Graduate School of Life and Environmental Sciences, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Ibaraki 305-8577, Japan.
FASEB J. 2009 Dec;23(12):4335-43. doi: 10.1096/fj.09-137778. Epub 2009 Aug 18.
In primitive erythroid cells of human beta-globin locus transgenic mice (TgM), the locus control region (LCR)-proximal epsilon- and gamma-globin genes are transcribed, whereas the distal delta- and beta-globin genes are silent. It is generally accepted that the beta-globin gene is competitively suppressed by gamma-globin gene expression at this developmental stage. Previously, however, we observed that epsilon-globin gene expression was severely attenuated when its distance from the LCR was extended, implying that beta-globin gene might also be silenced because of its great distance from the LCR. Here, to clarify the beta-globin gene silencing mechanism, we established TgM lines carrying either gamma- or epsilon- plus gamma-globin promoter deletions, without significantly altering the distance between the beta-globin gene and the LCR. Precocious expression of delta- and beta-globin genes was observed in primitive erythroid cells of mutant, but not wild-type TgM, which was most evident when both the epsilon and gamma promoters were deleted. Thus, we clearly demonstrated that the repression of the delta- and beta-globin genes in primitive erythroid cells is dominated by competitive silencing by the epsilon- and gamma-globin gene promoters, and that epsilon- and the other beta-like globin genes might be activated by two distinct mechanisms by the LCR.
在人类β-球蛋白基因座转基因小鼠（TgM）的原始红细胞中，LCR 近端的ε和γ-球蛋白基因被转录，而远端的δ和β-球蛋白基因则处于沉默状态。通常认为，在这个发育阶段，β-球蛋白基因受到γ-球蛋白基因表达的竞争性抑制。然而，先前我们观察到，当ε-球蛋白基因与 LCR 的距离延长时，其表达严重减弱，这意味着β-球蛋白基因也可能因为与 LCR 的巨大距离而被沉默。在这里，为了阐明β-球蛋白基因沉默的机制，我们建立了携带γ或ε+γ-球蛋白启动子缺失的 TgM 系，而β-球蛋白基因与 LCR 之间的距离没有明显改变。在突变型 TgM 的原始红细胞中观察到δ和β-球蛋白基因的早熟表达，但在野生型 TgM 中没有观察到，当ε和γ启动子都缺失时，这种现象最为明显。因此，我们清楚地证明了原始红细胞中δ和β-球蛋白基因的抑制主要是由ε和γ-球蛋白基因启动子的竞争性沉默所主导，并且ε和其他β-样球蛋白基因可能通过 LCR 被两种不同的机制激活。
