Grahn R A, Rinehart T A, Cantrell M A, Wichman H A
Department of Biological Sciences, University of Idaho, Moscow, ID 83844-3051, USA.
Cytogenet Genome Res. 2005;110(1-4):407-15. doi: 10.1159/000084973.
LINE-1 transposable elements (L1s) are ubiquitous in mammals and are thought to have remained active since before the mammalian radiation. Only one L1 extinction event, in South American rodents in the genus Oryzomys, has been convincingly demonstrated. Here we examine the phylogenetic limits and evolutionary tempo of that extinction event by characterizing L1s in related rodents. Fourteen genera from five tribes within the Sigmodontinae subfamily were examined. Only the Sigmodontini, the most basal tribe in this group, demonstrate recent L1 activity. The Oryzomyini, Akodontini, Phyllotini, and Thomasomyini contain only L1s that appear to have inserted long ago; their L1s lack open reading frames, have mutations at conserved amino acid residues, and show numerous private mutations. They also lack restriction site-defined L1 subfamilies specific to any species, genus or tribe examined, and fail to form monophyletic species, genus or tribal L1 clusters. We determine here that this L1 extinction event occurred roughly 8.8 million years ago, near the divergence of Sigmodon from the remaining Sigmodontinae species. These species appear to be ideal model organisms for studying the impact of L1 inactivity on mammalian genomes.
LINE-1转座元件（L1s）在哺乳动物中普遍存在，并且被认为自哺乳动物辐射之前就一直保持活跃。只有在稻鼠属南美啮齿动物中发生的一次L1灭绝事件得到了令人信服的证明。在这里，我们通过对相关啮齿动物的L1s进行特征分析，研究了该灭绝事件的系统发育界限和进化速度。我们检查了稻鼠亚科五个部落中的14个属。只有该群体中最基部的部落稻鼠族表现出近期的L1活性。稻鼠属、阿根廷鼠属、叶鼠属和托马斯鼠属仅包含似乎很久以前就已插入的L1s；它们的L1s缺乏开放阅读框，在保守氨基酸残基处有突变，并显示出许多私有突变。它们还缺乏特定于所检查的任何物种、属或部落的限制性位点定义的L1亚家族，并且未能形成单系的物种、属或部落L1簇。我们在此确定，这次L1灭绝事件大约发生在880万年前，接近稻鼠与其余稻鼠亚科物种分化之时。这些物种似乎是研究L1不活跃对哺乳动物基因组影响的理想模式生物。
