Mathiopoulos K D, della Torre A, Santolamazza F, Predazzi V, Petrarca V, Coluzzi M
Istituto di Parassitologia, Università La Sapienza, Roma, Italy.
Parassitologia. 1999 Sep;41(1-3):119-23.
Chromosomal rearrangements abound in nature and can be studied in detail in organisms with polytene chromosomes. In Drosophila and in Anopheline mosquitoes most speciation processes seem to be associated with the establishment of chromosomal rearrangements, particularly of paracentric inversions. It is not known what triggers inversions in natural populations. In the laboratory inversions are commonly generated by X-rays, mutagens or after the activity of certain transposable elements (TEs). The Anopheles gambiae complex is comprised of six sibling species, each one characterized by the presence of fixed paracentric inversions on their chromosomes. Two of these, An. gambiae s.s. and An. arabiensis, are the most important vectors of human malaria and are structured into sub-populations, each carrying a characteristic set of polymorphic chromosomal inversions. We have cloned the breakpoints of the naturally occurring polymorphic inversion In(2R)d' of An. arabiensis. Analysis of the surrounding sequences demonstrated that adjacent to the distal breakpoint lies a transposable element that we called Odysseus. Characteristics of Odysseus' terminal region and its cytological distribution in different strains as well as within the same strain indicate that Odysseus is an actively transposing element. The presence of Odysseus at the junction of the naturally occurring inversion In(2R)d' suggests that the inversion may be the result of the TEs activity. Cytological evidence from Drosophila melanogaster has also implicated the hobo transposable element in the generation of certain Hawaiian endemic inversions. This picture supports the hypothesis of the important role of TEs in generating natural inversions.
染色体重排在自然界中很常见，并且可以在具有多线染色体的生物体中进行详细研究。在果蝇和按蚊中，大多数物种形成过程似乎都与染色体重排的建立有关，尤其是臂内倒位。目前尚不清楚是什么触发了自然种群中的倒位。在实验室中，倒位通常由X射线、诱变剂或某些转座元件（TEs）的活性产生。冈比亚按蚊复合体由六个姐妹种组成，每个姐妹种的染色体上都有固定的臂内倒位。其中两个，冈比亚按蚊指名亚种和阿拉伯按蚊，是人类疟疾最重要的传播媒介，并被构建成亚种群，每个亚种群都携带一组特征性的多态性染色体倒位。我们已经克隆了阿拉伯按蚊自然发生的多态性倒位In(2R)d'的断点。对周围序列的分析表明，在远端断点附近有一个转座元件，我们称之为奥德修斯。奥德修斯末端区域的特征及其在不同菌株以及同一菌株内的细胞学分布表明，奥德修斯是一个活跃的转座元件。奥德修斯出现在自然发生的倒位In(2R)d'的交界处，这表明该倒位可能是转座元件活动的结果。来自黑腹果蝇的细胞学证据也表明，hobo转座元件与某些夏威夷特有倒位的产生有关。这一情况支持了转座元件在产生自然倒位中起重要作用的假说。
