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Articles 1 - 24 of 24
Full-Text Articles in Life Sciences
Antipredator Behavior And Physiology Determine Lestes Species Turnover Along The Pond-Permanence Gradient, Robby Stoks, Mark A. Mcpeek
Antipredator Behavior And Physiology Determine Lestes Species Turnover Along The Pond-Permanence Gradient, Robby Stoks, Mark A. Mcpeek
Dartmouth Scholarship
Identifying key traits that shape trade-offs that restrict species to only a subset of environmental gradients is crucial to understanding and predicting species turnover. Previous field experiments have shown that larvae of Lestes damselfly species segregate along the entire gradient of pond permanence and predator presence and that differential predation risk and life history constraints together shape their distribution. Here, we report laboratory experiments that identify key differences in behavior and physiology among species that structure their distributions along this gradient. The absence of adaptive antipredator behavioral responses against large dragonfly larvae and fish of Lestes dryas, the only species …
Disulfide Bond Formation Involves A Quinhydrone-Type Charge–Transfer Complex, James Regeimbal, Stefan Gleiter, Bernard L. Trumpower, Chang-Ang Yu
Disulfide Bond Formation Involves A Quinhydrone-Type Charge–Transfer Complex, James Regeimbal, Stefan Gleiter, Bernard L. Trumpower, Chang-Ang Yu
Dartmouth Scholarship
The chemistry of disulfide exchange in biological systems is well studied. However, the detailed mechanism of how oxidizing equivalents are derived to form disulfide bonds in proteins is not clear. In prokaryotic organisms, it is known that DsbB delivers oxidizing equivalents through DsbA to secreted proteins. DsbB becomes reoxidized by reducing quinones that are part of the membrane-bound electron-transfer chains. It is this quinone reductase activity that links disulfide bond formation to the electron transport system. We show here that purified DsbB contains the spectral signal of a quinhydrone, a charge-transfer complex consisting of a hydroquinone and a quinone in …
Converting Plant Biomass To Fuels And Commodity Chemicals In South Africa: A Third Chapter?, L R. Lynd, H H Von Blottnitz, B Tait, J De Boer, I S. Pretorius, K Rumbold, W H. Van Zyl
Converting Plant Biomass To Fuels And Commodity Chemicals In South Africa: A Third Chapter?, L R. Lynd, H H Von Blottnitz, B Tait, J De Boer, I S. Pretorius, K Rumbold, W H. Van Zyl
Dartmouth Scholarship
There have been two distinct chapters in the history of converting cellulosic biomass to fuels and commodity chemicals in South Africa. The first chapter, fromthe late 1970s to the early 1990s, involved some of the most active research and development efforts of their kind anywhere in the world. Thereafter, during the second chapter, there has been very little activity in the field in South Africa while there has been an unprecedented awakening to the potential of biomass conversion elsewhere. This paper considers the rationale and possible benefits of a potential third chapter based on a revitalized effort on biomass conversion …
Il-23 Produced By Cns-Resident Cells Controls T Cell Encephalitogenicity During The Effector Phase Of Experimental Autoimmune Encephalomyelitis, Burkhard Becher, Brigit G. Durell, Randolph J. Noelle
Il-23 Produced By Cns-Resident Cells Controls T Cell Encephalitogenicity During The Effector Phase Of Experimental Autoimmune Encephalomyelitis, Burkhard Becher, Brigit G. Durell, Randolph J. Noelle
Dartmouth Scholarship
CNS-resident cells, in particular microglia and macrophages, are a source of inflammatory cytokines during inflammation within the CNS. Expression of IL-23, a recently discovered cytokine, has been shown to be critical for the development of experimental autoimmune encephalomyelitis (EAE) in mice. Expression of the p40 subunit of IL-12 and IL-23 by microglia has been shown in situ and in vitro, but direct evidence for a functional significance of p40 expression by CNS cells during an immune response in vivo is still lacking. Here we report that p40 plays a critical role in maintaining encephalitogenicity during the disease course. By using …
A Role For Yip1p In Copii Vesicle Biogenesis, Matthew Heidtman, Catherine Z. Chen, Ruth N. Collins, Charles Barlowe
A Role For Yip1p In Copii Vesicle Biogenesis, Matthew Heidtman, Catherine Z. Chen, Ruth N. Collins, Charles Barlowe
Dartmouth Scholarship
