No existence of translocus balancer to coordinate the expression and regulation of human hemoglobin genes in transgenic mice study

Identification of long range regulatory elements of mouse alpha-globin gene cluster by quantitative associated chromatin trap (QACT)

Chromatin from different regions of the genome frequently forms steady associations that play important roles in regulating gene expression. The widely used chromatin conformation capture (3C) assay allows determination of the in vivo structural organization of an active endogenous locus. However, unpredicted chromatin associations within a given genomic locus can not be identified by 3C. Here, we describe a new strategy, quantitative associated chromatin trap (QACT), which incorporates a modified 3C method and a quantitative assay tool, to capture and quantitatively analyzes all possible associated chromatin partners (ACPs) of a given chromatin fragment. Using QACT, we have analyzed the chromatin conformation of the mouse alpha-globin gene cluster and proved the extensive interaction between HS26 and alpha-globin genes. In addition, we have identified a candidate alpha1-globin gene specific silencer 475A8 which shows the differentiation-stage specific DNase I hypersensitivity. Functional analysis suggests that 475A8 may regulate the alpha1-globin gene during terminal differentiation of committed erythroid progenitor cells. ChIP (chromatin immunoprecipitation) and cotransfection assays demonstrate that GATA-1, a hemopoietic specific transcriptional factor, may increase alpha1-globin gene expression by suppressing the function of 475A8 in terminally differentiated erythroid cells.

The binding of the ubiquitous transcription factor Sp1 at the locus control region represses the expression of beta-like globin genes

To investigate the function of transcription factor Sp1 in beta-like globin gene activation, we analyzed the recruitment of Sp1, fetal Krüppel-like factor 2 (FKLF2), and related factors at the human beta-globin locus in a human fetal liver and mouse erythroleukemia hybrid cell (A181gamma cell) that contains a single copy of human chromosome 11. Sp1 binds at the GT boxes of the cis-elements throughout the beta-locus, but it is phosphorylated and lost over DNase I hypersensitive site (HS)2, HS3, HS4, and the human beta-globin gene promoter after A181gamma cell differentiation. The binding of FKLF2 at HS2 and HS3 was unchanged. Histone deacetylase 1, which could be recruited by Sp1, is also lost over HS2 and HS3 after differentiation, resulting in the acetylation of histones 3 and 4 across the human beta-globin locus. We previously detected in vivo GT footprints over the beta-globin locus after A181gamma differentiation. Here, we report that after differentiation, the p300/CREB-binding protein-associated factor is recruited by FKLF2 to the locus control region to acetylate histones 3 and 4 at the human beta-globin gene locus. Our results suggest that Sp1 is an inhibitor of beta-like globin gene transcription during erythroid terminal differentiation. Its phosphorylation and release allow the erythroid-specific FKLF2 or erythroid Krüppel-like factor to interact with other erythroid-specific transcription factors to initiate the transcription of beta-like globin genes.