Wagstaff Bradley J, Wang Linda, Lai Susan, Derbes Rebecca S, Roy-Engel Astrid M
Tulane Cancer Center SL-66, Dept. of Epidemiology, Tulane University Health Sciences Center, 1430 Tulane Ave., New Orleans, LA 70112.
Gene Rep. 2018 Jun;11:74-78. doi: 10.1016/j.genrep.2018.02.007. Epub 2018 Mar 21.
Mobile elements have significantly impacted genome structure of most organisms. The continued activity of the mobile element, LINE-1 (L1), through time has contributed to the accumulation of over half a million L1 copies in the human genome. Most copies in the human genome belong to evolutionary older extinct L1s. Here we apply our previous published approach to "revive" the extinct L1 PA13A; an L1 family that was active about 60 million year ago (mya). The reconstructed L1PA13A is retrocompentent in culture, but shows a significantly lower level of activity in HeLa cells when compared to the modern L1 element (L1PA1) and a 40 million year old L1PA8. L1 elements code for two proteins (ORF1p and ORF2p) that are necessary for retrotransposition. Using PA13A-PA1 and PA13A-PA8 L1 chimeric elements, we determined that both the ORF1p and ORF2p contribute to the observed decrease in retrotransposition efficiency of L1PA13A. The lower retrotransposition rate of L1PA13A is consistent in both human and rodent cell lines. However, in rodent cells, the chimeric element L1PA:1-13 containing the modern L1PA1 ORF1p shows a recovery in the retrotransposition rate, suggestive that the L1PA13A ORF2p efficiently drives retrotransposition in these cells. The functionality of the L1PA13A ORF2p was further confirmed by demonstrating its ability to drive Alu retrotransposition in rodent cells. The variation in L1PA13A retrotransposition rates observed between rodent and human cells are suggestive that cellular environment significantly affects retrotransposition efficiency, which may be mediated through an interaction with ORF1p. Based on these observations, we speculate that the observed differences between cell lines may reflect an evolutionary adaptation of the L1 element to its host cell.
移动元件对大多数生物的基因组结构产生了重大影响。随着时间的推移，移动元件LINE-1（L1）的持续活动促使人类基因组中积累了超过50万个L1拷贝。人类基因组中的大多数拷贝属于进化上较古老的已灭绝L1。在这里，我们应用我们之前发表的方法来“复活”已灭绝的L1 PA13A；这是一个约6000万年前（mya）活跃的L1家族。重建的L1PA13A在培养中具有反转录能力，但与现代L1元件（L1PA1）和一个4000万年前的L1PA8相比，在HeLa细胞中的活性水平显著较低。L1元件编码两种蛋白质（ORF1p和ORF2p），它们是反转录转座所必需的。使用PA13A-PA1和PA13A-PA8 L1嵌合元件，我们确定ORF1p和ORF2p都导致了L1PA13A反转录转座效率的降低。L1PA13A较低的反转录转座率在人类和啮齿动物细胞系中都是一致的。然而，在啮齿动物细胞中，含有现代L1PA1 ORF1p的嵌合元件L1PA:1-13的反转录转座率有所恢复，这表明L1PA13A ORF2p在这些细胞中有效地驱动了反转录转座。L1PA13A ORF2p的功能通过证明其在啮齿动物细胞中驱动Alu反转录转座的能力得到了进一步证实。在啮齿动物和人类细胞之间观察到的L1PA13A反转录转座率的差异表明，细胞环境显著影响反转录转座效率，这可能是通过与ORF1p的相互作用介导的。基于这些观察结果，我们推测在细胞系之间观察到的差异可能反映了L1元件对其宿主细胞的进化适应。
