α4 integrin expression in embryonic tissues and adult BM. Flow cytometrical analysis of α4 integrin coexpression with hematopoietic markers at key developmental stages. Dead cells were excluded using 7-AAD. Red blood cells were gated out for all adult bone marrow samples using forward scatter/side scatter plots, except where indicated (‡; all BM samples were unlyzed). Quadrants were placed according to appropriate isotype controls. (Collagenase-dispase treatment of BM produces similar staining patterns/intensities [data not shown].)