The Ple34-lacZ transgene (pEMS1505) was designed with the 3845 bp Ple34 minipromoter (CLDN5-C; derived from a portion of the promoter of the CLDN5 gene and two upstream putative regulatory elements from the Claudin 5 (CLDN5) 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.