Transcriptional regulation of early transposon elements, an active family of mouse long terminal repeat retrotransposons
Transcriptional regulation of early transposon elements, an active family of mouse long terminal repeat retrotransposons
复制标题
DOI：
10.1128/jvi.79.22.13865-13874.2005
复制
发表时间：
2005-11-01
影响因子：
5.4
通讯作者：
Mager, DL
中科院分区：
文献类型：
--
作者：
Maksakova, IA;Mager, DL
虽然已知早期转座子(ETN)内源性逆转录病毒(ERV)样元件是小鼠体内的活性插入突变剂，但对其转录调控知之甚少。在胚胎干细胞(ES)和胚胎癌细胞(EC)中，ETN在小鼠胚胎发生的早期被转录。尽管缺乏编码能力，但一些ETN通过使用由一组相关的ERV-MU.S.元件编码的逆转录酶来保持转座能力。在这项研究中，我们证实了ETN和MU.S.元件在ES和EC细胞中的高表达，并证明了ETnII元件在EC P19细胞系中的拷贝数增加。通过瞬时转染，我们发现ETnII和MUSDLTRs在P19细胞中作为启动子比在NIH3T3细胞中更活跃，这表明基因组环境和甲基化并不是决定ETN内源转录活性的唯一因素。长末端重复序列(LTR)5‘端的3个位点与Sp1和Sp3转录因子结合，并在P19细胞中对高LTR启动子活性起重要作用，提示尚未确定的Sp结合伙伴参与了未分化细胞ETN活性的调节。最后，我们在ETN LTR中发现了多个转录起始点，并表明在没有其非规范TATA盒的情况下，LTR仍具有显著的启动子活性。这些发现有助于深入了解这类可移动的小鼠反转录转座子家族的转录调控。
While early transposon (ETn) endogenous retrovirus (ERV)-like elements are known to be active insertional mutagens in the mouse, little is known about their transcriptional regulation. ETns are transcribed during early mouse embryogenesis in embryonic stem (ES) and embryonic carcinoma (EC) cell lines. Despite their lack of coding potential, some ETns remain transposition competent through their use of reverse transcriptase encoded by a related group of ERVs-MusD elements. In this study, we have confirmed high expression levels of ETn and MusD elements in ES and EC cells and have demonstrated an increase in the copy number of ETnII elements in the EC P19 cell line. Using transient transfections, we have shown that ETnII and MusD LTRs are much more active as promoters in P19 cells than in NIH 3T3 cells, indicating that genomic context and methylation are not the only factors determining endogenous transcriptional activity of ETns. Three sites in the 5' part of the long terminal repeat (LTR) were demonstrated to bind Sp1 and Sp3 transcription factors and were found to be important for high LTR promoter activity in P19 cells, suggesting that as yet unidentified Sp binding partners are involved in the regulation of ETn activity in undifferentiated cells. Finally, we found multiple transcription start sites within the ETn LTR and have shown that the LTR retains significant promoter activity in the absence of its noncanonical TATA box. These findings lend insight into the transcriptional regulation of this family of mobile mouse retrotransposons.