Transgenic blow flies for SIT

Australian sheep blowfly.jpg

Lucilia cuprina

Yan and Scott have constructed transgenic Lucilia cuprina, Australian sheep blowfly, resulting in conditional lethality of female embryos and their results are reported in Scientific Reports.

With an interest in enabling the development of efficient systems for producing male blowflies that could be used in a population suppression/eradication program based on the Sterile Insect Technique, Yan and Scott have created L. cuprina with genotypes resulting in early conditional lethality of female embryos under controlled rearing conditions.

The rationale for creating these transgenic lines is a familiar one and there is a particularly long history of interest in genetics-based control of L. cuprina. The authors describe the creation of a potentially useful genotype that could be useful should there be an interest in the genetic control of L. cuprina using the SIT. The work of the authors is probably of more immediate relevance to the SIT program against the related calliphorid Cochliomyia hominivorax which is currently controlled using the SIT however this program does not separate males from females and therefore rears millions of insects (females) at considerable costs that contribute nothing to the program.

Current SIT against Cochliomyia hominivorax involves mass-rearing and releasing males and females.

Female embryonic lethality was achieved by constructing transgenic lines based on the tet-off system in combination with the proapoptotic gene hid (head involution defective), the female-specifically spliced intron of the gene tra (transformer) and the promoters from the embryonic gene bnk (bottleneck) and hsp83 (heat shock 83).

The genetic engineering associated with this work is impressive and involved isolating and using bits and pieces from the genomes of Lucilia serricata (hid gene, bottleneck promoter), Lucilia cuprina (hsp83 promoter) and Cochliomyia hominivorax (intron from tra).

piggyBac was used as a vector and multiple transgenic lines were created demonstrating the efficacy of this transposon in this species.

DsRed expression in transgenic Lucilia. Photo from the website of Dr. Max Scott.

DsRed expression in transgenic Lucilia. Photo from the website of Dr. Max Scott.

The authors created lines in which each contained either the tet transcription factor or the hid gene. In addition they also combined both components into one gene vector. While their system worked more or less according to plan they did encounter some unexpected misexpression that lead to the system having some unwanted characteristics but clearly all of their components were functional.

One unexpected finding was a cis effect of the tet-operator and activator on their DsRed marker gene that was under the regulatory control of the hsp83 promoter from L. serricata. In the absence of tetracycline DsRed expression was enhanced significantly. Expression of DsRed was so high that male larvae were bright red under normal white-light. UV illumination was not required. The authors’ figure 6 impressively illustrates this effect.

Dr. Max Scott is not only the author of the paper featured in this post but also a member of the Steering Committee of the IGTRCN

This paper is a good example of insect genetic engineering and demonstrates the robustness of current transposon-based technology in calliphorids.

Ying Yan & Maxwell J. Scott (2015) A transgenic embryonic sexing system for the Australian sheep blow fly Lucilia cuprina. Scientific Reports 5:16090 DOI: 10.1038/srep16090


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