Transcription and activation under environmental stress of the complex telomeric repeats of Chironomus thummi J. L. Martı ´nez-Guitarte 1 , J. L. Dı ´ez 2 & G. Morcillo 1 * 1 Grupo de Biologı´a y Toxicologı´a Ambiental, Facultad de Ciencias, Universidad Nacional de Educacio´n a Distancia, UNED, Senda del Rey 9, 28040 Madrid, Spain; Tel: 0034-913987328; Fax: 0034-913987628; E-mail: gmorcillo@ccia.uned.es; 2 Centro de Investigaciones Biolo´gicas, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain * Correspondence Received 20 June 2008. Received in revised form and accepted for publication by Herbert Macgregor 8 August 2008 Key words: Chironomus, complex telomeres, non-coding RNAs, telomere transcripts Abstract In contrast to their traditional role, telomeres seem to behave as transcriptionally active regions. RNAs complementary to the short DNA repeats characteristic of telomerase-maintained telomeres have recently been identified in various mammalian cell lines, representing a new and unexpected element in telomere architecture. Here, we report the existence of transcripts complementary to telomeric sequences characteristic of Chironomus thummi telomeres. As in other Diptera, the non-canonical telomeres of chironomids lack the simple telomerase repeats and have instead more complex repetitive sequences. Northern blots of total RNA hybridized with telomere probes and RT-PCR with telomere-specific tailed primers confirm the existence of small non-coding RNAs of around 200 bp, the size of the DNA repeated telomeric unit. Telomere transcripts are heterogeneous in length, and they appear as a ladder pattern that probably corresponds to multimers of the repeat. Moreover, telomeres are activated under conditions of environmental stress, such as heat shock, appearing highly decondensed and densely labelled with acetylated H4 histone, as well as with RNA polymerase II antibodies, both marks of transcriptional activity. Changes in the expression levels of telomeric RNA were detected after heat shock. These findings provide evidence that transcriptional activity of the repetitive telomere sequences is an evolutionarily conserved feature, not limited to telomerase telomeres. The functional significance of this non- coding RNA as a new additional element in the context of telomere biology remains to be explained. Abbreviations DAPI 4¶,6-diamino-2-phenylindole FITC fluorescein isothiocyanate HSE heat shock element HSF heat shock factor HSP heat shock protein LINE long interspersed elements ncRNA non-coding RNA non-LTR non-long tandem repeats RNP ribonucleoprotein RT reverse transcription RT-PCR reverse transcription polymerase chain reaction SINE short interspersed element T-BRIII telomeric balbiani ring III TsA telomeric sequence A TsB telomeric sequence B TsC telomeric sequence C Introduction Telomeres form a specialized domain, which protects the chromosome termini from degradation and fusion Chromosome Research (2008) # Springer 2008 DOI: 10.1007/s10577-008-1260-4