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Search Results: 1 - 10 of 84672 matches for " Luther W. Pollard "
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UCS Protein Rng3p Is Essential for Myosin-II Motor Activity during Cytokinesis in Fission Yeast
Benjamin C. Stark, Michael L. James, Luther W. Pollard, Vladimir Sirotkin, Matthew Lord
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0079593
Abstract: UCS proteins have been proposed to operate as co-chaperones that work with Hsp90 in the de novo folding of myosin motors. The fission yeast UCS protein Rng3p is essential for actomyosin ring assembly and cytokinesis. Here we investigated the role of Rng3p in fission yeast myosin-II (Myo2p) motor activity. Myo2p isolated from an arrested rng3-65 mutant was capable of binding actin, yet lacked stability and activity based on its expression levels and inactivity in ATPase and actin filament gliding assays. Myo2p isolated from a myo2-E1 mutant (a mutant hyper-sensitive to perturbation of Rng3p function) showed similar behavior in the same assays and exhibited an altered motor conformation based on limited proteolysis experiments. We propose that Rng3p is not required for the folding of motors per se, but instead works to ensure the activity of intrinsically unstable myosin-II motors. Rng3p is specific to conventional myosin-II and the actomyosin ring, and is not required for unconventional myosin motor function at other actin structures. However, artificial destabilization of myosin-I motors at endocytic actin patches (using a myo1-E1 mutant) led to recruitment of Rng3p to patches. Thus, while Rng3p is specific to myosin-II, UCS proteins are adaptable and can respond to changes in the stability of other myosin motors.
Tumour-stromal interactions: Transforming growth factor-beta isoforms and hepatocyte growth factor/scatter factor in mammary gland ductal morphogenesis
Jeffrey W Pollard
Breast Cancer Research , 2001, DOI: 10.1186/bcr301
Abstract: The development of the mammary gland largely occurs postnatally. Initially, the ductal system begins to develop from the nipple, and is characterized by specialized structures - the terminal end buds (TEBs) – capping the end of the ducts. TEBs grow out across the fat pad and, by bifurcation, lay down by puberty the minimally branched structure that covers the fat pad, at which point the TEBs disappear. Throughout the estrus cycle there is modest development of the ductal system, but it is during pregnancy that a dramatic outgrowth of secondary branches occurs that, together with the formation of the lobuloalveolar structures, results in the milk-producing gland. Once weaning has occurred, this fully developed structure regresses to a virgin-like state.It has been well established that these events are under the control of a complex interplay of circulating hormones, particularly estrogen, progesterone, glucocorticoids and prolactin gene family members [1]. However, it has also become clear that local mesenchymal–epithelial interactions are essential for mammary development, and that many of these are mediated by growth factors that are often synthesized in response to the circulating hormones. These include wnt family proteins, TGF-α, fibroblast growth factors, insulin-like growth factors, epidermal growth factor [2], colony stimulating factor-1 [3], and – the subjects of the present review – the TGF-β family of proteins and HGF/SF.The three classical members of the TGF-β family belong to a much larger family. In humans this family contains almost 30 members, including bone morphogenic proteins, activins, and Mullerian inhibiting substance [4]. These TGF-β family members have profound effects during development, regulating cell fate by affecting proliferation, differentiation and cell death, and therefore they are important for the development of many tissues.All three of the classical TGF-β isoforms (TGF-βs) activate intracellular responses by binding to and hetero
Temporal stereophotogrammetric analysis of retrogressive thaw slumps on Herschel Island, Yukon Territory
H. Lantuit,W. H. Pollard
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2005,
Abstract: The western Canadian Arctic is identified as an area of potentially significant global warming. Thawing permafrost, sea level rise, changing sea ice conditions and increased wave activity will result in accelerated rates of coastal erosion and thermokarst activity in areas of ice-rich permafrost. The Yukon Coastal Plain is widely recognized as one of the most ice-rich and thaw-sensitive areas in the Canadian Arctic. In particular, Herschel Island displays extensive coastal thermokarst. Retrogressive thaw slumps are a common thermokarst landform along the Herschel Island coast that have been increasing in both frequency and extent have in recent years due to increased thawing of massive ground ice and coastal erosion. The volume of sediment and ground ice eroded by retrogressive slump activity and the potential release of climate change related materials like organic carbon, carbon dioxide and methane are largely unknown. The remote setting of Herschel Island, and the Arctic in general, make direct observation of this type of erosion and the analysis of potential climate feedbacks extremely problematic. Remote sensing provides possibly the best solution to this problem. This study looks at two retrogressive thaw slumps located on the western shore of Herschel Island and using stereophotogrammetric methods attempts to (1) develop the first three-dimensional geomorphic analysis of this type of landform, and (2) provide an estimation of the volume of sediment/ground ice eroded through back wasting thermokarst activity. Digital Elevation Models were extracted for the years 1952, 1970 and 2004 and validated using data collected in the field using Kinematic Differential Global Positioning System. Estimates of sediment volumes eroded from retrogressive thaw slumps were found to vary greatly. In one case the total volume of material lost for the 1970–2004 period was approximately 1560000m3. The estimated volume of sediment alone was 360000m3. The temporal analysis of the DEMs suggest that second generation retrogressive thaw slump activity within the floor of a large polycyclic retrogressive thaw slump is possible.
