The targeting cassette inserted into exon 1 upstream of the translation start site a rabbit HBB2 splice donor, intron and splice acceptor; an inducible improved cre fused to two modified Esr1 binding domains (icre/Esr1*); and an FRT-flanked neomycin resistance cassette. Flp-mediated recombination removed the selection cassette. (J:219867)