Influence of temperature and carbon dioxide concentration on juvenile hormone titre and dependent parameters of adult worker honey bees (Apis mellifera L.)

It is known that juvenile hormone plays an important role in the regulation of labour division and of the different life spans, and that the microclimate of the bee hive is characterized by its high CO₂ concentration and its varying temperature depending on the presence of brood.We have investigated the influence of microclimates characteristic of breeding and broodless areas on the juvenile hormone titre in the haemolymph and whole body extracts, on the corpora allata in vitro activity, on the degradation of juvenile hormone and on the dry weight of the hypopharyngeal glands using bees of known ages. A microclimate of 35°C and 1.5% CO₂, as observed in the breeding area, induces a rapid and pronounced increase in the juvenile hormone titre. On the other hand, this titre remains low in bees kept at 27°C and 1.5% CO₂, a microclimate associated with broodless combs. Rates of juvenile hormone synthesis by corpora allata in vitro were found to be extremely low, even in the presence of farnesenic acid, and not related to the juvenile hormone titre. In vitro incubation of juvenile hormone in haemolymph revealed no degradation while injected juvenile hormone was found to be degraded and taken up by the gut at rates only weakly correlated with the juvenile hormone titre.We propose a hypothetical model for the regulation of the juvenile hormone titre as well as the course of labour division by the varying microclimates observed in the bee hive.     

X-ray crystallographic snapshots of reaction intermediates in pyruvate oxidase and transketolase illustrate common themes in thiamin catalysis

Thiamin diphosphate (ThDP)-dependent enzymes play pivotal roles in intermediary metabolism of virtually all organisms. Although extensive mechanistic work on cofactor models and various enzymes has served as a guide to understand general principles of catalysis, high-resolution structural information of reaction intermediates along the catalytic pathway was scarcely available until recently. Here, we review cryocrystallographic studies on the prototypical ThDP enzymes pyruvate oxidase and transketolase, which provided exciting insights into the chemical nature and structural features of several key intermediates and into the stereochemical course of substrate processing. The structures revealed a conserved (S)-configuration at the C2alpha stereocenter of the initially formed tetrahedral intermediate in the different enzymes with the scissile C2alpha–C2beta bond being directed perpendicular to the aromatic ring plane of the thiazolium portion of ThDP confirming the proposed maximum overlap mechanism. Elimination of the respective leaving groups (carbon dioxide, sugar phosphates) appears to be driven – amongst other factors such as stereoelectronic control – by strain relief as the C2–C2alpha bond, which connects C2 of ThDP with the carbonyl of the substrate, substantially deviates from planarity and relaxes to an in-plane conformation only after bond fission to give an enamine-type intermediate with considerable delocalization of the free electron pair onto the thiazolium ring. Except for the apparent flexibility of the cofactor itself, no major structural rearrangements are detectable indicating that the enzyme active centers are poised for catalysis. The structures also provide the basis for understanding the origins of substrate and reaction specificity.     

Stimulation of DNA synthesis in cultured mouse peritoneal macrophages after fusion injection of macrophage growth factor

Macrophage growth factor (MGF), when injected into cultivated mouse peritoneal macrophages by Sendai virus-fusion with loaded human erythrocyte ghosts, induced macrophage DNA synthesis within 40 h. DNA synthesis was observed in approx. 10% of the injected cells. Fusion products between macrophages and red cell ghosts were identified by co-injection of ¹²⁵I-labelled human serum albumin. These studies suggest that the mechanism of the physiological effect of MGF may depend on the endocytosis of at least part of the MGF molecule.     

Human Innate Mycobacterium tuberculosis–Reactive αβTCR+ Thymocytes

The control of Mycobacterium tuberculosis (Mtb) infection is heavily dependent on the adaptive Th1 cellular immune response. Paradoxically, optimal priming of the Th1 response requires activation of priming dendritic cells with Th1 cytokine IFN-γ. At present, the innate cellular mechanisms required for the generation of an optimal Th1 T cell response remain poorly characterized. We hypothesized that innate Mtb-reactive T cells provide an early source of IFN-γ to fully activate Mtb-exposed dendritic cells. Here, we report the identification of a novel population of Mtb-reactive CD4⁻ αβTCR⁺ innate thymocytes. These cells are present at high frequencies, respond to Mtb-infected cells by producing IFN-γ directly ex vivo, and display characteristics of effector memory T cells. This novel innate population of Mtb-reactive T cells will drive further investigation into the role of these cells in the containment of Mtb following infectious exposure. Furthermore, this is the first demonstration of a human innate pathogen-specific αβTCR⁺ T cell and is likely to inspire further investigation into innate T cells recognizing other important human pathogens.     

How accurately can we assess zoonotic risk?

Identifying the animal reservoirs from which zoonotic viruses will likely emerge is central to understanding the determinants of disease emergence. Accordingly, there has been an increase in studies attempting zoonotic “risk assessment.” Herein, we demonstrate that the virological data on which these analyses are conducted are incomplete, biased, and rapidly changing with ongoing virus discovery. Together, these shortcomings suggest that attempts to assess zoonotic risk using available virological data are likely to be inaccurate and largely only identify those host taxa that have been studied most extensively. We suggest that virus surveillance at the human–animal interface may be more productive.

Determining which organisms harbour viruses that could potentially infect humans is of great topical interest. This Essay demonstrates that the data on which such zoonotic risk assessments are conducted are incomplete, biased, and rapidly changing with ongoing virus discovery.     

Ectopic Expression of NCAM in Mouse Fibroblasts Stimulates Self-aggregation, and Promotes Integration into Primary Cerebellum Cell Aggregates

We have undertaken aggregation experiments using mouse LMTK-fibroblasts transfected with various isotypes of the neural cell adhesion molecule, NCAM. We found that selfaggregation of NCAM-positive fibroblasts is enhanced compared to control-transfected cells. The aggregation properties are partly dependent on the expressed NCAM isotype. Fibroblasts expressing a NCAM 140 isotype with exons a₃ and π were further tested in primary cerebellum cell re-aggregation experiments. While control-transfected fibroblasts could not be found in forming aggregates, fibroblasts ectopically expressing NCAM were integrated into neural cell aggregates. Time-lapse photography indicated that the nascent primary cell aggregates actively participated in the integration process by migration and attachment to nearby NCAM-positive fibroblasts.     

Zur formalen Genetik der Phosphoglucomutasen (EC: 2.7.5.1); Untersuchung von 366 Familien

Summary The polymorphism of PGM₁ has been investigated in a series of 366 families from Southwestern Germany with 676 children. The segregation of the children's phenotypes is in agreement with the formal genetic model.

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Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.