Browsing by Author "Wang, H"
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Item Restricted c-Myc is required for maintenance of glioma cancer stem cells.(PLoS One, 2008) Wang, J; Wang, H; Li, Z; Wu, Q; Lathia, JD; McLendon, RE; Hjelmeland, AB; Rich, JNBACKGROUND: Malignant gliomas rank among the most lethal cancers. Gliomas display a striking cellular heterogeneity with a hierarchy of differentiation states. Recent studies support the existence of cancer stem cells in gliomas that are functionally defined by their capacity for extensive self-renewal and formation of secondary tumors that phenocopy the original tumors. As the c-Myc oncoprotein has recognized roles in normal stem cell biology, we hypothesized that c-Myc may contribute to cancer stem cell biology as these cells share characteristics with normal stem cells. METHODOLOGY/PRINCIPAL FINDINGS: Based on previous methods that we and others have employed, tumor cell populations were enriched or depleted for cancer stem cells using the stem cell marker CD133 (Prominin-1). We characterized c-Myc expression in matched tumor cell populations using real time PCR, immunoblotting, immunofluorescence and flow cytometry. Here we report that c-Myc is highly expressed in glioma cancer stem cells relative to non-stem glioma cells. To interrogate the significance of c-Myc expression in glioma cancer stem cells, we targeted its expression using lentivirally transduced short hairpin RNA (shRNA). Knockdown of c-Myc in glioma cancer stem cells reduced proliferation with concomitant cell cycle arrest in the G(0)/G(1) phase and increased apoptosis. Non-stem glioma cells displayed limited dependence on c-Myc expression for survival and proliferation. Further, glioma cancer stem cells with decreased c-Myc levels failed to form neurospheres in vitro or tumors when xenotransplanted into the brains of immunocompromised mice. CONCLUSIONS/SIGNIFICANCE: These findings support a central role of c-Myc in regulating proliferation and survival of glioma cancer stem cells. Targeting core stem cell pathways may offer improved therapeutic approaches for advanced cancers.Item Open Access Changes to the North Atlantic subtropical high and its role in the intensification of summer rainfall variability in the southeastern United States(Journal of Climate, 2011-03-01) Li, W; Li, L; Fu, R; Deng, Y; Wang, HThis study investigates the changes of the North Atlantic subtropical high (NASH) and its impact on summer precipitation over the southeastern (SE) United States using the 850-hPa geopotential height field in the National Centers forEnvironmental Prediction (NCEP) reanalysis, the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), long-term rainfall data, and Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) model simulations during the past six decades (1948-2007). The results show that the NASH in the last 30 yr has become more intense, and its western ridge has displaced westward with an enhanced meridional movement compared to the previous 30 yr. When the NASH moved closer to the continental United States in the three most recent decades, the effect of the NASH on the interannual variation of SE U.S. precipitation is enhanced through the ridge's north-south movement. The study's attribution analysis suggested that the changes of the NASH are mainly due to anthropogenic warming. In the twenty-first century with an increase of the atmospheric CO2 concentration, the center of the NASH would be intensified and the western ridge of the NASH would shift farther westward. These changes would increase the likelihood of both strong anomalously wet and dry summers over the SEUnited States in the future, as suggested by the IPCC AR4 models. © 2011 American Meteorological Society.Item Open Access Does an ‘iron gate’ carbon preservation mechanism exist in organic–rich wetlands?