Aggregation of CD16/7-mCherry–Nck SH3 domains induces actin comet tails. (A) Representative confocal image of an NIH-3T3 cell cotransfected with GFP-actin and CD16/7-mCherry–Nck SH3 domains. Antibody-induced aggregation of Nck SH3 domains results in robust actin comet tails. A higher magnification of clusters is shown in the inset. Bar, 10 µm. (B) Time-lapse confocal images of two representative (n = 145) aggregate/actin comet tails (white and yellow arrows) demonstrate aggregate motility. Images were taken at 30-s intervals over the course of 4.5 min. Bars, 1 µm. (C) Quantitative analysis of individual actin comets. A plot of Nck SH3 molecules in aggregate versus aggregate velocity (n = 145) shows no apparent correlation.