Inhibition of enhancer-promoter interaction involved in the developmental-stage specific gene regulation

点击翻译按钮获取中文摘要

The human (3-globin locus contains five developmentally regulated (3-type globin genes. All five genes depend on the locus control region (LCR), located at the 5' end of the locus, for abundant globin gene transcription. The LCR is composed of five DNase I hypersensitive sites (HSs), at least a subset of which appear to cooperate to form a holocomplex in activating genes within the locus. We previously tested the requirement for proper LCR polarity by inverting it in human β-globin YAC transgenic mice (TgM) and observed reduced expression of all the β-type globin genes, regardless of developmental stage. This phenotype clearly demonstrated an orientation-dependent activity of the LCR, although the mechanistic basis for the observed activity was obscure. In this research project, we obtained genetic evidence demonstrating that human HSS includes enhancer-blocking (insulator) activity that was dependent on the presence of an intact CTCF-binding motif within LCR HSS. Curiously, this CTCF-dependent activity appeared to be both gene and developmental-stage specific. These observations demonstrated that the phenotype observed in the LCR-inverted locus was, in part, attributable to placing the HSS insulator between the LCR HS "enhancers (HS1-4)" and the promoter of the β-globin gene, but further that the HS5 sequence also beared a primitive erythroid silencing activity that is CTCF-independent.