Yeast Ypt1p-interacting protein (Yip1p) belongs to a conserved family of transmembrane proteins that interact with Rab GTPases. We encountered Yip1p as a constituent of ER-derived transport vesicles, leading us to hypothesize a direct role for this protein in transport through the early secretory pathway. Using a cell-free assay that recapitulates protein transport from the ER to the Golgi complex, we find that affinity-purified antibodies directed against the hydrophilic amino terminus of Yip1p potently inhibit transport. Surprisingly, inhibition is specific to the COPII-dependent budding stage. In support of this in vitro observation, strains bearing the temperature-sensitive yip1-4 allele accumulate ER membranes …
On Friction And Surface Cracking During Sliding Of Ice On Ice, Maurine Montagnat, Erland M. Schulson
On Friction And Surface Cracking During Sliding Of Ice On Ice, Maurine Montagnat, Erland M. Schulson
Dartmouth Scholarship
As a complement to earlier measurements on the friction of both granular fresh-water ice and S2 columnar salt-water ice, new experiments were performed on the friction of S2 columnar fresh-water ice sliding against itself at low velocities (5 × 10−7 to 5 × 10−1 m s−1) and at −10°C, using the same double-shear device as was used earlier. The results showed that under a given set of experimental conditions the kinetic coefficient of friction of S2 fresh-water ice compares favorably with that of the other two variants.The experiments also revealed friction-induced surface cracks and recrystallized grains.These deformation features are explained, …
The Virulence Activator Apha Links Quorum Sensing To Pathogenesis And Physiology In Vibrio Cholerae By Repressing The Expression Of A Penicillin Amidase Gene On The Small Chromosome, Gabriela Kovacikova, Wei Lin, Karen Skorupski
The Virulence Activator Apha Links Quorum Sensing To Pathogenesis And Physiology In Vibrio Cholerae By Repressing The Expression Of A Penicillin Amidase Gene On The Small Chromosome, Gabriela Kovacikova, Wei Lin, Karen Skorupski
Dartmouth Scholarship
Activation of the tcpPH promoter on the Vibrio pathogenicity island by AphA and AphB initiates the Vibrio cholerae virulence cascade and is regulated by quorum sensing through the repressive action of HapR on aphA expression. To further understand how the chromosomally encoded AphA protein activates tcpPH expression, site-directed mutagenesis was used to identify the base pairs critical for AphA binding and transcriptional activation. This analysis revealed a region of partial dyad symmetry, TATGCA-N6-TNCNNA, that is important for both of these activities. Searching the V. cholerae genome for this binding site permitted the identification of a second one upstream of a …
Salicylic Acid Attenuates Virulence In Endovascular Infections By Targeting Global Regulatory Pathways In Staphylococcus Aureus, Leon Iri Kupferwasser, Michael R. Yeaman, Cynthia C. Nast, Deborah Kupferwasser, Yan-Qiong Xiong, Marco Palma, Ambrose L. Cheung, Arnold S. Bayer
Salicylic Acid Attenuates Virulence In Endovascular Infections By Targeting Global Regulatory Pathways In Staphylococcus Aureus, Leon Iri Kupferwasser, Michael R. Yeaman, Cynthia C. Nast, Deborah Kupferwasser, Yan-Qiong Xiong, Marco Palma, Ambrose L. Cheung, Arnold S. Bayer
Dartmouth Scholarship
Aspirin has been previously shown to reduce the in vivo virulence of Staphylococcus aureus in experimental endocarditis, through antiplatelet and antimicrobial mechanisms. In the present study, salicylic acid, the major in vivo metabolite of aspirin, mitigated two important virulence phenotypes in both clinical and laboratory S. aureus strains: α-hemolysin secretion and fibronectin binding in vitro. In addition, salicylic acid reduced the expression of the α-hemolysin gene promoter, hla, and the fibronectin gene promoter, fnbA. Transcriptional analysis, fluorometry, and flow cytometry revealed evidence of salicylic acid–mediated activation of the stress-response gene sigB. Expression of the sigB-repressible global …
Crystal Structure Of The Sars Protein From Staphylococcus Aureus, Ronggui Li, Adhar C. Manna, Shaodong Dai, Ambrose L. Cheung, Gongyi Zhang
Crystal Structure Of The Sars Protein From Staphylococcus Aureus, Ronggui Li, Adhar C. Manna, Shaodong Dai, Ambrose L. Cheung, Gongyi Zhang
Dartmouth Scholarship
The expression of virulence determinants in Staphylococcus aureus is controlled by global regulatory loci (e.g., sarA and agr). One of these determinants, protein A (spa), is activated by sarS, which encodes a 250-residue DNA-binding protein. Genetic analysis indicated that the agr locus likely mediates spa repression by suppressing the transcription of sarS. Contrary to SarA and SarR, which require homodimer formation for proper function, SarS is unusual within the SarA protein family in that it contains two homologous halves, with each half sharing sequence similarity to SarA and SarR. Here we report the 2.2 Å …
Enhancer Trapping Reveals Widespread Circadian Clock Transcriptional Control In Arabidopsis, Todd P. Michael, C Robertson Mcclung
