Early replication timing of the chicken α-globin gene domain correlates with its open chromatin state in cells of different lineages

The vertebrate α-globin gene domain is an open chromatin domain overlapping a neighboring house-keeping gene. The tissue-specific cluster of α-globin genes and the overlapping housekeeping gene share the same replication origin. We have studied the replication timing of chicken α-globin genes in cells of different lineages using the FISH-based approach and found that α-globin genes replicate early both in erythroid and in non-erythroid cells, i.e. regardless of their transcriptional activity. Early replication timing of chicken α-globin genes in cells of different lineages was in good correlation with the open chromatin configuration of the α-globin gene domain in both erythroid and non-erythroid cells. We propose that active transcription of the housekeeping gene overlapping the α-globin gene domain enables an access of Origin Recognition Complex (ORC) proteins to the replication origin resulting in early replication of α-globin genes even in non-erythroid cells.