Classical genetic screens can be limited by the selectivity of mutational targeting, the complexities of anatomically based phenotypic analysis, or difficulties in subsequent gene identification. Focusing on signaling response to the secreted morphogen Hedgehog (Hh), we used RNA interference (RNAi) and a quantitative cultured cell assay to systematically screen functional roles of all kinases and phosphatases, and subsequently 43% of predicted Drosophila genes. Two gene products reported to function in Wingless (Wg) signaling were identified as Hh pathway components: a cell surface protein (Daily-like protein) required for Hh signal reception, and casein kinase 1α, a candidate tumor suppressor that regulates basal activities of both Hh and Wg pathways. This type of cultured cell-based functional genomics approach may be useful in the systematic analysis of other biological processes.
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