The allele was generated by introducing a cassette containing a CreERT2 upstream of IRES-nlacZ followed by a FRT-flanked neo cassette (CreERT2-IRES-nLacZ-FRT-neo-FRT) into the ATG translational site in exon 3 of the Prdm1 gene via homologous recombination in embryonic stem (ES) cells. Correctly targeted ES cell clones were transiently transfected with a FLP expression construct to excise the neo cassette. (J:257197)