Specific Localization of the Drosophila Telomere Transposon Proteins and RNAs, Give Insight in Their Behavior, Control and Telomere Biology in This Organism

Drosophila telomeres constitute a remarkable exception to the telomerase mechanism. Although maintaining the same cytological and functional properties as telomerase maintain telomeres, Drosophila telomeres embed the telomere retrotransposons whose specific and highly regulated terminal transposition maintains the appropriate telomere length in this organism. Nevertheless, our current understanding of how the mechanism of the retrotransposon telomere works and which features are shared with the telomerase system is very limited. We report for the first time a detailed study of the localization of the main components that constitute the telomeres in Drosophila, HeT-A and TART RNAs and proteins. Our results in wild type and mutant strains reveal localizations of HeT-A Gag and TART Pol that give insight in the behavior of the telomere retrotransposons and their control. We find that TART Pol and HeT-A Gag only co-localize at the telomeres during the interphase of cells undergoing mitotic cycles. In addition, unexpected protein and RNA localizations with a well-defined pattern in cells such as the ovarian border cells and nurse cells, suggest possible strategies for the telomere transposons to reach the oocyte, and/or additional functions that might be important for the correct development of the organism. Finally, we have been able to visualize the telomere RNAs at different ovarian stages of development in wild type and mutant lines, demonstrating their presence in spite of being tightly regulated by the piRNA mechanism.果蝇端粒是端粒酶机制的显著例外。尽管其在细胞学与功能层面的端粒维持机制与端粒酶体系一致，但果蝇端粒本身嵌入了端粒逆转录转座子，这类转座子通过特异性且受高度调控的末端转座过程，维持该物种端粒的适宜长度。然而，当前学界对这类逆转录转座子介导的端粒运作机制，以及其与端粒酶系统共有的特征的认知仍十分有限。本研究首次针对果蝇端粒的核心组成成分——HeT-A与TART的RNA及蛋白质的定位模式开展了系统性详细研究。我们通过对野生型与突变株系的实验分析，揭示了HeT-A Gag与TART Pol的定位特征，为解析端粒逆转录转座子的行为模式及其调控机制提供了关键线索。研究发现，TART Pol与HeT-A Gag仅在处于有丝分裂周期的细胞的间期阶段，才会共同定位于端粒区域。此外，我们在卵巢边界细胞与滋养细胞等细胞类群中观察到了具有明确特征的意外蛋白质与RNA定位现象，这提示端粒转座子可能存在抵达卵母细胞的潜在通路，亦或存在对生物体正常发育至关重要的额外功能。最终，我们成功在野生型与突变株系的不同卵巢发育阶段可视化了端粒RNA，证实即便受piRNA (Piwi-interacting RNA) 机制的严格调控，这类RNA仍稳定存在于细胞中。