CXCR4-mediated migration and VLA4/FAK-mediated adhesion to VCAM-1 in proB and preB cells. (A) CXCR4 expression in proB and preB cells. (B) In vitro transwell (5-µm pore) migration assay of C57BL/6 BM cells toward CXCL12 gradients. Y axis indicates frequency of migrated cells; x axis shows CXCL12 concentration (nanograms per milliliter). (C) α4 integrin expression in proB and preB cells. (D) FAK expression (encoded by Ptk2) in proB and preB cells. (E) Ikaros (encoded by Ikzf1) expression in proB and preB cells. (F) ProB and preB cell migration across VCAM-1–coated transwells (5 µm) toward CXCL12 gradient (300 ng/ml). Y axis indicates percent reduction in migratory cells; x axis shows VCAM-1 concentration (micrograms per milliliter) used for coating transwells. (B and F) Error bars indicate SD of three individual experiments. Numbers inside all histograms indicate geometric mean fluorescence intensity ± SD (n = 3 mice in each group). *, P < 0.05 by unpaired Student’s t test. Data in all panels are representative of three to five independent experiments.