title: Endogenous and ectopic expression of telomere regulating genes in chicken embryonic fibroblasts.
abstract: In this study, we compared the endogenous expression of genes encoding telomere regulating proteins in cultured chicken embryonic fibroblasts (CEFs) and 10-day-old chicken embryos. CEFs maintained in vitro senesced and senescence was accompanied by reduced telomere length, telomerase activity, and expression of the chicken (c) TRF1 gene. There was no change in TRF2 gene expression although the major TRF2 transcript identified in 10-day-old chicken embryos encoded a truncated TRF2 protein (TRF2'), containing an N-terminal dimerisation domain but lacking a myb-related DNA binding domain and nuclear localisation signal. Senescence of the CEFs in vitro was associated with the loss of the TRF2' transcript, indicative of a novel function for the encoded protein. Senescence was also coupled with decreased expression of RAD51, but increased RAD52 expression. These data support that RAD51 independent recombination mechanisms do not function in vitro to maintain chicken telomeres. To attempt to rescue the CEFs from replicative senescence, we stably transfected passage 3 CEFs with the human telomerase reverse transcriptase (hTERT) catalytic subunit. While hTERT expression was detected in the stable transfectants neither telomerase activity nor the stabilisation of telomere length was observed, and the transfectant cells senesced at the same passage number as the untransfected cells. These data indicate that the human TERT is incompatible with the avian telomere maintenance apparatus and suggest the functioning of a species specific telomere system in the avian.
authors.affiliation: Institute of Cell and Molecular Biosciences, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, UK.
authors.forename: Georgios
authors.initials: G
authors.lastname: Michailidis
authors.forename: Gabriele
authors.initials: G
authors.lastname: Saretzki
authors.forename: Judith
authors.initials: J
authors.lastname: Hall
mesh_terms: D000818:Animals; D030161:Avian Proteins; D002478:Cells, Cultured; D002642:Chick Embryo; D002645:Chickens / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics; D005347:Fibroblasts / Q000378:metabolism*; D015870:Gene Expression; D051135:Rad51 Recombinase; D051721:Rad52 DNA Repair and Recombination Protein; D019098:Telomerase / Q000378:metabolism; D016615:Telomere / Q000378:metabolism*; D035321:Telomeric Repeat Binding Protein 1 / Q000235:genetics; D035341:Telomeric Repeat Binding Protein 2 / Q000235:genetics
chemical_list: D030161:Avian Proteins; D004268:DNA-Binding Proteins; D051721:Rad52 DNA Repair and Recombination Protein; D035321:Telomeric Repeat Binding Protein 1; D035341:Telomeric Repeat Binding Protein 2; C495150:RAD51 protein, Gallus gallus; D051135:Rad51 Recombinase; D019098:Telomerase