bluuebunny/crossref_metadata_2025 huggingface dataset:
A 700‐year record of atmospheric circulation developed from the Law Dome ice core, East Antarctica
Authors: Souney Joseph M. , Mayewski Paul A. , Goodwin Ian D. , Meeker Loren D. , Morgan Vin , Curran Mark A. J. , van Ommen Tas D. , Palmer Anne S.
Published: December 2002

A 700‐year, high‐resolution, multivariate ice core record from Dome Summit South (DSS) (66°46′S, 112°48′E; 1370 m), Law Dome, is used to investigate sea level pressure (SLP) variability in the region of East Antarctica. Empirical orthogonal function (EOF) analysis reveals that the first EOF (LDEOF1) of the combined glaciochemical, oxygen isotope ratio, and accumulation rate record from DSS represents most of the variability in sea salt seen in the record. LDEOF1 is positively correlated (at least 95% confidence level) to instrumental June mean SLP across most of East Antarctica. Over the last 700 years, LDEOF1 levels at Law Dome were the highest during the nineteenth century, suggesting an increase in intensification of winter circulation during this period. The Law Dome DSS oxygen isotope ratio series also indicates that the nineteenth century had the coldest winters of any century in the record. In contrast, LDEOF1 levels were the lowest at Law Dome during the eighteenth century, suggesting a significant shift in the patterns and/or intensity of East Antarctic atmospheric circulation between the eighteenth and the nineteenth centuries. The LDEOF1 sea salt record is characterized by significant decadal‐scale variability with a strong 25‐year periodic structure.
Stratospheric versus pollution influences on ozone at Bermuda: Reconciling past analyses
Authors: Li Qinbin , Jacob Daniel J. , Fairlie T. Duncan , Liu Hongyu , Martin Randall V. , Yantosca Robert M.
Published: December 2002

Conflicting interpretations of the spring ozone maximum observed at Bermuda (32°N, 65°W) have fueled the debate on stratospheric influence versus tropospheric production as sources of tropospheric ozone. We use a global three‐dimensional (3‐D) model of tropospheric ozone‐NOx‐hydrocarbon chemistry driven by assimilated meteorological observations to reconcile these past interpretations. The model reproduces the observed seasonal cycle of surface ozone at Bermuda and captures the springtime day‐to‐day variability (r = 0.82, n = 122, p < 0.001) driven by high‐ozone events. We find that transport of North American pollution behind cold fronts is the principal contributor to springtime surface ozone at Bermuda and is responsible for all the high‐ozone events. The model reproduces the observed positive correlations of surface ozone with 7Be and 210Pb at Bermuda; the correlation with 7Be reflects the strong subsidence behind cold fronts, resulting in the mixing of middle‐tropospheric air with continental outflow in the air arriving at Bermuda, as indicated by the positive 7Be‐210Pb correlation. This mixing appears to have been an obfuscating factor in past interpretations of subsiding back‐trajectories at Bermuda as evidence for a stratospheric or upper tropospheric origin for ozone. Isentropic back‐trajectories computed in our model reproduce the previously reported subsidence associated with high‐ozone events. Even in the free troposphere, we find that the stratosphere contributes less than 5 ppbv (<10%) to spring ozone over Bermuda. Positive O3‐7Be and negative O3‐210Pb correlations observed at Tenerife (28°N, 16°W, 2.4 km) in summer are reproduced by the model and are consistent with a middle‐tropospheric source of ozone, not an upper tropospheric or stratospheric source as previously suggested. A regional budget for the North Atlantic in spring indicates that the stratosphere contributes less than 10 ppbv ozone (<5%) below 500 hPa, while the lower troposphere contributes 20–40 ppbv ozone throughout the troposphere.
Recent changes in climate extremes in the Caribbean region
Authors: Peterson Thomas C. , Taylor Michael A. , Demeritte Rodger , Duncombe Donna L. , Burton Selvin , Thompson Francisca , Porter Avalon , Mercedes Mejia , Villegas Elba , Semexant Fils Rony , Klein Tank Albert , Martis Albert , Warner Robert , Joyette Antonio , Mills Willis , Alexander Lisa , Gleason Byron
Published: December 2002

A January 2001 workshop held in Kingston, Jamaica, brought together scientists and data from around the Caribbean region and made analysis of indices of extremes derived from daily weather observation in the region possible. The results of the analyses indicate that the percent of days having very warm maximum or minimum temperatures increased strongly since the late 1950s while the percent of days with very cold temperatures decreased. One measure of extreme precipitation shows an increase over this time period while the one analyzed measure of dry conditions, the maximum number of consecutive dry days, is decreasing. These changes generally agree with what is observed in many other parts of the world.
Liver transplant and familial amyloidotic polyneuropathy
Authors: Lewis David W.
Published: December 2002

Nineteen patients, who had undergone liver transplantation for familial amyloidotic polyneuropathy, had answered a quality of life questionnaire including 61 questions on somatic and mental symptoms, social aspects of life, confidence and satisfaction before, one year, and two years after transplantation. We found that patient satisfaction was generally good two years or more after the transplantation. Most of the patients were very or quite satisfied with the result. All of them had the drive to go on and felt hopeful about the future. However, on the second follow-up, 37% of the patients noted that they felt more insecure in their everyday life and there was a significant difference between the two assessments. The diarrhea score became worse between one and two years after the transplantation and was closely related to the duration of the gastrointestinal symptoms and to the duration of the disease before transplantation. The mental symptoms also increased significantly between the evaluations and this related to the severity of the somatic symptoms. Our conclusion is that liver transplantation should be performed before advanced somatic symptoms start to develop in order to improve the patients’ chances of a good quality of life following liver transplantation.
Risk factors for invasive aspergillosis in liver transplant recipients
Authors: Fortún Jesús , Martín-Dávila Pilar , Moreno Santiago , de Vicente Emilio , Nuño Javier , Candelas Angel , Bárcena Rafael , García Miguel
Published: December 2002

