Behavior of <Emphasis Type="Italic">Nemopsis bachei</Emphasis> L. Agassiz, 1849 medusae in the presence of physical gradients and biological thin layers

In pelagic systems, thin layers (discontinuities with narrow vertical extents and high concentrations of organisms) create patches of food, and aggregations of gelatinous zooplankton can exploit such resources. The establishment, maintenance, and trophic effects of these functional relationships depend on behavioral responses to thin layers by individuals, which remain largely unexplored. In this study, we used laboratory experiments to test the hypothesis that a common and abundant hydromedusa predator, Nemopsis bachei L. Agassiz, 1849, would respond similarly to salinity gradients with and without thin layers of algae and copepods. Approximately 75% of the hydromedusae remained in both types of discontinuities. These distributions were not created solely by passive responses related to osmoconformation or an inability to swim through salinity gradients because approximately 25% of hydromedusae swam through or away from salinity gradients or biological thin layers. Biological thin layers stimulated feeding. Feeding success was related directly to encounter rates and it was independent of swimming, as expected for an ambush predator. Feeding increased at higher prey densities, and capture, handling time, and ingestion were not saturated even at 150–200 copepods l⁻¹. The proportion of N. bachei that ceased feeding and began swimming increased when encounters with prey decreased to approximately 2 encounters hydromedusa⁻¹ 10 min⁻¹. Thus, hydromedusae may seek new patches of prey once encounter rates and subsequent feeding success fall below a threshold. Exposing N. bachei to salinity gradients with and without biological thin layers indicated that these hydromedusae will remain in discontinuities and exert predation pressure that should be considered when assessing trophic webs and estimating carbon flux.     

IGF-IR signaling attenuates the age-related decline of diastolic cardiac function

Insulin-like growth factor (IGF-I) signaling has been implicated to play an important role in regulation of cardiac growth, hypertrophy, and contractile function and has been linked to the development of age-related congestive heart failure. Here, we address the question to what extent cardiomyocyte-specific IGF-I signaling is essential for maintenance of the structural and functional integrity of the adult murine heart. To investigate the effects of IGF-I signaling in the adult heart without confounding effects due to IGF-I overexpression or adaptation during embryonic and early postnatal development, we inactivated the IGF-I receptor (IGF-IR) by a 4-hydroxytamoxifen-inducible Cre recombinase in adult cardiac myocytes. Efficient inactivation of the IGF-IR (iCMIGF-IRKO) as assessed by Western analysis and real-time PCR went along with reduced IGF-I-dependent Akt and GSK3β phosphorylation. Functional analysis by conductance manometry and MRI revealed no functional alterations in young adult iCMIGF-IRKO mice (age 3 mo). However, when induced in aging mice (11 mo) diastolic cardiac function was depressed. To address the question whether insulin signaling might compensate for the defective IGF-IR signaling, we inactivated β-cells by streptozotocin. However, the diabetes-associated functional depression was similar in control and iCMIGF-IRKO mice. Similarly, analysis of the cardiac gene expression profile on 44K microarrays did not reveal activation of overt adaptive processes. Endogenous IGF-IR signaling is required for conservation of cardiac function of the aging heart, but not for the integrity of cardiac structure and function of young hearts.     

Contact-dependent growth inhibition requires the essential outer membrane protein BamA (YaeT) as the receptor and the inner membrane transport protein AcrB

Contact-dependent growth inhibition (CDI) is a phenomenon by which bacterial cell growth is regulated by direct cell-to-cell contact via the CdiA/CdiB two-partner secretion system. Characterization of mutants resistant to CDI allowed us to identify BamA (YaeT) as the outer membrane receptor for CDI and AcrB as a potential downstream target. Notably, both BamA and AcrB are part of distinct multi-component machines. The Bam machine assembles outer membrane beta-barrel proteins into the outer membrane and the Acr machine exports small molecules into the extracellular milieu. We discovered that a mutation that reduces expression of BamA decreased binding of CDI+ inhibitor cells, measured by flow cytometry with fluorescently labelled bacteria. In addition, alpha-BamA antibodies, which recognized extracellular epitopes of BamA based on immunofluorescence, specifically blocked inhibitor-target cells binding and CDI. A second class of CDI-resistant mutants identified carried null mutations in the acrB gene. AcrB is an inner membrane component of a multidrug efflux pump that normally forms a cell envelope-spanning complex with the membrane fusion protein AcrA and the outer membrane protein TolC. Strikingly, the requirement for the BamA and AcrB proteins in CDI is independent of their multi-component machines, and thus their role in the CDI pathway may reflect novel, import-related functions.     

Mechanistic and structural analysis of aminoglycoside N-acetyltransferase AAC(6')-Ib and its bifunctional, fluoroquinolone-active AAC(6')-Ib-cr variant

