Toxoplasma gondii targets a protein phosphatase 2C to the nuclei of infected host cells

Intracellular pathogens have evolved a wide array of mechanisms to invade and co-opt their host cells for intracellular survival. Apicomplexan parasites such as Toxoplasma gondii employ the action of unique secretory organelles named rhoptries for internalization of the parasite and formation of a specialized niche within the host cell. We demonstrate that Toxoplasma gondii also uses secretion from the rhoptries during invasion to deliver a parasite-derived protein phosphatase 2C (PP2C-hn) into the host cell and direct it to the host nucleus. Delivery to the host nucleus does not require completion of invasion, as evidenced by the fact that parasites blocked in the initial stages of invasion with cytochalasin D are able to target PP2C-hn to the host nucleus. We have disrupted the gene encoding PP2C-hn and shown that PP2C-hn-knockout parasites exhibit a mild growth defect that can be rescued by complementation with the wild-type gene. The delivery of parasite effector proteins via the rhoptries provides a novel mechanism for Toxoplasma to directly access the command center of its host cell during infection by the parasite.     

Verprolin function in endocytosis and actin organization. Roles of the Las17p (yeast WASP)-binding domain and a novel C-terminal actin-binding domain

Vrp1p (verprolin, End5p) is the yeast ortholog of human Wiskott-Aldrich syndrome protein (WASP)-interacting protein (WIP). Vrp1p localizes to the cortical actin cytoskeleton, is necessary for its polarization to sites of growth and is also essential for endocytosis. At elevated temperature, Vrp1p becomes essential for growth. A C-terminal Vrp1p fragment (C-Vrp1p) retains the ability to localize to the cortical actin cytoskeleton and function in actin-cytoskeleton polarization, endocytosis and growth. Here, we demonstrate that two submodules in C-Vrp1p are required for actin-cytoskeleton polarization: a novel C-terminal actin-binding submodule (CABS) that contains a novel G-actin-binding domain, which we call a verprolin homology 2 C-terminal (VH2-C) domain; and a second submodule comprising the Las17p-binding domain (LBD) that binds Las17p (yeast WASP). The LBD localizes C-Vrp1p to membranes and the cortical actin cytoskeleton. Intriguingly, the LBD is sufficient to restore endocytosis and growth at elevated temperature to Vrp1p-deficient cells. The CABS also restores these functions, but only if modified by a lipid anchor to provide membrane association. Our findings highlight the role of Las17p binding for Vrp1p membrane association, suggest general membrane association may be more important than specific targeting to the cortical actin cytoskeleton for Vrp1p function in endocytosis and cell growth, and suggest that Vrp1p binding to individual effectors may alter their physiological activity.     

Contrasting patterns of genetic structure and phylogeography in the marine agarophytes Gelidiophycus divaricatus and G. freshwateri (Gelidiales,Rhodophyta) from East Asia

The evolutionary and population demographic history of marine red algae in East Asia is poorly understood. Here, we reconstructed the phylogeographies of two upper intertidal species endemic to East Asia, Gelidiophycus divaricatus and G. freshwateri. Phylogenetic and phylogeographic inferences of 393 mitochondrial cox1, 128 plastid rbcL, and 342 nuclear ITS2 sequences were complemented with ecological niche models. Gelidiophycus divaricatus, a southern species adapted to warm water, is characterized by a high genetic diversity and a strong geographical population structure, characteristic of stable population sizes and sudden reduction to recent expansion. In contrast, G. freshwateri, a northern species adapted to cold temperate conditions, is genetically relatively homogeneous with a shallow population structure resulting from steady population growth and recent equilibrium. The overlap zone of the two species roughly matches summer and winter isotherms, indicating that surface seawater temperature is a key feature influencing species range. Unidirectional genetic introgression was detected at two sites on Jeju Island where G. divaricatus was rare while G. freshwateri was common, suggesting the occurrence of asymmetric natural hybrids, a rarely reported event for rhodophytes. Our results illustrate that Quaternary climate oscillations have left strong imprints on the current day genetic structure and highlight the importance of seawater temperature and sea level change in driving speciation in upper intertidal seaweed species.     

Cellular hydrophobicity of Listeria monocytogenes involves initial attachment and biofilm formation on the surface of polyvinyl chloride

Aims: To clarify the cellular properties of Listeria monocytogenes involved in adhesion to and biofilm formation on polyvinyl chloride, a widely used material in the food manufacturing process. Methods and Results: A significant correlation between the ability of initial adherence to and biofilm formation on PVC was observed for 24 L. monocytogenes strains (Spearman rank‐correlation coefficient, r_s = 0·89). The swimming motility assay revealed no relationship between initial adherence and motility of L. monocytogenes. The microbial adhesion to solvent assay revealed an interaction of L. monocytogenes cells with nonpolar solvents, and a significant correlation was also observed between the degree of interaction with nonpolar solvents and initial adherence to PVC (r_s = 0·87 and r_s = 0·84, between initial adherence and affinities to decane and hexadecane, respectively). Conclusions: Results indicate that cellular hydrophobicity of L. monocytogenes is an important property involved in the initial adherence to and biofilm formation on PVC. Significance and Impact of Study: This study clarified the factors involved in the adherence to and biofilm formation ability of L. monocytogenes strains with PVC.     

