[Show abstract][Hide abstract] ABSTRACT: TRF1 is a component of the shelterin complex that protects chromosome ends. TRF1 deficiency leads to early embryonic lethality and to severe organ atrophy when deleted in adult tissues. Here we generate a reporter mouse carrying a knock-in eGFP-TRF1 fusion allele to study the role of TRF1 in stem cell biology and tissue homeostasis. We find that eGFP-TRF1 expression in mice is maximal in known adult stem cell compartments and show that TRF1 ensures their functionality. eGFP-TRF1 is highly expressed in induced pluripotent stem cells, uncoupled from the telomere elongation associated with reprogramming. Selection of eGFP-TRF1-high induced pluripotent stem cells correlates with higher pluripotency as indicated by their ability to form teratomas and chimeras. We further show that TRF1 is necessary for both induction and maintenance of pluripotency, and that TRF1 is a direct transcriptional target of Oct3/4.
[Show abstract][Hide abstract] ABSTRACT: Activating mutations in the gene encoding β-catenin have been identified in the paediatric form of human craniopharyngioma (adamantinomatous craniopharyngioma, ACP), a histologically benign but aggressive pituitary tumour accounting for up to 10% of paediatric intracranial tumours. Recently, we generated an ACP mouse model and revealed that, as in human ACP, nucleocytoplasmic accumulation of β-catenin (β-catnc) and over-activation of the Wnt/β-catenin pathway occurs only in a very small proportion of cells, which form clusters. Here, combining mouse genetics, fluorescence labelling and flow-sorting techniques, we have isolated these cells from tumorigenic mouse pituitaries and shown that the β-catnc cells are enriched for colony-forming cells when cultured in stem cell-promoting media, and have longer telomeres, indicating shared properties with normal pituitary progenitors/stem cells (PSCs). Global gene profiling analysis has revealed that these β-catnc cells express high levels of secreted mitogenic signals, such as members of the SHH, BMP and FGF family, in addition to several chemokines and their receptors, suggesting an important autocrine/paracrine role of these cells in the pathogenesis of ACP and a reciprocal communication with their environment. Finally, we highlight the clinical relevance of these findings by showing that these pathways are also up-regulated in the β-catnc cell clusters identified in human ACP. As well as providing further support to the concept that pituitary stem cells may play an important role in the oncogenesis of human ACP, our data reveal novel disease biomarkers and potential pharmacological targets for the treatment of these devastating childhood tumours.
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[Show abstract][Hide abstract] ABSTRACT: Murine embryonic stem (ES) cells have unusually long telomeres, much longer than those in embryonic tissues. Here we address whether hyper-long telomeres are a natural property of pluripotent stem cells, such as those present at the blastocyst inner cell mass (ICM), or whether it is a characteristic acquired by the in vitro expansion of ES cells. We find that ICM cells undergo telomere elongation during the in vitro derivation of ES-cell lines. In vivo analysis shows that the hyper-long telomeres of morula-injected ES cells remain hyper-long at the blastocyst stage and longer than telomeres of the blastocyst ICM. Telomere lengthening during derivation of ES-cell lines is concomitant with a decrease in heterochromatic marks at telomeres. We also found increased levels of the telomere repeat binding factor 1 (TRF1) telomere-capping protein in cultured ICM cells before telomere elongation occurs, coinciding with expression of pluripotency markers. These results suggest that high TRF1 levels are present in pluripotent cells, most likely to ensure proficient capping of the newly synthesized telomeres. These results highlight a previously unnoticed difference between ICM cells at the blastocyst and ES cells, and suggest that abnormally long telomeres in ES cells are likely to result from continuous telomere lengthening of proliferating ICM cells locked at an epigenetic state associated to pluripotency.
Proceedings of the National Academy of Sciences 08/2011; 108(37):15207-12. DOI:10.1073/pnas.1105414108 · 9.67 Impact Factor