Aspergillosis is a potential, severe, and usually early complication of liver transplantation. New promising strategies, such as detecting Aspergillus antigenemia, have been used for the diagnosis of aspergillosis in immunosuppressed patients, but the impact in solid organ transplantation is not well known. A case-control study in 260 adults who underwent liver transplantation from January 1994 to June 2000 was performed. A case was defined as any liver transplant recipient with a proven or probable diagnosis of invasive aspergillosis. Controls were defined as a liver transplant recipient without aspergillosis infection with a survival longer than two months after transplantation. Clinical and analytical variables, including Aspergillus antigenemia, were compared. A special analysis was performed in patients in whom late aspergillosis developed (after day 100 posttransplantation). Among 260 patients, invasive aspergillosis developed in 15 (5.6%). Median time from transplantation to aspergillosis in 13 patients with sufficient data for analysis was 126 days (range, 22 to 1117). Seven (54%) developed the infection after day 100 posttransplantation. Thirty-eight patients were used as controls. Antigenemia was available in nine of 13 cases and in 33 of 38 controls. By multivariate analysis, retransplantation (OR, 29.9 [95% CI, 2.1 to 425.1]), dialysis requirements after transplantation (OR, 24.5 [95% CI, 1.25 to 354]), and the presence of Aspergillus antigenemia in serum at any time point after transplantation (OR, 50.0 [95% CI, 3.56 to 650]) were independently associated to aspergillosis. In the subgroup of patients that developed late aspergillosis, cytomegalovirus infection (OR, 6.7 [95% CI, 1.0 to 42.5]) was the only independent factor associated. Hepatic and renal dysfunction predispose to Aspergillus infection in liver transplant recipients. Cytomegalovirus infection and increased immunosuppression favor invasive aspergillosis during the late posttransplantation period. Aspergillus antigenemia seems to be a good predictor of invasive aspergillosis.
Viscosity of silica
Authors: Doremus Robert H.
Published: December 2002

Experimental measurements of the viscosity of silica (SiO2) are critically examined; the best measurements show an activation energy of 515 kJ/mole above 1400 °C and 720 kJ/mole below this temperature. The diffusion of silicon and oxygen in silica have temperature dependencies close to that of the high temperature viscosity. Mechanisms of viscous flow and diffusion of silicon and oxygen in silica are proposed that involve motion of SiO molecules. Viscous flow is proposed to result from the motion of line defects composed of SiO molecules At temperatures below 1400 °C the fraction of SiO molecules in line defects changes with temperature. The relaxation of this fraction to an equilibrium value depends on the time. These proposed mechanisms are consistent with experimental measurements of silica viscosity.
A nanosecond near-infrared step-scan Fourier transform absorption spectrometer: Monitoring singlet oxygen, organic molecule triplet states, and associated thermal effects upon pulsed-laser irradiation of a photosensitizer
Authors: Andersen Lars Klembt , Ogilby Peter R.
Published: December 2002

A step-scan Fourier transform (FT) near infrared (IR) spectrometer has been used to record nanosecond time-resolved absorption spectra of singlet molecular oxygen (a1Δg→b1Σg+) created by pulsed-laser irradiation of a photosensitizer dissolved in a solvent. In addition to oxygen’s a→b transition at ∼5200 cm−1, other laser-induced changes in absorbance can be monitored over the spectral range ∼4000–11 000 cm−1. These include transients derived from the singlet oxygen sensitizer, and examples are provided with triplet state absorption spectra of several molecules in benzene as well as water. In this report, issues pertinent to the use of a step-scan FT spectrometer to monitor weak laser-induced near-IR signals are discussed. Specifically, key modifications to a commercially available instrument are described, and the relevant sources of noise from electronic components are outlined. Transient laser-induced thermal effects such as thermal lenses and temperature-dependent shifts in solvent absorption bands can also interfere with the detection of a given signal, and these complications are likewise described. The significance of these issues is apparent when monitoring oxygen’s a→b transition in D2O, a scenario in which the present detection limits of this technique are embodied. Much of the information in this report transcends the specific problem of singlet oxygen detection, however, and addresses issues general to the use of a step-scan FT spectrometer for time-resolved IR measurements.
InAs quantum dot infrared photodetectors with In0.15Ga0.85As strain-relief cap layers
Authors: Ye Zhengmao , Campbell Joe C. , Chen Zhonghui , Kim Eui-Tae , Madhukar Anupam
Published: December 2002

We report InAs quantum dot infrared photodetectors that utilize In0.15Ga0.85As strain-relief cap layers. These devices exhibited normal-incidence photoresponse peaks at 8.3 or 8.8 μm for negative or positive bias, respectively. At 77 K and −0.2 V bias the responsivity was 22 mA/W and the peak detectivity D* was 3.2×109 cm Hz1/2/W.
Sample-detector coupling in atomic resolution magnetic resonance diffraction
Authors: Barbic Mladen , Scherer Axel
Published: December 2002

