INVIVO EXPRESSION OF 2 HIGHLY CONSERVED DROSOPHILA GENES IN THE AUSTRALIAN SHEEP BLOWFLY, LUCILIA-CUPRINA

The expression of foreign genes in insects has often relied on the use of the promoter from the heat-shock-70 gene (hsp70) of Drosophila melanogaster. It has been generally assumed that because this gene is highly conserved it will be expressed efficiently in other insects. We examined the efficiency of the hsp70 promoter and the actin 5C promoter from D. melanogaster in regulating gene expression in the Australian sheep blowfly, Lucilia cuprina (family: Calliphoridae). Plasmids containing these promoters 5' of the coding region of the E. coli chloramphenical acetyltransferase (CAT) gene were microinjected into preblastoderm embryos and CAT activities subsequently measured from either developing embryos or newly hatched larvae. We report that the amount of CAT activity present in injected embryos was a function of both the plasmid copy number within the embryo and the species injected. The hsp70 promoter was expressed 10-100 times less efficiently in L. cuprina compared to D. melanogaster and was not heat inducible, even at temperatures at which heat shock is known to occur in this insect. The actin 50 promoter was expressed approx. 10 times as efficiently in both species compared to the hsp70 promoter. As with the hsp 70 promoter, the actin 5C promoter was more efficiently expressed in D. melanogaster compared to L. cuprina. The significance of these results in relation to heterologous gene expression systems and developing gem line transformation in non-drosophilid insects is discussed.