Fig. 5. Effects of PD98059 on nuclear accumulation of GFP-PCNA in both unfertilized and fertilized eggs. GFP-PCNA fusion protein was microinjected into sea urchin eggs and the fluorescence intensity was observed in the presence of MEK inhibitor PD98059. (A) Confocal images of GFP-PCNA nuclear fluorescence in 20 µM PD98059-treated and control eggs. Scale bar: 50 µm. (B) Intensity of nuclear GFP-PCNA fluorescence in unfertilized eggs treated with 2. 5µM and 20 µM PD98059, and with 20 µM PD98059 in the presence of aphidicolin (20 µg/ml 15 minutes before addition of PD98059). (C) [³H]-Thymidine incorporation in unfertilized eggs treated with ionophore (Control) or 20 µM PD98059. Representative of three independent experiments. (D) PD98059 (20 µM) does not inhibit the nuclear accumulation of GFP-PCNA in embryos after fertilization. Each graph in B and D represents mean±s.e.m. from three or five experiments; in each experiment different females were used.