Pak2 kinase activity and its interaction with β-Pix regulate HSPC homing and CA-CDC42 rescued defective homing of Pak2 deletion. (A) Homing of LSK BM cells. WT and Pak2^fl/fl LSK cells were transduced with indicated retroviruses and 2 × 10⁵ sorted EGFP⁺ cells were injected into lethally irradiated mice. Sixteen hours postinfusion, homing to the BM was measured after harvesting femur, tibia, and iliac crest bones. The homing efficiency of indicated genotypes is expressed as a mean of the percentage of control (WT LSK transduced with Cre) for each mouse with mean shown as horizontal bar, n = 12-27 mice per group. (B) Sorted EGFP⁺ LSK cells (2 × 10⁵) from WT (control) and Pak2^fl/fl mice were transduced with vectors expressing Cre alone (Pak2^Δ/Δ) or Cre and CA-CDC42 and injected into lethally irradiated mice. Sixteen hours postinfusion, the homing to the BM was measured from cells harvested from femur, tibia, and iliac crest. The homing efficiency of individual animals of the indicated genotypes is shown as a percent of control with mean (horizontal bar) ± SEM of 5 to 13 mice per group. The statistical significance was determined using the Mann-Whitney U test. ****P < .0001, ***P < .001, **P < .01, *P < .05.