State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Nankai University, Tianjin, China.
PLoS One. 2013 Sep 30;8(9):e74202. doi: 10.1371/journal.pone.0074202. eCollection 2013.
Telomere reprogramming and silencing of exogenous genes have been demonstrated in mouse and human induced pluripotent stem cells (iPS cells). Pigs have the potential to provide xenotransplant for humans, and to model and test human diseases. We investigated the telomere length and maintenance in porcine iPS cells generated and cultured under various conditions. Telomere lengths vary among different porcine iPS cell lines, some with telomere elongation and maintenance, and others telomere shortening. Porcine iPS cells with sufficient telomere length maintenance show the ability to differentiate in vivo by teratoma formation test. IPS cells with short or dysfunctional telomeres exhibit reduced ability to form teratomas. Moreover, insufficient telomerase and incomplete telomere reprogramming and/or maintenance link to sustained activation of exogenous genes in porcine iPS cells. In contrast, porcine iPS cells with reduced expression of exogenous genes or partial exogene silencing exhibit insufficient activation of endogenous pluripotent genes and telomerase genes, accompanied by telomere shortening with increasing passages. Moreover, telomere doublets, telomere sister chromatid exchanges and t-circles that presumably are involved in telomere lengthening by recombination also are found in porcine iPS cells. These data suggest that both telomerase-dependent and telomerase-independent mechanisms are involved in telomere reprogramming during induction and passages of porcine iPS cells, but these are insufficient, resulting in increased telomere damage and shortening, and chromosomal instability. Active exogenes might compensate for insufficient activation of endogenous genes and incomplete telomere reprogramming and maintenance of porcine iPS cells. Further understanding of telomere reprogramming and maintenance may help improve the quality of porcine iPS cells.
端粒重编程和外源基因沉默已在小鼠和人诱导多能干细胞（iPS 细胞）中得到证实。猪具有为人类提供异种移植的潜力，并可用于模拟和测试人类疾病。我们研究了在不同条件下生成和培养的猪 iPS 细胞中端粒的长度和维持情况。不同的猪 iPS 细胞系中端粒长度存在差异，有些细胞系中端粒延长和维持，而有些细胞系中端粒缩短。具有足够端粒长度维持的猪 iPS 细胞具有通过畸胎瘤形成试验在体内分化的能力。端粒短或功能失调的 IPS 细胞形成畸胎瘤的能力降低。此外，端粒酶不足和端粒重编程和/或维持不完全与猪 iPS 细胞中外源基因的持续激活有关。相比之下，表达外源基因减少或部分沉默外源基因的猪 iPS 细胞表现出内源性多能基因和端粒酶基因激活不足，伴随着端粒随着传代的增加而缩短。此外，在猪 iPS 细胞中还发现了可能涉及通过重组延长端粒的端粒二联体、端粒姐妹染色单体交换和 t 环。这些数据表明，在猪 iPS 细胞的诱导和传代过程中，端粒重编程既涉及端粒酶依赖机制，也涉及端粒酶非依赖机制，但这些机制还不够充分，导致端粒损伤和缩短增加，以及染色体不稳定。活性的外源基因可能补偿内源性基因激活不足和猪 iPS 细胞中端粒重编程和维持不完全。进一步了解端粒重编程和维持可能有助于提高猪 iPS 细胞的质量。