(Soil Biology and Biochemistry, 2019-08-01) Wang, H; River, M; Richardson, CJ© 2019 Recent research suggested that iron oxidation may protect carbon from drought-accelerated decomposition in wetlands by promoting the sorption of lignin derivatives and decreasing phenolic oxidase activities. Here we examined whether this mechanism exists in organic-rich peatlands, which store over 30% of the world's soil carbon, by simulating drought and flooded conditions in peat soil with and without the addition of reduced iron. Our results suggest that iron does not protect carbon from decomposition in organic-rich peatlands, and in fact iron may exacerbate carbon decomposition via precipitation of phenolic compounds, which otherwise have been shown to inhibit microbial activity. In addition, scanning electron microscopy analyses of different types of peat soil from Minnesota to Peru showed evidence of iron-sulfide minerals (pyrite), indicating that some portion of the reduced iron in peatlands is effectively immobilized and therefore does not interact with the carbon cycle.Item Open Access Dual controls on carbon loss during drought in peatlands(Nature Climate Change, 2015-01-01) Wang, H; Richardson, CJ; Ho, M© 2015 Macmillan Publishers Limited. Peatlands store one-third of global soil carbon. Drought/drainage coupled with climate warming present the main threat to these stores. Hence, understanding drought effects and inherent feedbacks related to peat decomposition has been a primary global challenge. However, widely divergent results concerning drought in recent studies challenge the accepted paradigm that waterlogging and associated anoxia are the overarching controls locking up carbon stored in peat. Here, by linking field and microcosm experiments, we show how previously unrecognized mechanisms regulate the build-up of phenolics, which protects stored carbon directly by reducing phenol oxidase activity during short-term drought and, indirectly, through a shift from low-phenolic Sphagnum/herbs to high-phenolic shrubs after long-term moderate drought. We demonstrate that shrub expansion induced by drought/warming in boreal peatlands might be a long-term self-adaptive mechanism not only increasing carbon sequestration but also potentially protecting historic soil carbon. We therefore propose that the projected 'positive feedback loop'between carbon emission and drought in peatlands may not occur in the long term.Item Open Access Iron Age landscape changes in the Benoué River Valley, Cameroon(Quaternary Research (United States), 2019-09-01) Wright, DK; MacEachern, S; Ambrose, SH; Choi, J; Choi, JH; Lang, C; Wang, HCopyright © 2019 University of Washington. Published by Cambridge University Press. The introduction of agriculture is known to have profoundly affected the ecological complexion of landscapes. In this study, a rapid transition from C3 to C4 vegetation is inferred from a shift to higher stable carbon (13C/12C) isotope ratios of soils and sediments in the Benoué River Valley and upland Fali Mountains in northern Cameroon. Landscape change is viewed from the perspective of two settlement mounds and adjacent floodplains, as well as a rock terrace agricultural field dating from 1100 cal yr BP to the recent past (<400 cal yr BP). Nitrogen (15N/14N) isotope ratios and soil micromorphology demonstrate variable uses of land adjacent to the mound sites. These results indicate that Early Iron Age settlement practices involved exploitation of C3 plants on soils with low δ15N values, indicating wetter soils. Conversely, from the Late Iron Age (>700 cal yr BP) until recent times, high soil and sediment δ13C and δ15N values reflect more C4 biomass and anthropogenic organic matter in open, dry environments. The results suggest that Iron Age settlement practices profoundly changed landscapes in this part of West Africa through land clearance and/or utilization of C4 plants.Item Open Access NCP activates chloroplast transcription by controlling phytochrome-dependent dual nuclear and plastidial switches(Nature communications, 2019) Yang, EJ; Yoo, CY; Liu, J; Wang, H; Cao, J; Li, F; Pryer, KM; Sun, T; Weigel, D; Zhou, PItem Open Access Response of fungal communities to fire in a subtropical peatland(Plant and Soil, 2021-09-01) Tian, J; Wang, H; Vilgalys, R; Ho, M; Flanagan, N; Richardson, CJPurpose: Wildfire, an increasing disturbance in peatlands, could dramatically change carbon stocks and reshape plant/microbial communities, with long-lasting effects on peatland functions. Soil fungi are important in controlling the belowground carbon and nutrient cycling in peatlands; however, the impact of altered fire regimes on these fungi is still unclear. Methods: We assessed fungal abundance, composition, and diversity across four soil depths (0–5 cm, 6–10 cm, 11–15 cm, 16–20 cm) under low-severity and high-severity fire in a subtropical peatland in the southeastern USA. Results: Low-severity fire