|Handler, Alfred - Al|
Submitted to: Area-Wide Control of Insect Pests: From Research to Field Implementation
Publication Type: Book / chapter
Publication Acceptance Date: 1/17/2006
Publication Date: 7/1/2007
Citation: Handler, A.M., Zimowska, G.J., Horn, C. 2007. Improving the ecological safety of transgenic insects for field release: New vectors for stability and genomic targeting. Area-Wide Control of Insect Pests: From Research to Field Implementation. 73-83. Interpretive Summary: The creation of transgenic strains of tephritid fruit fly pest insects for the development of more effective biological control programs is major goal of our laboratory at the Center for Medical, Agricultural and Veterinary Entomology, Gainesville, FL. Ongoing development of this methodology and strategies to effectively and safely utilize transgenic insects for biological control will depend upon new vector systems that can be stabilized after initial genomic intregration to minimize strain breakdown and ecological risks related to unintended movement of the transgenes to other organisms. The ability to target these vectors to specific genomic integration sites will also improve transgenic strain development and transgene expression. This article describes the development of a new genetic transformation vectors based on the piggyBac transposon system, that allow the creation of target site strains that can be comprehensively analyzed and pre-defined for host strain viability and fitness, and genomic position effects on gene expression. Optimal target strains can then be used for efficient and repetitive integrations. This vector targeting and stabilization system was first tested in Drosophila, but its use can be extended to any insect. Vectors having the stabilization system have already been integrated into the genomes of the Mediterranean and Caribbean fruit fly. These vector systems should provide a significant improvement for the development and safety of transgenic insect strains intended for field release.
Technical Abstract: Genetically transformed insect pests provide significant opportunities to create strains for improved sterile insect technique and new strategies based on conditional lethality. A major concern for programs that rely on the release of transgenic insects is the stability of the transgene, and maintenance of consistent expression of genes of interest within the transgene. Transgene instability could influence the integrity of the transformant strain upon which the effectiveness of the biological control program depends. Loss or intra-genomic transgene movement could result in strain attributes important to the program being lost or diminished, and the mass-release of such insects could significantly exacerbate the insect pest problem. Instability resulting in intra-genomic movement may also be a prelude to inter-genomic transgene movement between species resulting in ecological risks. This is a minor concern for short-term releases where transgenic insects should not survive in the environment beyond one or two generations, but transgene movement may occur into infectious agents during mass-rearing, and the potential for movement after release is a possibility for programs using many millions of insects. Random genomic insertions is also problematic for transgenic strain development due to genomic position effects that influence transgene expression, and insertional mutations that negatively affect host fitness and viability. We describe new types of vectors that allow post-integration immobilization by deleting terminal vector sequences required for transposition, and genomic targeting by a recombinase-mediated cassette exchange strategy.