Fig. 9. Inactivation of Ciona ERK blocks metamorphosis. (A,B) Nuclei of cells of the tail are negative for ERK activation (red fluorescence) and apoptosis (green fluorescence) at 18 hpf (A is the phase contrast image of the same fluorescent field shown in B). (C) At 28 hpf, numerous nuclei of cells of the tail extremity are labeled either for ERK activation (red), apoptosis (green) or very rarely for both (yellow, arrow). Scale bars: 40 µm in A,B; 25 µm in C. (D) Extracts from untreated larvae at 18 hpf (lane 1) and at 24 hpf (lane 2), and larvae at 24 hpf treated with 2 µM U0126 MEK inhibitor (lane 3) were run on SDS-PAGE, stained with Coomassie brilliant blue (upper panel) and western blotted with the anti-phosphorylated ERK monoclonal antibody (lower panel). (E) U0126 MEK inhibitor blocks the metamorphosis of Ciona intestinalis. Data represent the mean of two independent experiments expressed as a percentage of total number of larvae. Vertical bars correspond to the interval of confidence for percentage at 5%. The results were assessed by variance analysis and were found to be significant (P<0.01). Note that during these experiments, a significant number of larvae did not hatch, but no effect of U0126 was detected at this stage.