Identification of Novel Endogenous Betaretroviruses Which Are Transcribed in the Bovine Placenta
Identification of Novel Endogenous Betaretroviruses Which Are Transcribed in the Bovine Placenta
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DOI：
10.1128/jvi.01234-10
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发表时间：
2011-02-01
影响因子：
5.4
通讯作者：
Miyazawa, Takayuki
中科院分区：
文献类型：
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作者：
Baba, Kenji;Nakaya, Yuki;Miyazawa, Takayuki
源自逆转录病毒的序列约占哺乳动物基因组的10%。各种传染性内源性逆转录病毒（erv）和功能性逆转录病毒元件已被报道在一些哺乳动物中，但没有牛。在这里，我们鉴定了牛内源性逆转录病毒K1 （BERV-K1）和BERV-K2两种原病毒，它们在牛基因组中含有全长包膜（env）基因。系统发育分析显示它们属于Betaretrovirus属。通过逆转录(RT)-PCR，在胎盘和培养的牛滋养细胞中检测到BERV-K1和-K2 env mrna。利用从牛组织中分离的rna进行实时RT-PCR分析，发现BERV-K1 env mRNA在胎盘中优先表达。此外，我们还发现了双剪接转录物的表达，命名为REBK1和REBK2基因。REBK1和REBK2蛋白都具有假定的核定位信号和核输出信号的基序。与绿色荧光蛋白融合的REBK1和REBK2在牛和猪细胞中表达时主要定位于细胞核内。在BERV-K1和-K2的env和3'长末端重复序列中，我们发现了负责病毒rna剪接和转运和/或env基因翻译的调控元件。虽然我们还没有在牛组织中发现表达的Env蛋白，但这些数据表明BERV-K1和BERV-K2都表达Env蛋白，并且这些蛋白在体内可能具有生理功能。
Sequences of retroviral origin occupy approximately 10% of mammalian genomes. Various infectious endogenous retroviruses (ERVs) and functional retroviral elements have been reported for several mammals but not cattle. Here, we identified two proviruses, designated bovine endogenous retrovirus K1 (BERV-K1) and BERV-K2, containing full-length envelope (env) genes in the bovine genome. Phylogenetic analysis revealed that they belong to the genus Betaretrovirus. By reverse transcription (RT)-PCR, both BERV-K1 and -K2 env mRNAs were detected in the placenta and cultured bovine trophoblast cells. Real-time RT-PCR analysis using RNAs isolated from various bovine tissues revealed that BERV-K1 env mRNA was preferentially expressed in the placenta. Moreover, we also found the expression of doubly spliced transcripts, named the REBK1 and REBK2 genes. Both the REBK1 and REBK2 proteins have motifs for a putative nuclear localization signal and a nuclear export signal. REBK1 and REBK2 fused with green fluorescent proteins were localized mainly in the nuclei when they were expressed in bovine and porcine cells. In the env and 3' long terminal repeats of BERV-K1 and -K2, we found regulatory elements responsible for the splicing and transport of viral RNAs and/or translation of the env genes. Although we have not identified the expressed Env proteins in bovine tissues, these data suggest that both BERV-K1 and BERV-K2 express Env proteins and that these proteins may have physiological functions in vivo.