Lack of GTP-bound Rho1p in secretory vesicles of Saccharomyces cerevisiae

Rho1p, an essential Rho-type GTPase in Saccharomyces cerevisiae, activates its effectors in the GTP-bound form. Here, we show that Rho1p in secretory vesicles cannot activate 1,3-β-glucan synthase, a cell wall synthesizing enzyme, during vesicular transport to the plasma membrane. Analyses with an antibody preferentially reacting with the GTP-bound form of Rho1p revealed that Rho1p remains in the inactive form in secretory vesicles. Rom2p, the GDP/GTP exchange factor of Rho1p, is preferentially localized on the plasma membrane even when vesicular transport is blocked. Overexpression of Rom2p results in delocalization of Rom2p and accumulation of 1,3-β-glucan in secretory vesicles. Based on these results, we propose that Rho1p is kept inactive in intracellular secretory organelles, resulting in repression of the activity of the cell wall–synthesizing enzyme within cells

Two regulatory steps of ER-stress sensor Ire1 involving its cluster formation and interaction with unfolded proteins

Chaperone protein BiP binds to Ire1 and dissociates in response to endoplasmic reticulum (ER) stress. However, it remains unclear how the signal transducer Ire1 senses ER stress and is subsequently activated. The crystal structure of the core stress-sensing region (CSSR) of yeast Ire1 luminal domain led to the controversial suggestion that the molecule can bind to unfolded proteins. We demonstrate that, upon ER stress, Ire1 clusters and actually interacts with unfolded proteins. Ire1 mutations that affect these phenomena reveal that Ire1 is activated via two steps, both of which are ER stress regulated, albeit in different ways. In the first step, BiP dissociation from Ire1 leads to its cluster formation. In the second step, direct interaction of unfolded proteins with the CSSR orients the cytosolic effector domains of clustered Ire1 molecules

From Traditional Factor Analysis Model to Causal Modeling by SEM : Exemplifying the Scale for the Measurement of Anthrophobic Tendency and the Interpersonal Stress-coping Inventory

心理学研究分野での構成概念の次元は、因子間に相関がある因子分析モデルのもとで、主に探索されてきている。Cattell(1966) は、因子間の相関的な関係性を、同じ水準だけではなく異なった水準あるいは層における因子の間での因果モデルヘと発展させた。McArdle(1984) によって示されたように、Cattellのアイデイアは構造方程式モデリングの分野において実現されてきている。本稿の目的は、構成概念妥当性を確認することへの構造方程式モデリングの有効性を示すことである。研究Iでは、堀井・小川(1996、1997) による対人恐怖心性の6因子を探索的因子分析で抽出した。これらの6因子を確認するために、項目による7種類の因子分析的モデルと下位尺度による5つのモデルと1つの因果モデルがAomsによって推定された。研究Ⅱでは、加藤(2000) による対人ストレスコーピング尺度の6因子が同様に抽出された。この尺度からの15項目に対して、6種類の因子分析モデルと1つの因果モデルが分析された。2つの研究共に、最も適合度の高いモデルは因果モデルであった。これらの結果の意味が議論された。The dimensions of the constructs in the fields of psychological research have mostly been explored under the factor analysis model with correlations among factors. Cattell (1966) had expanded such correlational relationships among factors to the causal modeling between factors not only at the same level also at different levels or strata. As indicated by McArdle (1984) Cattell\u27s idea has been actual in the field of structural equation modeling. The purpose of this paper is to demonstrate the utility of structural equation modeling for confirming the construct validities. In study I, the six factors of anthrophobic tendency by Hoii & Ogawa (1996, 1997) are extracted by the exploratory factor analysis. To confirm the structure of these six factors, seven kinds of factor analytical models using items and five models and one causal model using sub-scales are estimated by the Amos. In study II, the six factors of the interpersonal stress-coping inventory by Kato (2000) are also extracted. For the 15 items from this inventory, six kinds of factor analytical models and one causal model are analyzed. In both studies, the model that fits best is the causal model. The implications of these findings are discussed

