Fig. 4. The effect of RBF-280 expression on S phase in the second mitotic wave. (A-D) Low-magnification view; (E-H) High-magnification view. (A,E) A wild-type eye disc; (B,F) A GMRRBF-280/GMRRBF-280 eye disc; (C,G) A GMRRBF-280/GMRDap eye disc; (D,H) A GMRDap/+ eye disc. The BrdU-positive cells in the second mitotic wave in wild-type eye discs are clustered together, indicating that cells finish S phase rapidly and synchronously. In GMRRBF-280⁴ eye discs, the second mitotic wave is broader and the BrdU staining is weaker in the second mitotic wave, indicating a prolongation of S phase and a loss of synchrony in the completion of S phase. (A,B,E,F) 1 hour of BrdU incorporation was used instead of 30 minutes to visualize the weaker staining in the second mitotic wave of GMRRBF-280⁴. In all the discs, posterior is oriented towards the right. Arrows indicate the second mitotic wave and arrowheads indicate the morphogenetic furrow.