|Handler, Alfred - Al|
Submitted to: Insect Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2006
Publication Date: 5/1/2006
Citation: Zimowska, G.J., Handler, A.M. 2006. HIGHLY CONSERVED PIGGYBAC ELEMENTS IN NOCTUID SPECIES OF LEPIDOPTERA. Insect Biochemistry and Molecular Biology. 3:421-428. Interpretive Summary: The creation of Genetically Modified Organisms strains of economically important insects for the development of more effective biological control programs is a major goal of our laboratory at Center for Medical, Agricultural and Veterinary Entomology Gainesville, FL. Development of this methodology depends upon an analysis of 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 the potential for movement of the transgene from the original host into other species. These risks are directly affected by the existence of the genes used for transformation, in the host species. If these genes or closely related element exists in the host, it may have the ability to "re-mobilize" once transfered. This may result in strain instability and/or inter-species transfer. This study shows that closely related sequences to the piggyBac genes exist in several moth species of agricultural importance, and this must be taken into consideration if piggyBac genes are used to create transgenic strains for their biological control.
Technical Abstract: The piggyBac transposable element was originally discovered in a Trichoplusia ni cell line, and subsequently, nearly identical elements were discovered in mutant and wild type strains of the oriental fruit fly, Bactrocera dorsalis. This suggested the existence of piggyBac in additional insects including lepidopteran species, and this study shows highly conserved, though not identical, piggyBac sequences in the noctuid species Heliocoverpa armigera, H. zea, and Spodoptera frigiperda, as well as new piggyBac sequences from the T. ni organismal genome. Genomic piggyBac elements could not be unambiguously identified in several other moth species indicating that the recent horizontal transfer of piggyBac among lepidopterans was discontinuous. Most of these sequences have greater than 94% nucleotide identity to the original IFP2 piggyBac, except for more diverged sequences in S. frugiperda, having ~77% identity. Variants of 1.3 kb and 0.8 kb piggyBac sequences found in both H. armigera and H. zea most likely became established by interbreeding, supporting the notion that the species are conspecific. None of the ten independent piggyBac sequences isolated from T. ni larval genomes are identical to IFP2, though all have an uninterrupted reading frame with the potential for encoding a functional transposase. Notably, all of these sequences, as well as the piggyBac sequences from the Helicoverpa species and those previously reported from B. dorsalis, all share three common nucleotide substitutions resulting in a single amino acid substitution in the transposase. This suggests that the original IFP2 piggyBac is a related variant of a predecessor element that became widespread. The existence of conserved piggyBac elements and the likelihood of their horizontal transfer among lepidopteran species raises important considerations for the stability and practical use of piggyBac transformation vectors.