Showing 31 - 40 of 733 Items
Rapid mechanisms for generating genome diversity: Whole ploidy shifts, aneuploidy, and loss of heterozygosity
Date: 2014-01-01
Creator: Richard J. Bennett, Anja Forche, Judith Berman
Access: Open access
- Human fungal pathogens can exist in a variety of ploidy states, including euploid and aneuploid forms. Ploidy change has a major impact on phenotypic properties, including the regulation of interactions with the human host. In addition, the rapid emergence of drug-resistant isolates is often associated with the formation of specific supernumerary chromosomes. Pathogens such as Candida albicans and Cryptococcus neoformans appear particularly well adapted for propagation in multiple ploidy states with novel pathways driving ploidy variation. In both species, heterozygous cells also readily undergo loss of heterozygosity (LOH), leading to additional phenotypic changes such as altered drug resistance. Here, we examine the sexual and parasexual cycles that drive ploidy variation in human fungal pathogens and discuss ploidy and LOH events with respect to their far-reaching roles in fungal adaptation and pathogenesis.
Global divergence of the human follicle mite Demodex folliculorum: Persistent associations between host ancestry and mite lineages
Date: 2015-12-29
Creator: Michael F. Palopoli, Daniel J. Fergus, Samuel Minot, Dorothy T. Pei, W. Brian, Simison, Iria Fernandez-Silva, Megan S. Thoemmes, Robert R. Dunn, Michelle Trautwein
Access: Open access
- Microscopic mites of the genus Demodex live within the hair follicles of mammals and are ubiquitous symbionts of humans, but little molecular work has been done to understand their genetic diversity or transmission. Here we sampled mite DNA from 70 human hosts of diverse geographic ancestries and analyzed 241 sequences from the mitochondrial genome of the species Demodex folliculorum. Phylogenetic analyses recovered multiple deep lineages including a globally distributed lineage common among hosts of European ancestry and three lineages that primarily include hosts of Asian, African, and Latin American ancestry. To a great extent, the ancestral geography of hosts predicted the lineages of mites found on them; 27% of the total molecular variance segregated according to the regional ancestries of hosts. We found that D. folliculorum populations are stable on an individual over the course of years and that some Asian and African American hosts maintain specific mite lineages over the course of years or generations outside their geographic region of birth or ancestry. D. folliculorum haplotypes were much more likely to be shared within families and between spouses than between unrelated individuals, indicating that transmission requires close contact. Dating analyses indicated that D. folliculorum origins may predate modern humans. Overall, D. folliculorum evolution reflects ancient human population divergences, is consistent with an out-of-Africa dispersal hypothesis, and presents an excellent model system for further understanding the history of human movement.
The initiation and development of small peat-forming ecosystems adjacent to lakes in the north central Canadian low arctic during the Holocene
Date: 2017-07-01
Creator: Philip Camill, Charles E. Umbanhowar, Christoph Geiss, Mark B. Edlund, Will O., Hobbs, Allison Dupont, Catherine Doyle-Capitman, Matthew Ramos
Access: Open access
- Small peat-forming ecosystems in arctic landscapes may play a significant role in the regional biogeochemistry of high-latitude systems, yet they are understudied compared to arctic uplands and other major peat-forming regions of the North. We present a new data set of 25 radiocarbon-dated permafrost peat cores sampled around eight low arctic lake sites in northern Manitoba (Canada) to examine the timing of peat initiation and controls on peat accumulation throughout the Holocene. We used macrofossils and charcoal to characterize changes in the plant community and fire, and we explored potential impacts of these local factors, as well as regional climatic change, on rates of C accumulation and C stocks. Peat initiation was variable across and within sites, suggesting the influence of local topography, but 56% of the cores initiated after 3000 B.P. Most cores initiated and remained as drier bog hummock communities, with few vegetation transitions in this landscape. C accumulation was relatively slow and did not appear to be correlated with Holocene-scale climatic variability, but C stocks in this landscape were substantial (mean = 45.4 kg C m ), potentially accounting for 13.2 Pg C in the Taiga Shield ecozone. To the extent that small peat-forming systems are underrepresented in peatland mapping, soil organic carbon (SOC) stocks may be underestimated in arctic regions. Mean fire severity appeared to be negatively correlated with C accumulation rates. Initiation and accumulation of soil C may respond to both regional and local factors, and substantial lowland soil C stocks have the potential for biogeochemical impacts on adjacent aquatic ecosystems. −2
