Pulsatile contractions and pattern formation in excitable actomyosin cortex

The actin cortex is an active adaptive material, embedded with complex regulatory networks that can sense, generate, and transmit mechanical forces. The cortex exhibits a wide range of dynamic behaviours, from generating pulsatory contractions and travelling waves to forming organised structures. Despite the progress in characterising the biochemical and mechanical components of the actin cortex, the emergent dynamics of this mechanochemical system is poorly understood. Here we develop a reaction-diffusion model for the RhoA signalling network, the upstream regulator for actomyosin assembly and contractility, coupled to an active actomyosin gel, to investigate how the interplay between chemical signalling and mechanical forces regulates stresses and patterns in the cortex. We demonstrate that mechanochemical feedback in the cortex acts to destabilise homogeneous states and robustly generate pulsatile contractions. By tuning active stress in the system, we show that the cortex can generate propagating contraction pulses, form network structures, or exhibit topological turbulence.     

Phosphodiesterase 4 conformers: preparation of recombinant enzymes and assay for inhibitors.

Cyclic nucleotides are key regulators of many cellular processes. Their immediate action is terminated through the activity of phosphodiesterases, a diverse family of enzymes. This diversity has given rise to drug discovery opportunities, and assay technology is therefore of key importance. Inhibitors of the cyclic-AMP-specific phosphodiesterases (the PDE4 family) are drug candidates for a variety of inflammatory disorders. However, PDE4 inhibitors, besides their immunomodulatory effects, also cause side effects including nausea and emesis. Recently, it has been suggested that PDE4 exists in two different conformations with respect to inhibition by the prototypical compound rolipram. Inhibition of the low-affinity conformer is thought to give rise to anti-inflammatory effects, and inhibition of the high-affinity conformer to side effects. Therefore, a selective inhibitor of the low-affinity conformer may have clinical utility. Methods are described to prepare recombinant forms of PDE4B that allow screening for compounds that could preferentially inhibit the low-affinity conformer. Furthermore, conditions for an efficient, scintillation proximity, microtiter plate-based assay are described, providing a considerable advance over previous assays in terms of throughput and automatability.     

A Simple Method for the Rapid Analysis of Animal Sounds

A simple, real-time method for displaying the information contained in the zero-crossings of acoustic signals is described. The method can be used even with many signals that have harmonics, and reveals a wealth of fine structure in bird song. Some of this structure may serve a communicatory function.     

Composition of scents from the larva of the milkweed bug Oncopeltus fasciatus

The dorsal abdominal scent glands of the larva of Oncopeltus fasciatus may have different, although not necessarily unrelated, functions. It has been found that oct-2-en-1-al is the major component of the scent from the anterior gland, 4-oxo-oct-2-en-1-al the major component of the scent from the posterior gland, and that the larva releases the secretion from the posterior gland more readily than it does from the anterior gland. Minor components of the scents include hex-2-en-1-al, 4-oxohex-2-en-1-al, and possibly hept-2-en-1-al. The secretions, after release onto the dorsal surface of the abdomen, are subsequently brushed off with the hind tarsi onto the surface on which the larva is standing. This behaviour can be elicited by stimulating the dorsal abdominal surface of the larva with the vapour of octenal and similar aldehydes.     

Proteomic analysis of the anti‐inflammatory action of minocycline

Minocycline possesses anti‐inflammatory properties independently of its antibiotic activity although the underlying molecular mechanisms are unclear. Lipopolysaccharide (LPS)‐induced cytokines and pro‐inflammatory protein expression are reduced by minocycline in cultured macrophages. Here, we tested a range of clinically important tetracycline compounds (oxytetracycline, doxycycline, minocycline and tigecycline) and showed that they all inhibited LPS‐induced nitric oxide production. We made the novel finding that tigecycline inhibited LPS‐induced nitric oxide production to a greater extent than the other tetracycline compounds tested. To identify potential targets for minocycline, we assessed alterations in the macrophage proteome induced by LPS in the presence or absence of a minocycline pre‐treatment using 2‐DE and nanoLC‐MS. We found a number of proteins, mainly involved in cellular metabolism (ATP synthase β‐subunit and aldose reductase) or stress response (heat shock proteins), which were altered in expression in response to LPS, some of which were restored, at least in part, by minocycline. This is the first study to document proteomic changes induced by minocycline. The observation that minocycline inhibits some, but not all, of the LPS‐induced proteomic changes shows that minocycline specifically affects some signalling pathways and does not completely inhibit macrophage activation.     

