Submitted to: Journal of Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2003
Publication Date: 3/1/2004
Citation: Handler, A.M. 2004. Understanding and improving transgene stability and expression in insects for SIT and conditional lethal release programs. Journal of Insect Biochemistry and Molecular Biology. 34:121-130. 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 CMAVE. Development of this methodology and strategies to effectively and safely utilize transgenic insects for biological control will depend upon a comprehensive analysis of various potential risks. These relate to the stability of the transgenic strain so that it maintains effectiveness over many generations, typically under mass-rearing. Of equal importance is ecological safety in terms of the potential for movement of the transgene from the original host into other species with which it interacts. This article addresses the major areas of concern for these risks in terms of the insect species being manipulated, the gene-transfer vector system used, and the specific genes and DNA sequences integrated into the transgenic host insect. Specific scientific protocols are also outlined that may be used for the development of more highly stable transgene vector sysetms. This information can then be used to develop guidelines for the creation of effective and ecologically safe transgenic insects, as well as methods to test and assess these attributes.
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 would influence the integrity of the transformant strain upon which the effectiveness of the biological control program depends. Loss or intra-genomic transgene movement would 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 less of a concern for short-term releases, where transgenic insects are not expected to survive in the environment beyond two or three generations. Transgene movement may occur, however, into infectious agents during mass-rearing, and the potential for movement after release is a possibility for programs using many millions of insects. The primary methods of addressing potential transgene instability relate to an understanding of the vector system used for gene transfer, the potential for its mobilization by the same or a related vector system, and methods required to identify transformants and determine if unexpected transgene movement has occurred. Methods also exist for preventing transposon-mediated mobilization, by deleting or rearranging vector sequences required for transposition using recombination systems. Stability of transgene expression is also a critical concern, especially in terms of potential epigenetic interactions with host genomes resulting in gene silencing that have been observed in plants and fungi, and it must be determined if this or related phenomena can occur in insects.