Faculty Scholarship
Showing 41 - 50 of 733 Items
The 'obligate diploid' Candida albicans forms mating-competent haploids
Date: 2013-02-07
Creator: Meleah A. Hickman, Guisheng Zeng, Anja Forche, Matthew P. Hirakawa, Darren, Abbey, Benjamin D. Harrison, Yan Ming Wang, Ching Hua Su, Richard J. Bennett, Yue Wang, Judith Berman
Access: Open access
- Candida albicans, the most prevalent human fungal pathogen, is considered to be an obligate diploid that carries recessive lethal mutations throughout the genome. Here we demonstrate that C. albicans has a viable haploid state that can be derived from diploid cells under in vitro and in vivo conditions, and that seems to arise through a concerted chromosome loss mechanism. Haploids undergo morphogenetic changes like those of diploids, including the yeast-hyphal transition, chlamydospore formation and a white-opaque switch that facilitates mating. Haploid opaque cells of opposite mating type mate efficiently to regenerate the diploid form, restoring heterozygosity and fitness. Homozygous diploids arise spontaneously by auto-diploidization, and both haploids and auto-diploids show a similar reduction in fitness, in vitro and in vivo, relative to heterozygous diploids, indicating that homozygous cell types are transient in mixed populations. Finally, we constructed stable haploid strains with multiple auxotrophies that will facilitate molecular and genetic analyses of this important pathogen. © 2013 Macmillan Publishers Limited. All rights reserved.
BCJ relations from a new symmetry of gauge-theory amplitudes
Date: 2016-10-01
Creator: Robert W. Brown, Stephen G. Naculich
Access: Open access
- We introduce a new set of symmetries obeyed by tree-level gauge-theory amplitudes involving at least one gluon. The symmetry acts as a momentum-dependent shift on the color factors of the amplitude. Using the radiation vertex expansion, we prove the invariance under this color-factor shift of the n-gluon amplitude, as well as amplitudes involving massless or massive particles in an arbitrary representation of the gauge group with spin zero, one-half, or one. The Bern-Carrasco-Johansson relations are a direct consequence of this symmetry. We also introduce the cubic vertex expansion of an amplitude, and use it to derive a generalized-gauge-invariant constraint on the kinematic numerators of the amplitude. We show that the amplitudes of the bi-adjoint scalar theory are invariant under the color-factor symmetry, and use this to derive the null eigenvectors of the propagator matrix. We generalize the color-factor shift to loop level, and prove the invariance under this shift of one-loop n-gluon amplitudes in any theory that admits a color-kinematic-dual representation of numerators. We show that the one-loop color-factor symmetry implies known relations among the integrands of one-loop color-ordered amplitudes.
Genome plasticity in candida albicans is driven by long repeat sequences
Date: 2019-06-01
Creator: Robert T. Todd, Tyler D. Wikoff, Anja Forche, Anna Selmecki
Access: Open access
- Genome rearrangements resulting in copy number variation (CNV) and loss of heterozygosity (LOH) are frequently observed during the somatic evolution of cancer and promote rapid adaptation of fungi to novel environments. In the human fungal pathogen Candida albicans, CNV and LOH confer increased virulence and antifungal drug resistance, yet the mechanisms driving these rearrangements are not completely understood. Here, we unveil an extensive array of long repeat sequences (65–6499 bp) that are associated with CNV, LOH, and chromosomal inversions. Many of these long repeat sequences are uncharacterized and encompass one or more coding sequences that are actively transcribed. Repeats associated with genome rearrangements are predominantly inverted and separated by up to ~1.6 Mb, an extraordinary distance for homology-based DNA repair/recombination in yeast. These repeat sequences are a significant source of genome plasticity across diverse strain backgrounds including clinical, environmental, and experimentally evolved isolates, and represent previously uncharacterized variation in the reference genome.
