The tissue-specific expression of ZAM depends on the EGF receptor pathway. (A) Scheme for the generation of Egfr−/− follicle cell clones. Flp-mediated recombination was induced in females trans-heterozygous for hs-myc and topCO, a null allele of the EGF receptor of Drosophila, torpedo. One daughter of a recombinant follicle cell carries two copies of myc, whereas the other lacks myc and is homozygous for topCO. (B) A stage 10 egg chamber carrying mutant topCO follicle cell clones at the posterior pole of the oocyte. In these mutant clones highlighted by broken lines, no LacZ expression (red) is detected. The wild-type clones express the myc marker (green) and LacZ at the posterior pole. In the whole structure, nuclei are in blue due to the ToPro3 marker.