Gene knockdowns that impair cell spreading. (A) Domain schematics of CG9175 (Dm Sec12), CG8465, and CG15231. (B) Representative fields of cells with the indicated gene knockdowns. This phenotype can be detected quantitatively by calculating the total actin staining intensity divided by the total surface area of the cell (Table II). The inset shows a wild-type cell. Bar, 20 µm. (C) CG8465-GFP (left) and Sar1-mCherry (an ER-resident protein; middle) expressed in the same cell. (D) GFP-CG9175 (left) and Sar1-mCherry (middle) expressed in the same cell. (E) Selected frames from time-lapse video of CG15231-GFP. The arrows follow the position of a punctum that can be tracked over time. At 3 s, the punctum disappears, and a radial burst of fluorescence (within dashed line) is seen, likely reflecting plasma membrane fusion and secretion into the medium (Video 1). (C–E) Bars, 5 µm. (F) Secretion of 15231-GFP into the media under the listed RNAi conditions (see Materials and methods). Secretion was measured by immunoblot analysis 12 h after induction and compared ratiometrically with tubulin levels (as a control for total protein; Fig. S1). Error bars indicate mean ± SD. (G) Quantitative rates of FRAP. Curves are means for at least 10 cells.