Insect Stage-Specific Receptor Adenylate Cyclases Are Localized to Distinct Subdomains of the Trypanosoma brucei Flagellar Membrane

Increasing evidence indicates that the Trypanosoma brucei flagellum (synonymous with cilium) plays important roles in host-parasite interactions. Several studies have identified virulence factors and signaling proteins in the flagellar membrane of bloodstream-stage T. brucei, but less is known about flagellar membrane proteins in procyclic, insect-stage parasites. Here we report on the identification of several receptor-type flagellar adenylate cyclases (ACs) that are specifically upregulated in procyclic T. brucei parasites. Identification of insect stage-specific ACs is novel, as previously studied ACs were constitutively expressed or confined to bloodstream-stage parasites. We show that procyclic stage-specific ACs are glycosylated, surface-exposed proteins that dimerize and possess catalytic activity. We used gene-specific tags to examine the distribution of individual AC isoforms. All ACs examined localized to the flagellum. Notably, however, while some ACs were distributed along the length of the flagellum, others specifically localized to the flagellum tip. These are the first transmembrane domain proteins to be localized specifically at the flagellum tip in T. brucei, emphasizing that the flagellum membrane is organized into specific subdomains. Deletion analysis reveals that C-terminal sequences are critical for targeting ACs to the flagellum, and sequence comparisons suggest that differential subflagellar localization might be specified by isoform-specific C termini. Our combined results suggest insect stage-specific roles for a subset of flagellar adenylate cyclases and support a microdomain model for flagellar cyclic AMP (cAMP) signaling in T. brucei. In this model, cAMP production is compartmentalized through differential localization of individual ACs, thereby allowing diverse cellular responses to be controlled by a common signaling molecule.     

Syntheses and pharmacological characterization of novel thiazole derivatives as potential mGluR5 PET ligands

Four novel thiazole containing ABP688 derivatives were synthesized and evaluated for their binding affinity towards the metabotropic glutamate receptor subtype 5 (mGluR5). (E)-3-((2-(Fluoromethyl)thiazol-4-yl)ethynyl)cyclohex-2-enone O-methyl oxime (FTECMO), the ligand with the highest binding affinity (K_i = 5.5 ± 1.1 nM), was labeled with fluorine-18. [¹⁸F]-FTECMO displayed optimal lipophilicity (log D_pH7.4 = 1.6 ± 0.2) and high stability in rat and human plasma as well as sufficient stability in rat liver microsomes. In vitro autoradiography with [¹⁸F]-FTECMO revealed a heterogeneous and displaceable binding in mGluR5-rich brain regions. PET imaging with [¹⁸F]-FTECMO in Wistar rats, however, showed low brain uptake. Uptake of radioactivity into the skull was observed suggesting in vivo defluorination. Thus, although [¹⁸F]-FTECMO is an excellent ligand for the detection of mGluR5 in vitro, its in vivo characteristics are not optimal for the imaging of mGluR5 in rats in vivo.     

The discovery and unique pharmacological profile of RO4938581 and RO4882224 as potent and selective GABAA α5 inverse agonists for the treatment of cognitive dysfunction

Lead optimisation of the imidazo[1,5-a][1,2,4]-triazolo[1,5-d][1,4]benzodiazepine class led to the identification of two clinical leads [RO4882224 (11) and RO4938581 (44)] functioning as novel potent and selective GABA_A α5 inverse agonists. The unique pharmacological profiles and optimal pharmacokinetic profiles resulted in in vivo activity in selected cognition models.     

Homing chemokines in rheumatoid arthritis

In about 20% of patients with rheumatoid arthritis, B and T lymphocytes recruited into the inflamed synovium are organized into complex microstructures, which resemble secondary lymphoid organs. The development of such lymphoid aggregates with germinal centers appears to contribute to the pathogenesis of the disease. Growing evidence indicates that chemokines and their receptors control the recruitment and positioning of leukocytes as well as their organization into node-like lymphoid structures. Here, we comment on recent studies highlighting the importance of chemokines in rheumatoid arthritis, in particular of B-cell-activating chemokine-1 in lymphoid neogenesis in the inflamed synovium.     

Vitalfärbestudien mit Methylrot

Ohne Zusammenfassung     

Deletion of the structural gene for the NADH-dehydrogenase subunit 4 of Synechocystis 6803 alters respiratory properties.

Chloroplasts and cyanobacteria contain genes encoding polypeptides homologous to some subunits of the mitochondrial respiratory NADH-ubiquinol oxidoreductase complex (NADH dehydrogenase). Nothing is known of the role of the NADH dehydrogenase complex in photosynthesis, respiration, or other functions in chloroplasts, and little is known about the specific roles of the perhaps 42 subunits of this complex in the mitochondrion. Inactivation of a gene for subunit 4 (ndhD-2, ndh4) of this complex in the cyanobacterium Synechocystis 6803 has no effect on photosynthesis, judging from the rate of photoautotrophic growth of mutant cells, but the mutant's respiratory rate is about 6 times greater than that of wild-type cells. Respiratory electron transport activity in cyanobacteria is associated both with photosynthetic thylakoid membranes and with the outer cytoplasmic membrane of the cell. Cytoplasmic membranes of mutant cells have much greater NADH-dependent cytochrome reductase activity than preparations from wild-type cells; this activity remains at wild-type levels in isolated thylakoid membranes. It is suggested that the 56.6-kD product of ndhD-2 is not essential for the activity of a cytoplasmic membrane-bound NADH dehydrogenase but that it regulates the rate of electron flow through the complex, establishing a link between this ndh gene and respiration. The activity of the molecularly distinct thylakoid-bound NADH dehydrogenase is apparently unaffected by the loss of ndhD-2.     

Testing sources of variation in nestling‐stage nest success of Florida Scrub‐Jays in suburban and wildland habitats

Human modification of habitats can reduce reproductive success by providing novel cues to which birds may respond with behaviors that are actually maladaptive in those environments. Ad libitum human‐provided foods may provide the perception that urban habitats are food‐rich even as natural food availability decreases. Similarly, human activity may increase the perception that predation risk is high even as natural predators may decrease in abundance. In response, birds may reduce parental care with a subsequent cost to successful reproduction. Florida Scrub‐Jays (Aphelocoma coerulescens) in suburban areas have lower nest success during the nestling period than do wildland jays, possibly the result of such maladaptive responses, but maybe because of ecological differences with wildlands. We manipulated adult perception of predation risk and the availability of nestling foods in suburban and wildland areas to determine if these factors influenced parental care and nestling begging, and if the behavioral responses of adults influence nest survival during the nestling stage. Experimentally increasing perception of predation risk reduced parental care by both suburban and wildland females, but did not influence care by males. Increasing food availability, but not predation risk, had little influence on parental care, but resulted in decreased nestling begging rates and an increase in the frequency (pitch) of begging calls in both habitats. However, neither parental care nor food availability influenced nest survival during the nestling stage. Instead, the presence of helpers was the most important variable in nest survival analyses, suggesting that habitat‐specific differences in nest survival during the nestling stage were not simply the result of maladaptive parental behavior or shortage of nestling food resources in the suburban habitat. The lack of helpers combined with ecological differences, such as the abundance of nest predators, may be why fewer nests of Florida Scrub‐Jays survive during this stage in suburban areas.