ABSTRACT
For more than 30 years it was believed that globin gene domains included only genes encoding globin chains. Here we show that in chickens, the domain of alpha-globin genes also harbor the non-globin gene TMEM8. It was relocated to the vicinity of the alpha-globin cluster due to inversion of an approximately 170-kb genomic fragment. Although in humans TMEM8 is preferentially expressed in resting T-lymphocytes, in chickens it acquired an erythroid-specific expression profile and is upregulated upon terminal differentiation of erythroblasts. This correlates with the presence of erythroid-specific regulatory elements in the body of chicken TMEM8, which interact with regulatory elements of the alpha-globin genes. Surprisingly, TMEM8 is not simply recruited to the alpha-globin gene domain active chromatin hub. An alternative chromatin hub is assembled, which includes some of the regulatory elements essential for the activation of globin gene expression. These regulatory elements should thus shuttle between two different chromatin hubs.
Subject(s)
Avian Proteins/genetics , Globins/genetics , Membrane Glycoproteins/genetics , Animals , Avian Proteins/metabolism , Cell Differentiation , Cell Line , Deoxyribonuclease I , Enhancer Elements, Genetic , Erythroblasts/metabolism , Erythroid Cells/cytology , Erythroid Cells/metabolism , Humans , Introns , K562 Cells , Locus Control Region , Membrane Glycoproteins/metabolism , Multigene Family , RNA Splicing , RNA, Messenger/metabolismABSTRACT
The vertebrate alpha-globin gene domain is an open chromatin domain overlapping a neighboring house-keeping gene. The tissue-specific cluster of alpha-globin genes and the overlapping housekeeping gene share the same replication origin. We have studied the replication timing of chicken alpha-globin genes in cells of different lineages using the FISH-based approach and found that alpha-globin genes replicate early both in erythroid and in non-erythroid cells, i.e. regardless of their transcriptional activity. Early replication timing of chicken alpha-globin genes in cells of different lineages was in good correlation with the open chromatin configuration of the alpha-globin gene domain in both erythroid and non-erythroid cells. We propose that active transcription of the housekeeping gene overlapping the alpha-globin gene domain enables an access of Origin Recognition Complex (ORC) proteins to the replication origin resulting in early replication of alpha-globin genes even in non-erythroid cells.
