Piezo1–Pannexin1 complex couples force detection to ATP secretion in cholangiocytes

Cholangiocytes actively contribute to the final composition of secreted bile. These cells are exposed to abnormal mechanical stimuli during obstructive cholestasis, which has a deep impact on their function. However, the effects of mechanical insults on cholangiocyte function are not understood. Combining gene silencing and pharmacological assays with live calcium imaging, we probed molecular candidates essential for coupling mechanical force to ATP secretion in mouse cholangiocytes. We show that Piezo1 and Pannexin1 are necessary for eliciting the downstream effects of mechanical stress. By mediating a rise in intracellular Ca²⁺, Piezo1 acts as a mechanosensor responsible for translating cell swelling into activation of Panx1, which triggers ATP release and subsequent signal amplification through P2X4R. Co-immunoprecipitation and pull-down assays indicated physical interaction between Piezo1 and Panx1, which leads to stable plasma membrane complexes. Piezo1–Panx1–P2X4R ATP release pathway could be reconstituted in HEK Piezo1 KO cells. Thus, our data suggest that Piezo1 and Panx1 can form a functional signaling complex that controls force-induced ATP secretion in cholangiocytes. These findings may foster the development of novel therapeutic strategies for biliary diseases.     

Dominance hierarchy and reproductive conflicts among subordinates in a monogynous queenless ant

In insect societies lacking morphologically specialized breedersand helpers, reproduction is often restricted to behaviorallydominant individuals. Such societies occur in about 100 speciesof ants that have secondarily lost the queen caste. All females,who are morphologically workers, can potentially mate and layeggs but only a few do so, and we demonstrate in Dinoponeraquadriceps that this is regulated by a dominance hierarchy.Six types of agonistic interactions allowed the ranking of 5-10workers in the hierarchy (n = 15 colonies). In particular, alphaand beta had characteristic behavioral profiles and were easily recognized.Only alpha mated, and workers ranking beta to delta sometimes producedunfertilized, male-destined eggs. Natural replacements (n = 19)and experimental removals (n = 15) of alpha demonstrated that betawas the individual most likely to replace alpha, although gammaand more rarely delta sometimes did, and we discuss the conflictthat occurs among high-ranking individuals over who should replacealpha. After such replacements, the new alpha behaved more aggressivelythan the overthrown alpha. Newly emerged workers tended to reachhigh ranks and displaced older high-ranking individuals downthe hierarchy. Low-ranking subordinates often prevented high-rankingindividuals from replacing alpha by biting and holding theirappendages (worker policing), which is consistent with the patternof relatedness associated with monogyny and monandry in D. quadriceps. Weinvestigated the relative importance of chemical communicationand dominance interactions to regulate reproduction. Alpha,beta, and sterile workers have different signatures of cuticularhydrocarbons, and these may provide honest information whichunderpins worker policing by low-ranking individuals.     

Recent patents on the synthesis and application of silica nanoparticles for drug delivery

Drug delivery systems are designed to improve therapy efficacy as well as patient compliance. This could be accomplished by specifically targeting a medication intact to its active site, therefore reducing side-effects and enabling high local drug concentrations. Silica nanoparticles have gained ground in the biomedical field for their biocompatibility and biodegradability, being themselves inert and stable, thus enabling a variety of formulation designs for application in the pharmaceutical industry. This paper is a review of the recent patents on the applications of silica nanoparticles for drug delivery and their preparation. The review will focus on the different techniques available to obtain silica nanoparticles with variable morphology and their drug targeting applications, providing an overview of silica particles synthesis described in the literature.     

IRAK4 kinase activity is redundant for interleukin-1 (IL-1) receptor-associated kinase phosphorylation and IL-1 responsiveness

