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Search Results: 1 - 10 of 403494 matches for " Keith M. Derbyshire "
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Distributive Conjugal Transfer in Mycobacteria Generates Progeny with Meiotic-Like Genome-Wide Mosaicism, Allowing Mapping of a Mating Identity Locus
Todd A. Gray ,Janet A. Krywy,Jessica Harold,Michael J. Palumbo,Keith M. Derbyshire
PLOS Biology , 2013, DOI: 10.1371/journal.pbio.1001602
Abstract: Horizontal gene transfer (HGT) in bacteria generates variation and drives evolution, and conjugation is considered a major contributor as it can mediate transfer of large segments of DNA between strains and species. We previously described a novel form of chromosomal conjugation in mycobacteria that does not conform to classic oriT-based conjugation models, and whose potential evolutionary significance has not been evaluated. Here, we determined the genome sequences of 22 F1-generation transconjugants, providing the first genome-wide view of conjugal HGT in bacteria at the nucleotide level. Remarkably, mycobacterial recipients acquired multiple, large, unlinked segments of donor DNA, far exceeding expectations for any bacterial HGT event. Consequently, conjugal DNA transfer created extensive genome-wide mosaicism within individual transconjugants, which generated large-scale sibling diversity approaching that seen in meiotic recombination. We exploited these attributes to perform genome-wide mapping and introgression analyses to map a locus that determines conjugal mating identity in M. smegmatis. Distributive conjugal transfer offers a plausible mechanism for the predicted HGT events that created the genome mosaicism observed among extant Mycobacterium tuberculosis and Mycobacterium canettii species. Mycobacterial distributive conjugal transfer permits innovative genetic approaches to map phenotypic traits and confers the evolutionary benefits of sexual reproduction in an asexual organism.
Restricted cell elongation in Arabidopsis hypocotyls is associated with a reduced average pectin esterification level
Paul Derbyshire, Maureen C McCann, Keith Roberts
BMC Plant Biology , 2007, DOI: 10.1186/1471-2229-7-31
Abstract: We present evidence that the degree of pectin methyl-esterification (DE%) limits cell growth, and that a minimum level of about 60% DE is required for normal cell elongation in Arabidopsis hypocotyls. When the average DE% falls below this level, as in two gibberellic acid (GA) mutants ga1-3 and gai, and plants expressing pectin methyl-esterase (PME1) from Aspergillus aculeatus, then hypocotyl elongation is reduced.Low average levels of pectin DE% are associated with reduced cell elongation, implicating PMEs, the enzymes that regulate DE%, in the cell elongation process and in responses to GA. At high average DE% other components of the cell wall limit GA-induced growth.Young, dividing and expanding cells are surrounded by an extensible primary wall that can allow turgor-driven increases in cell volume. In dicotyledonous plants, primary cell walls are composed of two major interpenetrating polysaccharide networks of cellulose-xyloglucan and pectin, in roughly equal proportions, but the contribution that each polymer class makes to wall extensibility is not yet understood.The cellulose-xyloglucan network is considered to be the major load-bearing structure [1,2]. Cellulose microfibrils are generally oriented perpendicular to the direction of cell expansion and, because of their tensile strength, define an axis of growth by limiting radial expansion [3]. Breaking and reforming of the xyloglucan chains, that inter-connect cellulose microfibrils, by wall glucanases [4] and xyloglucan-endotransglycosylases (XETs) [5,6], and/or disruption of attachment sites between cellulose and xyloglucan by expansins [7], may then promote longitudinal growth through slippage of the microfibrils. However, little is known about how the surrounding pectin matrix might play a role in this process, either independently or in concert with the cellulose-xyloglucan network. A unique property of pectin is its ability to form gels with varying mechanical strength. Removal of methyl-esters from th