Insights into mycorrhizal colonisation at elevated CO2: a simple carbon partitioning model

A simulation model was used to investigate the effect of an increased rate of plant photosynthesis at enhanced atmospheric CO2 concentration on a non-leguminous plant-mycorrhizal fungus association. The model allowed the user to modify carbon allocation patterns at three levels: (1) within the plant (shoot–root), (2) between the plant and the mycorrhizal fungus and (3) within the mycorrhizal fungus (intraradical–extraradical structures). Belowground (root and fungus) carbon losses via respiration (and turnover) could also be manipulated. The specific objectives were to investigate the dynamic nature of the potential effects of elevated CO2 on mycorrhizal colonisation and to elucidate some of the various mechanisms by which these effects may be negated. Many of the simulations showed that time (i.e. plant age) had a more significant effect on the observed stimulation of mycorrhizal colonisation by elevated CO2 than changes in carbon allocation patterns or belowground carbon losses. There were two main mechanisms which negated a stimulatory effect of elevated CO2 on internal mycorrhizal colonisation: an increased mycorrhizal carbon allocation to the external hyphal network and an increased rate of mycorrhizal respiration. The results are discussed in relation to real experiments. The need for studies consisting of multiple harvests is emphasised, as is the use of allometric analysis. Implications at the ecosystem level are discussed and key areas for future research are presented.     

The accessory gland and metathoracic scent gland function in Oncopeltus fasciatus

The paper provides further clues as to the physiological function and biological significance of the ‘accessory gland’ in the metathoracic scent apparatus of the lygaeid Oncopeltus fasciatus. From various lines of evidence (gas chromatographic, cytochemical) it is concluded as probable that the accessory gland secretes small quantities of a mucopolysaccharide secretory product together with water. The difficulty of reconciling these data with other data indicating that the accessory gland is involved in the biosynthesis of the scent aldehydes is discussed. It is suggested that the water secreted into the median scent reservoir by the accessory gland provides O. fasciatus with a means of volumetric compensation for a diminished output of scent repellent.     

Soil microbial diversity and community structure across a climatic gradient in western Canada

Soil microbial functional diversity was assessed along a climatic gradient in Western Canada. Mineral soil samples were collected from jack pine (Pinus banksiana Lamb.) stands along an 800km transect between Prince Albert, Saskatchewan and Gillam, Manitoba. Microbial communities were isolated from the soil samples, washed and inoculated into wells of Gram-negative Biolog microplates. Optical density values were used to calculate Shannon diversity indices and to perform principal component analysis. Colour development rank plots (CDR) were created by expressing optical density values as a percentage of total colour development and plotting the wells in descending order. Soil microbial functional diversity decreased with increasing latitude and correlated positively with measures of atmospheric temperature and pH. Soil microbial diversity may be lower in northern sites due to decreased productivity, nutrient limitation and higher acidity. CDR plots are consistent with a trend of increasing environmental harshness moving north along the transect.     

Mycorrhizas and global environmental change: research at different scales

Global environmental change (GEC), in particular rising atmospheric CO₂ concentration and temperature, will affect most ecosystems. The varied responses of plants to these aspects of GEC are well documented. As with other key below-ground components of terrestrial ecosystems, the response of the ubiquitous mycorrhizal fungal root symbionts has received limited attention. Most of the research on the effects of GEC on mycorrhizal fungi has been pot-based with a few field (especially monoculture) studies. A major question that arises in all these studies is whether the GEC effects on the mycorrhizal fungi are independent of the effects on their plant hosts. We evaluate the current knowledge on the effects of elevated CO₂ and increased temperature on mycorrhizal fungi and focus on the few available field examples. The value of using long-term and large-scale field experiments is emphasised. We conclude that the laboratory evidence to date shows that the effect of elevated CO₂ on mycorrhizal fungi is dependent on plant growth and that temperature effects seen in the past might have reflected a similar dependence. Therefore, how temperature directly affects mycorrhizal fungi remains unknown. In natural ecosystems, we predict that GEC effects on mycorrhizal fungal communities will be strongly mediated by the effects on plant communities to the extent that community level interactions will prove to be the key mechanism for determining GEC-induced changes in mycorrhizal fungal communities.