Location of the isoleucine arrest point in CHO and 3T3 cells

An isoleucine arrest point in G1 was determined by two methods for CHO and 3T3 cells. In the first method the fraction of cells entering S after isoleucine deprivation was assessed by [³H]thymidine labelling and autoradiography. In the second method cells entering S after isoleucine deprivation were identified by double-label autoradiography using [³H] and [¹⁴C]thymidine. From the fraction of cells entering S, determined by the two methods, the arrest point in G1 (and entry into G0) is located within the last 40 min of G1.     

Gas chromatographic determination of low concentrations of benzoic acid in human plasma and urine

A method for the determination of benzoic acid down to concentrations of 10 ng/ml in plasma or urine is described. After addition of an internal standard, benzoic acid is extracted at acid pH into diethyl ether. Both compounds are derivatized with pentafluorobenzyl bromide. The derivatives are determined by gas chromatography using a ⁴³Ni electron-capture detector. Hippuric acid is hydrolysed in plasma and urine and total benzoic acid is determined by the same technique.     

Views,landmarks, and routes: how do desert ants negotiate an obstacle course?

The Australian desert ant Melophorus bagoti often follows stereotypical routes through a cluttered landscape containing both distant panoramic views and obstacles (plants) to navigate around. We created an artificial obstacle course for the ants between a feeder and their nest. Landmarks comprised natural objects in the landscape such as logs, branches, and tussocks. Many ants travelled stereotypical routes home through the obstacle course in training, threading repeatedly the same gaps in the landmarks. Manipulations altering the relations between the landmarks and the surrounding panorama, however, affected the routes in two major ways. Both interchanging the positions of landmarks (transpositions) and displacing the entire landmark set along with the starting position of the ants (translations) (1) reduced the stereotypicality of the route, and (2) increased turns and meanders during travel. The ants might have used the entire panorama in view-based travel, or the distal panorama might prime the identification and use of landmarks en route. Despite the large data set, both options (not mutually exclusive) remain viable.     

Validity of an ultra-wideband local positioning system to assess specific movements in handball

The aim of this study was to examine the concurrent validity of the Kinexon local positioning system (LPS) in comparison with the Vicon motion capture system used as the reference. Five recreationally active men performed ten repetitions of linear sprints, medio-lateral side-to-side and handball-specific movements both in the centre and on the side of an indoor field. Validity was assessed for peak speed, peak acceleration and peak deceleration using standardised biases, Pearson coefficient of correlation (r), and standardised typical error of the estimate. With the exception of peak decelerations during specific movements in the centre and peak acceleration and deceleration during linear sprints on the side of the field, the standardised typical error of the estimate (TEE) values were all small to moderate (0.06–0.48), standardised bias ranged between 0.01 and 2.85 and Pearson coefficient values were all > 0.90 for all variables in all conditions. Peak acceleration and deceleration during linear sprints on the side of the field showed the largest TEEs and the greatest differences between the two systems. The ultra-wideband based (UWB) local positioning system had acceptable validity compared with Vicon to assess players’ movements in handball with the exception of high accelerations and decelerations during linear sprints on the side of the field.     

Multiphasic On/Off Pheromone Signalling in Moths as Neural Correlates of a Search Strategy

Insects and robots searching for odour sources in turbulent plumes face the same problem: the random nature of mixing causes fluctuations and intermittency in perception. Pheromone-tracking male moths appear to deal with discontinuous flows of information by surging upwind, upon sensing a pheromone patch, and casting crosswind, upon losing the plume. Using a combination of neurophysiological recordings, computational modelling and experiments with a cyborg, we propose a neuronal mechanism that promotes a behavioural switch between surge and casting. We show how multiphasic On/Off pheromone-sensitive neurons may guide action selection based on signalling presence or loss of the pheromone. A Hodgkin-Huxley-type neuron model with a small-conductance calcium-activated potassium (SK) channel reproduces physiological On/Off responses. Using this model as a command neuron and the antennae of tethered moths as pheromone sensors, we demonstrate the efficiency of multiphasic patterning in driving a robotic searcher toward the source. Taken together, our results suggest that multiphasic On/Off responses may mediate olfactory navigation and that SK channels may account for these responses.     

