Hoxb1^tm1Mist

A loxP site was inserted into the Hoxb1 locus upstream of the r4 enhancer (Rr140). A loxP-flanked neo cassette was inserted into intron 1. Internal to the first two loxP sites, two heterospecific Frt sites were also inserted such that by recombinase-mediated cassette exchange, exogenous sequences could be knocked into Hoxb1. Electroporation of a cre-expressing plasmid into an ES cell clone containing the modified locus resulted in excision of the regions between the different combinations of loxP sites. Deletion of the neo marker produced the Hoxb1flox allele. (J:197162)