Development and evaluation of male-only strains of the Australian sheep blowfly, Lucilia cuprina.
Bottom Line: From the 1960s to the 1980s there was a major effort to develop "field female killing" or FFK strains of L. cuprina that could be used for a cost-effective genetic control program.Males did not die in the field as normal copies of the eye color genes had been translocated to the Y chromosome and an autosome.Although the FFK strains showed some promise in field tests, a genetic control program in mainland Australia was never implemented for several reasons including instability of the FFK strains during mass rearing.
The Australian sheep blowfly Lucilia cuprina (Wiedemann) is a major pest of sheep in Australia and New Zealand. From the 1960s to the 1980s there was a major effort to develop "field female killing" or FFK strains of L. cuprina that could be used for a cost-effective genetic control program. The FFK strains carried eye color mutations that were lethal to females in the field but not under conditions in the mass rearing facility. Males did not die in the field as normal copies of the eye color genes had been translocated to the Y chromosome and an autosome. Although the FFK strains showed some promise in field tests, a genetic control program in mainland Australia was never implemented for several reasons including instability of the FFK strains during mass rearing. A stable transgenic strain of L. cuprina that carried one or more dominant repressible female lethal genes offered the potential for efficient genetic control of blowfly populations. Here I review our research on tetracycline-repressible female lethal genetic systems, Lucilia germ-line transformation and sex determination genes that ultimately led to the successful development of transgenic "male-only" strains of L. cuprina. The technology developed for L. cuprina should be directly transferable to other blowfly livestock pests including L. sericata and the New World and Old World screwworm. 29.
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Mentions: To achieve female-specific gene expression, it was apparent that this required either a gene promoter that was female-specific or an intron that was sex-specifically spliced. For the latter, we turned to the genes that are part of the well-characterized Drosophila sex determination regulatory pathway . Transcripts from the master gene Sex lethal, from the transformer (tra) gene and from the doublesex (dsx) gene were all known at that time to be sex-specifically spliced. Wilkins had suggested that the genes at the bottom of the regulatory pathway, dsx and fruitless, would be more highly conserved than the master gene at the top of the pathway . This hypothesis has largely proven to be correct. Consequently, we focused on using the sex-specifically spliced intron from the D. melanogaster dsx (Dmdsx) gene as we reasoned that dsx transcripts were also likely to be sex-specifically spliced in L. cuprina. Steller and colleagues had shown that widespread expression of the proapoptotic gene head involution defective (hid), also known as Wrinkled (W), led to organismal death . Thus we decided to insert the Dmdsx intron within the hid gene to obtain a female-specific lethal gene. Expression was controlled with the heat inducible hsp70 gene promoter  (Figure 1). The expectation was that after a heat shock, D. melanogaster females would die, as only the female hid transcript would code for fully functional HID protein. Unfortunately, after heat shock both males and females died as in both sexes hid transcripts were spliced using the weak female-specific Dmdsx splice acceptor site. It appeared that the hid transcript contained a nucleotide sequence that enhanced the use of the weak female acceptor site in both sexes .