Fission yeast Bgs1 glucan synthase participates in the control of growth polarity and membrane traffic.

Rod-shaped fission yeast grows through cell wall expansion at poles and septum, synthesized by essential glucan synthases. Bgs1 synthesizes the linear β(1,3)glucan of primary septum at cytokinesis. Linear β(1,3)glucan is also present in the wall poles, suggesting additional Bgs1 roles in growth polarity.

Comprehensive metabolic profiling of Geotrichum candidum and comparison with Saccharomyces cerevisiae.

Geotrichum candidum is a dimorphic yeast used in cheese processing. To our knowledge, no major metabolites have been identified to date in G. candidum except for some amino acid and fatty acid metabolites.

A cryo-TSEM with temperature cycling capability allows deep sublimation of ice to uncover fine structures in thick cells.

The scanning electron microscope (SEM) has been reassembled into a new type of cryo-electron microscope (cryo-TSEM) by installing a new cryo-transfer holder and anti-contamination trap, which allowed simultaneous acquisition of both transmission images (STEM images) and surface images (SEM images) in the frozen state. The ultimate temperatures of the holder and the trap reached - 190 °C and - 210 °C, respectively, by applying a liquid nitrogen slush. The STEM images at 30 kV were comparable to, or superior to, the images acquired with conventional transmission electron microscope (100 kV TEM) in contrast and sharpness.

Ultrastructural analysis in yeast reveals a meiosis-specific actin-containing nuclear bundle.

Actin polymerises to form filaments/cables for motility, transport, and the structural framework in a cell. Recent studies show that actin polymers are present not only in the cytoplasm but also in the nuclei of vertebrate cells. Here, we show, by electron microscopic observation with rapid freezing and high-pressure freezing, a unique bundled structure containing actin in the nuclei of budding yeast cells undergoing meiosis.

Inhibition of cell membrane ingression at the division site by cell walls in fission yeast.

Eukaryotic cells assemble actomyosin rings during cytokinesis to function as force-generating machines to drive membrane invagination and to counteract the intracellular pressure and the cell surface tension. How the extracellular matrix affects actomyosin ring contraction has not been fully explored. While studying the  1,3-β-glucan-synthase mutant -191, which is defective in division septum synthesis and arrests with a stable actomyosin ring, we found that weakening of the extracellular glycan matrix caused the generated spheroplasts to divide under the nonpermissive condition.

Two septation phases differ in ingression rate, septum structure, and response to F-actin loss.

In fission yeast, cytokinesis requires a contractile actomyosin ring (CR) coupled to membrane and septum ingression. Septation proceeds in two phases. In anaphase B, the septum ingresses slowly.

Specific detection of fission yeast primary septum reveals septum and cleavage furrow ingression during early anaphase independent of mitosis completion.

It is widely accepted in eukaryotes that the cleavage furrow only initiates after mitosis completion. In fission yeast, cytokinesis requires the synthesis of a septum tightly coupled to cleavage furrow ingression. The current cytokinesis model establishes that simultaneous septation and furrow ingression only initiate after spindle breakage and mitosis exit.

A New Membrane Protein Sbg1 Links the Contractile Ring Apparatus and Septum Synthesis Machinery in Fission Yeast.

Cytokinesis in many organisms requires a plasma membrane anchored actomyosin ring, whose contraction facilitates cell division. In yeast and fungi, actomyosin ring constriction is also coordinated with division septum assembly. How the actomyosin ring interacts with the plasma membrane and the plasma membrane-localized septum synthesizing machinery remains poorly understood.

Fission yeast septation.

In animal cells cytokinesis relies on the contraction of an actomyosin ring that pulls the plasma membrane to create a cleavage furrow, whose ingression finally divides the mother cell into two daughter cells. Fungal cells are surrounded by a tough and flexible structure called cell wall, which is considered to be the functional equivalent of the extracellular matrix in animal cells. Therefore, in addition to cleavage furrow ingression, fungal cytokinesis also requires the centripetal formation of a septum wall structure that develops between the dividing cells, whose genesis must be strictly coordinated with both the actomyosin ring closure and plasma membrane ingression.

