Spatial configuration of the chicken α-globin gene domain:: immature and active chromatin hubs

The spatial configuration of the chicken alpha-globin gene domain in erythroid and lymphoid cells was studied by using the Chromosome Conformation Capture (3C) approach. Real-time PCR with TaqMan probes was employed to estimate the frequencies of cross-linking of different restriction fragments within the domain. In differentiated cultured erythroblasts and in 10-day chick embryo erythrocytes expressing adult alpha(A) and alpha(D) globin genes the following elements of the domain were found to form an active chromatin hub: upstream Major Regulatory Element (MRE), -9 kb upstream DNase I hypersensitive site (DHS), -4 kb upstream CpG island, alpha(D) gene promoter and the downstream enhancer. The alpha(A) gene promoter was not present in the active chromatin hub although the level of alpha(A) gene transcription exceeded that of the alpha(D) gene. Formation of the active chromatin hub was preceded by the assembly of multiple incomplete hubs containing MRE in combination with either 9 kb DHS or other regulatory elements of the domain. These incomplete chromatin hubs were present in proliferating cultured erythroblasts which did not express globin genes. In lymphoid cells only the interaction between the alpha(D) promoter and the CpG island was detected.