CSA formation by hematopoietic stem cells in the presence of membrane-bound dlk. (A) Bars labeled BFC are from five groups (nontransfected BFC012 cells, two control pZeo-transfected BFC012 populations, and two clones derived from the pZeo-transfected populations). Bars labeled BFC-dlk are from three groups shown to express transfected dlk; one dlk-transfected BFC012 population and two individual transfected clones. Error bars represent SEM. ∗∗, P < 0.001 days 3, 4, and 5; ∗, P < 0.01 days 6 and 7 (Student’s t test). (B) A clone derived from the dlk-transfected populations of BFC012 cells (BFC-dlk-5) and a clone derived from pZeo-transfected populations (BFC-Zeo-1) were used for CSA assay with purified fetal liver stem cells. CSA/1000 input stem cells are expressed as the mean of three individual experiments, error bars represent the SEM. ∗∗, P < 0.001 at days 4, 6, and 8 (Student’s t test).