Control of NPM-ALK lymphoma cell shape by Cdc42 or Rac1. NPM-ALK, NPM-ALK;Cdc42^fl/fl, NPM-ALK;Rac1^fl/fl, and NPM-ALK;Cdc42^fl/fl;Rac1^fl/fl lymphoma cell lines were immortalized from primary tumors arising in mice with the indicated genotype. Cells were transduced with CreER^T2 and Bcl2 retroviruses and then conditionally deleted for the indicated floxed genes by treatment with 10 nM 4-hydroxytamoxifen for 4 hours as described above. Stable cell lines were obtained by culturing deleted cells for at least 3 weeks. (A) Cell morphology and cell shape were evaluated by immunofluorescence using phycoerythrin-conjugated phalloidin staining to detect actin filaments. Scale bar, 5 μm. NPM-ALK;CreERT2 (NPM-ALK), NPM-ALK;CreERT2;Cdc42^fl/fl;Bcl2 (NPM-ALK/Cdc42KO), NPM-ALK;CreERT2;Rac1^fl/fl;Bcl2 (NPM-ALK/Rac1KO), NPM-ALK;CreERT2;Cdc42^fl/fl;Rac1^fl/fl;Bcl2 (NPM-ALK/Cdc42/Rac1KO). (B-D) Histograms represent the percentage of round versus polarized cells expressed as cell shape (B), average diameter (C), and actin distribution around the membrane or in the lamellipodial membrane protrusion (D). Each quantification was obtained by counting at least 100 cells for each condition. Two independent lymphoma cell lines for each genotype were studied in triplicate experiments. Error bars indicate SEM. ***P < .001; **P < .002; *P < .05.