A technique for potential realization of atomic resolution magnetic resonance diffraction was recently proposed for the case of a crystalline sample in proximity of a ferromagnetic sphere [M. Barbic, J. Appl. Phys. 91, 9987 (2002)]. This article predicted the detection of distinct peaks in the number of resonant spin sites at different magnetic field values for specific sphere and crystal configurations. Here, the focus is on the specific detection coupling mechanisms between the resonant spin population of the sample and the magnetic sphere probe. We investigate and compare the force, torque, and flux detection mechanisms in order to provide guidance to the experimental efforts towards the realization of the atomic resolution magnetic resonance diffraction. We also investigate the dependence of the magnetic resonance diffraction spectrum on the relative position of the magnetic sphere with respect to the crystal lattice.
Terahertz pulse generation in an organic crystal by optical rectification and resonant excitation of molecular charge transfer
Authors: Carey John J. , Bailey Ray T. , Pugh D. , Sherwood J. N. , Cruickshank F. R. , Wynne Klaas
Published: December 2002

Organic molecular crystals that are extremely efficient at terahertz-pulse generation are in- vestigated. Terahertz pulses produced by optical rectification at 800 nm in (−)2-(α-methylbenzyl-amino)-5-nitropyridine have an order of magnitude higher power than those generated in the commonly used inorganic crystal ZnTe. The organic molecular crystals were also found to generate terahertz pulses when excited on resonance at 400 nm. This may pave the way for studying ultrafast charge-transport dynamics in three dimensions.
Geographies of Knowing, Geographies of Ignorance: Jumping Scale in Southeast Asia
Authors: van Schendel Willem
Published: November 2002

‘Area studies' use a geographical metaphor to visualise and naturalise particular social spaces as well as a particular scale of analysis. They produce specific geographies of knowing but also create geographies of ignorance. Taking Southeast Asia as an example, in this paper I explore how areas are imagined and how area knowledge is structured to construct area ‘heartlands' as well as area ‘borderlands‘. This is illustrated by considering a large region of Asia (here named Zomia) that did not make it as a world area in the area dispensation after World War 2 because it lacked strong centres of state formation, was politically ambiguous, and did not command sufficient scholarly clout. As Zomia was quartered and rendered peripheral by the emergence of strong communities of area specialists of East, Southeast, South, and Central Asia, the production of knowledge about it slowed down. I suggest that we need to examine more closely the academic politics of scale that create and sustain area studies, at a time when the spatialisation of social theory enters a new, uncharted terrain. The heuristic impulse behind imagining areas, and the high-quality, contextualised knowledge that area studies produce, may be harnessed to imagine other spatial configurations, such as ‘crosscutting’ areas, the worldwide honeycomb of borderlands, or the process geographies of transnational flows. Scholars of all conventional areas can be involved in this project to ‘jump scale’ and to develop new concepts of regional space.
Is India Part of Asia?
Authors: Palat Ravi Arvind
Published: November 2002

In casting Asia as Europe's ‘Other’, it is often assumed that European spatial imaginaries are unproblematically assimilated by the peoples of Asia themselves. In this paper I challenge this assumption by charting the changing characterization of India, from being virtually synonymous with Asia for centuries to being virtually excluded from the reigning conceptions of Asia. I provide a thumbnail sketch of the spatial imaginaries of some of the peoples inhabiting the cartographic quadrant labeled ‘Asia‘. Against this background, I examine how these imaginaries were subverted by the incorporation of Asia within the capitalist world system. I then chart the impact of modernization theories on the newly independent states of the region. I argue that as several major centers of capital accumulation emerged in Asia, and capitalism ceased to be a Euro-American narrative, a new conception of Asia emerged in the 1980s. If India's lack of industrial development marginalized it from these imaginaries, it is suggested that the meltdown of the Asian ‘miracles' has once again destabilized hitherto-dominant conceptions of Asia.
Reconstituting Motherhood: Milk Powder Marketing in Sri Lanka
Authors: Greenaway Alison , Larner Wendy , Le Heron Richard
Published: November 2002

Representations of motherhood are central to the process of constituting a market for milk powder in Sri Lanka. Mothers are the primary providers of food and nutrition for their families and communities and have a profound influence on food production and consumption. Consequently, a focus on mothers shapes the efforts of both the New Zealand Dairy Board, the main supplier of milk powder to Sri Lanka, and the Movement of Mothers to Combat Malnutrition, a nongovernmental organisation that promotes home gardening to combat high levels of malnutrition, and whose educational programmes discourage purchasing of milk powder in order to resist multinational food production. In drawing on specific representations of motherhood, each organisation articulates the needs of mothers in a specific form. In this paper we show how the market for milk powder in Sri Lanka emerges through and against these processes.
The Spaces and Subjects of a Globalising Economy: A Situated Exploration of Method
Authors: Larner Wendy , Le Heron Richard
Published: November 2002

In this paper we aspire to develop a situated method in order to interrogate the spaces and subjects of the globalising economy. In our brief review of the social science literatures on economic globalisation, we identify a promising intellectual convergence around the theme of imaginaries. We develop an argument that global imaginaries involve both discourses and practices that are, in turn, constitutive of new spaces and subjects. We identify the particular significance of calculative practices such as benchmarking and allied techniques in constituting global imaginaries in the New Zealand context. We then demonstrate how our method might inform a case study of the globalising retail-banking sector by revealing multiple spaces and subjects. In analysing the emergence of new economic spaces and subjectivities in this way, our aim is to give situated content to the concept of global imaginaries and to make visible the constitutive power of governing practices.
To Each According to his Power? Participation, Access, and Vulnerability in Irrigation and Flood Management in Pakistan
Authors: Mustafa Daanish
Published: November 2002

