Patrone Lisa, Henson Sarah E, Wall Randolph, Malone Cindy Sue
Department of Microbiology, Immunology, & Molecular Genetics, University of California, Los Angeles, CA 90095, USA.
Mol Biol Rep. 2004 Mar;31(1):1-11. doi: 10.1023/b:mole.0000013489.04734.5e.
The human, murine, and rat B29 (Ig beta, CD79b) genes are highly conserved in sequence and organization and exhibit strict B cell-specific expression. In the human and rat genomes, the B29 gene is located between the skeletal muscle-specific Na-channel alpha subunit (SCN4A) gene and the pituitary-specific growth hormone (GH-N) gene. The human pituitary-specific GH-N gene is controlled by a tissue-specific locus control region (LCR) located just upstream of the B29 promoter that mediates tissue-specific enhancement, histone acetylation, and an open chromatin conformation across the B29 gene in growth hormone (GH)-expressing pituitary cells. Here we show that B29 mRNA is not detected in a GH-expressing pituitary cell line and that GH-N mRNA is not detected in B cells. This differential expression suggests that the B29 gene is insulated or otherwise protected from the regulatory influences of the closely proximal GH LCR. We searched available sequences upstream of the human, mouse, and rat B29 genes and found a highly conserved sequence that fulfills the criteria recently established for non-coding DNA elements potentially involved in gene control. This B29 conserved sequence (BCS) bound ubiquitously expressed nuclear protein complexes. DNase I protection analysis of the BCS revealed a central 'footprinted' core which was confirmed to bind the multifunctional transcription factor, YY1. However, neither the BCS nor the YY1-binding core motif exhibited silencer or enhancer activity in transient transfections or position-independent insulator activity in enhancer-blocking assays. Thus, the BCS may function as a tissue-specific LCR or position-dependent insulator specifically countering the influences of the 5' GH LCR and controlling B29 gene expression.
人类、小鼠和大鼠的B29（Igβ，CD79b）基因在序列和结构上高度保守，并表现出严格的B细胞特异性表达。在人类和大鼠基因组中，B29基因位于骨骼肌特异性钠通道α亚基（SCN4A）基因和垂体特异性生长激素（GH-N）基因之间。人类垂体特异性GH-N基因由位于B29启动子上游的组织特异性位点控制区（LCR）调控，该LCR在表达生长激素（GH）的垂体细胞中介导组织特异性增强、组蛋白乙酰化以及B29基因上开放染色质构象的形成。在此我们发现，在表达GH的垂体细胞系中未检测到B29 mRNA，在B细胞中也未检测到GH-N mRNA。这种差异表达表明B29基因被隔离或受到其他方式的保护，免受紧邻的GH LCR的调控影响。我们搜索了人类、小鼠和大鼠B29基因上游的可用序列，发现了一个高度保守的序列，该序列符合最近为可能参与基因调控的非编码DNA元件所确立的标准。这个B29保守序列（BCS）能结合广泛表达的核蛋白复合物。对BCS进行的DNase I保护分析揭示了一个中心“足迹”核心，证实该核心能结合多功能转录因子YY1。然而，在瞬时转染中，BCS和YY1结合核心基序均未表现出沉默子或增强子活性，在增强子阻断试验中也未表现出位置独立的绝缘子活性。因此，BCS可能作为一种组织特异性LCR或位置依赖性绝缘子，特异性地对抗5' GH LCR的影响并控制B29基因的表达。