Enhancer Trapping Reveals Widespread Circadian Clock Transcriptional Control In Arabidopsis, Todd P. Michael, C Robertson Mcclung
Dartmouth Scholarship
The circadian clock synchronizes the internal biology of an organism with the environment and has been shown to be widespread among organisms. Microarray experiments have shown that the circadian clock regulates mRNA abundance of about 10% of the transcriptome in plants, invertebrates, and mammals. In contrast, the circadian clock regulates the transcription of the virtually all cyanobacterial genes. To determine the extent to which the circadian clock controls transcription in Arabidopsis, we used in vivo enhancer trapping. We found that 36% of our enhancer trap lines display circadian-regulated transcription, which is much higher than estimates of circadian regulation based on …
Predators And Life Histories Shape Lestes Damselfly Assemblages Along A Freshwater Habitat Gradient, Robby Stoks, Mark A. Mcpeek
Predators And Life Histories Shape Lestes Damselfly Assemblages Along A Freshwater Habitat Gradient, Robby Stoks, Mark A. Mcpeek
Dartmouth Scholarship
Survey data from New England showed that assemblages of Lestes damselflies are organized along the entire gradient of pond permanence and predator presence. One assemblage occupies vernal ponds lacking large dragonfly predators and fish; four are largely confined to temporary ponds that typically contain dragonfly predators; one dominates fishless permanent ponds and lakes where dragonflies are the top predators; and one dominates permanent ponds and lakes where fish are the top predators. We determined the role of life history and predation in maintaining this striking pattern by conducting a series of transplant experiments in the field and a laboratory experiment …
Estimating Community Stability And Ecological Interactions From Time-Series Data, A. R. Ives, B. Dennis, K. L. Cottingham, S. R. Carpenter
Estimating Community Stability And Ecological Interactions From Time-Series Data, A. R. Ives, B. Dennis, K. L. Cottingham, S. R. Carpenter
Dartmouth Scholarship
Natural ecological communities are continuously buffeted by a varying environment, often making it difficult to measure the stability of communities using concepts requiring the existence of an equilibrium point. Instead of an equilibrium point, the equilibrial state of communities subject to environmental stochasticity is a stationary distribution, which is characterized by means, variances, and other statistical moments. Here, we derive three properties of stochastic multispecies communities that measure different characteristics associated with community stability. These properties can be estimated from multispecies time-series data using first-order multivariate autoregressive (MAR(1)) models. We demonstrate how to estimate the parameters of MAR(1) models and …
Genomic And Proteomic Profiling Of Responses To Toxic Metals In Human Lung Cells, Angeline S. Andrew, Amy J. Warren, Aaron Barchowsky, Kaili A. Temple, Linda Klei, Nicole V. Soucy, Kimberly A. O'Hara, Joshua W. Hamilton
Genomic And Proteomic Profiling Of Responses To Toxic Metals In Human Lung Cells, Angeline S. Andrew, Amy J. Warren, Aaron Barchowsky, Kaili A. Temple, Linda Klei, Nicole V. Soucy, Kimberly A. O'Hara, Joshua W. Hamilton
Dartmouth Scholarship
Examining global effects of toxic metals on gene expression can be useful for elucidating patterns of biological response, discovering underlying mechanisms of toxicity, and identifying candidate metal-specific genetic markers of exposure and response. Using a 1,200 gene nylon array, we examined changes in gene expression following low-dose, acute exposures of cadmium, chromium, arsenic, nickel, or mitomycin C (MMC) in BEAS-2B human bronchial epithelial cells. Total RNA was isolated from cells exposed to 3 M Cd(II) (as cadmium chloride), 10 M Cr(VI) (as sodium dichromate), 3 g/cm2 Ni(II) (as nickel subsulfide), 5 M or 50 M As(III) (as sodium arsenite), or …
Alpha-Toxin Is Required For Biofilm Formation By Staphylococcus Aureus, Nicky C. Caiazza, George A. O'Toole
Alpha-Toxin Is Required For Biofilm Formation By Staphylococcus Aureus, Nicky C. Caiazza, George A. O'Toole
Dartmouth Scholarship
Staphylococcus aureus is a common pathogen associated with nosocomial infections. It can persist in clinical settings and gain increased resistance to antimicrobial agents through biofilm formation. We have found that alpha-toxin, a secreted, multimeric, hemolytic toxin encoded by the hla gene, plays an integral role in biofilm formation. The hla mutant was unable to fully colonize plastic surfaces under both static and flow conditions. Based on microscopy studies, we propose that alpha-hemolysin is required for cell-to-cell interactions during biofilm formation.