In this paper I draw upon a realist conceptualization of power to inform the analysis of ethnographic data on access to irrigation water and vulnerability to flood hazard in Pakistan. I undertake an integrated analysis of the role of different types of power in influencing differential vulnerability to flood hazard and access to irrigation water in four local-level villages in central Pakistan. Three modes of power are identified: the feudal mode, the bourgeoisie mode, and the communal mode. Each of the modes relies on force, socialization, and control over resources, respectively, to ensure compliance. The villages which are dominated by large landowners tend to have the feudal mode of power as the predominant power structure, whereas the villages with relatively equal property ownership tend to have the communal mode as the dominant power structure. The analyses of power suggest that the participatory reforms in the water sector of Pakistan proposed by the World Bank are unlikely to lead to gains in either equity or efficiency as long as issues of differential power remain unaddressed.
Subjects of Heritage in Urban Southern India
Authors: Hancock Mary
Published: November 2002

In this paper I deal with a recent effort, conducted jointly by corporate and voluntary bodies, to create a themed cultural environment in Chennai (formerly Madras), the capital city of the southern Indian state of Tamil Nadu. This project, not yet completed, fuses craft center with architectural reconstruction, and is the work of upper-caste, globally connected elites. The site, Dakshina Chitra, envisions southern Indian culture and history in ways that are tied to consumerism and to elite perceptions of regional and national heritage. This effort departs from and poses a critique of the versions of culture, history, and identity that have been inscribed by the state in urban public space during the second half of the 20th century—the statues, monuments, and memorials that celebrate Tamil ethnicity as promulgated in the Dravidianist sociopolitical movement. This movement, which originated in the late 19th century, provided a platform for anticolonial and subaltern social movements. It continues in the hands of the political parties who have controlled, at different times, the government of Tamil Nadu since 1967. The competing discourses on heritage posed by these different projects are indicative of political, economic, and cultural transformations associated with liberalization that are now reconfiguring the relations between state and society in southern India. The constructions of locality and history that became visible during the anticolonial struggle of the first half of the 20th century are being challenged by alternative formulations as heritage becomes a marketable good and consumption becomes a vehicle of political participation. With this case I consider the ways that themed urban environments serve not only as indices of the changing political economy, but also as markers of changes in the cultural mediation of political subjectivity.
Localized suppression of RhoA activity by Tyr31/118-phosphorylated paxillin in cell adhesion and migration
Authors: Tsubouchi Asako , Sakakura Junko , Yagi Ryohei , Mazaki Yuichi , Schaefer Erik , Yano Hajime , Sabe Hisataka
Published: November 2002

RhoA activity is transiently inhibited at the initial phase of integrin engagement, when Cdc42- and/or Rac1-mediated membrane spreading and ruffling predominantly occur. Paxillin, an integrin-assembly protein, has four major tyrosine phosphorylation sites, and the phosphorylation of Tyr31 and Tyr118 correlates with cell adhesion and migration. We found that mutation of Tyr31/118 caused enhanced activation of RhoA and premature formation of stress fibers with substantial loss of efficient membrane spreading and ruffling in adhesion and migration of NMuMG cells. These phenotypes were similar to those induced by RhoA(G14V) in parental cells, and could be abolished by expression of RhoA(T19N), Rac1(G12V), or p190RhoGAP in the mutant-expressing cells. Phosphorylated Tyr31/118 was found to bind to two src homology (SH)2 domains of p120RasGAP, with coprecipitation of endogenous paxillin with p120RasGAP. p190RhoGAP is known to be a major intracellular binding partner for the p120RasGAP SH2 domains. We found that Tyr31/118-phosphorylated paxillin competes with p190RhoGAP for binding to p120RasGAP, and provides evidence that p190RhoGAP freed from p120RasGAP efficiently suppresses RhoA activity during cell adhesion. We conclude that Tyr31/118-phosphorylated paxillin serves as a template for the localized suppression of RhoA activity and is necessary for efficient membrane spreading and ruffling in adhesion and migration of NMuMG cells.
Activation of myosin V–based motility and F-actin–dependent network formation of endoplasmic reticulum during mitosis
Authors: Wöllert Torsten , Weiss Dieter G. , Gerdes Hans-Hermann , Kuznetsov Sergei A.
Published: November 2002

It is widely believed that microtubule- and F-actin–based transport of cytoplasmic organelles and membrane fusion is down-regulated during mitosis. Here we show that during the transition of Xenopus egg extracts from interphase to metaphase myosin V–driven movement of small globular vesicles along F-actin is strongly inhibited. In contrast, the movement of ER and ER network formation on F-actin is up-regulated in metaphase extracts. Our data demonstrate that myosin V–driven motility of distinct organelles is differently controlled during the cell cycle and suggest an active role of F-actin in partitioning, positioning, and membrane fusion of the ER during cell division.
Uroplakin IIIb, a urothelial differentiation marker, dimerizes with uroplakin Ib as an early step of urothelial plaque assembly
Authors: Deng Fang-Ming , Liang Feng-Xia , Tu Liyu , Resing Katheryn A. , Hu Ping , Supino Mark , Hu Chih-Chi Andrew , Zhou Ge , Ding Mingxiao , Kreibich Gert , Sun Tung-Tien
Published: November 2002