Interleukin-1 (IL-1) stimulation leads to the recruitment of interleukin-1 receptor-associated kinase (IRAK) to the IL-1 receptor, where IRAK is phosphorylated, ubiquitinated, and eventually degraded. Kinase-inactive mutant IRAK is still phosphorylated in response to IL-1 stimulation when it is transfected into IRAK-deficient cells, suggesting that there must be an IRAK kinase in the pathway. The fact that IRAK4, another IRAK family member necessary for the IL-1 pathway, is able to phosphorylate IRAK in vitro suggests that IRAK4 might be the IRAK kinase. However, we now found that the IRAK4 kinase-inactive mutant had the same ability as the wild-type IRAK4 in restoring IL-1-mediated signaling in human IRAK4-deficient cells, including NFkappaB-dependent reporter gene expression, the activation of NFkappaB and JNK, and endogenous IL-8 gene expression. These results strongly indicate that the kinase activity of human IRAK4 is not necessary for IL-1 signaling. Furthermore, we showed that the kinase activity of IRAK4 was not necessary for IL-1-induced IRAK phosphorylation, suggesting that IRAK phosphorylation can probably be achieved either by autophosphorylation or by trans-phosphorylation through IRAK4. In support of this, only the impairment of the kinase activity of both IRAK and IRAK4 efficiently abolished the IL-1 pathway, demonstrating that the kinase activity of IRAK and IRAK4 is redundant for IL-1-mediated signaling. Moreover, consistent with the fact that IRAK4 is a necessary component of the IL-1 pathway, we found that IRAK4 was required for the efficient recruitment of IRAK to the IL-1 receptor complex.     

Metastable spiking networks in the replica-mean-field limit

Characterizing metastable neural dynamics in finite-size spiking networks remains a daunting challenge. We propose to address this challenge in the recently introduced replica-mean-field (RMF) limit. In this limit, networks are made of infinitely many replicas of the finite network of interest, but with randomized interactions across replicas. Such randomization renders certain excitatory networks fully tractable at the cost of neglecting activity correlations, but with explicit dependence on the finite size of the neural constituents. However, metastable dynamics typically unfold in networks with mixed inhibition and excitation. Here, we extend the RMF computational framework to point-process-based neural network models with exponential stochastic intensities, allowing for mixed excitation and inhibition. Within this setting, we show that metastable finite-size networks admit multistable RMF limits, which are fully characterized by stationary firing rates. Technically, these stationary rates are determined as the solutions of a set of delayed differential equations under certain regularity conditions that any physical solutions shall satisfy. We solve this original problem by combining the resolvent formalism and singular-perturbation theory. Importantly, we find that these rates specify probabilistic pseudo-equilibria which accurately capture the neural variability observed in the original finite-size network. We also discuss the emergence of metastability as a stochastic bifurcation, which can be interpreted as a static phase transition in the RMF limits. In turn, we expect to leverage the static picture of RMF limits to infer purely dynamical features of metastable finite-size networks, such as the transition rates between pseudo-equilibria.     

Biological invasions in soil: DNA barcoding as a monitoring tool in a multiple taxa survey targeting European earthworms and springtails in North America

Biological invasions are increasingly recognized as a potent force altering native ecosystems worldwide. Many of the best documented cases involve the massive invasions of North America by plant and animal taxa native to Europe. In this study, we use DNA barcoding to survey the occurrence and genetic structure of two major groups of soil invertebrates in both their native and introduced ranges: Collembola and earthworms. Populations of ten species of earthworms and five species of Collembola were barcoded from both continents. Most of these species exhibited a similar genetic structure of large and stable populations in North America and Europe, a result supporting a scenario of multiple invasions. This was expected for earthworm species involved in human economic activities, but not foreseen for Collembola species de facto unintentionally introduced. This study also establishes that invasive species surveys employing DNA barcoding gain additional resolution over those based on morphology as they allow evaluation of cryptic lineages exhibiting different invasion histories.     

Soil functioning in a mosaic of herbaceous communities of a chalky environment: temporal variations of water availability and N dynamics

Background and aims

Although changes in water and nitrogen (N) supply have been largely used to explain modifications in plant communities, the spatio-temporal variability of those factors has been little studied in chalky environments.

Methods

In this study, we explored for 1?year the temporal variations in soil water content, N inorganic forms and net N-mineralization and nitrification for two horizons in three herbaceous communities (short grasslands, tall grasslands, and encroached grasslands) in the Hénouville Nature Reserve (Upper-Normandy, France). Plant available soil water and permanent wilting points of seven plant species were also characterized.

Results

We found that plant available soil water was lower in short grasslands than in tall grasslands and encroached grasslands. Soil water content was below permanent wilting point during four months in short grasslands and only three months in the other communities. Seasonal patterns for inorganic N content and N-mineralization and nitrification were observed with peaks of NH ₄ ⁺ –N in summer and peaks of N-mineralization in spring.

