A re-examination of host relations in the Aphelinidae (Hymenoptera: Ghalcidoidea)

Host relations among the Aphelinidae (Hymenoptera: Chalcidoidea) are highly intriguing from an evolutionary view. Females are usually primary endoparasitoids of whiteflies or scale insects, whereas the development of the male is different and has been used for classification. In heteronomous hyperparasitoids (adelphoparasitoids or autoparasitoids) the male develops as a hyperparasitoid of conspecific females or other endoparasitoid species. We review the consequences of this mode of development which is unique because decisions concerning host selection are inextricably linked with progeny sex ratio. Autoparasitoid field sex ratios can fluctuate dramatically concurrent with changes in the relative availability of male and female hosts. A recent adaptive explanation for these sex ratios involves understanding the reproductive constraints acting on heteronomous parasitoids. Host relations in these parasitoids can show a degree of plasticity. We argue that in many instances autoparasitism may be facultative in nature and should not be used for classification. Heterotrophic parasitism, wherein the male develops as a primary parasitoid of lepidopterous eggs, has been poorly understood in the past due to uncertainties in reports of the biology and taxonomy of heterotrophic parasitoids. The host relations of this group are clarified.     

Mixed Infection with cagA-Positive and cagA-Negative Strains of Helicobacter pylori

Background Helicobacter pylori infection has been implicated strongly in the pathogenesis of gastritis, peptic ulcer disease, gastric adenocarcinoma, and gastric lymphoma, but the reasons for these widely different clinical outcomes are unknown. The aim of this study was to determine whether these differences could be due in part to mixed infection in the same individual, with bacteria having differences in pathogenic factors associated with ulcers.
Materials and Methods. The cagA gene of H. pylori was used to test for mixed infection because it is present in only some strains, and its presence has been associated with ulcers. Polymerase chain reaction (PCR) assays for the cagA gene were applied to H. pylori culture isolates and endoscopic gastric aspirates. Individual bacterial clones were tested for genetic similarity by random primer amplification and restriction endonuclease digestion of urease gene PCR products.
Results. The majority of H. pylori -positive patients had strongly cagA -positive culture isolates and endoscopic samples (62.5% and 69.6%, respectively). However, many of these patients had evidence of mixed infection with cagA negative and cagA positive strais in cultures isolates and endoscopic samples (25% and 17.4%, respectively). Mixed infection was found to be due to genetically unrelated strains in two patients in whom genetic analysis was performed.
Conclusion. Mixed infection with differences in substrain pathogenic factors might occur in H. pylori infection and might contribute to differences in clinical outcome.     

Modulation of Intracellular Cyclic AMP Levels by Different Human Dopamine D4 Receptor Variants

Abstract: To investigate whether polymorphic forms of the human dopamine D4 receptor have different functional characteristics, we have stably expressed cDNAs of the D4.2, D4.4, and D4.7 isoforms in several cell lines. Chinese hamster ovary CHO-K1 cell lines expressing D4 receptor variants displayed pharmacological profiles that were in close agreement with previous data from transiently expressed D4 receptors in COS-7 cells. Dopamine stimulation of the D4 receptors resulted in a concentration-dependent inhibition of the forskolin-stimulated cyclic AMP (cAMP) levels. The potency of dopamine to inhibit cAMP formation was about twofold reduced for D4.7 (EC₅₀ of ∼37 n M ) compared with the D4.2 and D4.4 variants (EC₅₀ of ∼16 n M ). Antagonists block the dopamine-mediated inhibition of cAMP formation with a rank order of potency of emonapride > haloperidol = clozapine ≫ raclopride. There was no obvious correlation between the efficacy of inhibition of forskolin-stimulated cAMP levels and the D4 subtypes. Dopamine could completely reverse prostaglandin E₂-stimulated cAMP levels for all three D4 receptor variants. Deletion of the repeat sequence does not affect functional activity of the receptor. The data presented indicate that the polymorphic repeat sequence causes only small changes in the ability of the D4 receptor to block cAMP production in CHO cells.     

