Bromodeoxyuridine treatment of normal adult erythroid colonies: an in vitro model for reactivation of human fetal globin genes.

We report that bromodeoxyuridine (BrdU) addition in semi-solid cultures of normal adult erythroid progenitors causes a sharp rise of gamma-globin gene expression in erythroid colonies. Control studies were carefully carried out to exclude the possibility of toxic effects exerted by the drug in these experimental conditions. In particular, BrdU addition induces a sharp increase in the level of relative gamma-globin synthesis and content in pooled BFU-E-derived colonies: this rise is clearly observed in single bursts of the mature type (largely composed of late erythroblasts) but not in immature ones (essentially comprising early erythroblasts). Furthermore, it is associated with an increase of the G gamma/G gamma + A gamma synthetic ratio from adult up to fetal like values. Reactivation of gamma-synthesis was observed even if BrdU was added to colonies composed essentially of early erythroblasts, ie, when BrdU was added to either bursts at day 10 of culture or late CFU-E-derived clones at day 1. These in vitro observations indicate modulation of gamma-synthesis at the stage of erythroblasts from normal adults. At the molecular level we suggest that BrdU, by replacing thymidine in DNA, may inhibit the switch from a fetal-like biosynthetic program expressed in early erythroblastic differentiation to the adult program expressed in later stages of maturation.