title: Telomere lengthening early in development.
abstract: 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. How early embryos reset telomere length remains poorly understood. Here, we show that oocytes actually have shorter telomeres than somatic cells, but their telomeres lengthen remarkably during early cleavage development. Moreover, parthenogenetically activated oocytes also lengthen their telomeres, thus the capacity to elongate telomeres must reside within oocytes themselves. Notably, telomeres also elongate in the early cleavage embryos of telomerase-null mice, demonstrating that telomerase is unlikely to be responsible for the abrupt lengthening of telomeres in these cells. Coincident with telomere lengthening, extensive telomere sister-chromatid exchange (T-SCE) and colocalization of the DNA recombination proteins Rad50 and TRF1 were observed in early cleavage embryos. Both T-SCE and DNA recombination proteins decrease in blastocyst stage embryos, whereas telomerase activity increases and telomeres elongate only slowly. We suggest that telomeres lengthen during the early cleavage cycles following fertilization through a recombination-based mechanism, and that from the blastocyst stage onwards, telomerase only maintains the telomere length established by this alternative mechanism.
authors.affiliation: Laboratory for Reproductive Medicine, Department of Obstetrics and Gynecology, University of South Florida College of Medicine, Tampa, Florida 33612, USA. liutelom@yahoo.com
authors.forename: Lin
authors.initials: L
authors.lastname: Liu
authors.forename: Susan M
authors.initials: SM
authors.lastname: Bailey
authors.forename: Maja
authors.initials: M
authors.lastname: Okuka
authors.forename: Purificación
authors.initials: P
authors.lastname: Muñoz
authors.forename: Chao
authors.initials: C
authors.lastname: Li
authors.forename: Lingjun
authors.initials: L
authors.lastname: Zhou
authors.forename: Chao
authors.initials: C
authors.lastname: Wu
authors.forename: Eva
authors.initials: E
authors.lastname: Czerwiec
authors.forename: Laurel
authors.initials: L
authors.lastname: Sandler
authors.forename: Andreas
authors.initials: A
authors.lastname: Seyfang
authors.forename: Maria A
authors.initials: MA
authors.lastname: Blasco
authors.forename: David L
authors.initials: DL
authors.lastname: Keefe
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D017766:Acid Anhydride Hydrolases; D000818:Animals; D001755:Blastocyst / Q000502:physiology; D004268:DNA-Binding Proteins; D004622:Embryo, Mammalian / Q000502:physiology*; D005260:Female; D008297:Male; D051379:Mice; D009865:Oocytes / Q000502:physiology; D010312:Parthenogenesis; D012854:Sister Chromatid Exchange; D019098:Telomerase / Q000502:physiology; D016615:Telomere / Q000502:physiology*; D035321:Telomeric Repeat Binding Protein 1 / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D004268:DNA-Binding Proteins; D035321:Telomeric Repeat Binding Protein 1; D019098:Telomerase; D017766:Acid Anhydride Hydrolases; C495198:Rad50 protein, mouse