SALL4 expression in human primary AML and myeloid leukemia cell lines. (A) SALL4 mRNA expression in AML. Real-time PCR quantification of SALL4A and SALL4B normalized to GAPDH showed that both SALL4A and SALL4B were expressed in purified CD34⁺ cells, but SALL4A was rapidly down-regulated and SALL4B turned off in normal bone marrow (n = 3) and normal peripheral blood (n = 3) cells. In contrast, in 15 primary AML samples and 3 myeloid leukemia cell lines (Kasumi-1, THP-1, and KG.1), the expression of SALL4A or SALL4B, or both, failed to be down-regulated. The results were calibrated against the expression of SALL4A or SALL4B in purified CD34⁺ cells. Y-axis: Log scale on the relative quantification. (B) Constitutive expression of SALL4 protein in human AML (FAB M1-M5, n = 81) is demonstrated by immunohistochemical staining. No SALL4 expression was detected in normal bone marrow (i), normal thymus (ii), or normal spleen (iii). All cell nuclei remained blue. Nuclei of CD34⁺ HSCs/HPCs showed brown staining indicating SALL4 expression (iv); acute myeloid leukemia blasts showed similar staining (v, low power [× 4]) in microarray leukemia tissue samples. Each circle represents one leukemia sample. (vi) High-power (× 400) view of one leukemia sample shown in panel vii. The red arrows indicate positive nuclear staining.