The role of c-myb during the maturation of murine CFU-E

Proper expression of the c-myb proto-oncogene is essential for definitive, but not primitive erythropoiesis. To examine the role of c-myb during adult erythropoiesis, we incubated purified murine colony-forming units (CFU-E) with a c-myb-specific antisense oligodeoxynucleotide (AS- oligo) in order to diminish expression levels. By western blot analysis, c- myb expression was reduced during the first seven hours of AS-oligo treatment as compared to untreated cells. We then quantitated the amount of heme synthesized in CFU-E treated with c-myb AS-oligo, a random sequence oligo or no oligo. No significant differences were seen in tile amount of heme synthesized during 42 hours of erythroid culture with either high levels (1 U/mL) or physiological levels (20 mU/mL) of Epo. In contrast, CFU-E treated with an AS-oligo directed toward mRNA encoding the first enzyme of the heme biosynthetic pathway in erythroid cells (d-aminolevulinate synthase) demonstrated a 65% reduction in the amount of heme synthesized. We conclude that the major role of c-myb during hematopoiesis must be in progenitor cells antecedent to the CFU-E stage and may possibly involve the establishment of the genetic program directing the formation of red blood cells.