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

Background: The beta-globin gene domains of vertebrate animals constitute popular models for studying the regulation of eukaryotic gene transcription. It has previously been shown that in the mouse the developmental switching of globin gene expression correlates with the reconfiguration of an active chromatin hub (ACH), a complex of promoters of transcribed genes with distant regulatory elements. Although it is likely that observations made in the mouse beta-globin gene domain are also relevant for this locus in other species, the validity of this supposition still lacks direct experimental evidence. Here, we have studied the spatial organization of the chicken beta-globin gene domain. This domain is of particular interest because it represents the perfect example of the so-called 'strong' tissue-specific gene domain flanked by insulators, which delimit the area of preferential sensitivity to DNase I in erythroid cells. Results: Using chromosome conformation capture (3C), we have compared the spatial configuration of the beta-globin gene domain in chicken red blood cells (RBCs) expressing embryonic (3-day-old RBCs) and adult (9-day-old RBCs) beta-globin genes. In contrast to observations made in the mouse model, we found that in the chicken, the early embryonic beta-globin gene, epsilon, 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 beta-globin gene, rho, with the promoter of the adult beta-globin gene, beta(A), was observed in RBCs from both 3-day and 9-day chicken embryos. Finally, we have demonstrated that insulators flanking the chicken beta-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. Conclusions: 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.