Studies on the gene expression involved in the placetal development.

我们在芳香化酶基因中发现了一个新的胎盘特异性增强子的顺式元件。芳香酶增强子区域中元件和滋养层特异性元件（TSE）的共同存在足以指导由异源tk启动子驱动的滋养层特异性表达。在从JEG-3细胞和人胎盘制备的核提取物中发现了与该位点的结合活性，但在从HeLa或Hep G2细胞制备的细胞提取物中没有发现。这种结合活性在蛋白质的蛋白质迁移率方面与结合芳香酶增强子中的TSE样元件的蛋白质不同。用于结合新的反式因子的核心DNA序列也不同于TSE结合蛋白的核心DNA序列。然而，在反向来源于a-hCG启动子的24碱基对滋养层特异性元件（TSE）中发现了类似的序列，因此该DNA片段也以低亲和力结合新因子。这个新的反式因子暂时被称为TSEBP 2。A2. 65 Kilobase cDNA克隆是使用具有TSEBP 2识别序列（GATCCATAAGACCTCATTCCAGAG）的酵母单杂交系统从人胎盘cDNA文库中分离的，其编码436个氨基酸。在sf 21细胞中用杆状病毒系统转染该克隆导致产生核蛋白，该核蛋白显示出与从Jeg 3制备的核提取物中的TSEBP 2相同的结合特异性。Northern-blot分析表明，对应于该克隆的mRNA仅在胎盘中发现。该蛋白可能是滋养层细胞特异性转录因子，赋予芳香化酶基因胎盘特异性表达。然而，试验性反式激活结构域的一级结构与其他已知的转录因子没有相似性。转录活性的证据正在路上。

We found a new cis-element neccessary for the placenta-specific enhancer in the aromatase gene. Co-presence of the element and the trophoblast specific element (TSE) in the aromatase enhancer region is sufficient to direct trophoblast specific expression driven by a heterologous tk promoter. The binding activity to this site was found in the nuclear extracts prepared from JEG-3 cells and the human placenta but not in the cell extract from HeLa or Hep G2 cells. This binding activity is distinct in electrophoreic mobility from the protein that binds to the TSE-like elements in aromatase enhancer. The core DNA sequence for the binding of the new trans-factor is also distinct from that of the TSE binding protein. The similar sequence is however found in the 24-base pair Trophoblast Specific Element (TSE) derived from the a-hCG promoter in reverse direction thus this DNA fragment also binds to the new factor with low affinity. This new trans-factor is tentatively called TSEBP2.A2.65 Kilobase cDNA clone that encodes a 436 amino acid was isolated from a human placental cDNA library using a yeast one-hybrid system with the TSEBP2 recognition sequence (GATCCATAAGACCCTCATTCCAGAG). The transfection of this clone with baculovirus system in sf21 cells resulted the production of a nuclear protein that showed the same binding specificity with the TSEBP2 in the nuclear extract prepared from Jeg 3. Northern-blot analysis showed that the mRNA coresponding to this clone was found exclusively in the placenta. This protein is likely to be a trophoblast specific transcription factor that confer placenta-specific expression of aromatase gene. The primary structure of the tentative transactivation domain however, has no similarity with other known transcription factors. The proof of transcriptional activity is on the way.