Ponce Rita
Department of Organismic and Evolutionary Biology, Harvard University, MA 02138, Cambridge, USA.
Genetica. 2007 Nov;131(3):315-24. doi: 10.1007/s10709-007-9141-x. Epub 2007 Mar 10.
Transposable elements comprise a considerable part of eukaryotic genomes, and there is increasing evidence for their role in the evolution of genomes. The number of active transposable elements present in the host genome at any given time is probably small relative to the number of elements that no longer transpose. The elements that have lost the ability to transpose tend to evolve neutrally. For example, non-LTR retrotransposons often become 5' truncated due to their own transposition mechanism and hence lose their ability to transpose. The resulting transposons can be characterized as "dead-on-arrival" (DOA) elements. Because they are abundant and ubiquitous, and evolve neutrally in the location where they were inserted, these DOA non-LTR elements make a useful tool to date molecular events. There are four copies of a "dead-on-arrival" RT1C element on the recently formed Sdic gene cluster of Drosophila melanogaster, that are not present in the equivalent region of the other species of the melanogaster subgroup. The life history of the RT1C elements in the genome of D. melanogaster was used to determine the insertion chronology of the elements in the cluster and to date the duplication events that originated this cluster.
转座元件构成了真核生物基因组的相当一部分，并且越来越多的证据表明它们在基因组进化中发挥作用。相对于不再转座的元件数量而言，在任何给定时间宿主基因组中存在的活跃转座元件数量可能较少。失去转座能力的元件往往会中性进化。例如，非LTR逆转座子常常因其自身的转座机制而在5'端被截短，从而失去转座能力。由此产生的转座子可被表征为“到达即死”（DOA）元件。由于这些DOA非LTR元件数量丰富且普遍存在，并且在其插入位置中性进化，它们成为了确定分子事件时间的有用工具。在黑腹果蝇最近形成的Sdic基因簇上有四个“到达即死”的RT1C元件拷贝，而在黑腹果蝇亚组的其他物种的等效区域中不存在这些拷贝。利用黑腹果蝇基因组中RT1C元件的生活史来确定该基因簇中元件的插入年代，并确定产生该基因簇的重复事件的时间。
