Efficient expression of genes in the Drosophila germline using a UAS-promoter free of interference by Hsp70 piRNAs

Abstract

Controlling the expression of genes using a binary system involving the yeast GAL4 transcription factor has been a mainstay of Drosophila melanogaster developmental genetics for twenty-five years. However, most existing GAL4 expression constructs only function effectively in somatic cells, but not in germ cells during oogenesis, for unknown reasons. A special UAS promoter, UASp was created that does express during oogenesis, but the need to use different constructs for somatic and female germline cells has remained a significant technical limitation. Here we show that the expression problem of UASt and many other Drosophila molecular tools in germline cells is caused by their core Hsp70 promoter sequences, which are targeted in female germ cells by Hsp70-directed piRNAs generated from endogenous Hsp70 gene sequences. In a genetic background lacking genomic Hsp70 genes and associated piRNAs, UASt-based constructs function effectively during oogenesis. By reducing Hsp70 sequences targeted by piRNAs, we created UASz, which functions better than UASp in the germline and like UASt in somatic cells.