Human globin gene expression and linkage in bone marrow and fetal liver

During embryonic development there is a transition from embryonic and fetal to adult beta-type globin chains. The high-molecular-weight RNA found in nuclei from embryonic and adult human erythropoietic tissues, fetal liver, and bone marrow, have been investigated for the presence of gamma(fetal)- and beta(adult)-globin messenger RNA sequences by molecular hybridization. Unlike alpha- and beta-globin mRNA sequences, gamma-globin mRNA sequences are absent from both total and high-molecular-weight nuclear RNA isolated from adult bone marrow. The amount of cytoplasmic gamma-globin mRNA is proportional to the level of gamma-chain synthesis, demonstrating that translational control is not a major control mechanism in the expression of globin genes. Since the gamma-, delta-, and beta-globin genes are known to be closely linked genetically, transcriptional control can discriminate between similar gene sequences that are spatially adjacent to one another.