Abstract
The epigenetic modifications of human telomeres play a relevant role in telomere functions and cell proliferation. Therefore, their study is becoming an issue of major interest. These epigenetic modifications are usually analyzed by microscopy or by chromatin immunoprecipitation (ChIP). However, these analyses could be challenged by subtelomeres and/or interstitial telomeric sequences (ITSs). Whereas telomeres and subtelomeres cannot be differentiated by microscopy techniques, telomeres and ITSs might not be differentiated in ChIP analyses. In addition, ChIP analyses of telomeres should be properly controlled. Hence, studies focusing on the epigenetic features of human telomeres have to be carefully designed and interpreted. Here, we present a comprehensive discussion on how subtelomeres and ITSs might influence studies of human telomere epigenetics. We specially focus on the influence of ITSs and some experimental aspects of the ChIP technique on ChIP analyses. In addition, we propose a specific pipeline to accurately perform these studies. This pipeline is very simple and can be applied to a wide variety of cells, including cancer cells. Since the epigenetic status of telomeres could influence cancer cells proliferation, this pipeline might help design precise epigenetic treatments for specific cancer types.
Highlights
The epigenetic modifications of human telomeres play a relevant role in telomere functions and cell proliferation
Since telomeres and subtelomeres cannot be differentiated by conventional microscopy techniques, it is important to consider the influence of subtelomeric regions when the epigenetic features of telomeres are analyzed by microscopy
The epigenetic modifications of telomeres are usually studied by microscopy or chromatin immunoprecipitation (ChIP)
Summary
The length of telomeres and the chromatin organization of telomeric regions influence telomeres function [1]. Active euchromatin can acquire a close and silenced conformation through the action of the polycomb complexes 1 and 2, which add the repressive H2AK119ub and H3K27me epigenetic marks, respectively [2,3] This polycomb chromatin can be referred to as facultative heterochromatin. Whereas subtelomeric regions in humans are clearly heterochromatic and exhibit enhanced levels of H3K9me, DNA methylation, and histones hypoacetylation, the epigenetic nature of human telomeres has remained controversial [6,7,8] This controversy might have been influenced by experimental limitations of the techniques used to study telomere epigenetics. We present a specific pipeline to assess the heterochromatic status of human telomeres by ChIP followed by hybridization and sequencing This pipeline can be applied to the study of multiple epigenetic modifications in a wide variety of human cell types. Cells 2019, 8, 1050 techniques can be used to analyze telomere epigenetics, to our knowledge, these techniques have not been used to study the epigenetic features of human telomeres, and they are not discussed here [9,10,11]
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