Bi-phenotypic B-lymphoid/myeloid cells expressing low levels of Pax5 - potential targets of BAL development. Mus musculus

Retroviral transduction of Pax5-deficient pro/preB cell lines with a doxycycline-inducible (TetON) form of the human Pax5 (huPax5) gene yielded cell clones which could be induced to different levels of huPax5 expression. Clones inducible to high levels developed B220+/CD19/+IgM+ B cells, while clones with low levels differentiated to B220+/CD19- /CD11b+/Gr-1- B-lymphoid/myeloid “bi-phenotypic” cells in vitro and in vivo. “Bi-phenotypic” cells could also be developed from high level-inducible cells by lower concentrations of doxycycline, inducing lower levels of huPax5 in vitro. Microarray analyses of genes expressed at these lower levels of huPax5 identified C/ebpα, C/ebpδ, Pu.1, Csf1r, Csf2r and Gata-3 as myeloid-related genes selectively expressed in the pro/preB cells which can develop under myeloid/lymphoid conditions to “bi-phenotypic” cells. Therefore, reduced expression of huPax5 during the induction of early lymphoid progenitors to B-lineage-committed cells can fix this cellular development at a stage that has previously been seen during embryonic development and in ALL-like “bi-phenotypic” acute leukemias (BAL). Overall design: Microarray experiments were performed as dual-color hybridizations. In order to compensate specific effects of the dyes and to ensure statistically relevant data analysis, a color-swap dye-reversal was performed.