Bockamp E O, McLaughlin F, Göttgens B, Murrell A M, Elefanty A G, Green A R
University of Cambridge, Department of Haematology, Medical Research Council Centre, Hills Road, Cambridge CB2 2QH, United Kingdom.
J Biol Chem. 1997 Mar 28;272(13):8781-90. doi: 10.1074/jbc.272.13.8781.
The SCL/tal-1 gene (hereafter designated SCL) encodes a basic helix-loop-helix transcription factor which is pivotal for the normal development of all hematopoietic lineages and which is expressed in committed erythroid, mast, and megakaryocytic cells as well as in hematopoietic stem cells. The molecular basis for expression of SCL in stem cells and its subsequent modulation during lineage commitment is of fundamental importance for understanding how early "decisions" are made during hematopoiesis. We now compare the activity of SCL promoters 1a and 1b in erythroid cells and in CD34 positive primitive myeloid cells. SCL mRNA expression in CD34 positive myeloid cells did not require GATA-1. Promoter 1a activity was weak or absent in CD34 positive myeloid cells and appeared to correlate with the presence or absence of low levels of GATA-1. However, promoter 1b, which was silent in committed erythroid cells, was strongly active in transient assays using CD34 positive myeloid cells, and functioned in a GATA-independent manner. Interestingly, RNase protection assays demonstrated that endogenous promoter 1b was active in both erythroid and CD34 positive myeloid cells. These results demonstrate that fundamentally different mechanisms regulate the SCL promoter region in committed erythroid cells and in CD34 positive myeloid cells. Moreover these observations suggest that in erythroid, but not in CD34 positive myeloid cells, promoter 1b required integration in chromatin and/or additional sequences for its activity. Stable transfection experiments showed that both core promoters were silent following integration in erythroid or CD34 positive myeloid cells. Our data therefore indicate that additional regulatory elements were necessary for both SCL promoters to overcome chromatin-mediated repression.
SCL/tal-1基因（以下简称SCL）编码一种碱性螺旋-环-螺旋转录因子，它对所有造血谱系的正常发育至关重要，并且在定向的红系、肥大细胞和巨核细胞以及造血干细胞中表达。SCL在干细胞中的表达及其在谱系定向过程中的后续调控的分子基础，对于理解造血过程中早期“决策”是如何做出的至关重要。我们现在比较SCL启动子1a和1b在红系细胞和CD34阳性原始髓系细胞中的活性。CD34阳性髓系细胞中SCL mRNA的表达不需要GATA-1。启动子1a在CD34阳性髓系细胞中的活性较弱或不存在，并且似乎与低水平GATA-1的有无相关。然而，在定向红系细胞中沉默的启动子1b，在使用CD34阳性髓系细胞的瞬时分析中具有强烈活性，并且以不依赖GATA的方式发挥作用。有趣的是，核糖核酸酶保护分析表明内源性启动子1b在红系细胞和CD34阳性髓系细胞中均有活性。这些结果表明，在定向红系细胞和CD34阳性髓系细胞中，调控SCL启动子区域的机制存在根本差异。此外，这些观察结果表明，在红系细胞而非CD34阳性髓系细胞中，启动子1b的活性需要整合到染色质和/或其他序列中。稳定转染实验表明，在红系细胞或CD34阳性髓系细胞中整合后，两个核心启动子均沉默。因此我们的数据表明，两个SCL启动子都需要额外的调控元件来克服染色质介导的抑制作用。
