Generation of Cdc42^−/− B cells by a loxP/Cre recombinase system. (A) The loxP/Cre-mediated gene-targeting strategy to generate Cdc42 gene–deleted (Cdc42⁻) allele in B cells. (B) Western blots showing Cdc42 expression in B220⁺ B cells, purified from bone marrow and spleen of WT and Cdc42^−/− (KO) mice using B220 microbeads. Parallel blots of beta-actin serve as loading controls. Vertical line has been inserted to indicate the gel lanes being switched in position from the original blot.