Conclusions

For the studied year, our data highlight the harsh soil desiccation that vegetation endured during the late spring (active growth period) and summer, and show that water shortage is an ecological factor affecting the N cycling in the three successional herbaceous communities.     

Metabolic correction of congenital erythropoietic porphyria with iPSCs free of reprogramming factors

Congenital erythropoietic porphyria (CEP) is due to a deficiency in the enzymatic activity of uroporphyrinogen III synthase (UROS); such a deficiency leads to porphyrin accumulation and results in skin lesions and hemolytic anemia. CEP is a candidate for retrolentivirus-mediated gene therapy, but recent reports of insertional leukemogenesis underscore the need for safer methods. The discovery of induced pluripotent stem cells (iPSCs) has opened up new horizons in gene therapy because it might overcome the difficulty of obtaining sufficient amounts of autologous hematopoietic stem cells for transplantation and the risk of genotoxicity. In this study, we isolated keratinocytes from a CEP-affected individual and generated iPSCs with two excisable lentiviral vectors. Gene correction of CEP-derived iPSCs was obtained by lentiviral transduction of a therapeutic vector containing UROS cDNA under the control of an erythroid-specific promoter shielded by insulators. One iPSC clone, free of reprogramming genes, was obtained with a single proviral integration of the therapeutic vector in a genomic safe region. Metabolic correction of erythroblasts derived from iPSC clones was demonstrated by the disappearance of fluorocytes. This study reports the feasibility of porphyria gene therapy with the use of iPSCs.     

Oxidases responsible for resistance to pyrethroids sensitize Helicoverpa armigera (Hübner) to triazophos in West Africa

Helicoverpa armigera (Hübner) is the major insect pest of cotton in Africa, Turkey, Asia, India, Indonesia and Australia. Populations recently developed resistance to pyrethroids in West Africa via the overproduction of cytochrome P450 (oxidases) increasing pyrethroid metabolism. One way to overcome pyrethroid resistance is to use compounds that show negative cross-resistance to pyrethroids. Triazophos is one of these compounds: it is slightly more toxic against pyrethroid resistant larvae of H. armigera than against susceptible ones. Overproduced oxidases transform the non active triazophos into its active form, triazophos-oxon, since this form was significantly more often found in larvae from pyrethroid resistant strain (23%) than in susceptible strain (15%). This suggests that oxidases, which provide resistance by degradation of pyrethroids in the resistant individuals, also activate triazophos in its toxic oxon form resulting in a negative cross-resistance.     

Evidence for a Multi-ion Pore Behavior in the Plant Potassium Channel KAT1

KAT1 is a cloned voltage-gated K⁺ channel from the plant Arabidopsis thaliana L., which displays an inward rectification reminiscent of `anomalous' rectification of the i <sub>f</sub> pacemaker current recorded in animal cells. Macroscopic conductance of KAT1 expressed in Xenopus oocytes was 5-fold less in pure Rb<sup>+</sup> solution than in pure K<sup>+</sup> solution, and negligible in pure Na<sup>+</sup> solution. Experiments in different K<sup>+</sup>/Na<sup>+</sup> or K<sup>+</sup>/Rb<sup>+</sup> mixtures revealed deviations from the principle of independence and notably two anomalous effects of the K<sup>+</sup>/Rb<sup>+</sup> mole fraction (i.e., the ratio [K<sup>+</sup>]/([K<sup>+</sup>]+[Rb<sup>+</sup>])). First, the KAT1 deactivation time constant was both voltage- and mole fraction-dependent (a so-called `foot in the door' effect was thus observed in KAT1 channel). Second, when plotted against the K⁺/Rb⁺ mole fraction, KAT1 conductance values passed through a minimum. This minimum is more important for two pore mutants of KAT1 (T259S and T260S) that displayed an increase in P_Rb/P_K. These results are consistent with the idea that KAT1 conduction requires several ions to be present simultaneously within the pore. Therefore, this atypical `green' member of the Shaker superfamily of K⁺ channels further shows itself to be an interesting model as well for permeation as for gating mechanism studies. Received: 9 February 1998/Revised: 28 July 1998