Molecular basis of the copulatory plug polymorphism in Caenorhabditis elegans
Date: 2008-08-21
Creator: Michael F. Palopoli, Matthew V. Rockman, Aye TinMaung, Camden Ramsay, Stephen, Curwen, Andrea Aduna, Jason Laurita, Leonid Kruglyak
Access: Open access
- Heritable variation is the raw material for evolutionary change, and understanding its genetic basis is one of the central problems in modern biology. We investigated the genetic basis of a classic phenotypic dimorphism in the nematode Caenorhabditis elegans. Males from many natural isolates deposit a copulatory plug after mating, whereas males from other natural isolates-including the standard wild-type strain (N2 Bristol) that is used in most research laboratories-do not deposit plugs. The copulatory plug is a gelatinous mass that covers the hermaphrodite vulva, and its deposition decreases the mating success of subsequent males. We show that the plugging polymorphism results from the insertion of a retrotransposon into an exon of a novel mucin-like gene, plg-1, whose product is a major structural component of the copulatory plug. The gene is expressed in a subset of secretory cells of the male somatic gonad, and its loss has no evident effects beyond the loss of male mate-guarding. Although C. elegans descends from an obligate-outcrossing, male?female ancestor, it occurs primarily as self-fertilizing hermaphrodites. The reduced selection on male-male competition associated with the origin of hermaphroditism may have permitted the global spread of a loss-of-function mutation with restricted pleiotropy. ©2008 Macmillan Publishers Limited. All rights reserved.
Identification and cardiotropic actions of sulfakinin peptides in the American lobster Homarus americanus
Date: 2007-07-01
Creator: Patsy S. Dickinson, Jake S. Stevens, Szymon Rus, Henry R. Brennan, Christopher C., Goiney, Christine M. Smith, Lingjun Li, David W. Towle, Andrew E. Christie
Access: Open access
- In arthropods, a group of peptides possessing a -Y(SO3H)GHM/ LRFamide carboxy-terminal motif have been collectively termed the sulfakinins. Sulfakinin isoforms have been identified from numerous insect species. In contrast, members of this peptide family have thus far been isolated from just two crustaceans, the penaeid shrimp Penaeus monodon and Litopenaeus vannamei. Here, we report the identification of a cDNA encoding prepro-sulfakinin from the American lobster Homarus americanus. Two sulfakinin-like sequences were identified within the open-reading frame of the cDNA. Based on modifications predicted by peptide modeling programs, and on homology to the known isoforms of sulfakinin, particularly those from shrimp, the mature H. americanus sulfakinins were hypothesized to be pEFDEY(SO3H)GHMRFamide (Hoa-SK I) and GGGEY(SO3H)DDY(SO3H)GHLRFamide (Hoa-SK II). Hoa-SK I is identical to one of the previously identified shrimp sulfakinins, while Hoa-SK II is a novel isoform. Exogenous application of either synthetic Hoa-SK I or Hoa-SK II to the isolated lobster heart increased both the frequency and amplitude of spontaneous heart contractions. In preparations in which spontaneous contractions were irregular, both peptides increased the regularity of the heartbeat. Our study provides the first molecular characterization of a sulfakinin-encoding cDNA from a crustacean, as well as the first demonstration of bioactivity for native sulfakinins in this group of arthropods.
Study of D0 decays into K̄0 and K̄*0
Date: 1993-01-01
Creator: M. Procario, S. Yang, D. S. Akerib, B. Barish, M., Chadha, S. Chan, D. F. Cowen, G. Eigen, J. S. Miller, J. Urheim, A. J. Weinstein, D. Acosta, M. Athanas, G. Masek, B. Ong, H. Paar, M. Sivertz, A. Bean, J. Gronberg, R. Kutschke, S. Menary, R. J. Morrison, S. Nakanishi, H. N. Nelson, T. K. Nelson, J. D. Richman, H. Tajima, D. Schmidt, D. Sperka, M. S. Witherell, R. Ballest
Access: Open access
- Using the CLEO II detector at CESR we have studied D0 decays into final states with a K̄0 or K̄*0, and have measured branching ratios for the decay modes D0→(K̄0K̄*0)π0,η, η′. These results are compared with predictions of various charm decay models, and contributions of final-state interactions are discussed. © 1993 The American Physical Society.
