Pathogenicity of trypanosomatids on insects

More and more effects of trypanosomatids on insects have been recognized in the past few years. Here, Günter A. Schaub reviews such effects, classifying the flagellates according to the intensity of the effects on the insect host into pathogenic, subpathogenic and apathogenic trypanosomatids. He emphasizes that subpathogenic trypanosomatids which cause only minor effects under optimal conditions might act synergistically with natural stressors, thereby being an important regulatory factor in insect populations.     

The effect of tropomyosin on the adenosine triphosphatase activity of desensitized actomyosin

1. Tropomyosin preparations of the Bailey type, and those prepared in the presence of dithiothreitol to prevent oxidation of protein thiol groups, inhibit the Ca²⁺-activated adenosine triphosphatase (ATPase) of desensitized actomyosin by up to 60%. 2. The inhibitory activity of myofibrillar extracts and tropomyosin survives various agents known to denature proteins but to the action of which tropomyosin is unusually stable, namely heating at 100° and mild tryptic digestion. It is destroyed by prolonged treatment with trypsin. 3. The ethylenedioxybis-(ethyleneamino)tetra-acetic acid (EGTA)-sensitizing factor present in extracts of natural actomyosin and myofibrils could be selectively destroyed, leaving unchanged the inhibitory effect on the Ca²⁺-activated ATPase. There was no correlation between the EGTA-sensitizing and the Ca²⁺-activated inhibitory activities of tropomyosin prepared under different conditions. 4. Optimum inhibition was achieved when tropomyosin and the myosin of desensitized actomyosin were present in approximately equimolar proportions. Tropomyosin had no effect on the Ca²⁺-activated ATPase of myosin measured under similar conditions. 5. Evidence is presented showing that the tropomyosin binds to desensitized actomyosin under the conditions in which the ATPase is inhibited.     

Lytic transglycosylases LtgA and LtgD perform distinct roles in remodeling,recycling and releasing peptidoglycan in Neisseria gonorrhoeae

Neisseria gonorrhoeae releases peptidoglycan (PG) fragments during infection that provoke a large inflammatory response and, in pelvic inflammatory disease, this response leads to the death and sloughing of ciliated cells of the Fallopian tube. We characterized the biochemical functions and localization of two enzymes responsible for the release of proinflammatory PG fragments. The putative lytic transglycosylases LtgA and LtgD were shown to create the 1,6‐anhydromuramyl moieties, and both enzymes were able to digest a small, synthetic tetrasaccharide dipeptide PG fragment into the cognate 1,6‐anhydromuramyl‐containing reaction products. Degradation of tetrasaccharide PG fragments by LtgA is the first demonstration of a family 1 lytic transglycosylase exhibiting this activity. Pulse‐chase experiments in gonococci demonstrated that LtgA produces a larger amount of PG fragments than LtgD, and a vast majority of these fragments are recycled. In contrast, LtgD was necessary for wild‐type levels of PG precursor incorporation and produced fragments predominantly released from the cell. Additionally, super‐resolution microscopy established that LtgA localizes to the septum, whereas LtgD is localized around the cell. This investigation suggests a model where LtgD produces PG monomers in such a way that these fragments are released, whereas LtgA creates fragments that are mostly taken into the cytoplasm for recycling.     

Feedforward architectures driven by inhibitory interactions

Directed information transmission is paramount for many social, physical, and biological systems. For neural systems, scientists have studied this problem under the paradigm of feedforward networks for decades. In most models of feedforward networks, activity is exclusively driven by excitatory neurons and the wiring patterns between them, while inhibitory neurons play only a stabilizing role for the network dynamics. Motivated by recent experimental discoveries of hippocampal circuitry, cortical circuitry, and the diversity of inhibitory neurons throughout the brain, here we illustrate that one can construct such networks even if the connectivity between the excitatory units in the system remains random. This is achieved by endowing inhibitory nodes with a more active role in the network. Our findings demonstrate that apparent feedforward activity can be caused by a much broader network-architectural basis than often assumed.     

Ciprostene, a stable prostacyclin analog, produces peripheral vasodilation, platelet inhibition and increased clot dissolution in the cat

The effect of the stable prostacyclin analog ciprostene on hemodynamic parameters, platelet aggregation and clot dissolution was examined in the sodium pentobarbital anesthetized cat. Hemodynamic and platelet aggregation effects were measured in 5 cats following infusion of 5, 10, 20, 40 and 80 μg/kg/min of ciprostene. Drug was dissolved in Tyrode's buffer (pH 7.4) and all doses were infused for 20 minute intervals in ascending order. The hemodynamic data were consistent with peripheral vasodilation. The total peripheral resistance and mean aortic pressure decreased with incresing dose. No change in heart rate, cardiac index, or left ventricle dP/dt (contractility) was observed. All doses infused produced inhibition of ADP induced platelet aggregation. In vivo fibrinolytic activity was assessed with an aortic thrombus positioned at the bifurcation of the aorta. Five cats were infused with vehicle and 5 cats each were infused with 8 and 20 μg/kg/min ciprostene respectively. All infusions were via a 4F catheter positioned in the aorta proximal to the thrombus. Infusion time was 3 hours. Infusion of 8 μg/kg/min did not enhance dissolution of the aortic thrombus. However, the 20 μg/kg/min infusion significantly reduced the thrombus weight (mean = 13.2 mg) compared to vehicle (mean = 38.7 mg) (p < 0.03). The results suggest that ciprostene is a potent vasodilator and platelet inhibitor with clot dissolution properties.     

Protein Synthesis in the Developing Neocortex at Near-Atomic Resolution Reveals Ebp1-Mediated Neuronal Proteostasis at the 60S Tunnel Exit

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Coexistence and niche segregation by field populations of the parasitoids Cotesia glomerata and C. rubecula in the Netherlands: predicting field performance from laboratory data

Field experiments with foraging parasitoids are essential to validate the conclusions from laboratory studies and to interpret differences in searching and host selection behaviour of parasitoid species. Furthermore, field experiments can indicate whether the parameters measured in the laboratory are relevant to elucidation of the ecological processes under study, such as adaptation or species interactions. In previous extensive laboratory studies we studied plant- and host-searching behaviour, host acceptance, host suitability; host plant preference, and learning of two congeneric parasitoids of Pieris caterpillars: the generalist Cotesia glomerata, which has been reported to attack several Pieridae species, and C. rubecula, a specialist of the small cabbage white Pieris rapae. In the present field study our aim was to verify the importance of these previous laboratory findings for explaining the performance of these two species in the field. We investigated experimentally whether parasitism on three Pieris species varied with parasitoid species and with food plant of the caterpillars. We exposed different types of host plants, infested with different Pieris species, to parasitism by natural populations of Cotesia species, by setting the experimental plants out in Brussels sprouts cabbage fields. Furthermore we made direct observations of parasitoid foraging in the field. In general, the field results confirmed our predictions on the range of host plant and host species used in the field. The two Cotesia species appear to coexist through niche segregation, since C. glomerata was mainly recovered from P. brassicae and C. rubecula from P. rapae. Although C. glomerata is a generalist at the species level, it can be a specialist at the population level under certain ecological circumstances. Our study shows the importance of variation in host plant attraction and host species acceptance in restricting host plant and host diet in the field. Furthermore the results suggest that, at least in the Netherlands, specialisation of C. glomerata on P. brassicae may occur as a result of C. rubecula outcompeting C. glomerata in P. rapae larvae. Received: 8 July 1999 / Accepted: 31 January 2000