Effects of signal transduction inhibition on CD34⁺ HSC migration. The effects of clostridial ToxB and ROCK-inhibitor Y27632 on CD34⁺ HSC migration were assessed in transwell assays. Cells were incubated (37°C, 5% CO₂) with increasing concentrations of ToxB (100, 200, and 500 ng/mL) for 18 hours prior to chemotaxis assays. Y27632 (10 μM) was included in the top chamber of transwells for the duration of the migration assay. (A) Pretreatment with ToxB markedly reduced the spontaneous migration of UTP-treated cells (P = .05) and toward CXCL12 gradients (P = .02). (B) Similarly, the migration of UTP-treated cells and their response to CXCL12 chemoattractant gradients were significantly inhibited by Y27632 treatment (P < .05). Results were obtained from 3 independent experiments and are shown as mean ± SEM. *P values less than .05.