An overview of approaches and challenges for retrieving marine inherent optical properties from ocean color remote sensing
Date: 2018-01-01
Creator: P. Jeremy Werdell, Lachlan I.W. McKinna, Emmanuel Boss, Steven G. Ackleson, Susanne E., Craig, Watson W. Gregg, Zhongping Lee, Stéphane Maritorena, Collin S. Roesler, Cécile S. Rousseaux, Dariusz Stramski, James M. Sullivan, Michael S. Twardowski, Maria Tzortziou, Xiaodong Zhang
Access: Open access
- Ocean color measured from satellites provides daily global, synoptic views of spectral water-leaving reflectances that can be used to generate estimates of marine inherent optical properties (IOPs). These reflectances, namely the ratio of spectral upwelled radiances to spectral downwelled irradiances, describe the light exiting a water mass that defines its color. IOPs are the spectral absorption and scattering characteristics of ocean water and its dissolved and particulate constituents. Because of their dependence on the concentration and composition of marine constituents, IOPs can be used to describe the contents of the upper ocean mixed layer. This information is critical to further our scientific understanding of biogeochemical oceanic processes, such as organic carbon production and export, phytoplankton dynamics, and responses to climatic disturbances. Given their importance, the international ocean color community has invested significant effort in improving the quality of satellite-derived IOP products, both regionally and globally. Recognizing the current influx of data products into the community and the need to improve current algorithms in anticipation of new satellite instruments (e.g., the global, hyperspectral spectroradiometer of the NASA Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission), we present a synopsis of the current state of the art in the retrieval of these core optical properties. Contemporary approaches for obtaining IOPs from satellite ocean color are reviewed and, for clarity, separated based their inversion methodology or the type of IOPs sought. Summaries of known uncertainties associated with each approach are provided, as well as common performance metrics used to evaluate them. We discuss current knowledge gaps and make recommendations for future investment for upcoming missions whose instrument characteristics diverge sufficiently from heritage and existing sensors to warrant reassessing current approaches.
Stolen Future, Broken Present: The Human Significance of Climate Change
Date: 2014-01-01
Creator: David A Collings
Access: Open access
- This book argues that climate change has a devastating effect on how we think about the future. Once several positive feedback loops in Earth’s dynamic systems, such as the melting of the Arctic icecap or the drying of the Amazon, cross the point of no return, the biosphere is likely to undergo severe and irreversible warming. Nearly everything we do is premised on the assumption that the world we know will endure into the future and provide a sustaining context for our activities. But today the future of a viable biosphere, and thus the purpose of our present activities, is put into question. A disappearing future leads to a broken present, a strange incoherence in the feel of everyday life. We thus face the unprecedented challenge of salvaging a basis for our lives today. That basis, this book argues, may be found in our capacity to assume an infinite responsibility for ecological disaster and, like the biblical Job, to respond with awe to the alien voice that speaks from the whirlwind. By owning disaster and accepting our small place within the inhuman forces of the biosphere, we may discover how to live with responsibility and serenity whatever may come. (Publisher's Description) Freely available online at https://quod.lib.umich.edu/o/ohp/12832550.0001.001.
With age comes immaturity: Do countries with older populations issue shorter maturity debt?
Date: 2021-12-01
Creator: Gonca Senel, Mark L.J. Wright
Access: Open access
- Recent work has found that countries with older populations face steeper yield curves and issue shorter maturity debt than do younger countries. We reexamine these findings using a new database of public debt maturity and yields for OECD countries. We first show that the behavior of eurozone countries in the pre-euro period drives these results. Next, including more recent data from the post-euro period, we show that the relationship between population age, maturity, and yield curve slopes disappears. This finding is robust to excluding high-credit-risk countries. Last, we show that these patterns reemerge after the European debt crisis, suggesting that eurozone capital markets have resegmented.
Neurocognitive predictors of treatment response to randomized treatment in adults with tic disorders
Date: 2017-03-06
Creator: Amitai Abramovitch, Lauren S. Hallion, Hannah E. Reese, Douglas W. Woods, Alan, Peterson, John T. Walkup, John Piacentini, Lawrence Scahill, Thilo Deckersbach, Sabine Wilhelm
Access: Open access
- Tourette's disorder (TS) and chronic tic disorder (CTD) are neurodevelopmental disorders characterized by involuntary vocal and motor tics. Consequently, TS/CTD have been conceptualized as disorders of cognitive and motor inhibitory control. However, most neurocognitive studies have found comparable or superior inhibitory capacity among individuals with TS/CTD relative to healthy controls. These findings have led to the hypothesis that individuals with TS/CTD develop increased inhibitory control due to the constant need to inhibit tics. However, the role of cognitive control in TS/CTD is not yet understood, particularly in adults. To examine the role of inhibitory control in TS/CTD, the present study investigated this association by assessing the relationship between inhibitory control and treatment response in a large sample of adults with TS/CTD. As part of a large randomized trial comparing behavior therapy versus supportive psychotherapy for TS/CTD, a battery of tests, including tests of inhibitory control was administered to 122 adults with TS/CTD at baseline. We assessed the association between neuropsychological test performance and change in symptom severity, as well as compared the performance of treatment responders and non-responders as defined by the Clinical Global Impression Scale. Results indicated that change in symptoms, and treatment response were not associated with neuropsychological performance on tests of inhibitory control, intellectual ability, or motor function, regardless of type of treatment. The finding that significant change in symptom severity of TS/CTD patients is not associated with impairment or change in inhibitory control regardless of treatment type suggests that inhibitory control may not be a clinically relevant facet of these disorders in adults.
