Silva-Sousa R, López-Panadѐs E, Casacuberta E
Institute of Evolutionary Biology, Barcelona, Spain.
Genome Dyn. 2012;7:46-67. doi: 10.1159/000337127. Epub 2012 Jun 25.
Telomeres have a DNA component composed of repetitive sequences. In most eukaryotes these repeats are very similar in length and sequence and are maintained by a highly conserved specialized cellular enzyme, telomerase. Some exceptions of the telomerase mechanism exist in eukaryotes of which the most studied are concentrated in insects, and from these, Drosophila species stand out in particular. The alternative mechanism of telomere maintenance in Drosophila is based on targeted transposition of 3 very special non-LTR retrotransposons, HeT-A, TART and TAHRE. The fingerprint of the co-evolution between the Drosophila genome and the telomeric retrotransposons is visible in special features of both. In this chapter, we will review the main aspects of Drosophila telomeres and the telomere retrotransposons that explain how this alternative mechanism works, is regulated, and evolves. By going through the different aspects of this symbiotic relationship, we will try to unravel which have been the necessary changes at Drosophila telomeres in order to exert their telomeric function analogously to telomerase telomeres, and also which particularities have been maintained in order to preserve the retrotransposon personality of HeT-A, TART and TAHRE. Drosophila telomeres constitute a remarkable variant that reminds us how exceptions should be treasured in order to widen our knowledge in any particular biological mechanism.
端粒具有由重复序列组成的DNA成分。在大多数真核生物中，这些重复序列在长度和序列上非常相似，并由一种高度保守的特殊细胞酶——端粒酶维持。真核生物中存在一些端粒酶机制的例外情况，其中研究最多的集中在昆虫中，而果蝇物种在这些昆虫中尤为突出。果蝇中端粒维持的替代机制基于3种非常特殊的非LTR逆转录转座子HeT-A、TART和TAHRE的靶向转座。果蝇基因组与端粒逆转录转座子之间共同进化的印记在两者的特殊特征中都可见。在本章中，我们将回顾果蝇端粒和端粒逆转录转座子的主要方面，这些方面解释了这种替代机制是如何工作、如何被调控以及如何进化的。通过探讨这种共生关系的不同方面，我们将试图揭示果蝇端粒为了发挥类似于端粒酶端粒的端粒功能而发生的必要变化，以及为了保持HeT-A、TART和TAHRE的逆转录转座子特性而保留的特殊性。果蝇端粒构成了一个显著的变体，它提醒我们，为了拓宽我们对任何特定生物学机制的认识，应该珍视例外情况。
