The Ple67-lacZ transgene (pEMS1539) was designed with the 2242 bp Ple67 minipromoter (FEV-D; derived from a portion of the promoter from the FEV (ETS oncogene family) (FEV) gene) upstream of a frt-flanked beta-galactosidase (lacZ) gene, an SV40 early polyA signal, and a human HPRT complementary sequence (containing exon1, intron1, exon2, and part of intron2). This construct was targeted as a single copy knockin to the Hprtb-m3 mutant locus on the X chromosome.