Haring E, Hagemann S, Pinsker W
Museum of Natural History, 1. Zoologische Abteilung, Chemosystematik, Burgring 7, 1014 Wien, Austria.
J Mol Evol. 2000 Dec;51(6):577-86. doi: 10.1007/s002390010121.
P elements of two different subfamilies designated as M- and O-type are thought to have invaded host species in the Drosophila obscura group via horizontal transmission from external sources. Sequence comparisons with P elements isolated from other species suggested that the horizontal invasion by the O-type must have been a rather recent event, whereas the M-type invasion should have occurred in the more distant past. To trace the phylogenetic history of O-type elements, additional taxa were screened for the presence of O- and M-type elements using type-specific PCR primers. The phylogeny deduced from the sequence data of a 927-bp section (14 taxa) indicate that O-type elements have undergone longer periods of regular vertical transmission in the lineages of the saltans and willistoni groups of Drosophila. However, starting from a species of the D. willistoni group they were transmitted horizontally into other lineages. First the lineage of the D. affinis subgroup was infected, and finally, in a more recent wave of horizontal spread, species of three different genera were invaded by O-type elements from the D. affinis lineage: Scaptomyza, Lordiphosa, and the sibling species D. bifasciata/D. imaii of the Drosophila obscura subgroup. The O-type elements isolated from these taxa are almost identical (sequence divergence <1%). In contrast, no such striking similarities are observed among M-type elements. Nevertheless, the sequence phylogeny of M-type elements is also not in accordance with the phylogeny of their host species, suggesting earlier horizontal transfer events. The results imply that P elements cross species barriers more frequently than previously thought but require a particular genomic environment and thus seem to be confined to a rather narrow spectrum of host species. Consequently, different P element types acquired by successive horizontal transmission events often coexist within the same genome.
两种不同亚家族的P因子，即M型和O型，被认为是通过从外部来源的水平转移侵入了果蝇暗果蝇组的宿主物种。与从其他物种分离的P因子进行序列比较表明，O型的水平入侵一定是相当近期的事件，而M型入侵应该发生在更遥远的过去。为了追溯O型因子的系统发育历史，使用类型特异性PCR引物筛选了其他分类群中O型和M型因子的存在情况。从一个927碱基对片段（14个分类单元）的序列数据推断的系统发育表明，O型因子在果蝇盐沼果蝇组和威氏果蝇组的谱系中经历了更长时间的常规垂直传递。然而，从威氏果蝇组的一个物种开始，它们通过水平方式传播到其他谱系中。首先，亲缘果蝇亚组的谱系被感染，最后，在最近一波水平传播中，来自亲缘果蝇谱系的O型因子侵入了三个不同属的物种：Scaptomyza、Lordiphosa以及果蝇暗果蝇亚组的同胞物种双带果蝇/今井果蝇。从这些分类单元中分离出的O型因子几乎相同（序列分歧<1%）。相比之下，在M型因子中没有观察到这种显著的相似性。尽管如此，M型因子的序列系统发育也与它们宿主物种的系统发育不一致，这表明早期存在水平转移事件。结果表明，P因子跨越物种屏障的频率比以前认为的更高，但需要特定的基因组环境，因此似乎局限于相当狭窄的宿主物种范围内。因此，通过连续水平传递事件获得的不同P因子类型常常在同一基因组中共存。
