Porter S D, Hu J, Gilks C B
Department of Pathology, University of British Columbia, Vancouver, Canada.
Dev Genet. 1999;25(1):40-8. doi: 10.1002/(SICI)1520-6408(1999)25:1<40::AID-DVG5>3.0.CO;2-L.
A distal upstream regulatory element of the mouse tyrosinase gene has locus control region (LCR)-like activity and is required for position-independent expression of linked genes. It consists of a DNAse I hypersensitive site, which has enhancer activity in neural crest-derived melanocytes, embedded within a scaffold/matrix attachment region (S/MAR), both of which are necessary for LCR activity. To address the role of the S/MAR in position-independent expression, we assessed the ability of a fragment containing most of the S/MAR to insulate a transgene from position effects. The S/MAR sequence showed a striking cell type specificity in its function in all six multicopy transgenic lines, dampening position effects considerably in cutaneous melanocytes while allowing no expression in other neural crest-derived melanocytes, and causing elevated expression in ocular melanocytes derived from the neural tube. The specificity of transgene expression in the eye suggested the presence of both positive and negative regulatory elements in this enhancer/S/MAR region, which was confirmed by transient transfection analyses. This is the first known regulatory element to exhibit different activities in melanocytes of different developmental origins.
小鼠酪氨酸酶基因的一个远端上游调控元件具有类位点控制区（LCR）活性，是连锁基因位置独立表达所必需的。它由一个DNA酶I超敏位点组成，该位点在神经嵴来源的黑素细胞中具有增强子活性，嵌入在一个支架/基质附着区域（S/MAR）内，这两者对于LCR活性都是必需的。为了研究S/MAR在位置独立表达中的作用，我们评估了一个包含大部分S/MAR的片段使转基因免受位置效应影响的能力。S/MAR序列在所有六个多拷贝转基因系中的功能表现出显著的细胞类型特异性，在皮肤黑素细胞中显著减弱位置效应，而在其他神经嵴来源的黑素细胞中不表达，并导致源自神经管的眼黑素细胞中表达升高。转基因在眼中表达的特异性表明在这个增强子/S/MAR区域存在正负调控元件，这通过瞬时转染分析得到了证实。这是第一个已知的在不同发育起源的黑素细胞中表现出不同活性的调控元件。
