Pak2 regulates CDC42 activation. (A) WT and Pak2^fl/fl LSK cells were transduced with indicated retroviruses and active GTP-bound CDC42 was determined by PBD pull-down assay in the FACS-sorted EGFP⁺ cells in control (WT) and Pak2^fl/f cells and cells coexpressing Cre and Pak2-WT, Pak2-KD, and Pak2-Δβ-Pix. CDC42 from total cell lysates was used as a loading control. (B) Normalized densitometric values comparing GTP-bound to total CDC42 from panel B. (C) Representative images of sorted SDF1-stimulated EGFP⁺ LSK cells from WT (control) and Pak2 ^fl/fl (Pak2^Δ/Δ) transduced as in panel B, showing F-actin (red), DAPI (blue), overlap (merge). The boxed region is enlarged in grayscale in the inset to show filopodia/abnormal protrusions. Red arrows indicate filopodia after stimulation with SDF1α, the white arrows indicate excessive protrusions, and the yellow arrows indicate spontaneous filopodia-like formations in unstimulated conditions. Data are from 1 of 2 independent experiments each with at least 50 cells.