Urothelial plaques consist of four major uroplakins (Ia, Ib, II, and III) that form two-dimensional crystals covering the apical surface of urothelium, and provide unique opportunities for studying membrane protein assembly. Here, we describe a novel 35-kD urothelial plaque-associated glycoprotein that is closely related to uroplakin III: they have a similar overall type 1 transmembrane topology; their amino acid sequences are 34% identical; they share an extracellular juxtamembrane stretch of 19 amino acids; their exit from the ER requires their forming a heterodimer with uroplakin Ib, but not with any other uroplakins; and UPIII-knockout leads to p35 up-regulation, possibly as a compensatory mechanism. Interestingly, p35 contains a stretch of 80 amino acid residues homologous to a hypothetical human DNA mismatch repair enzyme-related protein. Human p35 gene is mapped to chromosome 7q11.23 near the telomeric duplicated region of Williams-Beuren syndrome, a developmental disorder affecting multiple organs including the urinary tract. These results indicate that p35 (uroplakin IIIb) is a urothelial differentiation product structurally and functionally related to uroplakin III, and that p35–UPIb interaction in the ER is an important early step in urothelial plaque assembly.
Iqg1p links spatial and secretion landmarks to polarity and cytokinesis
Authors: Osman Mahasin A. , Konopka James B. , Cerione Richard A.
Published: November 2002

Cytokinesis requires the polarization of the actin cytoskeleton, the secretion machinery, and the correct positioning of the division axis. Budding yeast cells commit to their cytokinesis plane by choosing a bud site and polarizing their growth. Iqg1p (Cyk1p) was previously implicated in cytokinesis (Epp and Chant, 1997; Lippincott and Li, 1998; Osman and Cerione, 1998), as well as in the establishment of polarity and protein trafficking (Osman and Cerione, 1998). To better understand how Iqg1p influences these processes, we performed a two-hybrid screen and identified the spatial landmark Bud4p as a binding partner. Iqg1p can be coimmunoprecipitated with Bud4p, and Bud4p requires Iqg1p for its proper localization. Iqg1p also appears to specify axial bud-site selection and mediates the proper localization of the septin, Cdc12p, as well as binds and helps localize the secretion landmark, Sec3p. The double mutants iqg1Δsec3Δ and bud4Δsec3Δ display defects in polarity, budding pattern and cytokinesis, and electron microscopic studies reveal that these cells have aberrant septal deposition. Taken together, these findings suggest that Iqg1p recruits landmark proteins to form a targeting patch that coordinates axial budding with cytokinesis.
K-loop insertion restores microtubule depolymerizing activity of a “neckless” MCAK mutant
Authors: Ovechkina Yulia , Wagenbach Michael , Wordeman Linda
Published: November 2002

Unlike most kinesins, mitotic centromere–associated kinesin (MCAK) does not translocate along the surface of microtubules (MTs), but instead depolymerizes them. Among the motile kinesins, refinements that are unique for specific cellular functions, such as directionality and processivity, are under the control of a “neck” domain adjacent to the ATP-hydrolyzing motor domain. Despite its apparent lack of motility, MCAK also contains a neck domain. We found that deletions and alanine substitutions of highly conserved positively charged residues in the MCAK neck domain significantly reduced MT depolymerization activity. Furthermore, substitution of MCAK's neck domain with either the positively charged KIF1A K-loop or poly-lysine rescues the loss of MT-depolymerizing activity observed in the neckless MCAK mutant. We propose that the neck, analogously to the K-loop, interacts electrostatically with the tubulin COOH terminus to permit diffusional translocation of MCAK along the surface of MTs. This weak-binding interaction may also play an important role in processivity of MCAK-induced MT depolymerization.
Recombinant expression of the voltage-dependent anion channel enhances the transfer of Ca2+ microdomains to mitochondria
Authors: Rapizzi Elena , Pinton Paolo , Szabadkai György , Wieckowski Mariusz R. , Vandecasteele Grégoire , Baird Geoff , Tuft Richard A. , Fogarty Kevin E. , Rizzuto Rosario
Published: November 2002

Although the physiological relevance of mitochondrial Ca2+ homeostasis is widely accepted, no information is yet available on the molecular identity of the proteins involved in this process. Here we analyzed the role of the voltage-dependent anion channel (VDAC) of the outer mitochondrial membrane in the transmission of Ca2+ signals between the ER and mitochondria by measuring cytosolic and organelle [Ca2+] with targeted aequorins and Ca2+-sensitive GFPs. In HeLa cells and skeletal myotubes, the transient expression of VDAC enhanced the amplitude of the agonist-dependent increases in mitochondrial matrix Ca2+ concentration by allowing the fast diffusion of Ca2+ from ER release sites to the inner mitochondrial membrane. Indeed, high speed imaging of mitochondrial and cytosolic [Ca2+] changes showed that the delay between the rises occurring in the two compartments is significantly shorter in VDAC-overexpressing cells. As to the functional consequences, VDAC-overexpressing cells are more susceptible to ceramide-induced cell death, thus confirming that mitochondrial Ca2+ uptake plays a key role in the process of apoptosis. These results reveal a novel function for the widely expressed VDAC channel, identifying it as a molecular component of the routes for Ca2+ transport across the mitochondrial membranes.
Neural cell adhesion molecule promotes accumulation of TGN organelles at sites of neuron-to-neuron contacts
Authors: Sytnyk Vladimir , Leshchyns'ka Iryna , Delling Markus , Dityateva Galina , Dityatev Alexander , Schachner Melitta
Published: November 2002

