The epsilon-(embryonic) globin gene is the first of the beta-like globin genes to be expressed during development. Assays of the 5' region of the gene reveal a silencer motif located around -275 bp. Mutation of this region has resulted in increase in transcription activity as measured in transient transfection assays and in vitro transcription in erythroid cells of embryonic and adult phenotype. A transgene has been constructed extending 5' to hypersensitivity site 2 in the beta-globin locus control region and 3' of the epsilon globin gene. When assayed in transgenic mice or in erythroid cell cultures, expression is observed in the embryonic or fetal stage, but not in the adult stage for the normal construct. When the construct is mutated in the silencer motif, expression is also observed in the adult stage. These data suggest that erythroid cell cultures, particularly cultures of primary erythroid cells, can be used in specific applications as an alternate to assessing developmental expression in transgenic mice. Other studies of the epsilon globin gene have led to insights on the expression and processing of other genes within the beta-globin cluster. Examination of epsilon-globin and gamma(fetal)-globin gene splicing in cultured erythroid precursors suggested that transcriptional and post-transcriptional processing contributed to the regulation of globin gene expression. Using hemin supplement in the culture system, the level of gamma-globin gene mRNA increased two fold and the splicing efficiency of gamma-globin increased as well as the level of gamma-globin message in the cytoplasm. Only the mature gamma-globin message was found in the cytoplasm. For epsilon-globin, hemin treatment decreases the level of unspliced message in the nucleus and increases the level of spliced message in the cytoplasm. These results suggest that the increase in gamma-globin production observed in the cultured erythroid precursors by hemin arrises from modification of both transcriptional and post-transcriptional processing, and raises the potential of such strategies to affect hemoglobin phenotype in erythroid cells.
