Development of transgenic strains of screwworm fly (Cochliomyia hominivorax) using the nullo and CG14427 early-acting promoter genes

Authors: Arp, Alex; VARGAS LOWMAN, AIDAMALIA - UNIVERSIDAD DE PANAMA; MARTINEZ, ANDREA - UNIVERSIDAD DE PANAMA; SCOTT, MAX - NORTH CAROLINA STATE UNIVERSITY

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/3/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: New World screwworm, Cochliomyia hominivorax, is an economically important ectoparasite of warm-blooded animals in South America and the Caribbean. It primarily effects livestock but can infest humans. Efforts to control C. hominivorax led to the development of the sterile insect technique (SIT) during the mid-twentieth century. Recent efforts have been aimed at producing male-only strains, which would reduce costs and/or increase production. No methods to produce male-only releases have been developed or utilized by the eradication program. Female-lethal transgenic strains have been developed for screwworm but producing strains with the performance and reliability needed for mass-rearing has been challenging. Strains the kill the female in the egg before hatching are beneficial since female lethality in later stages would increase the cost of feeding and could cause fouling of the diet. Three strains of C. hominivorax with one of two predicted early embryo female lethal transgenes were created and evaluated for performance and if the transgene functioned as predicted. Both strains utilizing one gene construct functioned as predicted but the female larvae died as pupae. The other strain was embryo lethal and had improved performance. Although none of these strains are yet viable for use in the mass rearing program, they provide important examples for strain creation, transgene design, and that transgene expression may not predict stage lethality.

Technical Abstract: The eradication and control program for the screwworm, Cochliomyia hominivorax, has historically been based on the releases of sterile flies of both sexes. However, releasing only sterile males is estimated to be up to five times more effective in controlling wild populations. Additionally, removal of females early in development could result in considerable reductions in diet and labor costs. While genetic sexing systems have been developed in other species through selective breeding for sex-linked traits, such as embryo heat tolerance or pupal color, such techniques are not viable for C. hominivorax. Therefore, female-specific lethality systems using transgenic constructs are being developed and tested in this species. These systems include single-pupal lethal strains and several embryo-lethal dual-component designs. Two new driver strains with cellularization-promoting genes were created: Nullo (DR6) and CmCg14427 (DR7), with the aim of producing female-only lethality in embryos. The results demonstrated that the gene expression patterns for both drivers were similar, but DR6 resulted in lethality in the pupal stage and DR7 presented female lethality during embryonic development. Although the performance of the DR7 strain was acceptable, when compared with the non-transgenic control line (J06), the transgenic strain is less competitive. Among the two transgenic strains, the one with higher activity resulted in lower biological yields. These findings highlight an important lesson regarding the selection of promoter genes, indicating that promoter genes do not always act according to expected expression, and choosing promoters with excessively high activity can result in inconsistent or lower strain performance. than strains with more moderate activity.