The action of theI(1)npr-1 + locus on theDrosophila glue geneSgs-3 is cell-autonomous

The 2B5 chromosomal locus inDrosophila contains a gene,I(1)npr-1 ⁺, whose product required intrans for the expression of the larval salivary gland-specific geneSgs-3. We have addressed the question as to whether this factor acts in a cell-autonomous manner or not. This was made possible by the use of a transformant strain that makes anSgs-3-E. coli β-galactosidase (lacZ) fusion protein, under the control of anSgs-3 promoter, allowing the cellular examination of gene expression by a histochemical assay for enzyme activity. Using genetic methods, larvae that were mosaic for the loss of function mutationl(l)npr-1 were generated. The expression of theSgs-3-lacZ fusion gene was assayed histochemically in such larvae. Our results strongly indicate a cell-autonomous requirement for the product ofl(1)npr-1+. This is in contrast to another factor, the hormone ecdysterone, which is also required forSgs-3 expression, but acts in a non-autonomous manner