The Cell Biology of Fission Yeast Septation.

In animal cells, cytokinesis requires the formation of a cleavage furrow that divides the cell into two daughter cells. Furrow formation is achieved by constriction of an actomyosin ring that invaginates the plasma membrane. However, fungal cells contain a rigid extracellular cell wall surrounding the plasma membrane; thus, fungal cytokinesis also requires the formation of a special septum wall structure between the dividing cells.

Cooperation between Paxillin-like Protein Pxl1 and Glucan Synthase Bgs1 Is Essential for Actomyosin Ring Stability and Septum Formation in Fission Yeast.

In fungal cells cytokinesis requires coordinated closure of a contractile actomyosin ring (CAR) and synthesis of a special cell wall structure known as the division septum. Many CAR proteins have been identified and characterized, but how these molecules interact with the septum synthesis enzymes to form the septum remains unclear. Our genetic study using fission yeast shows that cooperation between the paxillin homolog Pxl1, required for ring integrity, and Bgs1, the enzyme responsible for linear β(1,3)glucan synthesis and primary septum formation, is required for stable anchorage of the CAR to the plasma membrane before septation onset, and for cleavage furrow formation.

Augmin-dependent microtubule nucleation at microtubule walls in the spindle.

The formation of a functional spindle requires microtubule (MT) nucleation from within the spindle, which depends on augmin. How augmin contributes to MT formation and organization is not known because augmin-dependent MTs have never been specifically visualized. In this paper, we identify augmin-dependent MTs and their connections to other MTs by electron tomography and 3D modeling.

Visualization of yeast cells by electron microscopy.

In the 1970s, hydrocarbon or methanol utilizable yeasts were considered as a material for foods and ethanol production. During the course of studies into the physiology of yeasts, we found that these systems provide a suitable model for the biogenesis and ultrastructure research of microbodies (peroxisomes). Microbodies of hydrocarbon utilizing Candida tropicalis multiply profusely from the preexisting microbody.

Fission yeast Ags1 confers the essential septum strength needed for safe gradual cell abscission.

Fungal cytokinesis requires the assembly of a dividing septum wall. In yeast, the septum has to be selectively digested during the critical cell separation process. Fission yeast cell wall α(1-3)glucan is essential, but nothing is known about its localization and function in the cell wall or about cooperation between the α- and β(1-3)glucan synthases Ags1 and Bgs for cell wall and septum assembly.

Hyphal surface architecture and cell morphology of Trichoderma reesei.

The filamentous fungus Trichoderma reesei which is known to secrete high amounts of cellulolytic enzymes was found to produce a massive amount of fibrous material at the outer surface of the cell wall as observed by ultrahigh-resolution low-voltage scanning electron microscopy. Using transmission electron microscopy, the cell wall ornamentation of the hyper-cellulosic mutant PC-3-7 was found to be less massive and much thinner than for QM9414. A significant amount of fibrous material was produced in Avicel-grown cultures that were less abundant in glucose-grown cultures and Avicel was occasionally found entangled within the cell wall-associated fibrous layer.

Breakage of the nuclear envelope by an extending mitotic nucleus occurs during anaphase in Schizosaccharomyces japonicus.

During open mitosis in higher eukaryotic cells, the nuclear envelope completely breaks down and then mitotic chromosomes are exposed in the cytoplasm. By contrast, mitosis in lower eukaryotes, including fungi, proceeds with the nucleus enclosed in an intact nuclear envelope. The mechanism of mitosis has been studied extensively in yeast, a closed mitosis organism.

Ubiquitin-mediated proteasomal degradation of ABC transporters: a new aspect of genetic polymorphisms and clinical impacts.