Cloning of a new aquaporin (AQP10) abundantly expressed in duodenum and jejunum

A new aquaporin (AQP10) was identified in human small intestine. This gene encoded a 264-amino-acid protein with high sequence identity with AQP3 (53%), 9 (52%), and 7 (43%). These AQPs constitute one subfamily of AQP family that is differentiated from the other subfamily of AQP (AQP0, 1, 2, 4, 5, 6, and 8) by sequence homology. Ribonuclease protection assay and Northern blotting demonstrated almost exclusive expression of AQP10 mRNA in the duodenum and jejunum. In situ hybridization localized it in absorptive jejunal epithelial cells. Xenopus oocytes expressing AQP10 exhibited an increased osmotic water permeability in a mercury-sensitive manner. Although AQP10 belongs to the AQP subfamily, which has been characterized by permeability to water and neutral solutes such as urea and glycerol, it was not permeable to urea nor glycerol. The specific expression of AQP10 suggests its contribution to the water transport in the upper portion of small intestine.     

ATP synthase: constrained stoichiometry of the transmembrane rotor

Recent structural data suggest that the number of identical subunits (c or III) assembled into the cation-powered rotor of F1F0 ATP synthase depends on the biological origin. Atomic force microscopy allowed individual subunits of the cylindrical transmembrane rotors from spinach chloroplast and from Ilyobacter tartaricus ATP synthase to be directly visualized in their native-like environment. Occasionally, individual rotors exhibit structural gaps of the size of one or more subunits. Complete rotors and arch-shaped fragments of incomplete rotors revealed the same diameter within one ATP synthase species. These results suggest the rotor diameter and stoichiometry to be determined by the shape of the subunits and their nearest neighbor interactions.     

Soybean curd refuse alleviates experimental tumorigenesis in rat colon

Adult Fischer-344 rats which underwent administration of azoxymethane were fed diets containing soybean curd refuse (SCR) or a high-molecular-weight fraction of soy protein digest (HMF), or Hammarsten casein (CAS) as a protein source over a period of 34 weeks. All the living rats of each group at 22, 28 or 34 weeks were endoscopically inspected for tumor incidence in the colon. SCR turned out to be comparable to HMF in anti-tumorigenicity, or rather better than HMF.     

Interleukin 1 induces multinucleation and bone-resorbing activity of osteoclasts in the absence of osteoblasts/stromal cells

Interleukin-1 (IL-1) is one of the most potent bone-resorbing factors involved in bone loss associated with inflammation. We previously reported that IL-1 prolonged the survival of multinucleated osteoclast-like cells (OCLs) formed in cocultures of murine osteoblasts/stromal cells and bone marrow cells via the prevention of spontaneously occurring apoptosis. It was reported that macrophage colony-stimulating factor (M-CSF/CSF-1) prolongs the survival of OCLs without the help of osteoblasts/stromal cells. The present study was conducted to determine whether IL-1 also directly induces the multinucleation and activation of OCLs. Mononuclear osteoclast-like cells (prefusion osteoclasts; pOCs) were purified using the "disintegrin" echistatin from cocultures of murine osteoblastic cells (MB 1.8 cells) and bone marrow cells. Both IL-1 and M-CSF prolonged the survival and induced the multinucleation of pOCs through their respective receptors. However, actin ring formation (a functional marker of osteoclasts) by multinucleated cells was observed in the pOC cultures treated with IL-1, but not those treated with M-CSF. We previously reported that enriched multinucleated OCLs as well as pOCs placed on bone/dentine slices formed few resorption pits, but their pit-forming activity was greatly increased by the addition of osteoblasts/stromal cells. Here, pit-forming activity of both pOCs and enriched OCLs placed on dentine slices was induced by adding IL-1, even in the absence of osteoblasts/stromal cells. M-CSF failed to induce pit-forming activity in pOC and enriched OCL cultures. These results indicate that IL-1 induces the multinucleation and bone-resorbing activity of osteoclasts even in the absence of osteoblasts/stromal cells.     

Enhanced calcium absorption in the small intestine by a phytate-removed deamidated soybean globulin preparation

Soybean globulins were deamidated after removing phytate using ion-exchange resins, and then hydrolyzed by digestive enzymes. The phytate-removed deamidated soybean globulins (PrDS) retained high calcium-binding ability even after the hydrolysis by digestive enzymes. PrDS and its hydrolysates enhanced calcium absorption from the small intestine when injected into the small intestine together with a calcium solution.