Fig. 2. Effect of U0126 on DNA synthesis. DNA replication was monitored by incubating P. lividus sea urchin eggs with BrdU as described in Materials and Methods. Untreated eggs, analyzed 1 hour after fertilization, show major BrdU incorporation (a). This was not observed when eggs were treated with 20 µM aphidicolin (b). Unfertilized eggs treated with 1 µM U0126 for 3 hours, and then incubated (d) with or (c) without 20 µM aphidicolin showed similar BrdU incorporation. Bar, 50 µm.