REGULATION OF CHICKEN BETA-GLOBIN GENE EXPRESSION (RETROVIRUS VECTOR, AVIAN ERYTHROBLASTOSIS VIRUS)

Expression of the vertebrate (beta)-globin gene families is regulated in a tissue- and developmentally-specific manner. The chicken (beta)-globin linkage has a unique structure in that two embryonic genes, (rho) and (epsilon), lie at the 5' and 3' ends, respectively, (relative to the direction of transcription) of four closely linked (beta)-globin genes. The (rho)-globin gene was sequenced in order to complete the structural characterization of the chicken (beta)-globin gene family. Comparison of the overall sequences of the (rho) and (epsilon) genes to that of the adult (beta) gene clearly suggests that the (epsilon)-globin gene has recently evolved from an adult (beta)-type globin gene by a process of gene conversion.;Little is known about the regulatory sequences conferring tissue-specificity and temporal regulation of (beta)-globin gene expression. In order to define cis-acting regulatory element(s) for the chicken adult (beta)-globin gene, we developed two genetic procedures (assays for transient and stable expression assay) using temperature-sensitive mutants of avian erythroblastosis virus (AEV). Analysis of the transient expression of deletion mutants of the (beta)-globin gene in a tsAEV-transformed erythroid precursor cell line (HD3) has identified an enhancer element 3' to the (beta)-globin transcription unit, which confers erythroid specificity and correct temporal induction of (beta)-globin transcription. For the stable expression assay, we designed an erythroid-specific, transforming retrovirus vector based on ts167AEV. This vector stably retains transduced (beta)-globin genes, and transforms erythroid precursor cells. The inducible expression from such a trans (beta)-globin gene requires the 3' enhancer element defined by transient assay.