Evidence for penguin-diagram decays: First observation of B→K*(892)γ
Date: 1993-01-01
Creator: R. Ammar, S. Ball, P. Baringer, D. Coppage, N., Copty, R. Davis, N. Hancock, M. Kelly, N. Kwak, H. Lam, Y. Kubota, M. Lattery, J. K. Nelson, S. Patton, D. Perticone, R. Poling, V. Savinov, S. Schrenk, R. Wang, M. S. Alam, I. J. Kim, B. Nemati, J. J. O'Neill, H. Severini, C. R. Sun, M. M. Zoeller, G. Crawford, M. Daubenmeir, R. Fulton, D. Fujino, K. K. Gan
Access: Open access
- We have observed the decays B0→K*(892)0γ and B-→K*(892)-γ, which are evidence for the quark-level process b→sγ. The average branching fraction is (4.5±1.5±0.9) ×10-5. This value is consistent with standard model predictions from electromagnetic penguin diagrams. © 1993 The American Physical Society.
Probing the mechanism of recognition of ssDNA by the Cdc13-DBD
Date: 2008-03-01
Creator: Aimee M. Eldridge, Deborah S. Wuttke
Access: Open access
- The Saccharomyces cerevisiae protein Cdc13 tightly and specifically binds the conserved G-rich single-stranded overhang at telomeres and plays an essential role in telomere end-protection and length regulation. The 200 residue DNA-binding domain of Cdc13 (Cdc13-DBD) binds an 11mer single-stranded representative of the yeast telomeric sequence [Tel11, d(GTGTGGGTGTG)] with a 3 pM affinity and specificity for three bases (underlined) at the 5′ end. The structure of the Cdc13-DBD bound to Tel11 revealed a large, predominantly aromatic protein interface with several unusual features. The DNA adopts an irregular, extended structure, and the binding interface includes a long (∼30 amino acids) structured loop between strands β2-β3 (L2-3) of an OB-fold. To investigate the mechanism of ssDNA binding, we studied the free and bound states of Cdc13-DBD using NMR spectroscopy. Chemical shift changes indicate that the basic topology of the domain, including L2-3, is essentially intact in the free state. Changes in slow and intermediate time scale dynamics, however, occur in L2-3, while conformational changes distant from the DNA interface suggest an induced fit mechanism for binding in the 'hot spot' for binding affinity and specificity. These data point to an overall binding mechanism well adapted to the heterogeneous nature of yeast telomeres. © 2008 The Author(s).
Combinatorial and metric properties of Thompson's group t
Date: 2009-02-01
Creator: José Burillo, Sean Cleary, Melanie Stein, Jennifer Taback
Access: Open access
- We discuss metric and combinatorial properties of Thompson's group T, including normal forms for elements and unique tree pair diagram representatives. We relate these properties to those of Thompson's group F when possible, and highlight combinatorial differences between the two groups. We define a set of unique normal forms for elements of T arising from minimal factorizations of elements into natural pieces. We show that the number of carets in a reduced representative of an element of T estimates the word length, that F is undistorted in T, and we describe how to recognize torsion elements in T. © 2008 American Mathematical Society Reverts to public domain 28 years from publication.
Atmospheric variability of methyl chloride during the last 300 years from an Antarctic ice core and firn air
Date: 2004-01-28
Creator: M. Aydin, E. S. Saltzman, W. J. De Bruyn, S. A. Montzka, J. H., Butler, M. Battle
Access: Open access
- Measurements of methyl chloride (CH3Cl) in Antarctic polar ice and firn air are used to describe the variability of atmospheric CH3Cl during the past 300 years. Firn air results from South Pole and Siple Dome suggest that the atmospheric abundance of CH3Cl increased by about 10% in the 50 years prior to 1990. Ice core measurements from Siple Dome provide evidence for a cyclic natural variability on the order of 10%, with a period of about 110 years in phase with the 20th century rise inferred from firn air. Thus, the CH3Cl increase measured in firn air may largely be a result of natural processes, which may continue to affect the atmospheric CH3Cl burden during the 21st century. Copyright 2004 by the American Geophysical Union.