Environmental Estrogens Alter Early Development In Xenopus Laevis, Cassandra L. Bevan, Donna M. Porter, Anita Prasad, Marthe J. Howard, Leslie P. Henderson
Environmental Estrogens Alter Early Development In Xenopus Laevis, Cassandra L. Bevan, Donna M. Porter, Anita Prasad, Marthe J. Howard, Leslie P. Henderson
Dartmouth Scholarship
A growing number of environmental toxicants found in pesticides, herbicides, and industrial solvents are believed to have deleterious effects on development by disrupting hormone-sensitive processes. We exposed Xenopus laevis embryos at early gastrula to the commonly encountered environmental estrogens nonylphenol, octylphenol, and methoxychlor, the antiandrogen, p,p-DDE, or the synthetic androgen, 17 alpha-methyltestosterone at concentrations ranging from 10 nM to 10 microM and examined them at tailbud stages (approximately 48 hr of treatment). Exposure to the three environmental estrogens, as well as to the natural estrogen 17 beta-estradiol, increased mortality, induced morphologic deformations, increased apoptosis, and altered the deposition and differentiation …
Two Arabidopsis Circadian Oscillators Can Be Distinguished By Differential Temperature Sensitivity, Todd P. Michael, Patrice A. Salome, C. Robertson Mcclung
Two Arabidopsis Circadian Oscillators Can Be Distinguished By Differential Temperature Sensitivity, Todd P. Michael, Patrice A. Salome, C. Robertson Mcclung
Dartmouth Scholarship
Circadian rhythms are widespread in nature and reflect the activity of an endogenous biological clock. In metazoans, the circadian system includes a central circadian clock in the brain as well as distinct clocks in peripheral tissues such as the retina or liver. Similarly, plants have distinct clocks in different cell layers and tissues. Here, we show that two different circadian clocks, distinguishable by their sensitivity to environmental temperature signals, regulate the transcription of genes that are expressed in the Arabidopsis thaliana cotyledon. One oscillator, which regulates CAB2 expression, responds preferentially to light–dark versus temperature cycles and fails to respond to …
Minus-End Capture Of Preformed Kinetochore Fibers Contributes To Spindle Morphogenesis, Alexey Khodjakov, Lily Copenagle, Michael B. Gordon, Duane A. Compton, Tarun M. Kapoor
Minus-End Capture Of Preformed Kinetochore Fibers Contributes To Spindle Morphogenesis, Alexey Khodjakov, Lily Copenagle, Michael B. Gordon, Duane A. Compton, Tarun M. Kapoor
Dartmouth Scholarship
Near-simultaneous three-dimensional fluorescence/differential interference contrast microscopy was used to follow the behavior of microtubules and chromosomes in living alpha-tubulin/GFP-expressing cells after inhibition of the mitotic kinesin Eg5 with monastrol. Kinetochore fibers (K-fibers) were frequently observed forming in association with chromosomes both during monastrol treatment and after monastrol removal. Surprisingly, these K-fibers were oriented away from, and not directly connected to, centrosomes and incorporated into the spindle by the sliding of their distal ends toward centrosomes via a NuMA-dependent mechanism. Similar preformed K-fibers were also observed during spindle formation in untreated cells. In addition, upon monastrol removal, centrosomes established a transient …
Rpb4p, A Subunit Of Rna Polymerase Ii, Mediates Mrna Export During Stress, Marganit Farago, Tal Nahari, Christopher Hammel, Charles N. Cole, Mordechai Choder
Rpb4p, A Subunit Of Rna Polymerase Ii, Mediates Mrna Export During Stress, Marganit Farago, Tal Nahari, Christopher Hammel, Charles N. Cole, Mordechai Choder
Dartmouth Scholarship
Changes in gene expression represent a major mechanism by which cells respond to stress. We and other investigators have previously shown that the yeast RNA polymerase II subunit Rpb4p is required for transcription under various stress conditions, but not under optimal growth conditions. Here we show that, in addition to its role in transcription, Rpb4p is also required for mRNA export, but only when cells are exposed to stress conditions. The roles of Rpb4p in transcription and in mRNA export can be uncoupled genetically by specific mutations in Rpb4p. Both functions of Rpb4p are required to maintain cell viability during …
Hierarchy Of Protein Assembly At The Vertex Ring Domain For Yeast Vacuole Docking And Fusion, Li Wang, Alexey J. Merz, Kevin M. Collins, William Wickner
Hierarchy Of Protein Assembly At The Vertex Ring Domain For Yeast Vacuole Docking And Fusion, Li Wang, Alexey J. Merz, Kevin M. Collins, William Wickner
Dartmouth Scholarship
