Polycombing Drosophila for Dynamic Developmental Footprints

Background: Previous studies have demonstrated that telomeres in somatic cells are not randomly distributed at the end of the chromosomes. We hypothesize that these chromosome arm specific differences in telomere length (the telomere length pattern) may be actively maintained. In this study we investigate the existence and maintenance of the telomere length pattern in stem cells. For this aim we studied telomere length in primary human mesenchymal stem cells (hMSC) and their telomerase-immortalised counterpart (hMSC-telo1) during extended proliferation as well as after irradiation. Telomere lengths were measured using Fluorescence In Situ Hybridization (Q-FISH). Results: A telomere length pattern was found to exist in primary hMSC's as well as in hMSC-telo1. This pattern is similar to what was previously found in lymphocytes and fibroblasts. The cells were then exposed to a high dose of ionizing radiation. Irradiation caused profound changes in chromosome specific telomere lengths, effectively destroying the telomere length pattern. Following long term culturing after irradiation, a telomere length pattern was found to re-emerge. However, the new telomere length pattern did not resemble the telomere length pattern observed before irradiation. Conclusion: Our findings indicate that a telomere length pattern does exist in mesenchymal stem cells and that the pattern is not actively re-established after destruction by irradiation. Background Telomeres consist of repetitive non-coding sequences located at the very end of all chromosomes in higher organisms [1]. The telomeres form a loop structure which in collaboration with a number of specific telomere associated proteins, protects chromosome ends from degradation and chromosome fusion [2]. Telomeres have been found to shorten with each cell division due to a process called the "end replication problem" and possibly due to acquired oxidative damage [3,4]. This gradual shortening of the telomeres during life continues until the telomeres reach a certain length, at which stage the presence of critiPublished: 13 June 2007 BMC Molecular Biology 2007, 8:49 doi:10.1186/1471-2199-8-49 Received: 31 January 2007 Accepted: 13 June 2007 This article is available from: http://www.biomedcentral.com/1471-2199/8/49 © 2007 Graakjaer et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.