title: Telomerase-immortalized sheep fibroblasts can be reprogrammed by nuclear transfer to undergo early development.
abstract: Telomere shortening and lack of telomerase activity have been implicated in cellular senescence in human fibroblasts. Expression of the human telomerase catalytic reverse transcriptase subunit (hTERT) in these cells reconstitutes telomerase activity and immortalizes the cells without tumor transformation. In this report, we show that sheep fibroblasts are similar to human cells. They do not have detectable telomerase activity and undergo only a finite numbers of cell divisions before replicative senescence. Telomere lengths in sheep fibroblasts are similar to those reported for human cells and shorten at a rate of 50-200 base pairs (bp) each cell division. Expression of the human telomerase catalytic subunit restored the telomerase activity in the sheep cells and extended their proliferative life span. None of the telomerase positive sheep fibroblasts exhibited a transformed phenotype after 200 days of continuous culture, and the higher hTERT expressing cells maintained their telomere lengths and normal cell characteristics for more than 500 days in culture. In cloning experiments using one of these cell lines as a nuclear donor, the reconstructed karyoplasts were reprogrammed and developed to the blastocyst stage at a similar frequency to that observed with the parental, telomerase negative cell line. After embryo transfer the blastocysts exhibited a relatively high frequency of implantation, early fetal development, and organogenesis. No fetuses survived beyond 40 days of development, however, showing that although these cells could be substantially reprogrammed, they were not fully competent for nuclear transfer.
authors.affiliation: Department of Gene Expression and Development, Roslin Institute, Roslin, Midlothian EH25 9PS, United Kingdom.
authors.forename: Wei
authors.initials: W
authors.lastname: Cui
authors.forename: Diana
authors.initials: D
authors.lastname: Wylie
authors.forename: Samena
authors.initials: S
authors.lastname: Aslam
authors.forename: Andres
authors.initials: A
authors.lastname: Dinnyes
authors.forename: Tim
authors.initials: T
authors.lastname: King
authors.forename: Ian
authors.initials: I
authors.lastname: Wilmut
authors.forename: A John
authors.initials: AJ
authors.lastname: Clark
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000166:cytology / Q000201:enzymology; D002455:Cell Division; D002461:Cell Line, Transformed; D016922:Cellular Senescence; D004268:DNA-Binding Proteins; D004624:Embryo Transfer; D005314:Embryonic and Fetal Development; D005260:Female; D005347:Fibroblasts / Q000166:cytology* / Q000201:enzymology*; D015870:Gene Expression; D006801:Humans; D053652:Nuclear Transfer Techniques; D010641:Phenotype; D011247:Pregnancy; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012756:Sheep; D019098:Telomerase / Q000235:genetics / Q000502:physiology*
chemical_list: D004268:DNA-Binding Proteins; D011994:Recombinant Proteins; D019098:Telomerase