|Handler, Alfred - Al|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 7/12/2006
Publication Date: 12/1/2006
Citation: Handler, A.M., Atkinson, P.W. 2006. Insect transgenesis: mechanisms, applications and ecological safety. In: Harding, S.E., editor. Biotechnology and Genetic Engineering Reviews. Vol. 23. Lavoisier/Intercept. p. 129-156. Interpretive Summary: The creation of transgenic strains of economically important insects for the development of more effective biological control programs is a major goal of our laboratory at the Center for Medical, Agricultural, and Veterinary Entomology in Gainesville, FL. Development of this methodology and strategies to effectively and safely utilize transgenic insects for biological control will depend upon a comprehensive knowledge of the mechanisms involved in transposon movement, the types of biocontrol strategies that transgenic strains can improve, and a critical analysis of potential risks involved in the release of transgenic insects. This article addresses the current knowledge of the mechanisms involved in transposon movement, with a focus on recent studies with the Hermes transposable element. The potential use of transgenic strains to improve the sterile insect technique and in new strategies using conditional lethal transgenes is discussed. Finally, factors that affect transgene stability and methods to improve stability after genomic integration are addrssed in the context of the field release of these strains. New vectors are described that allow targeting into predefined acceptor sites in the genome, with immobilization facilitated by removal of target site sequences needed for mobility. This information will be used to facilitate the creation of effective and ecologically safe transgenic insects, as well as methods to test and assess these attributes.
Technical Abstract: The recent explosion of available genomic sequence information, which will only increase in volume for many years, makes the need for routine transformation in species of interest critical to the meaningful understanding of this sequence data. A prime example for the various analyses possible with transformation methodology has been the application of transposon-mediated germ-line transformation in Drosophila melanogaster. Gene identification has been most straightforwardly approached by testing the ability of a putative recombinant wild type allele to phenotypically rescue a mutated null allele after transformation. More detailed gene-structure-function relationships have been approached by assessing the phenotypic effect of systematic sequence modifications (generally nucleotide substitution or deletion) of the recombinant allele. Gene identification has also been approached by methods generally described as "insertional mutagenesis". These include transposon tagging and a variety of "trap" systems including those for enhancers, exons, and introns. These systems generally identify coding or regulatory sequence function by genomic vector insertions resulting in a mutation phenotype or reporter gene expression, with subsequent isolation of relevant sequences by probing for the vector DNA. The recent extension of transposon-mediated germ-line transformation to nearly 20 non-drosophilid insect species now allows the use of these methods in non-model systems, facilitating an understanding of genetic mechanisms in diverse species that would have been intractable only a few years ago. Significantly, germ-line transformation can also be used for applied purposes by genomic integration of genetic constructs that can alter the development, behavior or population size of many species that negatively or positively impact agriculture or human health. While the types of potential transgenic strains for applied use are numerous, those used in field release programs engender special concerns related to ecological safety. Insects and fish, unlike most other transgenic organisms, have the ability to easily disperse and so cannot be contained or retrieved once released from cages, pens or ponds. Thus, it is critical that we understand the mechanisms that underlie the mobility properties of the transposons used as gene vectors for most transgenic insects, and evaluate new vector systems that can ensure transgenic strain integrity and transgene stability.