Transformation of a contact between axon and dendrite into a synapse is accompanied by accumulation of the synaptic machinery at this site, being delivered in intracellular organelles mainly of TGN origin. Here, we report that in cultured hippocampal neurons, TGN organelles are linked via spectrin to clusters of the neural cell adhesion molecule (NCAM) in the plasma membrane. These complexes are translocated along neurites and trapped at sites of initial neurite-to-neurite contacts within several minutes after initial contact formation. The accumulation of TGN organelles at contacts with NCAM-deficient neurons is reduced when compared with wild-type cells, suggesting that NCAM mediates the anchoring of intracellular organelles in nascent synapses.
Clustering of neuronal potassium channels is independent of their interaction with PSD-95
Authors: Rasband Matthew N. , Park Eunice W. , Zhen Dongkai , Arbuckle Margaret I. , Poliak Sebastian , Peles Elior , Grant Seth G.N. , Trimmer James S.
Published: November 2002

Voltage-dependent potassium channels regulate membrane excitability and cell–cell communication in the mammalian nervous system, and are found highly localized at distinct neuronal subcellular sites. Kv1 (mammalian Shaker family) potassium channels and the neurexin Caspr2, both of which contain COOH-terminal PDZ domain binding peptide motifs, are found colocalized at high density at juxtaparanodes flanking nodes of Ranvier of myelinated axons. The PDZ domain–containing protein PSD-95, which clusters Kv1 potassium channels in heterologous cells, has been proposed to play a major role in potassium channel clustering in mammalian neurons. Here, we show that PSD-95 colocalizes precisely with Kv1 potassium channels and Caspr2 at juxtaparanodes, and that a macromolecular complex of Kv1 channels and PSD-95 can be immunopurified from mammalian brain and spinal cord. Surprisingly, we find that the high density clustering of Kv1 channels and Caspr2 at juxtaparanodes is normal in a mutant mouse lacking juxtaparanodal PSD-95, and that the indirect interaction between Kv1 channels and Caspr2 is maintained in these mutant mice. These data suggest that the primary function of PSD-95 at juxtaparanodes lies outside of its accepted role in mediating the high density clustering of Kv1 potassium channels at these sites.
The Xenopus Xmus101 protein is required for the recruitment of Cdc45 to origins of DNA replication
Authors: Van Hatten Ruth A. , Tutter Antonin V. , Holway Antonia H. , Khederian Alyssa M. , Walter Johannes C. , Michael W. Matthew
Published: November 2002

The initiation of eukaryotic DNA replication involves origin recruitment and activation of the MCM2-7 complex, the putative replicative helicase. Mini-chromosome maintenance (MCM)2-7 recruitment to origins in G1 requires origin recognition complex (ORC), Cdt1, and Cdc6, and activation at G1/S requires MCM10 and the protein kinases Cdc7 and S-Cdk, which together recruit Cdc45, a putative MCM2-7 cofactor required for origin unwinding. Here, we show that the Xenopus BRCA1 COOH terminus repeat–containing Xmus101 protein is required for loading of Cdc45 onto the origin. Xmus101 chromatin association is dependent on ORC, and independent of S-Cdk and MCM2-7. These results define a new factor that is required for Cdc45 loading. Additionally, these findings indicate that the initiation complex assembly pathway bifurcates early, after ORC association with the origin, and that two parallel pathways, one controlled by MCM2-7, and the other by Xmus101, cooperate to load Cdc45 onto the origin.
REF1/Aly and the additional exon junction complex proteins are dispensable for nuclear mRNA export
Authors: Gatfield David , Izaurralde Elisa
Published: November 2002

The metazoan proteins UAP56, REF1, and NXF1 are thought to bind sequentially to mRNA to promote its export to the cytoplasm: UAP56 is thought to recruit REF1 to nascent mRNA; REF1 acts as an adaptor protein mediating the association of NXF1 with mRNA, whereas NXF1 translocates the mRNA across the nuclear pore complex. REF1 is a component of the exon–exon junction complex (EJC); thus, the EJC is thought to play a role in the export of spliced mRNA. NXF1 and UAP56 are essential for mRNA export. An essential role for metazoan REF1 or the additional EJC proteins in this process has not been established. Contrary to expectation, we show that REF1 and the additional components of the EJC are dispensable for export of bulk mRNA in Drosophila cells. Only when REF1 and RNPS1 are codepleted, or when all EJC proteins are simultaneously depleted is a partial nuclear accumulation of polyadenylated RNAs observed. Because a significant fraction of bulk mRNA is detected in the cytoplasm of cells depleted of all EJC proteins, we conclude that additional adaptor protein(s) mediate the interaction between NXF1 and cellular mRNAs in metazoa. Our results imply that the essential role of UAP56 in mRNA export is not restricted to the recruitment of REF1.
Missense mutation in the tubulin-specific chaperone E (Tbce) gene in the mouse mutant progressive motor neuronopathy, a model of human motoneuron disease
Authors: Bömmel Heike , Xie Gang , Rossoll Wilfried , Wiese Stefan , Jablonka Sibylle , Boehm Thomas , Sendtner Michael
Published: November 2002

