ORE-R was used as the wild-type stock. To examine the early nullo phenotype, we used embryos from Df(1)6F1-2/LVII9 females carrying a nullo-hemagglutinin (HA)-tagged transgene on the third chromosome. nullo mutant embryos from this line can be identified during cycle 13 by their lack of HA staining. The ArmGAL4 line containing GAL4-VP16 under control of the zygotic Armadillo promoter was the gift of J.P. Vincent (National Institute for Medical Research, MRC, London, UK). The mat67.15 stock containing the second and third chromosomal inserts of GAL4-VP16 under the control of the maternal α-tubulin promoter was the gift of D. St. Johnston (University of Cambridge, UK). The GAL4 lines were crossed to a third chromosomal insert of the UASnullo construct (N39) and control crosses were performed using flies lacking a UAS insertion.