Transcription of the rat testis-specific Rtdpoz-T1 and-T2 retrogenes during embryo development: co-transcription and frequent exonisation of transposable element sequences
Transcription of the rat testis-specific Rtdpoz-T1 and-T2 retrogenes during embryo development: co-transcription and frequent exonisation of transposable element sequences
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DOI：
10.1186/1471-2199-10-74
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发表时间：
2009-07-25
影响因子：
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通讯作者：
Choo, Kong-Bung
中科院分区：
文献类型：
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作者：
Huang, Chiu-Jung;Lin, Wan-Yi;Choo, Kong-Bung
背景：逆转录转座是产生新的、具有潜在功能的无内含子基因的重要进化力量，这些基因统称为逆转录基因。许多逆转录基因在睾丸中表达，并且基因产物已被证明积极参与精子发生和雄性生殖系的其他独特功能。我们之前报道了大鼠基因组中的一组逆转录基因，它们编码假定的 TRAF 和 POZ 结构域蛋白。其中两个基因 Rtdpoz-T1 和 -T2（缩写为 T1 和 T2）已被进一步证明在大鼠睾丸中特异性表达。结果：我们在此表明，T1 和 T2 基因也在大鼠胚胎中表达，直至发育第 16-17 天，此时这些基因被沉默，直到在成年睾丸中重新激活。在数据库查询中，我们发现一些 T1/T2 外显子在染色体上复制为 2 或 3 个外显子的盒，与逆向复制一致。胚胎T1/T2转录本的特征是RT-PCR克隆和cDNA末端的快速扩增，进一步发现在5'-非翻译区(5'-UTR)中获得了一个或多个非编码外显子。最重要的是，T1/T2 基因座嵌入在主要源自 LINE1 和 ERV 序列的转座元件 (TE) 遗迹的密集区域中，并且 TE 序列经常通过选择性剪接外显，形成 T1/T2 转录本的 5'-UTR 序列。在 T1 转录物的情况下，3'-末端延伸至 L1 序列并终止于 L1 序列内。由于这两个基因共享一个共同的外显子 1，因此由单个启动子调控，因此提出了 T2 到 T1 共转录模型。我们进一步证明，外显子化的 5'-UTR TE 序列可能导致上游开放阅读框的产生，从而导致翻译抑制。结论：TE 序列的外显子化是胚胎发育和睾丸中逆转录基因转录的常见事件，可能有助于逆转录基因表达的转录后调节。
Background: Retrotransposition is an important evolutionary force for the creation of new and potentially functional intronless genes which are collectively called retrogenes. Many retrogenes are expressed in the testis and the gene products have been shown to actively participate in spermatogenesis and other unique functions of the male germline. We have previously reported a cluster of retrogenes in the rat genome that encode putative TRAF- and POZ-domain proteins. Two of the genes, Rtdpoz-T1 and -T2 (abbreviated as T1 and T2), have further been shown to be expressed specifically in the rat testis.Results: We show here that the T1 and T2 genes are also expressed in the rat embryo up to days 16-17 of development when the genes are silenced until being re-activated in the adult testis. On database interrogation, we find that some T1/T2 exons are chromosomally duplicated as cassettes of 2 or 3 exons consistent with retro-duplication. The embryonic T1/T2 transcripts, characterised by RT-PCR-cloning and rapid amplification of cDNA ends, are further found to have acquired one or more noncoding exons in the 5'-untranslated region (5'-UTR). Most importantly, the T1/T2 locus is embedded within a dense field of relics of transposable element (TE) derived mainly from LINE1 and ERV sequences, and the TE sequences are frequently exonised through alternative splicing to form the 5'-UTR sequences of the T1/T2 transcripts. In a case of T1 transcript, the 3'-end is extended into and terminated within an L1 sequence. Since the two genes share a common exon 1 and are, therefore, regulated by a single promoter, a T2-to-T1 co-transcription model is proposed. We further demonstrate that the exonised 5'-UTR TE sequences could lead to the creation of upstream open reading frames resulting in translational repression.Conclusion: Exonisation of TE sequences is a frequent event in the transcription of retrogenes during embryonic development and in the testis and may contribute to post-transcriptional regulation of expression of retrogenes.