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Letter

Nature Cell Biology 9, 1436–1441 (1 December 2007) | doi:10.1038/ncb1664

Telomere lengthening early in development

Lin Liu , Susan M. Bailey , Maja Okuka , Purificaci|[oacute]|n Mu|[ntilde]|oz , Chao Li , Lingjun Zhou , Chao Wu , Eva Czerwiec , Laurel Sandler , Andreas Seyfang , Maria A. Blasco & David L. Keefe

Stem cells and cancer cells maintain telomere length mostly through telomerase. Telomerase activity is high in male germ line and stem cells, but is low or absent in mature oocytes and cleavage stage embryos, and then high again in blastocysts.