We have read with interest the article “Telomere length regulates TERRA levels through increased trimethylation of telomeric H3K9 and HP1α” by Arnoult and colleagues . This study focuses on human telomeric chromatin structure using different techniques like Chromatin Immunoprecipitation (ChIP), cytolocalization or RT-qPCR. However, it has been performed without taking into consideration the presence of Interstitial Telomeric Sequences (ITSs) in the human genome. Some of the conclusions of the article are undoubtedly clear but there are others that might be explained in alternative ways, considering the existence of ITSs. Following, we mention some comments that arise from this interesting article.
 N. Arnoult, A. Van Beneden and A. Decottignies, “Telomere Length Regulates TERRA Levels through Increased Trimethylation of Telomeric H3K9 and HP1α,” Nature Structural & Molecular Biology, Vol. 19, 2012, pp. 948-957
 G. Fourel, E. Revardel, C. Koering and E. Gilson, “Cohabitation of Insulators and Silencing Elements in Yeast Subtelomeric Regions,” EMBO Journal, Vol. 18, 1999, pp. 2522-2537. doi:10.1093/emboj/18.9.2522
 M. Bryk, M. Banerjee, M. Murphy, K. Knudsen, K. Garfinkel and M. Curcio, “Transcriptional Silencing of Ty1 Elements in the RDN1 Locus of Yeast,” Genes and Development, Vol. 11, 1997, pp. 255-269. doi:10.1101/gad.11.2.255
 J. Vrbsky, S. Akimcheva, J. Watson, T. Turner, L. Daxinger, B. Vyskot, W. Aufsatz and K. Riha, “siRNA-Mediated Methylation of Arabidopsis Telomeres,” PLoS Genetics, Vol. 6, No. 6, 2010, e1000986. doi:10.1371/journal.pgen.1000986
 C. Azzalin, P. Reichenbach, L. Khoriauli, E. Giulotto and J. Lingner, “Telomeric Repeat Containing RNA and RNA Surveillance Factors at Mammalian Chromosome Ends,” Science, Vol. 318, 2007, pp. 798-801.
 S. Feuerhahn, N. Iglesias, A. Panza, A. Porro and J. Lingner, “TERRA Biogenesis, Turnover and Implications for Function,” FEBS Letters, Vol. 584, No. 17, 2010, pp. 3812-3818. doi:10.1016/j.febslet.2010.07.032
 D. Yang, Y. Xiong, H. Kim, Q. He, Y. Li, R. Chen and Z. Songyang, “Human Telomeric Proteins Occupy Selective Interstitial Sites,” Cell Research, Vol. 21, 2011, pp. 1013-1027. doi:10.1038/cr.2011.39
 T. Simonet, L. E. Zaragosi, C. Philippe, K. Lebrigand, C. Schouteden, A. Augereau, S. Bauwens, J. Ye, M. Santagostino, E. Giulotto, F. Magdinier, B. Horard, P. Barbry, R. Waldmann and E. Gilson, “The Human TTAGGG Repeat Factors 1 and 2 Bind to a Subset of Interstitial Telomeric Sequences and Satellite Repeats,” Cell Research, Vol. 21, 2011, pp. 1028-1038. doi:10.1038/cr.2011.40