A mosaic analysis in Drosophila fat body cells of the control of antimicrobial peptide genes by the Rel proteins Dorsal and DIF

Expression of the gene encoding the antifungal peptide Drosomycin in Drosop hila adults is controlled by the Toll signaling pathway, The Rel proteins D orsal and DIF (Dorsal-related immunity factor) are possible candidates for the transactivating protein in the Toll pathway that directly regulates the drosomycin gene. We have examined the requirement of Dorsal and DIF for dr osomycin expression in larval fat body cells, the predominant immune-respon sive tissue, using the yeast site-specific flp/FRT recombination system to generate cell clones homozygous for a deficiency uncovering both the dorsal and the dif genes. Here we show that in the absence of both genes, the imm une-inducibility of drosomycin is lost but can be rescued by overexpression of either dorsal or dif under the control of a heat-shock promoter. This r esult suggests a functional redundancy between both Rel proteins in the con trol of drosomycin gene expression in the larvae of Drosophila, Interesting ly, the gene encoding the antibacterial peptide Diptericin remains fully in ducible in the absence of the dorsal and dif genes, Finally, we have used f at body cell clones homozygous for various mutations to show that a linear activation cascade Spaetzle-->Toll-->Cactus-->Dorsal/DIF leads to the induc tion of the drosomycin gene in larval fat body cells.