Progressive motor neuronopathy (pmn) mutant mice have been widely used as a model for human motoneuron disease. Mice that are homozygous for the pmn gene defect appear healthy at birth but develop progressive motoneuron disease, resulting in severe skeletal muscle weakness and respiratory failure by postnatal week 3. The disease starts at the motor endplates, and then leads to axonal loss and finally to apoptosis of the corresponding cell bodies. We localized the genetic defect in pmn mice to a missense mutation in the tubulin-specific chaperone E (Tbce) gene on mouse chromosome 13. The human orthologue maps to chromosome 1q42.3. The Tbce gene encodes a protein (cofactor E) that is essential for the formation of primary α-tubulin and β-tubulin heterodimeric complexes. Isolated motoneurons from pmn mutant mice exhibit shorter axons and axonal swelling with irregularly structured β-tubulin and tau immunoreactivity. Thus, the pmn gene mutation provides the first genetic evidence that alterations in tubulin assembly lead to retrograde degeneration of motor axons, ultimately resulting in motoneuron cell death.
A caspase cleavage fragment of p115 induces fragmentation of the Golgi apparatus and apoptosis
Authors: Chiu Raymond , Novikov Leonid , Mukherjee Shaeri , Shields Dennis
Published: November 2002

In mammalian cells, the Golgi apparatus undergoes extensive fragmentation during apoptosis. p115 is a key vesicle tethering protein required for maintaining the structural organization of the Golgi apparatus. Here, we demonstrate that p115 was cleaved during apoptosis by caspases 3 and 8. Compared with control cells expressing native p115, those expressing a cleavage-resistant form of p115 delayed Golgi fragmentation during apoptosis. Expression of cDNAs encoding full-length or an NH2-terminal caspase cleavage fragment of p115 had no effect on Golgi morphology. In contrast, expression of the COOH-terminal caspase cleavage product of p115 itself caused Golgi fragmentation. Furthermore, this fragment translocated to the nucleus and its expression was sufficient to induce apoptosis. Most significantly, in vivo expression of the COOH-terminal fragment in the presence of caspase inhibitors, or upon coexpression with a cleavage-resistant mutant of p115, showed that p115 degradation plays a key role in amplifying the apoptotic response independently of Golgi fragmentation.
Cytoplasmic linker proteins promote microtubule rescue in vivo
Authors: Komarova Yulia A. , Akhmanova Anna S. , Kojima Shin-ichiro , Galjart Niels , Borisy Gary G.
Published: November 2002

The role of plus end–tracking proteins in regulating microtubule (MT) dynamics was investigated by expressing a dominant negative mutant that removed endogenous cytoplasmic linker proteins (CLIPs) from MT plus ends. In control CHO cells, MTs exhibited asymmetric behavior: MTs persistently grew toward the plasma membrane and displayed frequent fluctuations of length near the cell periphery. In the absence of CLIPs, the microtubule rescue frequency was reduced by sevenfold. MT behavior became symmetrical, consisting of persistent growth and persistent shortening. Removal of CLIPs also caused loss of p150Glued but not CLIP-associating protein (CLASP2) or EB1. This result raised the possibility that the change in dynamics was a result of the loss of either CLIPs or p150Glued. To distinguish between these possibilities, we performed rescue experiments. Normal MT dynamics were restored by expression of the CLIP-170 head domain, but p150Glued was not recruited back to MT plus ends. Expression of p150Glued head domain only partially restored MT dynamics. We conclude that the CLIP head domain is sufficient to alter MT dynamics either by itself serving as a rescue factor or indirectly by recruiting a rescue factor. By promoting a high rescue frequency, CLIPs provide a mechanism by which MT plus ends may be concentrated near the cell margin.
Membrane proximal lysosomes are the major vesicles responsible for calcium-dependent exocytosis in nonsecretory cells
Authors: Jaiswal Jyoti K. , Andrews Norma W. , Simon Sanford M.
Published: November 2002

Similar to its role in secretory cells, calcium triggers exocytosis in nonsecretory cells. This calcium-dependent exocytosis is essential for repair of membrane ruptures. Using total internal reflection fluorescence microscopy, we observed that many organelles implicated in this process, including ER, post-Golgi vesicles, late endosomes, early endosomes, and lysosomes, were within 100 nm of the plasma membrane (in the evanescent field). However, an increase in cytosolic calcium led to exocytosis of only the lysosomes. The lysosomes that fused were predominantly predocked at the plasma membrane, indicating that calcium is primarily responsible for fusion and not recruitment of lysosomes to the cell surface.
hNuf2 inhibition blocks stable kinetochore–microtubule attachment and induces mitotic cell death in HeLa cells
Authors: DeLuca Jennifer G. , Moree Ben , Hickey Jennifer M. , Kilmartin John V. , Salmon E.D.
Published: November 2002

Identification of proteins that couple kinetochores to spindle microtubules is critical for understanding how accurate chromosome segregation is achieved in mitosis. Here we show that the protein hNuf2 specifically functions at kinetochores for stable microtubule attachment in HeLa cells. When hNuf2 is depleted by RNA interference, spindle formation occurs normally as cells enter mitosis, but kinetochores fail to form their attachments to spindle microtubules and cells block in prometaphase with an active spindle checkpoint. Kinetochores depleted of hNuf2 retain the microtubule motors CENP-E and cytoplasmic dynein, proteins previously implicated in recruiting kinetochore microtubules. Kinetochores also retain detectable levels of the spindle checkpoint proteins Mad2 and BubR1, as expected for activation of the spindle checkpoint by unattached kinetochores. In addition, the cell cycle block produced by hNuf2 depletion induces mitotic cells to undergo cell death. These data highlight a specific role for hNuf2 in kinetochore–microtubule attachment and suggest that hNuf2 is part of a molecular linker between the kinetochore attachment site and tubulin subunits within the lattice of attached plus ends.
UTP-dependent Inhibition of Na+ Absorption Requires Activation of PKC in Endometrial Epithelial Cells
Authors: Palmer-Densmore Melissa , Deachapunya Chatsri , Kannan Mathur , O'Grady Scott M.
Published: November 2002

