GENERATING LOSS-OF-FUNCTION PHENOTYPES OF THE FUSHI-TARAZU GENE WITH A TARGETED RIBOZYME IN DROSOPHILA

THE ability to isolate gene sequences and analyse their expression pat terns has generated demand for mutations created to assess their biolo gical functions. In Drosophila melanogaster this can be achieved by tr aditional mutagenesis, but this is time-consuming, labour-intensive an d not always successful. Moreover, the functions of genes that are exp ressed several times during development are often obscured in the late r stages because of disruptions caused by the absence of early gene fu nction. Here we propose a new strategy to create conditional knock-out mutations using a targeted heat-inducible ribozyme. Ribozymes are cat alytic RNA molecules that specifically cleave RNAs1-11 and are potenti ally useful for studying gene function during animal development becau se the expression of critical regulatory genes is usually low and thei r function is often dosage-dependent. The ribozyme can be delivered to a specific region or at a particular developmental stage using a regi on-specific or inducible promoter. The Drosophila fushi tarazu (ftz) g ene is a good candidate for testing this approach12-17. We generated t ransgenic flies carrying a ribozyme against the ftz gene. The two deve lopmental phases of ftz function can be distinguished by timed inducti on of the ribozyme. Activation of the ribozyme in the blastoderm disru pts the ftz seven-stripe pattern and produces ftz-like pair-rule defec ts in larvae. The involvement of ftz in neurogenesis was verified by a ctivation of the ribozyme during the early phase of formation of the c entral nervous system.