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Fig. 1 The I-SceI meganuclease system can be used to reduce mosaicism effectively in transient transgenic animals. In a series of experiments, it was found that the full and normal pattern of expression can be recapitulated using either the lmo2 or gata1 promoters in ~30% of the injected embryos. Shown are representative examples of embryos derived from fertilized eggs that had been injected with transgenes and the meganuclease. (A,B) Two independent examples using the I(lmo2;gfp)I transgene examined at the 10-somite stage. GFP expression is present throughout the two stripes of lateral mesoderm (arrows). Views are dorsal, anterior towards the left. (C) A similar embryo analyzed at 20 hpf, with GFP expression throughout the ICM (arrow) and also anterior lateral mesoderm (arrowhead). The view is lateral, anterior towards the left. (D) A representative embryo, viewed as in C, derived from eggs injected with the I(gata1:gfp)I construct at 20 hpf. GFP expression is restricted to the ICM (arrow).