The objective of this study was to investigate the mechanism of uridine 5′-triphosphate (UTP)-dependent inhibition of Na+ absorption in porcine endometrial epithelial cells. Acute stimulation with UTP (5 μM) produced inhibition of sodium absorption and stimulation of chloride secretion. Experiments using basolateral membrane–permeabilized cell monolayers demonstrated a reduction in benzamil-sensitive Na+ conductance in the apical membrane after UTP stimulation. The UTP-dependent inhibition of sodium transport could be mimicked by PMA (1 μM). Several PKC inhibitors, including GF109203X and Gö6983 (both nonselective PKC inhibitors) and rottlerin (a PKCδ selective inhibitor), were shown to prevent the UTP-dependent decrease in benzamil-sensitive current. The PKCα-selective inhibitors, Gö6976 and PKC inhibitor 20–28, produced a partial inhibition of the UTP effect on benzamil-sensitive Isc. Inhibition of the benzamil-sensitive Isc by UTP was observed in the presence of BAPTA-AM (50 μM), confirming that activation of PKCs, and not increases in [Ca2+]i, were directly responsible for the inhibition of apical Na+ channels and transepithelial Na+ absorption.
Modulation of Rat Chorda Tympani NaCl Responses and Intracellular Na+ Activity in Polarized Taste Receptor Cells by pH
Authors: Lyall Vijay , Alam Rammy I. , Phan Tam-Hao T. , Russell Oneal F. , Malik Shahbaz A. , Heck Gerard L. , DeSimone John A.
Published: November 2002

Mixture interactions between sour and salt taste modalities were investigated in rats by direct measurement of intracellular pH (pHi) and Na+ activity ([Na+]i) in polarized fungiform taste receptor cells (TRCs) and by chorda tympani (CT) nerve recordings. Stimulating the lingual surface with NaCl solutions adjusted to pHs ranging between 2.0 and 10.3 increased the magnitude of NaCl CT responses linearly with increasing external pH (pHo). At pH 7.0, the epithelial sodium channel (ENaC) blocker, benzamil, decreased NaCl CT responses and inhibited further changes in CT responses induced by varying pHo to 2.0 or 10.3. At constant pHo, buffering NaCl solutions with potassium acetate/acetic acid (KA/AA) or HCO3−/CO2 inhibited NaCl CT responses relative to CT responses obtained with NaCl solutions buffered with HEPES. The carbonic anhydrase blockers, MK-507 and MK-417, attenuated the inhibition of NaCl CT responses in HCO3−/CO2 buffer, suggesting a regulatory role for pHi. In polarized TRCs step changes in apical pHo from 10.3 to 2.0 induced a linear decrease in pHi that remained within the physiological range (slope = 0.035; r2 = 0.98). At constant pHo, perfusing the apical membrane with Ringer's solutions buffered with KA/AA or HCO3−/CO2 decreased resting TRC pHi, and MK-507 or MK-417 attenuated the decrease in pHi in TRCs perfused with HCO3−/CO2 buffer. In parallel experiments, TRC [Na+]i decreased with (a) a decrease in apical pH, (b) exposing the apical membrane to amiloride or benzamil, (c) removal of apical Na+, and (d) acid loading the cells with NH4Cl or sodium acetate at constant pHo. Diethylpyrocarbonate and Zn2+, modification reagents for histidine residues in proteins, attenuated the CO2-induced inhibition of NaCl CT responses and the pHi-induced inhibition of apical Na+ influx in TRCs. We conclude that TRC pHi regulates Na+-influx through amiloride-sensitive apical ENaCs and hence modulates NaCl CT responses in acid/salt mixtures.
Fine Gating Properties of Channels Responsible for Persistent Sodium Current Generation in Entorhinal Cortex Neurons
Authors: Magistretti Jacopo , Alonso Angel
Published: November 2002

The gating properties of channels responsible for the generation of persistent Na+ current (INaP) in entorhinal cortex layer II principal neurons were investigated by performing cell-attached, patch-clamp experiments in acutely isolated cells. Voltage-gated Na+-channel activity was routinely elicited by applying 500-ms depolarizing test pulses positive to −60 mV from a holding potential of −100 mV. The channel activity underlying INaP consisted of prolonged and frequently delayed bursts during which repetitive openings were separated by short closings. The mean duration of openings within bursts was strongly voltage dependent, and increased by e times per every ∼12 mV of depolarization. On the other hand, intraburst closed times showed no major voltage dependence. The mean duration of burst events was also relatively voltage insensitive. The analysis of burst-duration frequency distribution returned two major, relatively voltage-independent time constants of ∼28 and ∼190 ms. The probability of burst openings to occur also appeared largely voltage independent. Because of the above “persistent” Na+-channel properties, the voltage dependence of the conductance underlying whole-cell INaP turned out to be largely the consequence of the pronounced voltage dependence of intraburst open times. On the other hand, some kinetic properties of the macroscopic INaP, and in particular the fast and intermediate INaP-decay components observed during step depolarizations, were found to largely reflect mean burst duration of the underlying channel openings. A further INaP decay process, namely slow inactivation, was paralleled instead by a progressive increase of interburst closed times during the application of long-lasting (i.e., 20 s) depolarizing pulses. In addition, long-lasting depolarizations also promoted a channel gating modality characterized by shorter burst durations than normally seen using 500-ms test pulses, with a predominant burst-duration time constant of ∼5–6 ms. The above data, therefore, provide a detailed picture of the single-channel bases of INaP voltage-dependent and kinetic properties in entorhinal cortex layer II neurons.