Burst of Young Retrogenes and Independent Retrogene Formation in Mammals

Retroposition and retrogenes gain increasing attention as recent studies show that they play an important role in human new gene formation. Here we examined the patterns of retrogene distribution in 8 mammalian genomes using 4 non-mammalian genomes as a contrast. There has been a burst of young retrogenes not only in primate lineages as suggested in a recent study, but also in other mammalian lineages. In mammals, most of the retrofamilies (the gene families that have retrogenes) are shared between species. In these shared retrofamilies, 14%–18% of functional retrogenes may have originated independently in multiple mammalian species. Notably, in the independently originated retrogenes, there is an enrichment of ribosome related gene function. In sharp contrast, none of these patterns hold in non-mammals. Our results suggest that the recruitment of the specific L1 retrotransposons in mammals might have been an important evolutionary event for the split of mammals and non-mammals and retroposition continues to be an important active process in shaping the dynamics of mammalian genomes, as compared to being rather inert in non-mammals.

逆转座作用（retroposition）与逆转座基因（retrogene）正受到学界越来越多的关注，近期研究证实二者在人类新基因形成过程中发挥着关键作用。本研究以4个非哺乳类基因组作为对照，分析了8个哺乳类基因组中的逆转座基因分布模式。正如既往一项研究指出的，年轻逆转座基因的爆发不仅存在于灵长类演化支系中，同样也出现在其他哺乳类演化支系中。在哺乳类中，绝大多数逆转座基因家族（retrofamilies，即携带逆转座基因的基因家族）在各物种类群间具有共通性；在这些共有的逆转座基因家族中，14%至18%的功能性逆转座基因可能在多个哺乳类物种类群中独立起源。值得注意的是，在独立起源的逆转座基因中，与核糖体相关的基因功能呈现显著富集现象。与之形成鲜明对比的是，非哺乳类基因组中并未出现上述任何分布模式。本研究结果表明，哺乳类中特异性L1反转录转座子（L1 retrotransposons）的募集事件，可能是区分哺乳类与非哺乳类的关键演化事件；相较于非哺乳类中逆转座作用近乎惰性的状态，逆转座作用至今仍是塑造哺乳类基因组动态特征的重要活跃过程。