CMS and the actin cytoskeleton are simultaneously recruited to the site of pre-TCR activation. Confocal microscopy analysis of (A) CMS-GFP–transfected SupT1 cells stained with an anti-CD3ϵ mAb plus Alexa555–anti-mouse and left at 4°C (top row), or incubated at 37°C for 2 minutes to induce pre-TCR aggregation (bottom row); or (B) CMS-GFP transfectants either untreated (top row) or stimulated with anti-CD3ϵ–coated beads for 5 and 15 minutes (middle and bottom rows) and stained with phalloidin-TRITC. Data are representative of at least 3 independent experiments.