Analysis of Linked Human ɛ and γ Transgenes: Effect of Locus Control Region Hypersensitive Sites 2 and 3 or a Distal YY1 Mutation on Stage-Specific Expression Patterns

Stage-specific expression of the human β-like globin genes is controlled by interactions between regulatory elements near the individual genes and additional elements located upstream in the Locus Control Region (LCR). Elucidation of the mechanisms that govern these interactions could suggest strategies to reactivate fetal (γ) or embryonic (ɛ) genes in individuals with severe hemoglobinopathies. This study extends an earlier analysis of a transgenic construct, HS3ɛγ, testing: (A) the effect of substitution of HS2 for HS3 on stage-specific expression of the ɛ and γ genes and, (B) the role of an evolutionarily conserved YY1 binding site in transcriptional regulation of the γ gene. The data show that both HS3ɛγ and HS2ɛγ can individually support embryonic expression of ɛ and fetal expression of Aγ. Thus, the cis regulators of distinct expression patterns for ɛ and γ are likely to reside near the genes, rather than in specific hypersensitive sites of the LCR. Alterations in Aγ expression patterns observed in transgenic lines carrying a construct with a mutation in a conserved YY1 binding site at −1086 indicate that this site might function to facilitate active transcription of the γ gene in fetal life.