The action of the I(1)npr-1<SUP>+</SUP> locus on the Drosophila glue gene Sgs-3 is cell-autonomous

The 2B5 chromosomal locus inDrosophila contains a gene, I(1)npr-1<SUP>+</SUP>, 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 an Sgs-3-E. coli &#946;-galactosidase (lacZ) fusion protein, under the control of an Sgs-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 the Sgs-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<SUP>+</SUP>. This is in contrast to another factor, the hormone ecdysterone, which is also required for Sgs-3 expression, but acts in a non-autonomous manner