Endosome coalescence occurs independently of the munc13-4 rab27 complex. (A) Quantitative analysis of rab11-rab27a–overlapping structures in control or munc13-4–deficient (FHL3) CTLs coexpressing DsRed-rab11 and GFP-rab27a as described previously.¹⁰  FHL3 CTLs were also cotransfected with wild-type (WT) or the munc13-4(FQL > AAA) construct. Data represent statistical image analysis of 2-color pixel intensity correlation in all optical sections and are the average (± SD) of the overlapping surface calculated by computer-assisted image analysis of at least 10 cells. (B) Confocal microscopy of RBL-2H3 cells stably expressing CFP-rab11 (blue), Cherry-rab27a (red), and YFP-munc13-4 constructs (green); endogenous rat munc 13-4 was silenced with siRNA #2. (C) Quantitation of codistribution of rab11 with munc13-4 and rab27a. Colocalization was determined in 10 cells using Volocity as described in the “Methods,” and is displayed as a percentage of rab11 over munc13-4 (black) and rab11 over rab27a (gray). Error bars are SEM of 3 experiments. Scale bars indicate 5 μm. **P < .01.