Activation of a chicken embryonic globin gene in adult erythroid cells by 5-azacytidine and sodium butyrate.

Adult White Leghorn chickens were rendered anemic by injection with 1-acetyl-2-phenylhydrazine and then treated with parenteral 5-azacytidine, and levels of embryonic globin RNA in circulating reticulocytes were measured. A very small but detectable amount of correctly initiated embryonic p-type globin RNA was detected in reticulocytes from birds treated with 5-azacytidine, while none was detected in reticulocytes from those receiving only phenylhydrazine or phenylhydrazine plus 1-beta-D-arabinofuranosylcytosine (cytosine arabinonucleoside). An attempt to increase embryonic globin RNA induction by treatment with parenteral sodium butyrate after 7 days of 5-azacytidine administration resulted in a 5- to 10-fold increase in the level of embryonic globin RNA. However, sodium butyrate did not induce embryonic gene expression when given alone or after treatment with cytosine arabinonucleoside. Sodium butyrate treatment also caused a DNase I-hypersensitive site to be exposed at the 5' end of the rho-globin gene only after 5-azacytidine induced demethylation of several CpG sites in and around the gene. The implications of this model of gene activation in vivo are discussed in the context of multistep gene regulation.