The bowed narrow plate model
David L. Russell,Luther W. White
Electronic Journal of Differential Equations , 2000,
Abstract: The derivation of a narrow plate model that accommodates shearing, torsional, and bowing effects is presented. The resulting system has mathematical and computational advantages since it is in the form of a system of differential equations depending on only one spatial variable. A validation of the model against frequency data observed in laboratory experiments is presented. The models may be easily combined to form more complicated structures that are hinged along all or portions of their junction boundaries or are coupled differentiably as through the insertion of dowels between the narrow plates. Computational examples are presented to illustrate the types of deformations possible by coupling these models.
New tricks for metastasis-associated macrophages
Bin-Zhi Qian, Jeffrey W Pollard
Breast Cancer Research , 2012, DOI: 10.1186/bcr3143
Abstract: Metastasis is the major cause of breast cancer lethality. In target organs, a series of events are required for the establishment of metastatic tumor cells. These events include: adherence to the blood vessel, extravasation, survival, establishment of micrometastases, and persistent growth into macrometastases. While tumor cell intrinsic factors can enhance metastatic efficiency and site selection [1], metastasis also relies on interactions between spreading tumor cells and host factors in the target organ [2]. These host factors include cytokines/growth factors, extracellular matrix, platelets, and different stromal and immune cells [2]. Particularly, a population of metastasis-associated macrophages has been identified that promotes breast cancer metastasis [3]. These cells, derived from a subset of inflammatory monocytic precursor cells, promote tumor cell extravasation through vascular endothelial growth factor production and their subsequent survival and growth [3,4].Chen and colleagues have provided a new mechanism for the metastasis-promoting function of metastasis-associated macrophages through their adherence to tumor cells that provides survival signals to the tumor cells [5]. Previous studies from this group compared gene expression changes of subclones of a human mammary carcinoma cell line, MDA-MB-231, which have differential metastatic efficiencies to target organs when introduced into the circulation of immune-deficient mice [6]. The hypothesis being that certain genes are preferentially expressed by cells with higher metastatic efficiency and that if their expression is correlated with poor prognosis and metastatic disease, this gene is likely to contribute to the metastatic process in patients. Based on this idea, a lung metastasis gene expression signature was identified by comparing subclones selected for lung metastasis with the parental MDA-MB-231 line and those subclones selected for metastasis to bone or brain [6]. The focus of the current stu
Metal–organic complexation in the marine environment
George W Luther, Timothy F Rozan, Amy Witter, Brent Lewis
Geochemical Transactions , 2001, DOI: 10.1186/1467-4866-2-65
Abstract: In the last two decades, our knowledge of trace metal speciation has grown tremendously. With the advent of trace metal clean sampling techniques[1] and sensitive voltammetric techniques, [2-4] the marine community now recognizes that metal speciation in seawater and estuarine waters is dominated by complexation with organic compounds of unknown composition and origin. [5-12] Recent culture work [13-18] has shown that microorganisms produce a variety of low molecular weight organic compounds that complex metals with high stability constants. These compounds have a variety of functional groups that include phosphate, carboxylic acids, amines, thiol and hydroxy groups. Specific functional groups such as hydroxamate, catecholate and β-hydroxyaspartate are bidentate groups and organisms make molecules with three bidentate groups in a molecule.[14,19-21] In addition, plant degradation products [22-30] such as porphyrins are significant organic ligands that bind metals through four N atoms in a square planar arrangement. These latter multidentate molecules have very high stability constants with metals and are also kinetically inert to metal–ligand dissociation processes. [31-34] For this reason, organisms generally uptake the free metal ion rather than a metal–ligand form.[35,36] Thus, an understanding of metal–organism interactions requires an understanding of the amount of dissolved free ion present relative to the total dissolved metal concentration as well as the metal acquisition methods that an organism can use. [35-37]In this paper we review and compare the principal voltammetric methods, which provide evidence for metal–organic complexes. Most voltammetric work is performed with the hanging mercury drop electrode (HMDE) or the rotating disk electrode (RDE) with a thin mercury film (TMF) because these permit the measurement of metal–organic complexation at (sub)nanomolar levels directly in the solution of interest. The actual experimental methods can be broken int
