Generation of the E2AER allele. (A) Targeting strategy for the generation of E2AER/+ and E2AER/ER mice. The 3' region of the mouse tcfe2a gene was used for targeting. Gene direction, the E47, E12, and 3' exons (gray boxes), and inserted tamoxifen-responsive estrogen receptor ligand binding domain (ER, black box) are shown. Regions mediating homologous recombination are denoted by dotted lines. The selection markers pgkneo and pgktk are located as shown. (B) Genotyping PCR of E2A+/+, E2AER/+, and E2AER/ER DNA using primers yz164, yz29, and bjE2Ar3 as shown in (A), that yield a 0.9 kb wild-type allele and 1.2 kb mutant allele. (C) RT-PCR of cDNA acquired from E2A+/+, E2AER/+, and E2AER/ER thymus RNA. E2A and GAPDH (control) expression was detected by semi-quantitative PCR of 5-fold serial dilutions.