On the encoding of movement vectors by honeybees. Are distance and direction represented independently?

Honeybees flying repeatedly over the same trajectory link it to an associated visual stimulus such that on viewing the stimulus they perform a trajectory in the habitual direction. To test if trajectory length can also be linked to a visual stimulus, bees were trained to fly through a multi-comparmented maze. Bees flew through a multi-compartmented maze. In one compartment a short trajectory could be linked to a stripe pattern oriented at 45° to the horizontal. In another compartment a longer trajectory could be linked to 135° stripes. Bees made both associations: their trajectories were short when viewing 45° stripes and longer when viewing 135° stripes. 90° stripes evoked trajectories of intermediate length.To test if distance and direction are linked independently to stripe orientation, a bee's trajectory was linked to 135° stripes in one compartment and to 45° stripes in another. These trajectories were the same length but differed in their horizontal direction by 60° or by 120°. 90° stripes evoked trajectories of intermediate direction which were shorter than those elicited by either training pattern. Bees were also trained to generate one long and one short trajectory with directions 120° apart. The trajectories elicited by 90° stripes were then biased towards the direction of the long training vector. Length and direction are not treated separately. The rules for combining trajectories resemble those of vector averaging.     

Homing and migration of mesenchymal stromal cells: How to improve the efficacy of cell therapy?

Mesenchymal stromal cells(MSCs) are currently being investigated for use in a wide variety of clinical applications. For most of these applications, systemic delivery of the cells is preferred. However, this requires the homing and migration of MSCs to a target tissue. Although MSC hominghas been described, this process does not appear to be highly efficacious because only a few cells reach the target tissue and remain there after systemic administration. This has been ascribed to low expression levels of homing molecules, the loss of expression of such molecules during expansion, and the heterogeneity of MSCs in cultures and MSC culture protocols. To overcome these limitations, different methods to improve the homing capacity of MSCs have been examined. Here, we review the current understanding of MSC homing, with a particular focus on homing to bone marrow. In addition, we summarize the strategies that have been developed to improve this process. A better understanding of MSC biology, MSC migration and homing mechanisms will allow us to prepare MSCs with optimal homing capacities. The efficacy of therapeutic applications is dependent on efficient delivery of the cells and can, therefore, only benefit from better insights into the homing mechanisms.     

Is induction of the exocellular lipase of Xanthomonas maltophila NK7 by fats and detergents simply the result of continual detachment from the cell surface?

The synthesis and release of the extracellular lipase of Xanthomonas maltophila NK7 grown in rich media was induced by non-substrates of the lipase: hexadecane, the non-hydrolysable detergents, Brij-35 and Triton X-100, and by oleic acid just as efficiently as by the triacylglycerols and hydrolysable detergents normally used to increase lipase yields. It is suggested that induction is the response to physical stripping by absorption of the lipase to micelles and emulsified droplets rather than to a metabolic effect. This view is supported by the following observations: (i) the longer chain triacylglycerols were better inducers than short chain triacylglycerols although they are hydrolysed more slowly by X. maltophila lipase; (ii) the yield of lipase increased with the concentration of olive oil and oleic acid well beyond the concentration which saturated the uptake system, as judged by the disappearance of oil from the medium.     

Are the conformational dynamics and the ligand binding properties of myoglobin affected by exposure to microwave radiation?

The global uptake of mobile communication emphasizes the question about possible adverse consequences of the exposure to low-level radiofrequency radiation from mobile phones on human health as result of so-called "non-thermal effects". In order to state safety guidelines it seems appropriate to start by excluding, if possible, non-specific effects on structural and dynamic properties of fundamental biomolecules such as proteins. Proteins are flexible polyelectrolytes; thus, they are susceptible, in principle, to the action of electromagnetic fields. In this article, we investigated the effects of microwaves on structural and functional properties of Tunnus tynnus myoglobin at 1.95 GHz, a frequency used by new wireless microwave communication systems. The protein solution was exposed for 2.5 h to 51 mW/g SAR (specific absorption rate) level. Measurements of absorption spectroscopy, circular dichroism and fluorescence emission decay in the frequency domain do not exhibit any influence of the radiation on the native structural state of protein macromolecules.     

Mitochondrial disappearance from cells: a clue to the role of autophagy in programmed cell death and disease?

When cells are induced to undergo apoptosis in the presence of general caspase inhibitors and then returned to their normal growth environment, there follows an extended period of life during which the entire cohort of mitochondria (including mitochondrial DNA) disappears from the cells. This phenomenon is widespread; it occurs in NGF-deprived sympathetic neurons, in NGF-maintained neurons treated with cytosine arabinoside, and in diverse cell lines treated with staurosporine, including HeLa, CHO, 3T3 and Rat 1 cells. Mitochondrial removal is highly selective since the structure of all other organelles remains unperturbed. Since Bcl2 overexpression blocks the removal of mitochondria without preventing death-inducing signals, it appears that the mitochondria are responsible for initiating their own demise. Degradation of mitochondria is not in itself a rare event. It occurs in large part by autophagy during normal cell house-keeping, during ecdysis in insects, as well as after induction of apoptosis. However, the complete and selective removal of an entire cohort of mitochondria in otherwise living mammalian cells has not been described previously. These findings raise several questions. What are the mechanisms which remove mitochondria in such a 'clean' fashion? What are the signals that target mitochondria for such selective degradation? How are cells that have lost their mitochondria different from rho0 cells (which retain mitochondria but lack mitochondrial DNA, and cannot carry out oxidative phosphorylation)? Are the cells which have lost mitochondria absolutely committed to die or might they be repaired by mitochondrial therapy? The answers will be especially relevant when considering treatment of diseases affecting long-lived and non-renewable organs such as the nervous system.     

