Efficient Expression of Genes in the Germline Using a UAS Promoter Free of Interference by Hsp70 piRNAs.

Controlling the expression of genes using a binary system involving the yeast GAL4 transcription factor has been a mainstay of developmental genetics for nearly 30 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 upstream activation sequence (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 molecular tools in germline cells is caused by their core promoter sequences, which are targeted in female germ cells by -directed Piwi-interacting RNAs (piRNAs) generated from endogenous gene sequences. In a genetic background lacking genomic genes and associated piRNAs, UASt-based constructs function effectively during oogenesis. By reducing sequences targeted by piRNAs, we created UASz, which functions better than UASp in the germline and like UASt in somatic cells.