Systematic Genetic Nomenclature for Type VII Secretion Systems
Wilbert Bitter ,Edith N. G. Houben,Daria Bottai,Priscille Brodin,Eric J. Brown,Jeffery S. Cox,Keith Derbyshire,Sarah M. Fortune,Lian-Yong Gao,Jun Liu,Nicolaas C. Gey van Pittius,Alexander S. Pym,Eric J. Rubin,David R. Sherman,Stewart T. Cole,Roland Brosch
PLOS Pathogens , 2009, DOI: 10.1371/journal.ppat.1000507
Abstract:
The Next Opportunity in Anti-Malaria Drug Discovery: The Liver Stage
Emily R. Derbyshire,Maria M. Mota,Jon Clardy
PLOS Pathogens , 2011, DOI: 10.1371/journal.ppat.1002178
Abstract:
Plasmodial sugar transporters as anti-malarial drug targets and comparisons with other protozoa
Ksenija Slavic, Sanjeev Krishna, Elvira T Derbyshire, Henry M Staines
Malaria Journal , 2011, DOI: 10.1186/1475-2875-10-165
Abstract: Today drug-resistant malaria is a persistent global health threat, resulting in an estimated one million human deaths worldwide. Of all malarial species, infection with Plasmodium falciparum is the cause of the greatest death toll, hitting sub-Saharan Africa hardest. Following the emergence of chloroquine resistance more than half a century ago, new drugs were introduced as alternative treatment regimens. The efficacy of these drugs deteriorated quickly, for some of them at an alarming rate, as malarial parasites evolved multiple mechanisms of drug resistance. For example, the first reports of sulphadoxine-pyrimethamine and atovaquone resistance arrived in the same year as their introduction [1]. With worsening resistance to all available anti-malarials in Southeast Asia, artemisinins, extracted from a plant used in traditional Chinese medicine for over two millennia, found worldwide application. Artemisinins are highly potent and safe anti-malarials, which are effective against multidrug-resistant P. falciparum [2-5].One of the major goals identified to control malaria has been to prolong the lifespan of existing drugs by using drug-combination treatments. Artemisinin-based combination therapy (ACT) today includes artesunate-mefloquine, artemether-lumefantrine, artesunate-amodiaquine, artesunate-sulphadoxine-pyrimethamine and dihydroartemisinin-piperaquine [6]. ACT is currently recommended by WHO as the first-line treatment for uncomplicated malaria whereas recommendations for the treatment of severe malaria include artesunate or quinine given parenterally, followed by a course of an ACT [6]. Given the essential role of artemisinins in anti-malarial treatment, it is of great concern that resistance to artemisinins has recently emerged at the Thai-Cambodian border region [7-9]. While immediate action is necessary to conquer the spread of artemisinin resistance, the development of new tools to tackle malaria is even more urgent. The availability of the complete P. fa
第四部分亚洲第四纪地质青藏高原的第四纪演化
Edward,Derbyshire
第四纪研究 , 1992,
Abstract: 对青藏高原演化的科学研究已有80多年的历史。温带沙漠、黄土区、山间盆地、活动构造、冰川和极地外围广泛分布的多年冻土以及世界屋脊等复杂多样的环境,向人们提出了重要的科学问题。11年前,中国科学院在北京组织了一次青藏高原国际科学讨论会。于1982年分两大卷出版的会议文集,对世界许多地学工作者来说,是关于这块浩瀚而遥
第四部分亚洲第四纪地质青藏高原的第四纪演化
Edward,Derbyshire
第四纪研究 , 1992,
Abstract: :对青藏高原演化的科学研究已有80多年的历史。温带沙漠、黄土区、山间盆地、活动构造、冰川和极地外围广泛分布的多年冻土以及世界屋脊等复杂多样的环境,向人们提出了重要的科学问题。11年前,中国科学院在北京组织了一次青藏高原国际科学讨论会。于1982年分两大卷出版的会议文集,对世界许多地学工作者来说,是关于这块浩瀚而遥
1977—1989中国冰川地质研究的新取向
E.,Derbyshire
第四纪研究 , 1994,
Abstract: 中国的传统冰川地质学研究是同李四光的名字紧密相连的。1977年以后,现代沉积学的原理和方法在中国冰川地质学的研究中得到了广泛的应用。中国西部的自然条件易于形成突发性的泥石流。区别冰川沉积物和泥石流沉积物在沉积学上的异同是冰川地层学研究中的关键问题。解决有关中国西部冰川扩张的次数和范围等重大问题,有待于冰川地层学和冰川地貌学新手段的综合运用。
Raccoon Use of Den Trees and Plant Associations in Western Mesophytic Forests: Tree Attributes and Availability or Landscape Heterogeneity?  [PDF]
Winston P. Smith, Keith M. Endres
Natural Resources (NR) , 2012, DOI: 10.4236/nr.2012.33012