Vesicle-Like Biomechanics Governs Important Aspects of Nuclear Geometry in Fission Yeast

It has long been known that during the closed mitosis of many unicellular eukaryotes, including the fission yeast (Schizosaccharomyces pombe), the nuclear envelope remains intact while the nucleus undergoes a remarkable sequence of shape transformations driven by elongation of an intranuclear mitotic spindle whose ends are capped by spindle pole bodies embedded in the nuclear envelope. However, the mechanical basis of these normal cell cycle transformations, and abnormal nuclear shapes caused by intranuclear elongation of microtubules lacking spindle pole bodies, remain unknown. Although there are models describing the shapes of lipid vesicles deformed by elongation of microtubule bundles, there are no models describing normal or abnormal shape changes in the nucleus. We describe here a novel biophysical model of interphase nuclear geometry in fission yeast that accounts for critical aspects of the mechanics of the fission yeast nucleus, including the biophysical properties of lipid bilayers, forces exerted on the nuclear envelope by elongating microtubules, and access to a lipid reservoir, essential for the large increase in nuclear surface area during the cell cycle. We present experimental confirmation of the novel and non-trivial geometries predicted by our model, which has no free parameters. We also use the model to provide insight into the mechanical basis of previously described defects in nuclear division, including abnormal nuclear shapes and loss of nuclear envelope integrity. The model predicts that (i) despite differences in structure and composition, fission yeast nuclei and vesicles with fluid lipid bilayers have common mechanical properties; (ii) the S. pombe nucleus is not lined with any structure with shear resistance, comparable to the nuclear lamina of higher eukaryotes. We validate the model and its predictions by analyzing wild type cells in which ned1 gene overexpression causes elongation of an intranuclear microtubule bundle that deforms the nucleus of interphase cells

On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective

Presented here are the observations and interpretations from a comprehensive analysis of 16 representative particles returned from the C-type asteroid Ryugu by the Hayabusa2 mission. On average Ryugu particles consist of 50% phyllosilicate matrix, 41% porosity and 9% minor phases, including organic matter. The abundances of 70 elements from the particles are in close agreement with those of CI chondrites. Bulk Ryugu particles show higher δ18O, Δ17O, and ε54Cr values than CI chondrites. As such, Ryugu sampled the most primitive and least-thermally processed protosolar nebula reservoirs. Such a finding is consistent with multi-scale H-C-N isotopic compositions that are compatible with an origin for Ryugu organic matter within both the protosolar nebula and the interstellar medium. The analytical data obtained here, suggests that complex soluble organic matter formed during aqueous alteration on the Ryugu progenitor planetesimal (several 10’s of km), <2.6 Myr after CAI formation. Subsequently, the Ryugu progenitor planetesimal was fragmented and evolved into the current asteroid Ryugu through sublimation

A pristine record of outer Solar System materials from asteroid Ryugu’s returned sample

Volatile and organic-rich C-type asteroids may have been one of the main sources of Earth’s water. Our best insight into their chemistry is currently provided by carbonaceous chondritic meteorites, but the meteorite record is biased: only the strongest types survive atmospheric entry and are then modified by interaction with the terrestrial environment. Here we present the results of a detailed bulk and microanalytical study of pristine Ryugu particles, brought to Earth by the Hayabusa2 spacecraft. Ryugu particles display a close compositional match with the chemically unfractionated, but aqueously altered, CI (Ivuna-type) chondrites, which are widely used as a proxy for the bulk Solar System composition. The sample shows an intricate spatial relationship between aliphatic-rich organics and phyllosilicates and indicates maximum temperatures of ~30 °C during aqueous alteration. We find that heavy hydrogen and nitrogen abundances are consistent with an outer Solar System origin. Ryugu particles are the most uncontaminated and unfractionated extraterrestrial materials studied so far, and provide the best available match to the bulk Solar System composition