Jones B K, Monks B R, Liebhaber S A, Cooke N E
Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia 19104, USA.
Mol Cell Biol. 1995 Dec;15(12):7010-21. doi: 10.1128/MCB.15.12.7010.
The five-member human growth hormone (hGH)/chorionic somatomammotropin (hCS) gene cluster encodes the pituitary-specific hGH-N gene and four highly related genes (hGH-V, hCS-A, hCS-B, and hCS-L) that are expressed only in the placenta. When the hGH-N or hCS-A gene, together with all previously identified cis-acting regulatory sequences, was integrated into the mouse genome, it was expressed only sporadically and at low levels in the transgenic target organs. DNase I mapping of chromatin from expressing and nonexpressing cell types was used to identify a pituitary-specific set of DNase I-hypersensitive sites (HS) and a set of HS common to both the pituitary and placenta, centered approximately 15 and 30 kb 5' of hGH-N, respectively. When contained on a cosmid insert in their native genomic configuration, these HS consistently directed high-level, pituitary-specific expression of hGH-N in transgenic mice and appeared to define a locus control region required for hGH-N expression. Individually, each set of HS was able to mediate position-independent hGH-N expression in the pituitary but demonstrated loss of physiologic control and loss of tissue specificity. The gene-proximal set of HS contained a potent enhancer activity in the pituitary, while the more distal set appeared to function primarily to establish site-of-integration independence. These data indicate that synergistic interactions among multiple elements are required to restrict hGH-N transcription to the pituitary and generate appropriate levels of expression. In addition, these results suggest a role for both shared and unique regulatory sequences in locus control region-mediated expression of the hGH/hCS gene cluster in the pituitary and possibly the placenta.
由五个成员组成的人生长激素（hGH）/绒毛膜促生长催乳素（hCS）基因簇编码垂体特异性的hGH-N基因以及四个高度相关的基因（hGH-V、hCS-A、hCS-B和hCS-L），这些基因仅在胎盘中表达。当hGH-N或hCS-A基因与所有先前鉴定出的顺式作用调控序列一起整合到小鼠基因组中时，它在转基因靶器官中仅偶尔且低水平表达。利用来自表达和不表达细胞类型的染色质的DNase I图谱来鉴定一组垂体特异性的DNase I超敏位点（HS）以及一组垂体和胎盘共有的HS，它们分别位于hGH-N上游约15 kb和30 kb处。当以其天然基因组构型包含在黏粒插入片段上时，这些HS一致地指导hGH-N在转基因小鼠中高水平、垂体特异性表达，并且似乎定义了hGH-N表达所需的一个基因座控制区。单独来看，每组HS都能够在垂体中介导hGH-N的位置独立表达，但表现出生理控制丧失和组织特异性丧失。基因近端的HS组在垂体中具有强大的增强子活性，而更远端的HS组似乎主要起建立整合位点独立性的作用。这些数据表明，多个元件之间的协同相互作用是将hGH-N转录限制在垂体并产生适当表达水平所必需的。此外，这些结果表明，共享和独特的调控序列在基因座控制区介导的hGH/hCS基因簇在垂体以及可能在胎盘中的表达中都发挥作用。