significantly increased fungal Shannon diversity and saprotrophic fungi in the 0–5 cm soil layer immediately after fire and then retracted within 2 years. This pattern was not observed below 5 cm soils. The dominant fungal class − Archaeorhizomycetes declined initially and then returned to pre-low-severity fires levels at 0–5 cm depths. Time since low-severity fire was a primary driver of fungal composition in the 0–10 cm soil depth, while spatial distance among sites affected the deeper soils (11–20 cm). The fungal Shannon diversity failed to recover in the unburned state even 30 years after high-severity fire, especially in 6–20 cm soil layers. Stratification patterns of the fungal community were diminished by high-severity fire. Soil properties (either phenolics or carbon) were the primary drivers in shaping fungal community reassembly after high-severity fire across all soil depths. Conclusion: Collectively, the fungal communities seem to be highly resilient to low-severity fire, but not to high-severity fire in the shrub-dominated coastal peatlands.Item Open Access Thermoelectric transport properties of CaMg 2Bi 2, EuMg 2Bi 2, and YbMg 2Bi 2(Physical Review B - Condensed Matter and Materials Physics, 2012-01-11) May, AF; McGuire, MA; Singh, DJ; Ma, J; Delaire, O; Huq, A; Cai, W; Wang, HThe thermoelectric transport properties of CaMg 2Bi 2, EuMg 2Bi 2, and YbMg 2Bi 2 were characterized between 2 and 650 K. As synthesized, the polycrystalline samples are found to have lower p-type carrier concentrations than single-crystalline samples of the same empirical formula. These low carrier concentration samples possess the highest mobilities yet reported for materials with the CaAl 2Si 2 structure type, with a mobility of ∼740 cm2/V/s observed in EuMg 2Bi 2 at 50 K. Despite decreases in the Seebeck coefficient (α) and electrical resistivity (ρ) with increasing temperature, the power factor (α2ρ) increases for all temperatures examined. This behavior suggests a strong asymmetry in the conduction of electrons and holes. The highest figure of merit (zT) is observed in YbMg 2Bi 2, with zT approaching 0.4 at 600 K for two samples with carrier densities of approximately 2×1018cm -3 and 8×1018 cm -3 at room temperature. Refinements of neutron powder diffraction data yield similar behavior for the structures of CaMg 2Bi 2 and YbMg 2Bi 2, with smooth lattice expansion and relative expansion in c being ∼35% larger than relative expansion in a at 973 K. First-principles calculations reveal an increasing band gap as Bi is replaced by Sb and then As, and subsequent Boltzmann transport calculations predict an increase in α for a given n associated with an increased effective mass as the gap opens. The magnitude and temperature dependence of α suggests higher zT is likely to be achieved at larger carrier concentrations, roughly an order of magnitude higher than those in the current polycrystalline samples, which is also expected from the detailed calculations. © 2012 American Physical Society.Item Open Access Vegetation and microbes interact to preserve carbon in many wooded peatlands(Communications Earth & Environment, 2021-12) Wang, H; Tian, J; Chen, H; Ho, M; Vilgalys, R; Bu, ZJ; Liu, X; Richardson, CJAbstractPeatlands have persisted as massive carbon sinks over millennia, even during past periods of climate change. The commonly accepted theory of abiotic controls (mainly anoxia and low temperature) over carbon decomposition cannot fully explain how vast low-latitude shrub/tree dominated (wooded) peatlands consistently accrete peat under warm and seasonally unsaturated conditions. Here we show, by comparing the composition and ecological traits of microbes between Sphagnum- and shrub-dominated peatlands, that slow-growing microbes decisively dominate the studied shrub-dominated peatlands, concomitant with plant-induced increases in highly recalcitrant carbon and phenolics. The slow-growing microbes metabolize organic matter thirty times slower than the fast-growing microbes that dominate our Sphagnum-dominated site. We suggest that the high-phenolic shrub/tree induced shifts in microbial composition may compensate for positive effects of temperature and/or drought on metabolism over time in peatlands. This biotic self-sustaining process that modulates abiotic controls on carbon cycling may improve projections of long-term, climate-carbon feedbacks in peatlands.