Targeted gene expression using the GAL4/UAS system in the silkworm Bombyx mori

The silkworm Bombyx mori is one of the most well-studied insects in terms of both genetics and physiology and is recognized as the model lepidopteran insect. To develop an efficient system for analyzing gene function in the silkworm, we investigated the feasibility of using the GAL4/UAS system in conjunction with piggyBac vector-mediated germ-line transformation for targeted gene expression. To drive the GAL4 gene, we used two endogenous promoters that originated from the B. mori actin A3 (BmA3) and fibroin light-chain (FiL) genes and the artificial promoter 3xP3. GFP was used as the reporter. In initial tests of the function of the GAL4/UAS system, we generated transgenic animals that carried the UAS-GFP construct plus either BmA3-GAL4 or 3xP3-GAL4. GFP fluorescence was observed in the tissues of GFP-positive animals, in which both promoters drove GAL4 gene expression. Animals that possessed only the GAL4 gene or UAS-GFP construct did not show GFP fluorescence. In addition, as a further test of the ability of the GAL4/UAS system to drive tissue-specific expression we constructed FiL-GAL4 lines with 3xP3-CFP as the transformation marker. FiL-GAL4 x UAS-GFP crosses showed GFP expression in the posterior silk gland, in which the endogenous FiL gene is normally expressed. These results show that the GAL4/UAS system is applicable to B. mori and emphasize the potential of this system for controlled analyses of B. mori gene function.