Effect of divalent cation ionophore (A 23187) on renal handling of phosphorus

Effect of divalent cation ionophore (A 23187) on renal handling of phosphorus. To evaluate the effect of an increase in intracellular calcium on renal handling of phosphorus, calcium ionophore, which facilitates passive entry of calcium into cytosol, was given i.v. to four groups of rats: group 1, animals with intact parathyroid glands; group 2, parathyroidectomized (PTX) rats; group 3, PTX animals receiving i.v. parathyroid hormone (PTH); and group 4, PTX animals pretreated with i.v. ionophore, then given i.v. PTH. During the administration of ionophore in group 1, serum calcium (Sca) decreased from 8.7 ± 0.2 (mean ±SEM) to 7.5 ± 0.2mg/100 ml (P < 0.001), fractional excretion of phosphorus (CP/CIn) decreased from 0.110 ± 0.020 to 0.019 ± 0.006 (P < 0.001), and urinary cyclic 3′, 5′-adenosine monophosphate (UcAMP) decreased from 131 ± 23 to 46 ± 16 pmoles/min (P < 0.0125). In group 2, during the administration of ionophore, Sca decreased from 6.5 ± 0.2 to 5.7 ± 0.2mg/100 ml (P < 0.001), but neither CP/CIn nor UcAMP were altered. In group 2, during the administration of ionophore, CP/Cm decreased from 0.43 ± 0.05 to 0.19 ± 0.04 (P < 0.005), UcAMP decreased from 254 ± 20 to 159 ± 11 (P < 0.001). In group 4, during combined i.v. administration of ionophore and PTH, CP/CIn was reduced from 0.19 ± 0.009 to 0.044 ± 0.012 (P < 0.005), and serum calcium was reduced from 6.5 ± 0.3 to 5.1 ± 0.3mg/100 ml (P < 0.01). These findings indicate that i.v. ionophore suppresses urinary excretion of phosphorus, only in the presence of either endogenous or exogenous PTH. The associated decrease in UcAMP suggests that this effect could be mediated through inhibition of PTH-dependent formation of cAMP, possibly resulting from the ionophore-induced increase in intracellular calcium in renal tubular cells.Effet d'un ionophore des cations divalents (A 23187) sur le comportement renal vis a vis du phosphate. Afin d'évaluer l'effet de l'augmentation du calcium intracellulaire sur le comportement rénal vis à vis du phosphore, on a donné à quatre groupes de rats un ionophore de calcium qui facilite l'entrée passive de ce cation dans le cytosol. Le groupe 1 est composé d'animaux dont les parathyroïdes sont intactes, le groupe 2 d'animaux parathyroïdectomisés (PTX), le groupe 3 d'animaux PTX recevant de l'hormone parathyroïdienne (PTH) par voie intra-veineuse et le groupe 4 d'animaux pré-traités par l'ionophore qui reçoivent de la PTH. Au cours de l'administration de l'ionophore au groupe 1, le calcium séreique (SCa) diminue de 8,7 ± 0,2 (m ±SEM) à 7,5 ± 0,2mg/100 ml (P < 0,001), l'excrétion fractionnelle du phosphore (CP/CIn) diminue de 0,110 ± 0,020 à 0,019 ± 0,006 (P < 0,001) et l'AMP cyclique urinaire (UcAMP) diminue de 131 ± 23 à 46 ± 16 pmoles/min (P < 0,0125).Dans le groupe 2, au cours de l'administration de l'ionophore, Sca diminue de 6,5 ± 0,2 a 5,7 ± 0,2 mg/100 ml (P < 0,001), mais ni CP/CIn ni UcAMP ne sont modifiés. Dans le groupe 3, au cours de l'administration de l'ionophore, CP/CIn diminue de 254 ± 20 à 159 ± 11 (P < 0,001). Dans le groupe 4, au cours de l'administration combinée d'ionophore et de PTH, CP/CIn diminue de 0,19 ± 0,009 à 0,004 ± 0,012 (P < 0,005) et Sca de 6,5 ± 0,3 à 5,1 ± 0,3 mg/100 ml (P < 0,01). Ces constatations indiquent que l'ionophore ne diminue l'excrétion urinaire de phosphate qu'en présence de PTH endogène ou exogène. La baisse associée de UcAMP suggère que cet effet peut avoir pour médiateur l'inhibition de la formation d'AMP cyclique dépendante de la PTH, conséquence de l'augmentation du calcium intracellulaire dans les cellules tubulaires rénales, induite par l'ionophore