Turnover of plant lineages shapes herbivore phylogenetic beta diversity along ecological gradients

Understanding drivers of biodiversity patterns is of prime importance in this era of severe environmental crisis. More diverse plant communities have been postulated to represent a larger functional trait‐space, more likely to sustain a diverse assembly of herbivore species. Here, we expand this hypothesis to integrate environmental, functional and phylogenetic variation of plant communities as factors explaining the diversity of lepidopteran assemblages along elevation gradients in the Swiss Western Alps. According to expectations, we found that the association between butterflies and their host plants is highly phylogenetically structured. Multiple regression analyses showed the combined effect of climate, functional traits and phylogenetic diversity in structuring butterfly communities. Furthermore, we provide the first evidence that plant phylogenetic beta diversity is the major driver explaining butterfly phylogenetic beta diversity. Along ecological gradients, the bottom up control of herbivore diversity is thus driven by phylogenetically structured turnover of plant traits as well as environmental variables.     

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Ca2+ phospholipid-dependent and independent phosphorylation of synthetic peptide substrates by protein kinase C

Several synthetic peptides reproducing fragments of protamines have been used as model substrates for Ca2+/phospholipid-dependent protein kinase C, tested both in the absence of any effector (basal conditions) and upon activation by either Ca2+ and phosphatidylserine (or diacylglycerol) or limited proteolysis. Only the peptide Arg4-Tyr-Gly-Ser-Arg6-Tyr [Ga(52-65)] shares the unique property of protamines of being readily phosphorylated even under basal conditions. Optimal activity in the absence of effectors is observed with Tris/HCl buffer pH 7.5; Pipes and Hepes are less effective at pH 7.5, and at pH 6.5 basal phosphorylation is reduced. Under the best conditions for basal phosphorylation of Ga(52-65), its derivative with ornithine replaced for arginine and those corresponding to its C-terminal fragments Gly-Ser-Arg6-Tyr [Ga(57-65)] and Gly-Ser-Arg3 [Ga(57-61)], as well as the peptides Pro-Arg5-Ser2-Arg-Pro-Val-Arg [Th(1-12)], Arg4-Tyr-Arg2-Ser-Thr-Val-Ala [Th(13-23)] and Arg2-Leu-Ser2-Leu-Arg-Ala are not significantly affected though all of them, like histones, are more or less readily phosphorylated upon activation of protein kinase C by Ca2+/phosphatidylserine. The peptide Ser2-Arg-Pro-Val-Arg [Th(7-12)] however, corresponding to the C-terminal part of Th(1-12), is not phosphorylated even in the presence of activators. Limited proteolysis can roughly mimic the Ca2+/phosphatidylserine effect inducing however different extents of activation depending on the nature of the peptide substrates. Our results support the following two conclusions. Basal phosphorylation by protein kinase C in the absence of any effector requires peptide substrates whose target residue(s) are included between two extended arginyl blocks and is also dependent on pH and nature of the buffer. Peptides having extended clusters of either arginyl or ornithyl residues on the C-terminal side of serine are also readily phosphorylated, but they need activation of protein kinase by either Ca2+/phosphatidylserine or limited proteolysis. The same is true of peptides having basic residues only on the N-terminal side, or even on both sides but in limited number.     

Three-dimensional reconstruction of a human metaphase chromosome from electron micrographs

A complete human metaphase chromosome has been reconstructed from a series of electron microscopical projections obtained by tilting the specimen stage at 3 degree intervals from –60 to +60 degrees. The reconstructed structure is about 3.0 m long, 1.6 m wide, and 0.8 m thick. The mass distribution was fairly homogeneous within the chromatids and neither a hollow nor a dense core was observed. The distribution and course of fibers observed are most consistent with a looping model of chromosome structure.     

A locus involved in kanamycin, chloramphenicol and L-serine resistance is located in the bglY-galU region of the Escherichia coli K12 chromosome

Summary Spontaneous mutants of Escherichia coli K12 displaying an increased level of the kanamycin resistance conferred by plasmid pGR71 were selected. Several mutants obtained in this way apparently carry large chromosomal deletions extending into galU and/or bglY (27 min). This positive selection of deletions allowed detection of a new locus located between galU and bglY. Deletions of this locus are responsible for increased resistance to kanamycin (Irk), decreased resistance to l-serine in minimal medium (Drs) and decreased resistance to chloramphenicol (Drc) when a cat gene is present in the bacteria.