Fablet Marie, McDonald John F, Biémont Christian, Vieira Cristina
UMR CNRS 5558, Biométrie et Biologie Evolutive, Université Claude Bernard Lyon 1, 69622 Villeurbanne Cedex, France.
Gene. 2006 Jun 21;375:54-62. doi: 10.1016/j.gene.2006.02.008. Epub 2006 Apr 19.
Tirant is a long terminal repeat (LTR) retrotransposon with an average of 11 insertion sites on the chromosome arms of Drosophila melanogaster flies collected from natural populations worldwide. In the sibling species Drosophila simulans, tirant is found only in African populations, which harbor a few insertion sites (1 to 5) on the chromosome arms, although some tirant sequences are present in the heterochromatin of most populations. This distribution in D. simulans reflects either the recent genomic invasion of African populations by a new variant of tirant, or a loss of tirant from the entire species apart from some sequence relics still present in Africa. In an attempt to clarify the situation, we focused on the LTR-UTR region of tirant copies from various populations of both D. melanogaster and D. simulans. We found two distinct types of regulatory region: one type was present in both D. melanogaster and D. simulans, and the other was present only in D. simulans. Copies of this latter type of tirant were transcriptionally inactive in gonads. Here we propose that the present day distribution of tirant in D. simulans populations reflects an ancient invasion of D. simulans by tirant copies followed by the loss of active copies from most populations, apart from the African ones, suggesting that this loss is still ongoing in this species.
蒂兰特是一种长末端重复序列（LTR）反转录转座子，在从世界各地自然种群收集的黑腹果蝇的染色体臂上平均有11个插入位点。在其近缘种拟果蝇中，蒂兰特仅在非洲种群中发现，这些种群在染色体臂上有少数插入位点（1至5个），尽管大多数种群的异染色质中存在一些蒂兰特序列。拟果蝇中的这种分布反映了非洲种群近期被一种新的蒂兰特变体进行的基因组入侵，或者是除了非洲仍存在的一些序列遗迹外，整个物种中蒂兰特的丢失。为了澄清这种情况，我们聚焦于来自黑腹果蝇和拟果蝇不同种群的蒂兰特拷贝的LTR-UTR区域。我们发现了两种不同类型的调控区域：一种类型在黑腹果蝇和拟果蝇中都存在，另一种仅存在于拟果蝇中。后一种类型的蒂兰特拷贝在性腺中转录无活性。在这里我们提出，如今蒂兰特在拟果蝇种群中的分布反映了蒂兰特拷贝对拟果蝇的古老入侵，随后除了非洲种群外，大多数种群中活性拷贝丢失，这表明这种丢失在该物种中仍在继续。
