Lox511 sites were inserted into the 5' and 3' UTRs of the Hoxb8 gene. An FRT-flanked neo selection cassette followed the 3' lox511 site. For temporal control of gene activation, an IRES-rtTA2M2 seqment was also introduced into the 3' UTR, along with an FRT-flanked neo selection cassette. The neo was subsequently removed by breeding with FLPe deleter animals. (J:162102)