BovB: Jumping the fine LINE between species

In higher organisms such as vertebrates, it is generally believed that lateral transfer of genetic information does not readily occur, with the exception of retroviral infection. However, horizontal transfer (HT) of protein coding repetitive elements is the simplest way to explain the patchy distribution of BovB, a LINE (Long Interspersed Nuclear Element) about 3.2kb long, that has been found in ruminants, marsupials, squamates, monotremes and African mammals. BovB sequnces are a major component of some of these genomes. Here we show that HT of BovB is significantly more widespread than believed, and we demonstrate for the first time the existence of two plausible arthropod vectors, specifically reptile ticks. A phylogenetic tree built from BovB sequences from species in all of these groups does not conform to expected evolutionary relationships of the species, and our analysis indicates that at least 9 HT events are required to explain the observed topology. Our results provide compelling evidence from HT of genetic material that has transformed vertebrate genomes.

在脊椎动物等高等生物中，学界普遍认为遗传信息的侧向转移难以自然发生，逆转录病毒感染是唯一例外。然而，编码蛋白质的重复元件的水平转移（Horizontal Transfer，下文简称HT），是解释BovB不连续分布的最简可行路径——BovB是一种长约3.2kb的长散在核元件（Long Interspersed Nuclear Element，简称LINE），目前已在反刍动物、有袋类、有鳞目动物、单孔目动物以及非洲哺乳动物中被检出。BovB序列是部分此类宿主基因组的重要组成部分。本研究证实，BovB的水平转移（HT）远比此前学界认知的更为广泛，并首次证明了两种可靠的节肢动物传播媒介——具体为爬行动物蜱。基于上述所有类群物种的BovB序列构建的系统发育树，与该类群物种的预期进化关系并不相符；我们的分析表明，至少需要发生9次HT事件才能解释观测到的系统发育拓扑结构。本研究结果为可改造脊椎动物基因组的遗传物质水平转移（HT）提供了极具说服力的证据。