1,721,007 research outputs found
Sex-specific genetic control of Ae. aegypti and Ae. albopictus
Full text link"One of the deadliest animals in the world", is the description given to the mosquito by the World Health Organisation. Collectively mosquitoes are a vector for a range of pathogens to humans. Recent developments in genetic engineering have demonstrated that the transgenic self-limiting technology developed by Oxitec Ltd can be deployed to reduce populations of Aedes aegypti. The technology uses a transgene that, when inherited, causes lethality if the mosquito does not have access to tetracycline during development. Recent advancements at Oxitec Ltd involve targeting the self-limiting system specifically to females. This allows for males (which are required for a release) to be readily separated from females without the need for costly mechanical separation.
The work presented in this thesis aims primarily to further development of the Oxitec Ltd technology in Ae. aegypti and Aedes albopictus. In Ae. aegypti this is achieved through the development of paternal effect, a male specific construct which render the sperm inviable if reared in the absence of tetracycline. This paternal effect is subsequently combined with a genetic sexing strain in an 'all in one' construct, such that when reared in the absence of tetracycline only sterile males are produced. Development in Ae. albopictus comes through characterisation of certain life history traits of the wild type strains currently maintained at Oxitec Ltd. It is important to develop self-limiting insects in a background strain with certain traits, such as the ability to be produced under mass rearing conditions, and sensitivity to insecticides.
In conclusion the work presented here represents a major advancement of Oxitec Ltd's self-limiting technology in Ae. aegypti, through production of a genetic sexing strain capable of producing sterile males. In Ae. albopictus wild type characterisation has laid the foundations for future transgenic development in a suitable background strain.</p
Improving transgenic approaches to mosquito population control
Full text linkThe disease vectors Aedes aegypti and Aedes albopictus are serious and growing threats to global health. As vectors of the arboviruses dengue fever and chikungunya, these mosquitoes are responsible for hundreds of millions of cases and thousands of deaths each year. Absent specific treatments or vaccines, effective control of mosquito populations remains the only option for tackling a growing public health challenge. More effective control tools are urgently needed. Recently, a novel approach to pest population control has been developed based on the release of insects carrying a repressible, dominant lethal allele. This approach has achieved dramatic reductions in Ae. aegypti populations in regulated open field experiments. Despite this success, there remains scope to improve upon the current technology. It is proposed that an 'ideal' strain would combine the following features: (i) repressible lethality in late juvenile phases; (ii) a mechanism for removing females at an early developmental stage in the release generation; and (iii) orthogonal expression control mechanisms allowing both these systems to be combined in a single strain. This thesis describes research undertaken in pursuit of a 'next generation' strain. Two novel promoters from putative Osiris genes have been identified which confer a 102-103 – fold up-regulation in transgene expression specific to late pupal stages. One of these 'Osiris' promoters has been used to develop transgenic Aedes aegypti strains. 5 lines showed pupal-specific lethality of 98-100% penetrance, which was repressed in the presence of tetracycline. An Ae. albopictus orthologue of the sex-determining gene doublesex (dsx) has been isolated and characterised and a female-specific expression system developed. Transgenic lines show female-specific expression of a transgene; however, there remains some 'leaky' expression in male insects. Finally, a potential expression control tool based on an auxin-inducible expression system has been investigated. 11 different transgenic lines were developed based on three different construct designs. None showed auxin-inducible expression of a transgene
The genetic control of agricultural pests (Plutella xylostella, L. and Tribolium castaneum, Herbst)
Full text linkThe interaction between an increasing global human population and a number of important long-term trends and issues are putting strain on food production. Insects represent a significant food security concern causing up to 15% of global crop losses. Conventional chemical methods are ineffective; inducing resistance and degrading the environment. Sustainable alternatives are sought. The sterile insect technique provides a sustainable solution. Genetic engineering can augment this historic technique by replacing radiation-induced sterilization with sperm-specific nuclease expression to introduce double-stranded DNA breaks in the gametes of mass-reared and released males. This paternal-effect system is dependent on elucidation of appropriate sperm-specific promoters and suitable chaperone-nuclease combinations. This thesis develops this technology in the SIT neglected insect orders, the Lepidoptera and Coleoptera. Specifically the Plutella xylostella (Plutella xylostella, L.) and the red flour beetle (Tribolium castaneum, Herbst). I provide the foundations for a paternal-effect genetic-control-system in both species by developing a conditional sperm-specific expression system in Plutella xylostella and a female-specific expression system in Tribolium. Mass-rearing insects for the genetic control of a species can be augmented by recent developments in RNAi. I show that the sex ratio of Tribolium can be adjusted by treatment with dsRNA transformer, producing pseudomales as an additional bonus. In addition, an exploratory data analysis of producing transgenic lines in insects using piggyBac was undertaken. As well as providing a comprehensive compendium and assessment of the transgenic literature, something not yet published elsewhere, a predictive model was produced that could be very useful to a wide diversity of researchers in insect molecular biology, developmental biology, disease biology and genetics. It is hoped that this work will contribute towards the effective control of the Plutella xylostella in the near term, and form a model for the sustainable control of other lepidopteran and coleopteran species through genetic pest management
C2H2 zinc finger genes of the Gli, Zic, KLF, SP, Wilms' tumour, Huckebein, Snail, Ovo, Spalt, Odd, Blimp-1, Fez and related gene families from Branchiostoma floridae.
No full textThe C2H2 zinc finger is one of the most common domains encoded by animal genomes and has been implicated in DNA binding as well as protein-protein interactions and RNA binding. Genes encoding C2H2 zinc finger domains include not only well-studied conserved transcription factors such as Gli and Snail but also include a large diversity of more rapidly evolving genes. Here, I focus on the description of amphioxus members of families and super-families of C2H2 zinc finger genes that have been the subject of functional studies in other species, specifically the Gli, Zic, Glis, Snail, Scratch, Krox, Wilms' tumour, Huckebein, SP, KLF, Ovo, Spalt, Blimp-1, Odd and Fez genes. Surveys of the Branchiostoma floridae genome reveal members of all of these groups of genes. Genes are named according to molecular phylogenetic analyses, such that the nomenclature reflects pre-existing gene names in the context of gene families that have descended from a single common ancestral gene in the common ancestor of chordates and insects. In total, this comprises 28 B. floridae C2H2 zinc finger genes, representing at least 15 gene families. For 17 of these genes, expressed sequence tag clusters and associated clone identification codes relating to the B. floridae gene collection are given
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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