Differential susceptibility of na?ve and activated human gammadelta T cells to activation-induced cell death by T-cell receptor cross-linking.

BACKGROUND: T cells undergo activation-induced cell death (AICD) through repeated stimulation of their T cell receptors (TCRs). Activated human gammadelta T cells were found to die by apoptosis when their TCRs were cross-linked by antibodies, whereas naïve gammadelta T cells freshly isolated from blood did not. Therefore, we investigated the factors that could contribute to this differential susceptibility. MATERIALS AND METHODS: Gammadelta T cells were isolated from the peripheral blood of healthy human volunteers and their TCRs were cross-linked either directly (naïve) or after an in vitro incubation of 11 days (activated). Their cell cycle profiles, cytokine, Fas and FasL mRNA messages, and surface expression of Fas and FasL were determined. RESULTS: The naïve cells were cycling while the activated T cells exited from the G1 to subG1 phase upon TCR cross-linking. IL-2 and IL-4 mRNAs and surface expression of FasL were detected only in activated T cells in the time period examined. In addition, cFLIP mRNA expression was found only in naïve gammadelta T cells and activated T cells treated with cyclosporin A (CsA), which inhibited AICD in the activated T cells. CsA also downregulated the surface expression of FasL in activated T cells. CONCLUSIONS: The differential expression of cytokines, apoptotic inducers and inhibitors provide the basis for the differential susceptibility of naïve and activated gammadelta T cells to AICD upon TCR cross-linking. This contributes to our understanding of the regulation and maintenance of gammadelta T-cell homeostasis, which would be important in many infectious as well as autoimmune diseases, where gammadelta T cells have been implicated.     

Do pH changes in the leaf apoplast contribute to rapid inhibition of leaf elongation rate by water stress? Comparison of stress responses induced by polyethylene glycol and down‐regulation of root hydraulic conductivity

We have dissected the influences of apoplastic pH and cell turgor on short-term responses of leaf growth to plant water status, by using a combination of a double-barrelled pH-selective microelectrodes and a cell pressure probe. These techniques were used, together with continuous measurements of leaf elongation rate (LER), in the (hidden) elongating zone of the leaves of intact maize plants while exposing roots to various treatments. Polyethylene glycol (PEG) reduced water availability to roots, while acid load and anoxia decreased root hydraulic conductivity. During the first 30 min, acid load and anoxia induced moderate reductions in leaf growth and turgor, with no effect on leaf apoplastic pH. PEG stopped leaf growth, while turgor was only partially reduced. Rapid alkalinization of the apoplast, from pH 4.9 ± 0.3 to pH 5.8 ± 0.2 within 30 min, may have participated to this rapid growth reduction. After 60 min, leaf growth inhibition correlated well with turgor reduction across all treatments, supporting a growth limitation by hydraulics. We conclude that apoplastic alkalinization may transiently impair the control of leaf growth by cell turgor upon abrupt water stress, whereas direct hydraulic control of growth predominates under moderate conditions and after a 30-60 min delay following imposition of water stress.     

Theoretical study of cyclohexane hydroxylation by three possible isomers of [FeIV(O)(R-TPEN)]2+: does the pentadentate ligand wrapping around the metal center differently lead to the different stability and reactivity?

Density functional theory calculations have been carried out to elucidate the mechanism of cyclohexane hydroxylation by three possible isomers of [Fe^IV(O)(N-R-N,N′,N′-tris(2-pyridylmethyl)ethane-1,2-diamine)]²⁺ (R is methyl or benzyl) (Klinker et al. in Angew Chem Int Ed 44:3690–3694, 2005). The calculations offer a mechanistic view and reveal the following features: (a) all the three isomers possess triplet ground states and low-lying quintet excited states, (b) the relative stability follows the order isomer A > isomer B > isomer C, in agreement with the conclusions of Klinker et al., (c) the theoretical investigations provide a rationale to explain the interconversion of the three isomers, (d) the reaction pathways of the C–H hydroxylation are initiated by a hydrogen-abstraction step, and (e) the three isomers react with cyclohexane via two-state-reactivity patterns on competing triplet and quintet spin-state surfaces. As such, in the gas phase, the relative reactivity exhibits the trend isomer B > isomer A, while at the highest level, B2//B1 with zero point energy and solvation corrections, the relative reactivity follows the order isomer B > isomer A > isomer C. Thus, the calculated reaction pathway shows that pyridine rings perpendicular to the Fe–O axis result in more reactive species, and a pyridine ring coordinated trans to the oxygen atom leads to the least reactive isomer. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.