Crb represses Rac1 activation and ROS production in photoreceptor cells. (A) Heads from wild-type flies or flies carrying crb mutant retinas were homogenized. A portion of each homogenate was kept to monitor Rac1 expression levels (input), and GST-PAK^CRIB was used to pull down active Rac1, which was detected by Western blotting. Native GST was used as a negative control. Western blotting controlled the amount of GST or GST-PAK^CRIB used in each experiment. (B) Lucigenin assays were performed to compare ROS production in control and crb mutant retinas. (C) Comparison of ROS production in retinas after knockdown of Crb or concomitant knockdown of Crb and Rac1 or Crb and Nox. Error bars represent the 95% confidence level.