INDUCIBLE TERNARY CONTROL OF TRANSGENE EXPRESSION AND CELL ABLATION IN DROSOPHILA

In Drosophila, P-GAL4 enhancer trap lines can target expression of a c loned gene, under control of a UAS(GAL) element, to any cells of inter est, However, additional expression of GAL4 in other cells can produce unwanted lethality or side-effects, particularly when It drives expre ssion of a toxic gene product. To target the toxic gene product ricin A chain specifically to adult neurons, we have superimposed a second l ayer of regulation on the GAL4 control. We have constructed flies in w hich an effector gene is separated from UAS(GAL), by a polyadenylation site flanked by two FRT sites in the same orientation; A recombinatio n event between the two FRT sites, catalysed by yeast FLP recombinase, brings the effector gene under control of UAS(GAL). Consequently, exp ression of tile effector gene is turned on in that cell and its descen dants, if they also express GAL4. Recombinase is supplied by heat shoc k induction of a FLP transgene, allowing both tinting and frequency of recombination events to be regulated, Using a lacZ effector (reporter ) to test the system, we have generated labelled clones in the embryon ic mesoderm and shown that most recombination events occur soon after FLP recombinase is supplied. By substituting the ricin A chain gene fo r lacZ, we have performed mosaic cell ablations in one GAL4 line that marks the adult giant descending neurons, and in a second which marks mushroom body neurons. In a number of cases we observed loss of one or both the adult giant descending neurons, or of subsets of mushroom bo dy neurons. In association with the mushroom body ablations, we also o bserved misrouting of surviving axons.