Genetic regulation of gibberellin deactivation in Pisum

The regulation of gibberellin (GA) deactivation was examined using the sin (slender) mutation in the garden pea (Pisum sativum L.). This mutation blocks the deactivation of GA₂₀, the precursor of the bioactive GA₁. Firstly, crosses were made to combine sin with the GA biosynthesis mutations na, lhⁱ and le-3. The combination sin na produced a novel phenotype, with long (‘slender’) basal internodes and extremely short (‘nana’) upper internodes. In contrast, the double mutant sin lhⁱ was phenotypically dwarf. The mutation sin causes an accumulation of GA₂₀ in maturing seeds, and this was unaffected by na, since the na mutation is not expressed in seeds. In contrast, lhⁱ seeds did not accumulate GA₂₀, since lhⁱ imposes an early block on GA biosynthesis. Secondly, the effects of sin on several steps in GA deactivation were investigated. In maturing seeds, the mutation sin blocks two steps in GA₂₀ metabolism, namely, GA₂₀ to GA₂₉, and GA₂₉ to GA₂₉-catabolite. In the vegetative plant, on the other hand, sin blocked the step GA₂₀ to GA₂₉, but not GA₂₉ to GA₂₉-catabolite; the steps GA₂₀ to GA₈₁ and GA₂₀ to GA₁ were also not impaired in this mutant. It is clear that the effects of sin, like those of na, are strongly organ-specific. The presence of separate enzymes for the steps GA₂₀ to GA₂₉ and GA₂₉ to GA₂₉-catabolite was suggested by the observation that GA₈ inhibited the latter step, but not the former, and by the inability of GA₂₀ and GA₂₉ to inhibit each other's metabolism. It is suggested that the Sin gene may be a regulatory gene controlling the expression of two structural genes involved in GA deactivation.     

Molecular genetic analysis of the response of three soil microbial communities to the application of 2, 4-D

The responses of three different soil microbial communities to the experimental application of 2, 4-dichlorophenoxyacetic acid (2, 4-D) were evaluated with a variety of molecular genetic techniques. Two of the three soil communities had histories of prior direct exposure to 2, 4-D, and one had no prior direct application of any herbicide. Dominant 2, 4-D degrading strains isolated from these soils the previous year were screened for hybridization with three catabolic genes (tfdA, tfdAII, and tfdB) cloned from the well-studied 2, 4-D degradative plasmid, pJP4, revealing varying degrees of similarity with the three genes. Hybridization of total community DNA from the three soils with the tfd gene probes also indicated that pJP4-like tfd genes were not harboured by a significant percentage of the community. Community level response was evaluated by the comparison of different treatments by Random Amplified Polymorphic DNA (RAPD) fingerprints and by community DNA cross-hybridization. No differences between treatments within the same soil were detected in any of the RAPD fingerprints generated with 17 primers. Community DNA cross-hybridization also indicated that the application of 2, 4-D at the applied rates did not quantitatively affect the structure of the soil microbial communities present in the three soils during the time-frame studied.     

Seasonal variation in thyrotropin-releasing hormone (TRH) content of different brain regions and the pineal in the mammalian hibernator, Citellus lateralis

We have measured the endogenous TRH concentration in the pineal and 9 brain regions of a seasonal hibernator, the golden-mantled ground squirrel, during euthermia and hibernation in order to investigate the possibility that changes in TRH concentration might occur in association with naturally-occurring changes in CNS-mediated physiological and behavioral processes. Regional TRH content was assessed by radioimmunoassay in adult animals that were killed during euthermia in the mid-portion of each season and during hibernation in mid-winter. No significant changes in TRH concentration related to season or to hibernation versus euthermic state were noted in the hippocampus, brainstem, or cerebellum. In the olfactory bulb, preoptic area, and pineal, seasonal variation within euthermic groups was evident. During hibernation, statistically significant decreases in TRH content occurred in the forebrain, olfactory bulb, hypothalamus, septum, preoptic area, and midbrain. Significant fluctuations during hibernation were also observed in the pineal. In this structure, TRH concentration varied in relation to the phase of the hibernation bout. TRH content in the last quarter of the bout was three times greater when compared to values observed in the first quarter of the bout. These results suggest that TRH may be involved in the control processes attributed to these regions and support a role for TRH in the neural control of hibernation.     

Characterization of an antigenically related family of cell-type specific proteins implicated in slug migration in Dictyostelium discoideum

The monoclonal antibody MUD50 recognizes a group of developmentally regulated proteins, which are almost exclusively expressed by prespore cells in developing aggregates of Dictyostelium discoideum. Some of these antigens are integrally associated with the cell membrane, as assessed by physical and detergent-fractionation procedures. The MUD50-reactive proteins are glycosylated and some are phosphorylated. Post-translational modification is the common antigenic feature that is recognized by the MUD50 antibody in these cell-type-specific proteins. A glycosylation-defective mutant, DL118, (modB) does not express the MUD50 epitope, but does express the MUD52 epitope, which is found on a different group of glycoproteins. Therefore, we conclude that MUD50 recognizes a particular carbohydrate epitope on a restricted group of proteins. These proteins are structurally diverse, but are apparently involved in the maintenance of structure and movement of the multicellular D. discoideum slug.