Amino acid substitution equivalent to human chorea-acanthocytosis I2771R in yeast Vps13 protein affects its binding to phosphatidylinositol 3-phosphate

The rare human disorder chorea-acanthocytosis (ChAc) is caused by mutations in hVPS13A gene. The hVps13A protein interacts with actin and regulates the level of phosphatidylinositol 4-phosphate (PI4P) in the membranes of neuronal cells. Yeast Vps13 is involved in vacuolar protein transport and, like hVps13A, participates in PI4P metabolism. Vps13 proteins are conserved in eukaryotes, but their molecular function remains unknown. One of the mutations found in ChAc patients causes amino acids substitution I2771R which affects the localization of hVps13A in skeletal muscles. To dissect the mechanism of pathogenesis of I2771R, we created and analyzed a yeast strain carrying the equivalent mutation. Here we show that in yeast, substitution I2749R causes dysfunction of Vps13 protein in endocytosis and vacuolar transport, although the level of the protein is not affected, suggesting loss of function. We also show that Vps13, like hVps13A, influences actin cytoskeleton organization and binds actin in immunoprecipitation experiments. Vps13-I2749R binds actin, but does not function in the actin cytoskeleton organization. Moreover, we show that Vps13 binds phospholipids, especially phosphatidylinositol 3-phosphate (PI3P), via its SHR_BD and APT1 domains. Substitution I2749R attenuates this ability. Finally, the localization of Vps13-GFP is altered when cellular levels of PI3P are decreased indicating its trafficking within the endosomal membrane system. These results suggest that PI3P regulates the functioning of Vps13, both in protein trafficking and actin cytoskeleton organization. Attenuation of PI3P-binding ability in the mutant hVps13A protein may be one of the reasons for its mislocalization and disrupted function in cells of patients suffering from ChAc

Phosphatidylinositol-3-phosphate regulates response of cells to proteotoxic stress

Human Nedd4 ubiquitin ligase, or its variants, inhibit yeast cell growth by disturbing the actin cytoskeleton organization and dynamics, and lead to an increase in levels of ubiquitinated proteins. In a screen for multicopy suppressors which rescue growth of yeast cells producing Nedd4 ligase with an inactive WW4 domain (Nedd4w4), we identified a fragment of ATG2 gene encoding part of the Atg2 core autophagy protein. Expression of the Atg2-C1 fragment (aa 1074-1447) improved growth, actin cytoskeleton organization, but did not significantly change the levels of ubiquitinated proteins in these cells. The GFP-Atg2-C1 protein in Nedd4w4-producing cells primarily localized to a single defined structure adjacent to the vacuole, surrounded by an actin filament ring, containing Hsp42 and Hsp104 chaperones. This localization was not affected in several atg deletion mutants, suggesting that it might be distinct from the phagophore assembly site (PAS). However, deletion of ATG18 encoding a phosphatidylinositol-3-phosphate (PI3P)-binding protein affected the morphology of the GFP-Atg2-C1 structure while deletion of ATG14 encoding a subunit of PI3 kinase suppressed toxicity of Nedd4w4 independently of GFP-Atg2-C1. Further analysis of the Atg2-C1 revealed that it contains an APT1 domain of previously uncharacterized function. Most importantly, we showed that this domain is able to bind phosphatidylinositol phosphates, especially PI3P, which is abundant in the PAS and endosomes. Together our results suggest that human Nedd4 ubiquitinates proteins in yeast and causes proteotoxic stress and, with some Atg proteins, leads to formation of a perivacuolar structure, which may be involved in sequestration, aggregation or degradation of proteins

Nanostructured carbon materials decorated with organophosphorus moieties: Synthesis and application

A new synthetic approach for the production of carbon nanomaterials (CNM) decorated with organophosphorus moieties is presented. Three different triphenylphosphine oxide (TPPO) derivatives were used to decorate oxidized multiwalled carbon nanotubes (ox-MWCNTs) and graphene platelets (GPs). The TPPOs chosen bear functional groups able to react with the CNMs by Tour reaction (an amino group), nitrene cycloaddition (an azido group) or CuAAC reaction (one terminal C–C triple bond). All the adducts were characterized by FTIR, Raman spectroscopy, TEM, XPS, elemental analysis and ICP-AES. The cycloaddition of nitrene provided the higher loading on ox-MWCNTs and GPs as well, while the Tour approach gave best results with nanotubes (CNTs). Finally, we investigated the possibility to reduce the TPPO functionalized CNMs to the corresponding phosphine derivatives and applied one of the materials produced as heterogeneous organocatalyst in a Staudinger ligation reaction

Two chemically distinct root lignin barriers control solute and water balance.

