Hiroki Tomoko, Song Young-Han, Liebhaber Stephen A, Cooke Nancy E
Department of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
Nucleic Acids Res. 2006 Apr 28;34(8):2154-65. doi: 10.1093/nar/gkl174. Print 2006.
The human vitamin D-binding protein (hDBP) gene is a member of a cluster that includes albumin, alpha-fetoprotein and alpha-albumin genes. The common origin, physical linkage and hepatic expression of these four genes predict shared regulatory element(s). However, separation of hDBP from the other three genes by 1.5 Mb argues that hDBP may be under autonomous control. To test for hDBP autonomy, mouse lines were generated with a transgene containing the hDBP gene along with extensive flanking sequences. Expression of this transgene was hepatic, robust and proportional to transgene copy number. DNase I hypersensitive site (HS) mapping revealed five liver-specific HS at the hDBP locus: HSI and HSIII at -2.1 kb and -0.13 kb upstream of the transcription initiation site, HSIV and HSV within intron 1 and HSVII located 3' to the poly(A) site. A second transgene with minimal flanking sequences confirmed the sufficiency of these gene-proximal determinants for hepatic activation. The hepatic-specific HS aligned with segments of phylogenetically conserved non-coding sequences. These data demonstrate the autonomy of the hDBP locus and suggest that this control is mediated by chromatin-based locus control determinants in close proximity to, and within the transcription unit.
人类维生素D结合蛋白（hDBP）基因是一个基因簇的成员，该基因簇包括白蛋白、甲胎蛋白和α-白蛋白基因。这四个基因的共同起源、物理连锁和肝脏表达预示着存在共享的调控元件。然而，hDBP基因与其他三个基因相隔1.5 Mb，这表明hDBP可能受自主控制。为了测试hDBP的自主性，构建了含有hDBP基因及大量侧翼序列的转基因小鼠品系。该转基因的表达具有肝脏特异性、表达水平高且与转基因拷贝数成正比。DNA酶I超敏感位点（HS）图谱显示在hDBP基因座有五个肝脏特异性HS：转录起始位点上游-2.1 kb处的HSI和-0.13 kb处的HSIII，内含子1中的HSIV和HSV，以及位于多聚腺苷酸化位点3'端的HSVII。另一个侧翼序列极少的转基因证实了这些基因近端决定簇对肝脏激活的充分性。肝脏特异性HS与系统发育保守的非编码序列片段对齐。这些数据证明了hDBP基因座的自主性，并表明这种调控是由紧邻转录单元并位于转录单元内的基于染色质的基因座控制决定簇介导的。
