研究在酵母菌當中三種不同端粒維持機制特性的研究

Abstract

端粒維持對於染色體的穩定，細胞生長分裂都有很重要的地位，在一般的細胞當中利用端粒酵素來維持端粒，而細胞缺乏端粒酵素時，會利用二種不同的重組方式來維持端粒，這樣的維持有助於癌症細胞的增生。在本研究中，我們於雙套染色體上提供兩種不同的端粒模式，再追蹤其端粒延長之形式。發現當有端粒酵素存在時，大部分細胞還是會以端粒酵素來維持其端粒，不過少數也會以Type II的重組方式延長端粒，可見單套正常的RNA模板並不足以維持所有的端粒延長。在雙套酵母菌中發現，在端粒酵素缺乏時，細胞如果先有一種端粒延長方式，細胞會延用這樣的機制去延長端粒，如果沒有任何預先給的延長方式，細胞在液態培養基中還是會以Type II方式延長端粒，而在固態培養基中，Type I發生頻率較高。 利用此菌株，觀察其他端粒特性，發現Type I端粒幾乎沒有端粒位置效應，不過端粒丟失情形則沒有太大差異。此外，藉著觀察單一染色體末端，我們發現細胞內可以同時存在不同的端粒-端粒重組形式，而且已經利用端粒-端粒重組方式的端粒也是會被端粒酵素作用。而不同的化學物質可以對於不同存活者有不同的影響，顯示細胞壓力的確也會對於端粒重組造成影響。

Telomere maintenance is required for chromosome stability and cell proliferation. Telomeres are replicated by the action of the reverse transcriptase, telomerase. In budding yeasts that lack telomerase, telomeres are maintained by two different pathways of telomere-telomere recombination. In this study, we created two different telomeric patterns in each diploid cell and followed their telomere pattern. We found that cells prefer to maintain their telomere by telomerase when telomerase activity is present. But in these strains, type II pattern of telomere-telomere recombination sometimes appears and quickly disappeared. One allele of wild type Tlc1 is not sufficient for maintaining all telomeres well. When one mechanism is predeposited in diploid strains, cell would use this mechanism to elongate their telomeres. In diploid strains, type II survivors appear in liquid culture when there is no predeposited telomere-telomere recombination pathway. By contrast, most survivors on solid plate are type I. Using these strains, study other telomere characteristics. We found that telomere position effect is decreased sharply in type I telomere, and telomere loss was not different. Using an assay to trace a single chromosome end, we show here that different telomere-telomere recombination mechanism can coexist in the same cell. And, some genomic toxic agents inhibit survivors’ growth differently. Moreover, suffering environmental pressure influence the preference of telomere recombination.