Enzymatic modification of aminoglycoside antibiotics mediated by regioselective aminoglycoside N-acetyltransferases is the predominant cause of bacterial resistance to aminoglycosides. A recently discovered bifunctional aminoglycoside acetyltransferase (AAC(6')-Ib variant, AAC(6')-Ib-cr) has been shown to catalyze the acetylation of fluoroquinolones as well as aminoglycosides. We have expressed and purified AAC(6')-Ib-wt and its bifunctional variant AAC(6')-Ib-cr in Escherichia coli and characterized their kinetic and chemical mechanism. Initial velocity and dead-end inhibition studies support an ordered sequential mechanism for the enzyme(s). The three-dimensional structure of AAC(6')-Ib-wt was determined in various complexes with donor and acceptor ligands to resolutions greater than 2.2 A. Observation of the direct, and optimally positioned, interaction between the 6'-NH 2 and Asp115 suggests that Asp115 acts as a general base to accept a proton in the reaction. The structure of AAC(6')-Ib-wt permits the construction of a molecular model of the interactions of fluoroquinolones with the AAC(6')-Ib-cr variant. The model suggests that a major contribution to the fluoroquinolone acetylation activity comes from the Asp179Tyr mutation, where Tyr179 makes pi-stacking interactions with the quinolone ring facilitating quinolone binding. The model also suggests that fluoroquinolones and aminoglycosides have different binding modes. On the basis of kinetic properties, the pH dependence of the kinetic parameters, and structural information, we propose an acid/base-assisted reaction catalyzed by AAC(6')-Ib-wt and the AAC(6')-Ib-cr variant involving a ternary complex.     

The alpha-helix 4 residue, Asn135, is involved in the oligomerization of Cry1Ac1 and Cry1Ab5 Bacillus thuringiensis toxins.

The insecticidal Cry toxins produced by the bacterium Bacillus thuringiensis are comprised of three structural domains. Domain I, a seven-helix bundle, is thought to penetrate the insect epithelial cell plasma membrane through a hairpin composed of alpha-helices 4 and 5, followed by the oligomerization of four hairpin monomers. The alpha-helix 4 has been proposed to line the lumen of the pore, whereas some residues in alpha-helix 5 have been shown to be responsible for oligomerization. Mutation of the Cry1Ac1 alpha-helix 4 amino acid Asn135 to Gln resulted in the loss of toxicity to Manduca sexta, yet binding was still observed. In this study, the equivalent mutation was made in the Cry1Ab5 toxin, and the properties of both wild-type and mutant toxin counterparts were analyzed. Both mutants appeared to bind to M. sexta membrane vesicles, but they were not able to form pores. The ability of both N135Q mutants to oligomerize was also disrupted, providing the first evidence that a residue in alpha-helix 4 can contribute to toxin oligomerization.     

Onset,Early Stages,and Prognosis of Rheumatoid Arthritis: A Clinical Study of 100 Patients with 11-year Follow-up

One hundred patients with “definite” or “classical” rheumatoid arthritis were followed in a hospital clinic from within one year of the onset of the arthritis. The average interval between onset and first attendance was 3·7 months. Onset was commoner in the winter, transient prodromal symptoms being noted in 23, with possible precipitating factors in 14. The serum rheumatoid factor test was positive at some time in 88.The patients were reassessed between eight and 14 years later. Seventeen died during this period, five possibly as a result of the disease or its treatment.The remaining patients had improved as a whole in terms of the blood sedimentation rate, haemoglobin, titre of the rheumatoid factor test, and status of the disease, but there was an overall deterioration in functional capacity. Both the rheumatoid factor titre and the functional capacity at an earlier review could be directly correlated with the outcome, but other factors were not found to influence the ultimate prognosis.     

Molecular structure and interrelationships of multiresistance beta-lactamase transposons

Transposons coding for beta-lactamases OXA-3, OXA-4, OXA-5, LCR-1, and CARB-3 have been isolated and compared functionally and structurally with transposons for TEM-1, OXA-1, PSE-1, PSE-2, and PSE-4 enzymes. Each beta-lactamase gene type occurred in a unit together with resistance to other antibiotics, particularly streptomycin and sulfonamide but also chloramphenicol, mercuric ion, or gentamicin, kanamycin, and tobramycin. Restriction mapping, gene cloning, and DNA hybridization were used to compare the transposons and to localize their functional components. Although the multiresistance beta-lactamase transposons varied in size from 8 to 25 kb, the similarity of some of their restriction maps suggested a common derivation. Six of 12 transposons contained DNA segments homologous to the tnpR gene of transposon Tn21 and could complement a tnpR- Tn21 derivative. Consequently, these six transposons appear to have evolved from a common progenitor by acquisition of DNA coding for various beta-lactamases and other resistance genes.     

Do neuroleptic drugs hasten cognitive decline in dementia? Prospective study with necropsy follow up.

OBJECTIVE: To investigate the contribution of neuroleptic drugs to cognitive decline in dementia. DESIGN: Two year prospective, longitudinal study consisting of interviews every four months, with necropsy follow up. SETTING: Community settings in Oxfordshire. SUBJECTS: 71 subjects with dementia, initially living at home with informant. MAIN OUTCOME MEASURES: Cognitive function (score from expanded minimental state examination); behavioural problems (physical aggression, hallucinations, persecutory ideas, and disturbance of diurnal rhythm); and postmortem neuropathological assessment (cortical Lewy body pathology). RESULTS: The mean (SE) decline in cognitive score in the 16 patients who took neuroleptics was twice that in the patients who did not (20.7 (2.9) v 9.3 (1.3), P = 0.002). An increased rate of decline was also associated with aggression, disturbed diurnal rhythm, and persecutory ideas. However, only use of neuroleptics and severity of persecutory ideas were independently associated with more rapid cognitive decline when all other variables were adjusted for. The start of neuroleptic treatment coincided with more rapid cognitive decline: median rate of decline was 5 (interquartile range 8.5) points per year before treatment and 11 (12) points per year after treatment (P = 0.02). Cortical Lewy body pathology did not account for association between neuroleptic use and more rapid decline. CONCLUSIONS: Neuroleptic drugs that are sometimes used to treat behavioural complications of dementia may worsen already poor cognitive function. Randomised controlled trials are needed to confirm a causal relation.