Figure 4.

Cre-recombinant activity and developmental stage. EIIaCre of maternal origin produced excision patterns suggesting that the transgene is expressed during mature oocyte stages, and, to a much lesser extent, after ovulation. This Cre-activity is strong enough to complete recombination of floxed segments when they are also maternally transmitted. EIIaCre is re-expressed from maternal and paternal transgene copies during the morula and blastocyst stages. In the presence of multiple loxP sites, this late EIIaCre expression is able to produce mosaic mice with partial excision patterns.