Expression of telomerase reverse transcriptase subunit (TERT) and telomere sizing in pig ovarian follicles.

Telomerase is crucial for chromosome stability because it maintains telomere length. Little is known about telomerase in ovarian follicles, where an intense cell division is crucial to sustain estrous cycle and to drive oocyte development. The present research was performed to detect, by immunohistochemistry, the distribution of telomerase catalytic subunit (TERT) during folliculogenesis and to study the effect of TERT expression on telomeres. To this aim, telomere length has been measured on fluorescence in situ hybridization (FISH)-processed sections either in follicular or in germ cells. In primary and preantral follicles, TERT was observed in granulosa and in germ cells, with a typical nuclear location. During antral differentiation, only somatic cells close to the antrum (antral layer) and cumulus cells maintained TERT expression. The relative oocytes located TERT in the ooplasm independent from the process of meiotic maturation. FISH results indicate that a correlation exists between TERT expression and telomere size. In fact, progressively bigger telomeres were observed from preantral to antral follicles where longer structures were recorded in cells of the cumulus oophorus and of the antral layer than those of the basal one. Stable and elongated telomeres were detected in fully grown oocytes that lost the functional TERT distribution within the nucleus.     

端粒酶激活机制研究进展

随着对端粒和端粒酶在衰老和肿瘤中重要性认识的不断深入,端粒酶的激活途径已日益成为这一研究领域的热点.已发现,MYC原癌蛋白(myelocytomatosis virus oncoprotein, MYC)在端粒酶的激活中起关键作用.它可以与TERT基因启动子区域内的E盒结合反式直接激活端粒酶,还可能介导了细胞内其他分子如人乳头瘤病毒E6癌蛋白(human papillomavirus E6 oncoprotein, HPV-E6)和雌激素等对端粒酶的激活.雌激素也可与雌激素受体形成复合物,直接与TERT基因启动子区域内的退化雌激素反应元件结合反式激活端粒酶.此外,腺瘤样结肠息肉癌蛋白(adenomatous polyposis coli protein,APC)、p53及调节蛋白质磷酸化和去磷酸化过程的酶类等亦可能参与了端粒酶活性的激活.     

端粒维持研究进展

端粒是现代生物学的研究热点,与肿瘤发生、基因表达调控、衰老有着密切的关系。本综述介绍当前对端粒维持机理研究的进展。在端粒维持过程中有两类重要的蛋白：端粒相关蛋白和端粒酶。端粒相关蛋白是直接或间接与端粒结合的蛋白 ,在维持端粒稳定性方面有重要作用。端粒酶,特别是其催化亚基ｈＴＥＲＴ,在端粒延长过程中起着不可替代的作用,与细胞永生化和癌变密切相关。此外还介绍了在某些细胞中存在的不依赖端粒酶的端粒延长机     

Telomerase regulation and progressive telomere shortening of rat hepatic stem-like epithelial cells during in vitro aging

Rat hepatic stem-like epithelial cells, LE/2, LE/6, and WB-F344, share some phenotypic properties with oval cells, observed in the early stages of hepatocarcinogenesis. Here, we describe regulations of telomerase and telomere length during in vitro aging of LEs and WB-F344. These cells displayed no apparent aging phenotypes for over 140 passages. Telomerase activity and telomere length of these cells progressively decreased with the passages, and at the late passages, telomere shortening appeared to be reduced as telomerase activity increased. Regulation of TERT and TR, key components of telomerase, was similar to that of the telomerase activity. LEs possessed weak telomerase activity with a slow rate of proliferation compared to WB-F344, and were not tumorigenic, whereas WB-F344 was transformed in vitro from intermediate passage. In conclusion, LEs and WB-F344 have different biochemical properties, and telomerase activation and short telomeres are unlikely necessary for the transformation of WB-F344. TERT and TR seem to be the regulators of the telomerase activity. The relationship between telomere length and telomerase activity suggests that telomerase contributes to the regulation of telomere length in these cells. Our findings provide a better understanding of mechanisms in neoplastic transformation of rat hepatic stem-like epithelial cells.     

A genetic interaction between RAP1 and telomerase reveals an unanticipated role for RAP1 in telomere maintenance

RAP1 is one of the components of shelterin, the capping complex at chromosome ends or telomeres, although its role in telomere length maintenance and protection has remained elusive. RAP1 also binds subtelomeric repeats and along chromosome arms, where it regulates gene expression and has been shown to function in metabolism control. Telomerase is the enzyme that elongates telomeres, and its deficiency causes a premature aging in humans and mice. We describe an unanticipated genetic interaction between RAP1 and telomerase. While RAP1 deficiency alone does not impact on mouse survival, mice lacking both RAP1 and telomerase show a progressively decreased survival with increasing mouse generations compared to telomerase single mutants. Telomere shortening is more pronounced in Rap1^?/? Terc^?/? doubly deficient mice than in the single‐mutant Terc^?/? counterparts, leading to an earlier onset of telomere‐induced DNA damage and degenerative pathologies. Telomerase deficiency abolishes obesity and liver steatohepatitis provoked by RAP1 deficiency. Using genomewide ChIP sequencing, we find that progressive telomere shortening owing to telomerase deficiency leads to re‐localization of RAP1 from telomeres and subtelomeric regions to extratelomeric sites in a genomewide manner. These findings suggest that although in the presence of sufficient telomere reserve RAP1 is not a key factor for telomere maintenance and protection, it plays a crucial role in the context of telomerase deficiency, thus in agreement with its evolutionary conservation as a telomere component from yeast to humans.     

Evolving views of telomerase and cancer

The maintenance of telomeres, nucleoprotein structures that constitute the ends of eukaryotic chromosomes, regulates many crucial cellular functions and might, in multicellular organisms, participate in the control of complex phenotypes such as aging and cancer. Stabilization of telomere length is strongly associated with cellular immortalization, and constitutive telomerase activation occurs in most human cancers. Such observations form the basis for the prevailing model that postulates that alterations in telomere biology both suppress and facilitate malignant transformation by regulating genomic stability and cell life span. However, recent findings suggest that telomere maintenance might not be an obligate requirement for initial tumor formation in some settings and that telomerase activation contributes to tumorigenesis independently of its role in maintaining telomere length. These recent developments indicate that our understanding of telomere biology remains incomplete and implicate additional complexity in the relationships among telomeres, telomerase and cancer.     

Characterization of tree shrew telomeres and telomerase

The use of tree shrews as experimental animals for biomedical research is a new practice. Several recent studies suggest that tree shrews are suitable for studying cancers, including breast cancer, glioblastoma,lung cancer, and hepatocellular carcinoma. However, the telomeres and the telomerase of tree shrews have not been studied to date. Here, we characterize telomeres and telomerase in tree shrews. The telomere length of tree shrews is approximately 23 kb, which is longer than that of primates and shorter than that of mice, and it is extended in breast tumor tissues according to Southern blot and flow-fluorescence in situ hybridization(FISH) analyses. Tree shrew spleen, bone marrow, testis, ovary, and uterus show high telomerase activities, which are increased in breast tumor tissues by telomeric repeat amplification protocol assays. The telomere length becomes shorter, and telomerase activity decreases with age. The tree shrew TERT and TERC are more highly similar to primates than to rodents. These findings lay a solid foundation for using tree shrews to study aging and cancers.