Wang Yisong, Erdmann Natalie, Giannone Richard J, Wu Jun, Gomez Marla, Liu Yie
Life Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6445, USA.
Proc Natl Acad Sci U S A. 2005 Jul 19;102(29):10256-60. doi: 10.1073/pnas.0504635102. Epub 2005 Jul 6.
Telomerase deficiency leads to a progressive loss of telomeric DNA that eventually triggers cell apoptosis in human primary cells during prolonged growth in culture. Rare survivors can maintain telomere length through either activation of telomerase or recombination-based telomere lengthening, and thus proliferate indefinitely. We have explored the possibility that telomeres may be maintained through telomere sister chromatid exchange (T-SCE) in murine telomere reverse transcriptase-deficient (mTert-/-) splenocytes and ES cells. Because telomerase deficiency leads to gradual loss of telomeric DNA in mTert-/- splenocytes and ES cells and eventually to chromosomes with telomere signal-free ends (SFEs), we examined these cell types for evidence of sister chromatid exchange at telomeres, and observed an increase in T-SCEs only in a subset of mTert-/- splenocytes or ES cells that possessed multiple SFEs. Furthermore, T-SCEs were more often detected in ES cells than in splenocytes that harbored a similar frequency of SFEs. In mTert heterozygous (mTert+/-) ES cells or splenocytes, which are known to exhibit a decrease in average telomere length but no SFEs, no increase in T-SCE was observed. In addition to T-SCE, other genomic rearrangements (i.e., SCE) were also significantly increased in mTert-/- ES cells possessing critically short telomeres, but not in splenocytes. Our results suggest that animals and cell culture differ in their ability to carry out genomic rearrangements as a means of maintaining telomere integrity when telomeres become critically shortened.
端粒酶缺陷会导致端粒DNA逐渐丢失，在原代人细胞长期培养过程中，最终会引发细胞凋亡。极少数存活细胞可通过激活端粒酶或基于重组的端粒延长来维持端粒长度，从而无限增殖。我们探讨了在小鼠端粒逆转录酶缺陷（mTert-/-）脾细胞和胚胎干细胞中，端粒是否可通过端粒姐妹染色单体交换（T-SCE）得以维持。由于端粒酶缺陷会导致mTert-/-脾细胞和胚胎干细胞中端粒DNA逐渐丢失，并最终形成无端粒信号末端（SFE）的染色体，我们检测了这些细胞类型中端粒处姐妹染色单体交换的证据，仅在具有多个SFE的部分mTert-/-脾细胞或胚胎干细胞中观察到T-SCE增加。此外，在具有相似SFE频率的情况下，胚胎干细胞中比脾细胞中更常检测到T-SCE。在已知平均端粒长度减少但无SFE的mTert杂合（mTert+/-）胚胎干细胞或脾细胞中，未观察到T-SCE增加。除了T-SCE，在具有极短端粒的mTert-/-胚胎干细胞中，其他基因组重排（即SCE）也显著增加，但在脾细胞中未增加。我们的结果表明，当端粒严重缩短时，动物和细胞培养在通过基因组重排来维持端粒完整性的能力方面存在差异。
