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Extensive allelic variation and ultrashort telomeres in senescent human cells


By imposing a limit on the proliferative lifespan of most somatic cells, telomere erosion represents an innate mechanism for tumor suppression1 and may contribute to age-related disease2. A detailed understanding of the pathways that link shortened telomeres to replicative senescence has been severely hindered by the inability of current methods to analyze telomere dynamics in detail. Here we describe single telomere length analysis (STELA), a PCR-based approach that accurately measures the full spectrum of telomere lengths from individual chromosomes. STELA analysis of human XpYp telomeres in fibroblasts identifies several features of telomere biology. We observe bimodal distributions of telomeres in normal fibroblasts; these distributions result from inter-allelic differences of up to 6.5 kb, indicating that unexpectedly large-scale differences in zygotic telomere length are maintained throughout development. Most telomeres shorten in a gradual fashion consistent with simple losses through end replication, and the rates of erosion are independent of allele size. Superimposed on this are occasional, more substantial changes in length, which may be the consequence of additional mutational mechanisms. Notably, some alleles show almost complete loss of TTAGGG repeats at senescence.

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We thank J. Skinner and J. Bond for cell samples and members of our laboratory for input. This work was supported by the Association for International Cancer Research. D.M.B. is a Research into Ageing Fellow.

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Correspondence to Duncan M. Baird.

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The authors declare no competing financial interests.

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Figure 1: The principle of STELA at the XpYp telomere.
Figure 2: STELA of primary fibroblast strains.
Figure 3: Senescent normal primary fibroblasts derived from the illustrated pedigree.
Figure 4: Variation at the XpYp telomere.
Figure 5: Telomere loss and the generation of heterogeneity at four separate telomeres during culture of MRC5 subclones to senescence.