Drosophila centrosomes are unable to trigger parthenogenetic development of Xenopus eggs

Centrosomes are powerful and exclusive parthenogenetic agents in the Xenopus egg. We have previously shown that heterologous centrosomes from various vertebrate species were able to promote egg cleavage in Xenopus and that human centrosome activity was associated with an insoluble proteinacious structure that is not significantly simpler than the native centrosome. In this work, we have investigated the parthenogenetic capacity of more evolutionary distant centrosomes. We show that centrosomes devoid of centrioles, such as SPBs isolated from Saccharomyces cerevisiae, do not form asters of microtubules in cytoplasmic extracts from Xenopus eggs, and are inactive in the parthenogenetic test. We further show that Drosophila centrosomes which possess a typical centriole architecture, and are quite active to nucleate microtubules in Xenopus cytoplasmic extracts, are unable to trigger egg cleavage. This was observed both with centrosomes isolated from Drosophila syncytial embryos and nucleus-centrosome complexes from the Drosophila Kc23 cell line. We demonstrate that this inability could not be restored after pre-incubation of Drosophila centrosomes in the egg cytoplasm before injection. We conclude that the parthenogenetic activity of a centrosome is not directly linked to its capacity to nucleate microtubules from the egg tubulin, and that the evolutionary conserved nine-fold symmetrical structure of the centriole cannot be considered as sufficient for triggering procentriole assembly.     

Detection of Anatoxin-a(s) in Environmental Samples of Cyanobacteria by Using a Biosensor with Engineered Acetylcholinesterases

Bioassays are little used to detect individual toxins in the environment because, compared to analytical methods, these assays are still limited by several problems, such as the sensitivity and specificity of detection. We tentatively solved these two drawbacks for detection of anatoxin-a(s) by engineering an acetylcholinesterase to increase its sensitivity and by using a combination of mutants to obtain increased analyte specificity. Anatoxin-a(s), a neurotoxin produced by some freshwater cyanobacteria, was detected by measuring the inhibition of acetylcholinesterase activity. By using mutated enzyme, the sensitivity of detection was brought to below the nanomole-per-liter level. However, anatoxin-a(s) is an organophosphorous compound, as are several synthetic molecules which are widely used as insecticides. The mode of action of these compounds is via inhibition of acetylcholinesterase, which makes the biotest nonspecific. The use of a four-mutant set of acetylcholinesterase variants, two mutants that are sensitive to anatoxin-a(s) and two mutants that are sensitive to the insecticides, allows specific detection of the cyanobacterial neurotoxin.     

Characterization of scorpion alpha-like toxin group using two new toxins from the scorpion Leiurus quinquestriatus hebraeus.

Two novel toxins, Lqh6 and Lqh7, isolated from the venom of the scorpion Leiurus quinquestriatus hebraeus, have in their sequence a molecular signature (8Q/KPE10) associated with a recently defined group of alpha-toxins that target Na channels, namely the alpha-like toxins [reviewed in Gordon, D., Savarin, P., Gurevitz, M. & Zinn-Justin, S. (1998) J. Toxicol. Toxin Rev. 17, 131-159]. Lqh6 and Lqh7 are highly toxic to insects and mice, and inhibit the binding of alpha-toxins to cockroach neuronal membranes. Although they kill rodents by intracerebroventricular injection, they do not inhibit the binding of antimammal alpha-toxins (e.g. Lqh2) to rat brain synaptosomes, not even at high concentrations. Furthermore, in voltage-clamp experiments, rat brain Na channels IIA (rNav1.2A) expressed in Xenopus oocytes are not affected by Lqh6 nor by Lqh7 below 3 micro m. In contrast, muscular Na channels (rNav1.4 and hNav1.5) expressed in the same cells respond to nanomolar concentrations of Lqh6 and Lqh7 by slowing of Na current inactivation and a leftward shift of the peak conductance-voltage curve. The structural and pharmacological properties of the new toxins are compared to those of other scorpion alpha-toxins in order to re-examine the hallmarks previously set for the alpha-like toxin group.     

VARIABILITY OF CELL WALL STRUCTURE AND HYDROCARBON TYPE IN DIFFERENT STRAINS OF BOTRYOCOCCUS BRAUNII1

Different samples of Botryococcus braunii Kütz., freshly collected from nature or laboratory-grown from culture collection strains, were studied by electron microscopy and their hydrocarbon content analyzed. Although the general internal structure of the cells was rather constant, the organization of the outer walls forming the hydrocarbon-rich matrix of the colonies differed greatly from one sample to another. In the majority of cultivated strains, the colonies were rather small, the different successive external walls remained distinct and all strains contained dienic or trienic hydrocarbons. In contrast, most of the collected samples possessed large colonies with a rather compact matrix formed by the hydrocarbon-rich part of the successive closely appressed external wall layers. These samples contained polyunsaturated hydrocarbons, i.e. botryococcenes. Well defined cell caps which sheared off the cells were observed only in those strains with a compact matrix. The Austin strain and some collected samples, however, were intermediate with rather small colonies, dense matrix, definite cell caps and dienic hydrocarbons. Thus, the hydrocarbon composition did not correlate directly with the variations in wall structure; however, the occurence of dienic and botryococcene-like hydrocarbons together in one strain was never observed, although analyzed at various stages of growth. Thus, the existence of distinct strains of Botryococcus braunii, some synthesizing dienes, others botryococcenes, appears highly probable.     