Radiotherapy in the treament of gastrointestinal stromal tumors
Christin A. Knowlton,Luther W. Brady,Rebecca C. Heintzelman
Rare Tumors , 2011, DOI: 10.4081/rt.2011.e35
Abstract: Gastrointestinal stromal tumors (GIST) are uncommon mesenchymal tumors of the gastrointestinal tract. Up to one-third of GISTs are malignant with a high rate of metastasis. Surgical resection is the mainstay of care for patients with resectable disease. Imatinib mesylate, a selective tyrosine kinase inhibitor, is the current standard of care for GISTs that cannot be completely resected or in cases of metastatic GIST. Although often overlooked, radiation therapy is a viable option for select patients with GIST. We report the case of a patient with unresectable GIST who was treated with local radiotherapy and achieved longterm response. We also present a review of the literature regarding the use of radiotherapy in the treatment of GIST. GIST has been shown to be a radiosensitive tumor. Radiotherapy can offer long-term local control and should be considered in the adjuvant or palliative setting. The role of radiotherapy delivered concurrently with imatinib in the treatment of GIST may warrant further investigation.
Evaluation of a present-day climate simulation with a new coupled atmosphere-ocean model GENMOM
J. R. Alder, S. W. Hostetler, D. Pollard,A. Schmittner
Geoscientific Model Development (GMD) & Discussions (GMDD) , 2011, DOI: 10.5194/gmd-4-69-2011
Abstract: We present a new, non-flux corrected AOGCM, GENMOM, that combines the GENESIS version 3 atmospheric GCM (Global Environmental and Ecological Simulation of Interactive Systems) and MOM2 (Modular Ocean Model version 2) nominally at T31 resolution. We evaluate GENMOM by comparison with reanalysis products (e.g., NCEP2) and three models used in the IPCC AR4 assessment. GENMOM produces a global temperature bias of 0.6 °C. Atmospheric features such as the jet stream structure and major semi-permanent sea level pressure centers are well simulated as is the mean planetary-scale wind structure that is needed to produce the correct position of stormtracks. Most ocean surface currents are reproduced except where they are not resolvable at T31 resolution. Overall, GENMOM captures reasonably well the observed gradients and spatial distributions of annual surface temperature and precipitation and the simulations are on par with other AOGCMs. Deficiencies in the GENMOM simulations include a warm bias in the surface temperature over the southern oceans, a split in the ITCZ and weaker-than-observed overturning circulation.
Evaluation of a present-day climate simulation with a new coupled atmosphere-ocean model GENMOM
J. R. Alder,S. W. Hostetler,D. Pollard,A. Schmittner
Geoscientific Model Development Discussions , 2010, DOI: 10.5194/gmdd-3-1697-2010
Abstract: We present a new, non-flux corrected AOGCM, GENMOM, that combines the GENESIS version 3 atmospheric GCM (Global ENvironmental and Ecological Simulation of Interactive Systems) and MOM2 (Modular Ocean Model version 2). We evaluate GENMOM by comparison with reanalysis products (e.g., NCEP2) and eight models used in the IPCC AR4 assessment. The overall present-day climate simulated by GENMOM is on par with the models used in IPCC AR4. The model produces a global temperature bias of 0.6 °C. Atmospheric features such as the jet stream structure and major semi-permanent sea level pressure centers are well simulated as is the mean planetary-scale wind structure that is needed to produce the correct position of stormtracks. The gradients and spatial distributions of annual surface temperature compare well both to observations and to the IPCC AR4 models. A warm bias of ~2 °C is simulated by MOM between 200–1000 m in the ocean. Most ocean surface currents are reproduced except where they are not resolved well by the T31 resolution. The two main weaknesses in the simulations is the development of a split ITCZ and weaker-than-observed overturning circulation.
Worker Participation
Luther Backer
South African Journal of Industrial Psychology , 1991, DOI: 10.4102/sajip.v17i2.521
Abstract: Werkdeelname is 'n gonswoord wat tans algemeen gebruik word.
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