Cdc42 and Rac1 induce filopodia and lamellipodia in activated B lymphocytes.

Constitutively active (CA), dominant negative (DN), or wild-type (WT)myc-tagged constructs of Cdc42 (A) or Rac1 (B) were transiently electroporated into B lymphocytes, preactivated with LPS for 46 to 50 hours. Cells were diluted in medium containing LPS or LPS plus IL-4 and cultured on anti-CD44–coated glass coverslips for an additional 3 to 4 hours, fixed, permeabilized, and visualized with anti-myc antibodies. Cells were photographed using a camera connected to a fluorescence microscope with a × 100 objective. (A) CA Cdc42 induced filopodia, long microspikes of polymerized actin, whereas DN Cdc42 failed to induce this structure and transfected cells were spherical. WT Cdc42 induced either short filopodialike structures or lamellipodia (not shown). (B) CA Rac1 induced lamellipodia, flattened sheets of polymerized actin, whereas DN Rac1-expressing cells were spherical. Similar observations were made using LPS or LPS plus IL-4–activated B cells. These cells are representative of the morphologic phenotypes detected in more than 5 experiments, including screening of at least 300 cells in each experiment.