Down-regulation and up-regulation of RARα expression during erythroid and myelomonocytic differentiation.

(A) Morphological analyses of untreated FDCP-mixA4 cells (d0) and cells treated with EPO or conditioned medium containing G-CSF and GM-CSF for d2, d4, and d8, respectively. The percentage of undifferentiated blasts (Bl), erythroblasts (EBl), myelomonocytic cells of the granulocytic and monocytic lineage (GM) and mature erythrocytes (E) are as indicated. (B) Differential expression of the RARα isoforms during multilineage maturation of A4 cells was examined with RT-PCR analysis. Total RNA was derived from untreated A4 cells (d0) and cells treated for different numbers of days (as indicated) with either myelomonocytic GFs or EPO (the same cell populations as used for morphological evaluation in panel A). P19 embryonal carcinoma cells were treated with 10⁻⁶ M RA for 24 hours and used as positive controls for RARα2 induction. Changes in the levels of GATA-1 and lysozyme expression reflect the differentiation status of the cells at the level of lineage-specific gene expression. (C) Expression of RARβ and RARγ isoforms in undifferentiated FDCP-mixA4 and cells differentiated along myelomonocytic and erythroid lineages as in panel A. When indicated, total mouse embryo RNA and/or picogram quantities of complementary DNA (cDNA) were used as positive controls. (D) Expression of RXRα, β, and γ in undifferentiated and maturing A4 cells. Positive controls were as in panel C.