Hybridization of probes for hematopoietic and housekeeping genes to cDNA samples from purified embryonic aorta-associated and liver HSCs. The lower right panel shows the set of samples stained with ethidium bromide before blotting onto nylon filters and probing with the indicated ³²P-labeled cDNA probes. Autoradiography times were 1 to 2 hours for β-actinand GAPDH and 8 to 24 hours for hematopoietic genes. Ao, 5-week CD34⁺CD45⁺ aortic cells; 5L, 5-week CD34⁺CD45⁺ liver cells; 6.5L, 6.5-week CD34⁺CD38⁻ liver cells.