RNAi interference by dsRNA injection into Drosophila embryos.

Genetic screening is one of the most powerful methods available for gaining insights into complex biological process (1). Over the years many improvements and tools for genetic manipulation have become available in Drosophila (2). Soon after the initial discovery by Frie and Mello (3) that double stranded RNA can be used to knockdown the activity of individual genes in Caenorhabditis elegans, RNA interference (RNAi) was shown to provide a powerful reverse genetic approach to analyze gene functions in Drosophila organ development (4, 5). Many organs, including lung, kidney, liver, and vascular system, are composed of branched tubular networks that transport vital fluids or gases (6, 7). The analysis of Drosophila tracheal formation provides an excellent model system to study the morphogenesis of other tubular organs (8). The Berkeley Drosophila genome project has revealed hundreds of genes that are expressed in the tracheal system. To study the molecular and cellular mechanism of tube formation, the challenge is to understand the roles of these genes in tracheal development. Here, we described a detailed method of dsRNA injection into Drosophila embryo to knockdown individual gene expression. We successfully knocked down endogenous dysfusion(dys) gene expression by dsRNA injection. Dys is a bHLH-PAS protein expressed in tracheal fusion cells, and it is required for tracheal branch fusion (9, 10). dys-RNAi completely eliminated dys expression and resulted in tracheal fusion defect. This relatively simple method provides a tool to identify genes required for tissue and organ development in Drosophila.