Homozygosity at the MTL locus in clinical strains of Candida albicans: Karyotypic rearrangments and tetraploid formation
Date: 2004-06-01
Creator: Melanie Legrand, Paul Lephart, Anja Forche, Frank Michael C. Mueller, T., Walsh, P. T. Magee, Beatrice B. Magee
Access: Open access
- One hundred and twenty Candida albicans clinical isolates from the late 1980s and early 1990s were examined for homosygosity at the MTL locus. Of these, 108 were heterozygous (MTLa/MTLα), whereas seven were MTLa and five were MTLα. Five of the homozygous isolates were able to switch to the opaque cell morphology, while opaque cells were not detectable among the remaining seven. Nevertheless, all but one of the isolates homozygous at the MTL locus were shown to mate and to yield cells containing markers from both parents; the non-mater was found to have a frameshift in the MTLα1 gene. In contrast to Saccharomyces cerevisiae, C. albicans homozygotes with no active MTL allele failed to mate rather than mating as a cells. There was no correlation between homoxygosity and fluconazole resistance, mating and fluconazole resistance or switching and fluconazole resistance, in part because most of the strains were isolated before the widespread use of this antifungal agent, and only three were in fact drug resistant Ten of the 12 homozygotes had rearranged karyotypes involving one or more homologue of chromosomes 4, 5, 6 and 7. We suggest that karyotypic rearrangement, drug resistance and homozygosity come about as the result of induction of hyperrecombination during the infection process; hence, they tend to occur together, but each is the independent result of the same event. Furthermore, as clinical strains can mate and form tetraploids, mating and marker exchange are likely to be a significant part of the life cycle of C. albicans in vivo.
Sutural loosening and skeletal flexibility during growth: Determination of drop-like shapes in sea urchins
Date: 2002-02-07
Creator: Amy S. Johnson, Olaf Ellers, Jim Lemire, Melissa Minor, Holly A., Leddy
Access: Open access
- The shape of sea urchins may be determined mechanically by patterns of force analogous to those that determine the shape of a water droplet. This mechanical analogy implies skeletal flexibility at the time of growth. Although comprised of many rigid calcite plates, sutural collagenous ligaments could confer such flexibility if the sutures between plates loosened and acted as joints at the time of growth. We present experimental evidence of such flexibility associated with weight gain and growth. Over 13-, 4-, and 2-week periods, fed urchins (Strongylocentrotus droebachiensis) gained weight and developed looser sutures than unfed urchins that maintained or lost weight. Further, skeletons of fed urchins force-relaxed more than did those of unfed urchins and urchins with loose sutures force-relaxed more than those with tight sutures. Urchins (Strongylocentrotus franciscanus) fed for two and a half weeks, gained weight, also had looser skeletons and deposited calcite at sutural margins, whereas unfed ones did not. In field populations of S. droebachiensis the percentage having loose sutures varied with urchin diameter and reflected their size-specific growth rate. The association between feeding, weight gain, calcite deposition, force relaxation and sutural looseness supports the hypothesis that urchins deform flexibly while growing, thus determining their drop-like shapes.
Using the very short form of the children’s behavior questionnaire for spanish-speaking populations in low-and middle-income countries: A psychometric analysis of dichotomized variables
Date: 2021-02-01
Creator: Elsa Lucia Escalante-Barrios, Sonia Mariel Suarez-Enciso, Samuel P. Putnam, Helen Raikes, Sergi, Fàbregues
Access: Open access
- While the psychometric properties of the Spanish version of the Very Short Form of the Children’s Behavior Questionnaire (CBQ-VSF) have been assessed in the US and Europe in samples composed of middle-and high-income parents with high levels of education, no studies have tested the instrument in low-income Spanish-speaking populations living in low-and middleincome countries. To fill this gap, our cross-sectional study assessed the psychometric properties of the Spanish version of the CBQ-VSF version in a sample of 315 low-income and low-educated parents with preschool children living in the Caribbean Region of Colombia. While our findings revealed problems that were similar to those identified in previous assessments of the CBQ-VSF Spanish version, they also showed unique problems related to the sociodemographic characteristics of our sample, containing many individuals with a low income and low educational level. Most of the participants gave extreme responses, resulting in a notable kurtosis and skewness of the data. This article describes how we addressed these problems by dichotomizing the variables into binary categories. Additionally, it demonstrates that merely translating the CBQ-VSF is insufficient to be able to capture many of the underlying latent constructs associated with low-income and low-educated Latino/Hispanic populations.