. ovale is susceptible to these hormones. Three strains ofP. ovale were grown in vitro in the presence of various concentrations oftestosterone, dehydroepiandrosterone, androstenedione, androstanedione, 5--dihydrotestosterone andprogesterone (10, 100, and 1000 µg/ml; agar dilution assays). In addition, three strains ofCandida albicans were also exposed to equal concentrations of the same androgens. As a result, allP. ovale strains were suppressed by 1000 µg/mlandrostenedione, which was the strongest inhibitor. The other androgenic steroids also significantly reducedP. ovale growth at different concentrations, depending on the hormone used and the strain tested.Progesterone was inhibitory at the highest concentration for oneP. ovale strain only.Candida albicans was not affected by any of the androgens. These findings demonstrate an in vitro susceptibility ofP. ovale to high concentrations of human androgenic steroids. A relevance of this interaction for the in vivo fungus-host relation is not apparent.     

An outer membrane protein (OmpA) of Escherichia coli can be translocated across the cytoplasmic membrane of Bacillus subtllis

The translocation of secretory proteins derived from a Gram-positive (Staphylococcus hyicus prolipase) or a Gram-negative (Escherichia coli pre-OmpA protein) bacterium across the cytoplasmic membrane was studied in E. coli and Bacillus subtilis. in both microorganisms, the prolipase was found to be secreted across the plasma membrane when either the pre-prolipase signal peptide (38 amino acids in length) or the pre-OmpA signal peptide (21 amino acids in length) was used. Expression of the gene encoding the authentic pre-OmpA protein in B. subtilis resulted in the translocation of mature OmpA protein across the plasma membrane. Processing of the OmpA precursor in B. subtilis required the electrochemical potential and was sensitive to sodium azide, suggesting that the B. subtilis SecA homologue was involved in the translocation process. The mature OmpA protein, which was most likely present in an aggregated state, was fully accessible to proteases in protoplasted cells. Therefore, our results clearly demonstrate that an outer membrane protein can be secreted by B. subtilis, supporting the notion that the basic mechanism of protein translocation is highly conserved in Gram-positive and Gram-negative bacteria.