A sub-fragment (nucleotides 354-731) of the AP2x enhancer (from upstream of TfAP-2), in which the the Dfd-exd binding sites in domain 2 of the enhancer have been mutated and the Dfd-exd binding sites in domain 3 of the enhancer have been optimized, is fused upstream of the Drosophila Synthetic Core Promoter (DSCP) followed by the GAL4 coding sequence.