“太空侵略者”在哺乳动物和爬行动物的基因组中殖民

根据一份新的报告，外来的遗传成分通过水平转移而不是传统的遗传从而把它们自己整合到了几种哺乳类和爬行类物中的基因组中。

CédricFeschotte及其同事发现了hAT (hobo/Activator/Tam3)转座子超家族此前未归类的成分，他们将其称之为“太空侵略者”。在大多数生物体内，基因是从亲代遗传或者说传递给子代的。遗传信息的横向或者说水平转移——这对于简单原核生物的进化至关重要——发生在外来遗传成分整合到宿主基因组中的时候。这些成分通常是由病毒、称为质粒的环状DNA或者转座子运送的。转座子是小片可转移的DNA片断。

这组科学家在调查夜间活动的灵长类动物——丛猴的DNA转座子的时候发现了这些成分，在经过进一步检查之后，他们在其他物种中也发现了这些“侵略者”，包括大鼠和小鼠、负鼠和非洲爪蛙。然而，其他许多脊椎动物的基因组中并没有“太空入侵者”。这组作者说，这种入侵现象是科学家**报告哺乳动物中出现转座子的水平转移，而且对受影响的物种的这种入侵很可能发生在大约1500万年到4600万年的类似时间段中。（创赛新闻中心Canspec.com）

原始出处：

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.