Spatial organization of the chicken beta-globin gene domain in erythroid cells of embryonic and adult lineages

Using chromosome conformation capture (3C), we have compared the spatial configuration of the β-globin gene domain in chicken red blood cells (RBCs) expressing embryonic (3-day-old RBCs) and adult (9-day-old RBCs) β-globin genes. In contrast to observations made in the mouse model, we found that in the chicken, the early embryonic β-globin gene, Ε, did not interact with the locus control region in RBCs of embryonic lineage (3-day RBCs), where this gene is actively transcribed. In contrast to the mouse model, a strong interaction of the promoter of another embryonic β-globin gene, ρ, with the promoter of the adult β-globin gene, βA, was observed in RBCs from both 3-day and 9-day chicken embryos. Finally, we have demonstrated that insulators flanking the chicken β-globin gene domain from the upstream and from the downstream interact with each other, which places the area characterized by lineage-specific sensitivity to DNase I in a separate chromatin loop.Taken together, our results strongly support the ACH model but show that within a domain of tissue-specific genes, the active status of a promoter does not necessarily correlate with the recruitment of this promoter to the ACH.The domain of chicken beta-globin genes is located on chromosome 1 and has a length of approximately 33 kb. It includes a cluster of four beta-globin genes: ρ (HBG1), βH (HBE1), βA (HBG2) and Ε (HBE) and several distant regulatory regions, which are marked with sites of hypersensitivity to DNase I (HS) and are necessary for the regulation of transcription, replication and chromatin status of the domain [1,2]. The locus control region of the domain (LCR) is located upstream of the embryonic β-globin gene ρ and is composed of three blocks co-localizing with the erythroid cell-specific HSs 1 to 3 [3,4]. A constitutive HS4 located upstream of the LCR marks the position of the well-studied CTCF-dependent (CTCF ‐ D？D？D？TC-binding protein factor) insulator [5-9]. The CTCF-dependent enhancer-blocking e