The human gene BAALC (Brain And Acute Leukemia, Cytoplasmic) implicated in normal hematopoiesis and leukemia is a marker of immature hematopoietic progenitor cells (

). To explore its role in hematopoiesis we investigated the regulation of BAALC during lineage specific differentiation. Semi-quantitative RT-PCR was performed on subsets of in vitro differentiated bone marrow CD34+ cells from healthy individuals using the cytokines G-CSF, M-CSF or EPO. Cultures were harvested on day 4, 8, 12, and 16. In addition, oligonucleotide microarray analyses (HG-U133A, Affymetrix) of in vitro stimulated CD34+ cells were independently carried out using EPO, TPO, G/GM-CSF to induce lineage-specific differentiation. For each of the lineages, cells were harvested at days 4, 7 and 11 for expression profiling. All experiments were done in triplicates for each time point and condition. RT-PCR revealed down-regulation of BAALC and CD34 as early as day 4 in cultures with G-CSF, M-CSF or EPO. In concordance, gene expression profiling showed significant down-regulation of BAALC and CD34 on day 4 of culture (BAALC: EPO p=0.04, G/GM-CSF p=0.17, TPO p=0.03; CD34: EPO p=0.01, G/GM-CSF p=0.003, TPO p=0.01). 275 genes showing a significant correlation (correlation coefficient r>0.95) to BAALC expression levels (at the 4 time points and using 3 different cytokines) were identified. Of these CD34 ranked second (r=0.99), and genes related to leukemia and neuronal cells included: Hepatic leukemia factor (HLF; r=0.99) and Paired box gene 5 (PAX5; r=0.99). It has been speculated that BAALC might be involved in cell movement or cell-cell interaction; we therefore investigated the association to genes implicated in cytoskeletal function. Expression of Myosin 5C (MYO5C; r=0.99) and Synaptic nulcei expressed gene 2 (SYNE2; r=0.95) were highly correlated with BAALC expression across all conditions (EPO, TPO, G/GM-CSF). In conclusion, using two independent approaches we show the significant down-regulation of BAALC during hematopoietic differentiation. This underscores the potential role of BAALC in early hematopoiesis and the possible contribution of aberrant BAALC expression in leukemogenesis. We postulate that similar to CD34, PAX, and HLF implicated in hematopoiesis and leukemia, down-regulation of BAALC and structural genes including Myosin 5C are critical steps during hematopoietic differentiation.

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