The interindividual variation in the rate of drug metabolism and disposition has been known for many years. Pharmacogenomics dealing with heredity and response to drugs is a part of science that attempts to explain variability of drug responses and to search for the genetic basis of such variations or differences. Genetic polymorphisms of drug metabolizing enzymes and drug transporters have been found to play a significant role in the patients' responses to medication.

Pob1 ensures cylindrical cell shape by coupling two distinct rho signaling events during secretory vesicle targeting.

Proper cell morphogenesis requires the co-ordination of cell polarity, cytoskeletal organization and vesicle trafficking. The Schizosaccharomyces pombe mutant pob1-664 has a curious lemon-like shape, the basis of which is not understood. Here, we found abundant vesicle accumulation in these cells, suggesting that Pob1 plays a role in vesicle trafficking.

Technical pitfalls and improvements for high-speed screening and QSAR analysis to predict inhibitors of the human bile salt export pump (ABCB11/BSEP).

Drug-induced hepatotoxicity is one of the major problems encountered in drug discovery and development. Selection of a candidate compound for pre-clinical studies in the drug discovery process is a critical step that can determine the speed and expenditure of clinical development. Because inhibition of human adenosine triphosphate-binding cassette transporter ABCB11 (SPGP/bile salt export pump) has severe consequences, which include intrahepatic cholestasis and hepatotoxicity, resulting from exposure to toxic xenobiotics or drug interactions, in vitro screening methods are necessary for quantifying and characterizing the inhibition of ABCB11.

The tetraspan protein Dni1p is required for correct membrane organization and cell wall remodelling during mating in Schizosaccharomyces pombe.

In fungi, success of mating requires that both cells agglutinate, modify their extracellular envelopes, and fuse their plasma membranes and nuclei to produce a zygote. Here we studied the role of the Schizosaccharomyces pombe Dni1 protein in the cell fusion step of mating. Dni1p is a tetraspan protein bearing a conserved cystein motif similar to that present in fungal claudin-related proteins.

Three-dimensional arrangement of F-actin in the contractile ring of fission yeast.

The contractile ring, which is required for cytokinesis in animal and yeast cells, consists mainly of actin filaments. Here, we investigate the directionality of the filaments in fission yeast using myosin S1 decoration and electron microscopy. The contractile ring is composed of around 1,000 to 2,000 filaments each around 0.

Intracellular trafficking pathway of yeast long-chain base kinase Lcb4, from its synthesis to its degradation.

Sphingoid long-chain base 1-phosphates act as bioactive lipid molecules in eukaryotic cells. In budding yeast, long-chain base 1-phosphates are synthesized mainly by the long-chain base kinase Lcb4. We recently reported that, soon after yeast cells enter into the stationary phase, Lcb4 is rapidly degraded by being delivered to the vacuole in a palmitoylation- and phosphorylation-dependent manner.

The (1,3)beta-D-glucan synthase subunit Bgs1p is responsible for the fission yeast primary septum formation.

Cytokinesis is a crucial event in the cell cycle of all living cells. In fungal cells, it requires co-ordinated contraction of an actomyosin ring and synthesis of both plasmatic membrane and a septum structure that will constitute the new cell wall end. Schizosaccharomyces pombe contains four essential putative (1,3)beta-d-glucan synthase catalytic subunits, Bgs1p to Bgs4p.

Fission yeast autophagy induced by nitrogen starvation generates a nitrogen source that drives adaptation processes.

Autophagy is a conserved bulk protein degradation process that is proposed to play a role in events that arise when organisms are forced to radically change their fate, including nutritional starvation, differentiation and development. In our present study, we have identified fission yeast autophagy as a bulk protein degradation process induced by the deprivation of environmental nitrogen, the effects of which are known to trigger sexual differentiation as an adaptive response. Autophagy-defective mutants were found to be sterile in the absence of environmental nitrogen, but could complete sexual differentiation when nitrogen was supplied, suggesting that the major function of autophagy is to provide a nitrogen source.