Vacuole tethering, docking, and fusion proteins assemble into a “vertex ring” around the apposed membranes of tethered vacuoles before catalyzing fusion. Inhibitors of the fusion reaction selectively interrupt protein assembly into the vertex ring, establishing a causal assembly hierarchy: (a) The Rab GTPase Ypt7p mediates vacuole tethering and forms the initial vertex ring, independent of t-SNAREs or actin; (b) F-actin disassembly and GTP-bound Ypt7p direct the localization of other fusion factors; (c) The t-SNAREs Vam3p and Vam7p regulate each other’s vertex enrichment, but do not affect Ypt7p localization. The v-SNARE Vti1p is enriched at vertices by a distinct pathway that …
Rhamnolipid Surfactant Production Affects Biofilm Architecture In Pseudomonas Aeruginosa Pao1, Mary E. Davey, Nicky C. Caiazza, George A. O'Toole
Rhamnolipid Surfactant Production Affects Biofilm Architecture In Pseudomonas Aeruginosa Pao1, Mary E. Davey, Nicky C. Caiazza, George A. O'Toole
Dartmouth Scholarship
In response to certain environmental signals, bacteria will differentiate from an independent free-living mode of growth and take up an interdependent surface-attached existence. These surface-attached microbial communities are known as biofilms. In flowing systems where nutrients are available, biofilms can develop into elaborate three-dimensional structures. The development of biofilm architecture, particularly the spatial arrangement of colonies within the matrix and the open areas surrounding the colonies, is thought to be fundamental to the function of these complex communities. Here we report a new role for rhamnolipid surfactants produced by the opportunistic pathogen Pseudomonas aeruginosa in the maintenance of biofilm architecture. …
Asymmetry Of The Central Apparatus Defines The Location Of Active Microtubule Sliding In Chlamydomonas Flagella, Matthew J. Wargo, Elizabeth F. Smith
Asymmetry Of The Central Apparatus Defines The Location Of Active Microtubule Sliding In Chlamydomonas Flagella, Matthew J. Wargo, Elizabeth F. Smith
Dartmouth Scholarship
Regulation of ciliary and flagellar motility requires spatial control of dynein-driven microtubule sliding. However, the mechanism for regulating the location and symmetry of dynein activity is not understood. One hypothesis is that the asymmetrically organized central apparatus, through interactions with the radial spokes, transmits a signal to regulate dynein-driven microtubule sliding between subsets of doublet microtubules. Based on this model, we hypothesized that the orientation of the central apparatus defines positions of active microtubule sliding required to control bending in the axoneme. To test this, we induced microtubule sliding in axonemes isolated from wild-type and mutant Chlamydomonas cells, and then …
Richard Goldschmidt: Hopeful Monsters And Other 'Heresies', Michael Dietrich
Richard Goldschmidt: Hopeful Monsters And Other 'Heresies', Michael Dietrich
Dartmouth Scholarship
Richard Goldschmidt is remembered today as one of the most controversial biologists of the twentieth century. Although his work on sex determination and physiological genetics earned him accolades from his peers, his rejection of the classical gene and his unpopular theories about evolution significantly damaged his scientific reputation. This article reviews Goldschmidt's life and work, with an emphasis on his controversial views.
The Delphic Boat: What Genomes Tell Us, Michael Dietrich
The Delphic Boat: What Genomes Tell Us, Michael Dietrich
Dartmouth Scholarship
A review of The Delphic Boat: What Genomes Tell Us by Antoine Danchin Alison Quayle, trans. Harvard University Press, 2003 380 pp. hardcover. ISBN 0-67400-930-4
Linking Dispersal To Local Population Dynamics: A Case Study Using A Headwater Salamander System, Winsor H. Lowe
Linking Dispersal To Local Population Dynamics: A Case Study Using A Headwater Salamander System, Winsor H. Lowe
Dartmouth Scholarship
Dispersal can strongly influence local population dynamics and may be critical to species persistence in fragmented landscapes. Theory predicts that dispersal by resident stream organisms is necessary to offset the loss of individuals to downstream drift. However, there is a lack of empirical data linking dispersal and drift to local population dynamics in streams, leading to uncertainty regarding the general demographic significance of these processes and the power of drift to explain observed dispersal patterns. I assessed the contribution of dispersal along a first-order stream to population dynamics of the headwater salamander Gyrinophilus porphyriticus (Plethodontidae). I conducted mark–recapture surveys of …