“太空侵略者”在哺乳動物和爬行動物的基因組中殖民

根據一份新的報告，外來的遺傳成分通過水平轉移而不是傳統的遺傳從而把它們自己整合到了幾種哺乳類和爬行類物中的基因組中。

CédricFeschotte及其同事發現了hAT (hobo/Activator/Tam3)轉座子超家族此前未歸類的成分，他們將其稱之為“太空侵略者”。在大多數生物體內，基因是從親代遺傳或者說傳遞給子代的。遺傳信息的橫向或者說水平轉移——這對于簡單原核生物的進化至關重要——發生在外來遺傳成分整合到宿主基因組中的時候。這些成分通常是由病毒、稱為質粒的環狀DNA或者轉座子運送的。轉座子是小片可轉移的DNA片斷。

這組科學家在調查夜間活動的靈長類動物——叢猴的DNA轉座子的時候發現了這些成分，在經過進一步檢查之后，他們在其他物種中也發現了這些“侵略者”，包括大鼠和小鼠、負鼠和非洲爪蛙。然而，其他許多脊椎動物的基因組中并沒有“太空入侵者”。這組作者說，這種入侵現象是科學家**報告哺乳動物中出現轉座子的水平轉移，而且對受影響的物種的這種入侵很可能發生在大約1500萬年到4600萬年的類似時間段中。（創賽新聞中心Canspec.com）

原始出處：

PNAS October 20, 2008, doi: 10.1073/pnas.0806548105

Repeated horizontal transfer of a DNA transposon in mammals and other tetrapods

John K. Pace II, ClémentGilbert,Marlena S. Clark, and Cédric Feschotte

Horizontal transfer (HT) is central to the evolution ofprokaryoticspecies. Selfish and mobile genetic elements, such asphages,plasmids, and transposons, are the primary vehicles for HTamongprokaryotes. In multicellular eukaryotes, the prevalenceandevolutionary significance of HT remain unclear. Here, weidentifieda set of DNA transposon familiesdubbed SPACE INVADERS (or SPIN) whose consensus sequences are ≈96% identical over theirentirelength (2.9 kb) in the genomes of murine rodents(rat/mouse),bushbaby (prosimian primate), little brown bat(laurasiatherian),tenrec (afrotherian), opossum (marsupial), andtwo non-mammaliantetrapods (anole lizard and African clawed frog).Incontrast,SPIN elements were undetectable in other species represented inthesequence databases, including 19 other mammals withdraftwhole-genome assemblies. This patchy distribution, coupledwith theextreme level of SPIN identity in widely divergent tetrapods and the overall lackofselective constraint acting on these elements, is incompatiblewithvertical inheritance, but strongly indicative ofmultiplehorizontal introductions. We show that these germlineinfiltrationslikely occurred around the same evolutionary time(15–46 mya) andspawned some of the largest bursts of DNA transposonactivity everrecorded in any species lineage(nearly100,000 SPIN copies per haploid genome in tenrec). The process also led totheemergence of a new gene in the murine lineage derivedfroma SPINtransposase. In summary, HT of DNA transposons hascontributedsignificantly to shaping and diversifying the genomes ofmultiplemammalian andtetrapodspecies.