13C-NMR spectroscopic investigation of α- and β-1,4-D-glucose homooligomers

A complete, unambiguous assignment of all the ¹³C signals of cellobiose and maltose has been achieved using methods such as selective proton decoupling, ¹³C selective spin labeling, and isotopic chemical shift induced by deuterium. The chemical-shift variation of the ¹³C signals with the degree of polymerization in each α or β (1 → 4) series is discussed. The chemical-shift dependence on temperature and solvent in these two series is shown and interpreted in terms of modifications of the solvation and of the conformation.     

Larch- and pine-feeding host races of the larch bud moth (Zeiraphera diniana) have cyclic and synchronous population fluctuations

Population cycles of many forest-defoliating insects often show synchronous fluctuations at both intra-specific (spatial synchrony) and inter-specific levels. However, population dynamics of different host-associated biotypes of the same species, such as those of the larch budmoth (LBM), Zeiraphera diniana (Lepidoptera: Tortricidae), have never been compared. This species causes extensive defoliation of larch forests every 8 to 9 years in the Alps, but it consists of two genetically-differentiated host races, the first one developing on European larch, Larix decidua , and the other one developing on Swiss stone pine, Pinus cembra . The dynamics of Zeiraphera populations have been extensively studied on larch, whereas little is known about larval density and possible population fluctuations on sympatric pines. A larval census on Swiss stone pine was conducted in the Swiss Alps intermittently between 1958 to 2004 and in the French Alps from 1992 to 2004. Population density of Zeiraphera on pine varied up to 5000-fold and showed periodic oscillations, with five peaks in Switzerland and one in France. Because the feeding activity of the pine race is restricted to the elongating shoot of the current year, no conspicuous defoliation of pine trees was noted during years of high larval densities. Zeiraphera populations on pine oscillated in significant synchrony with larch-associated populations, and peak densities were observed either the same year or shifted by±one year. Our results did not allow any explanation for cyclic fluctuations of LBM on pine, but the synchrony with the larch race's cycle suggests that studies on genetics as well as on parasitism should be intensified.     

The Effect of Age on a Sexually Selected Acoustic Display

Models of sexual selection suggest that females should prefer to mate with older males because old age is evidence of heritable high viability. In a longitudinal analysis, we demonstrate that male field crickets (Gryllus campestris) alter their calling song with age. Carrier frequency, a calling song character related to growing condition and the main song component under female preference, changed towards higher sexual attractiveness with age. Body mass decreased slightly with age, while chirp rate, an indicator of current condition, remained stable. By choosing males singing at a low frequency, female field crickets would base their mate choice decision on a sexual trait that indicates superior growing conditions as juvenile and on viability, i.e. enhanced current condition as adult.     

Neuromuscular fatigue differs with biofeedback type when performing a submaximal contraction.

The aim of the study was to examine alterations in contractile and neural processes in response to an isometric fatiguing contraction performed with EMG feedback (constant-EMG task) when exerting 40% of maximal voluntary contraction (MVC) torque with the knee extensor muscles. A task with a torque feedback (constant-torque task) set at a similar intensity served as a reference task. Thirteen men (26+/-5 yr) attended two experimental sessions that were randomized across days. Endurance time was greater for the constant-EMG task compared with the constant-torque task (230+/-156 s vs. 101+/-32s, P<0.01). Average EMG activity for the knee extensor muscles increased from 33.5+/-4.5% to 54.7+/-21.7% MVC EMG during the constant-torque task (P<0.001), whereas the torque exerted during the constant-EMG task decreased from 42.8+/-3.0% to 17.9+/-5.6% MVC torque (P<0.001). Comparable reductions in knee extensors MVC (-15.7+/-8.7% for the constant-torque task vs. -17.5+/-9.8% for the constant-EMG task, P>0.05) and voluntary activation level were observed at exhaustion. In contrast, excitation-contraction coupling process, assessed with an electrically evoked twitch and doublet, was altered significantly more at the end of the constant-EMG task despite the absence of M-wave changes for both tasks. Present results suggest that prolonged contractions using EMG biofeedback should be used cautiously in rehabilitation programs.     

Effects of progressive and maximal exercise on plasma levels of adhesion molecules in athletes with sickle cell trait with or without alpha-thalassemia.

The aim of the study was to examine the effects of exercise on soluble vascular cell adhesion molecule-1 (sVCAM-1) and intercellular adhesion molecule-1 (sICAM-1) in sickle cell trait (SCT) athletes with or without alpha-thalassemia. Six athletes with SCT, seven athletes with both SCT and alpha-thalassemia (SCTAT), and seven control athletes (Cont) performed an incremental and maximal test on cycloergometer. Levels of sICAM-1 and sVCAM-1 were assessed at rest, immediately after the end of exercise, and 1, 2, and 24 h after exercise. Although Cont and SCTAT groups exhibited similar basal plasma levels of inflammatory and adhesion molecules, the SCT group had higher sVCAM-1 basal concentrations. Incremental exercise resulted in a significant increase of sVCAM-1 in all subjects, which remained elevated only in the SCT group during the recovery period. In conclusion, as sVCAM-1 increased with exercise and during the recovery period, our findings support the concept that SCT athletes might be at risk for microcirculatory disturbances and adhesive phenomena developing at rest and several hours after exercise. alpha-Thalassemia might be considered protective among exercising SCT subjects.