Genetic Analysis by Targeted Misexpression and Gene Silencing

Analysis of gene function is crucial for understanding the mechanism of biological processes. Critical clues to gene functions in vivo can be obtained from altered mutant phenotypes in genetic model organisms. Phenotypes are expressed mainly by loss-of-functionloss-of-function mutations. However, loss-of-function mutations can often be compensated by the function of related genes or parallel pathways, causing hurdles in gene function studies. In such cases, gain-of-function mutations offer alternative means to reveal the gene function by eliciting dominant phenotypes. Despite such merits, gain-of-function mutations are rare and difficult to isolate compared to loss-of-function mutations. Overexpression of engineered transgenes is an alternative approach for mimicking gain-of-function conditions. This chapter will introduce the Gal4-UASGal4-UAS bipartite system in Drosophila, a transposon-based strategy for misexpressing any gene of interest in targeted tissues. We will also discuss applications of the Gal4-UAS system for identifying new genes that can induce gain-of-function phenotypes by targeted misexpression. In addition, similar usages of transgenes in fish and mice will also be discussed. Lastly, RNA interferenceRNA interference will be introduced as a powerful method for inducing loss of functions in C. elegans. RNA interference can be extended to targeted gene silencinggene silencing by overexpression of interfering RNA using the Gal4-UAS system.