Abstract: We monitored 15 radio-collared raccoons (Procyon lotor) on Davies Island in March 1987 - May 1988 to determine the extent to which individual tree attributes or spatial configuration of plant associations (habitat types) across the landscape influenced den use. Of 1091 verified den sites, 428 were in tree cavities. Raccoon occurrence among 4 cover types differed from that expected based on the total area of each across the island and varied across all seasons for all habitat types except Cedar Wood. Preference varied among age and sex groups and across seasons with some groups showing opposite selection for the same cover type in different seasons. Species and diameter-class distributions of selected den trees differed from a random sample of trees across the landscape. Species composition of trees with cavities also differed from the species composition across the study area. American beech (Fagus grandifolia—relative abundance 8.7%) was over-represented in the sample of trees with cavities (29.4%) and trees selected as dens (65%); diameter at breast height (dbh) of beech den trees averaged 80.0 cm, whereas all beech trees averaged 71.2 cm. For all species combined, mean dbh of den trees was 78.4 cm as compared to trees with cavities (67.6 cm), or all trees (50.4 cm). The relative availability of large, cavity-prone tree species was related to previous logging practices.
Smartphone Medical Applications for Women’s Health: What Is the Evidence-Base and Feedback?
Emma Derbyshire,Darren Dancey
International Journal of Telemedicine and Applications , 2013, DOI: 10.1155/2013/782074
Abstract: Background. Smartphone medical applications have a major role to play in women’s health with their roles being very broad, ranging from improving health behaviours to undertaking personalised tests. Objective(s). Using Medline, Web of Knowledge, and the PRISMA guidelines 15 randomized controlled trials (RCTs) were identified, with mobile interventions being tested on 1603 females, in relation to key aspects of health. Using a similar systematic approach an iPhone database search identified 47 applications (apps) developed to improve women’s health. Findings. Ten RCTs used text messaging or app interventions to support weight loss, with significant improvements being observed in eight studies. For other aspects of women’s health RCTs are needed to determine possible health benefits. iPhone store data analysis identified that a substantial number of women’s health apps did not have star ratings or feedback comments (68 and 49 per cent, resp.), raising concerns about their validity. Conclusion. Peer-review systems, supporting statements of evidence, or certification standards would be beneficial in maintaining the quality and credibility of future health-focused apps. Patient groups should also ideally be involved in the development and testing of mobile medical apps. 1. Introduction Women appear to be taking the lead when it comes to smartphone technology (ST) phone use, with 56 percent owning a smartphone compared with 51 percent men. This also translates when it comes to using health applications (apps) with around 9 percent women more likely to use these compared with 4 percent men [1]. One American survey studying over two thousand people ( ) found that women tend to seek technology that keeps up with their busy lifestyles, with 51 percent owning some form of apple device and 93 percent women keeping their smartphone within arms’ length [2]. It is also becoming clear that certain phases of the life cycle for, example, pregnancy, may also affect the level of ST phone usage. For example, one survey of 203 pregnant women found that 94 percent reported that ST had changed their life for better, with 65 percent reporting that they had downloaded pregnancy apps, with an average of three being downloaded during the gestation period [3]. In low- and middle-income countries smartphones also provide an excellent platform to support and improve the quality of healthcare systems for women [4]. There is also growing interest in harnessing smartphone apps to promote behaviour change. These provide a unique opportunity to help users stay healthy, while potentially
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