Optimization of electroporation conditions. (A) Embryos at stage 17 were incubated with 10 μg/ml fluorescein for 40 minutes at 27°C. Subsequent electroporation was performed at 35 kHz with varying voltages and pulse lengths. Relative fluorescence indicates fold quantified signal compared to that of non-electroporated, but otherwise equally treated reference embryos. Similar results were obtained for early (B, B’, stage 4) and late (C, C’, stage 31) embryos. Embryos are shown in lateral (B,B’) and dorso-lateral (C,C’) view. Scale bar 250 μM.