Lignin is a complex polymer deposited in the cell wall of specialised plant cells, where it provides essential cellular functions. Plants coordinate timing, location, abundance and composition of lignin deposition in response to endogenous and exogenous cues. In roots, a fine band of lignin, the Casparian strip encircles endodermal cells. This forms an extracellular barrier to solutes and water and plays a critical role in maintaining nutrient homeostasis. A signalling pathway senses the integrity of this diffusion barrier and can induce over-lignification to compensate for barrier defects. Here, we report that activation of this endodermal sensing mechanism triggers a transcriptional reprogramming strongly inducing the phenylpropanoid pathway and immune signaling. This leads to deposition of compensatory lignin that is chemically distinct from Casparian strip lignin. We also report that a complete loss of endodermal lignification drastically impacts mineral nutrients homeostasis and plant growth

Genome-wide sexually antagonistic variants reveal long-standing constraints on sexual dimorphism in fruit flies

The evolution of sexual dimorphism is constrained by a shared genome, leading to ‘sexual antagonism’, in which different alleles at given loci are favoured by selection in males and females. Despite its wide taxonomic incidence, we know little about the identity, genomic location, and evolutionary dynamics of antagonistic genetic variants. To address these deficits, we use sex-specific fitness data from 202 fully sequenced hemiclonal Drosophila melanogaster fly lines to perform a genome-wide association study (GWAS) of sexual antagonism. We identify approximately 230 chromosomal clusters of candidate antagonistic single nucleotide polymorphisms (SNPs). In contradiction to classic theory, we find no clear evidence that the X chromosome is a hot spot for sexually antagonistic variation. Characterising antagonistic SNPs functionally, we find a large excess of missense variants but little enrichment in terms of gene function. We also assess the evolutionary persistence of antagonistic variants by examining extant polymorphism in wild D. melanogaster populations and closely related species. Remarkably, antagonistic variants are associated with multiple signatures of balancing selection across the D. melanogaster distribution range and in their sister species D. simulans, indicating widespread and evolutionarily persistent (about 1 million years) genomic constraints on the evolution of sexual dimorphism. Based on our results, we propose that antagonistic variation accumulates because of constraints on the resolution of sexual conflict over protein coding sequences, thus contributing to the long-term maintenance of heritable fitness variation

Genomic landscape of drug response reveals novel mediators of anthelmintic resistance

Like other pathogens, parasitic helminths can rapidly evolve resistance to drug treatment. Understanding the genetic basis of anthelmintic drug resistance in parasitic nematodes is key to tracking its spread and improving the efficacy and sustainability of parasite control. Here, we use an in vivo genetic cross between drug-susceptible and multi-drug-resistant strains of Haemonchus contortus in a natural host-parasite system to simultaneously map resistance loci for the three major classes of anthelmintics. This approach identifies new alleles for resistance to benzimidazoles and levamisole and implicates the transcription factor cky-1 in ivermectin resistance. This gene is within a locus under selection in ivermectin-resistant populations worldwide; expression analyses and functional validation using knockdown experiments support that cky-1 is associated with ivermectin survival. Our work demonstrates the feasibility of high-resolution forward genetics in a parasitic nematode and identifies variants for the development of molecular diagnostics to combat drug resistance in the field

All-sky search for time-integrated neutrino emission from astrophysical sources with 7 years of IceCube data

Since the recent detection of an astrophysical flux of high energy neutrinos, the question of its origin has not yet fully been answered. Much of what is known about this flux comes from a small event sample of high neutrino purity, good energy resolution, but large angular uncertainties. In searches for point-like sources, on the other hand, the best performance is given by using large statistics and good angular reconstructions. Track-like muon events produced in neutrino interactions satisfy these requirements. We present here the results of searches for point-like sources with neutrinos using data acquired by the IceCube detector over seven years from 2008--2015. The discovery potential of the analysis in the northern sky is now significantly below $E_\nu^2d\phi/dE_\nu=10^{-12}\:\mathrm{TeV\,cm^{-2}\,s^{-1}}$, on average $38\%$ lower than the sensitivity of the previously published analysis of four years exposure. No significant clustering of neutrinos above background expectation was observed, and implications for prominent neutrino source candidates are discussed.Comment: 19 pages, 17 figures, 3 tables; ; submitted to The Astrophysical Journa