More on the Lack of Correlation between Terra Expression and Telomere Length

Valerio Vitelli,Lela Khoriauli,Marco Santagostino,Elena Giulotto,Solomon George Nergadze,Alexandra Smirnova,Riccardo Gamba,Paolo Falvo

doi:10.3389/fonc.2013.00245

Abstract

More on the Lack of Correlation between Terra Expression and Telomere Length

Highlights

Which is the most appropriate method to analyze TElomeric Repeat containing RNA (TERRA) levels? With qRT-PCR, specific primer pairs are used to amplify reverse-transcribed fragments complementary to a portion of the subtelomeric region adjacent to the telomere; the number of transcripts containing subtelomeric fragments is measured while no information on the number of UUAGGG repeats within TERRA molecules is obtained
Most likely the function of TERRA is related to the UUAGGG repeats for the following reasons: (i) the subtelomeric tract contained in TERRA molecules is relatively short while the UUAGGG repeats can reach several kilobases; in particular, in TERRA molecules transcribed from the XqYq human subtelomere, the distance between the transcription start site and the first telomeric repeat is 257 nt [4, 5]; (ii) UUAGGG oligonucleotides interact with several telomere associated proteins, including TRF1 and TRF2 [6]
It was demonstrated that different members of the heterogeneous nuclear ribonucleoprotein family bind abundantly to TERRA repeats [7, 8] and, more recently, 115 proteins, binding to UUAGGG repeats, were identified [9]. (iii) The UUAGGG repeats of TERRA molecules are able to fold into G-quadruplex structures [10] that are required for the binding of TERRA to chromatin [11]. (iv) TERRA repeats can inhibit the telomerase enzymatic activity in vitro [12] through base pairing with the telomeric repeat template but their role in the regulation of telomerase in vivo is more controversial [8, 13]

Summary

Introduction

With qRT-PCR, specific primer pairs are used to amplify reverse-transcribed fragments complementary to a portion of the subtelomeric region adjacent to the telomere; the number of transcripts containing subtelomeric fragments is measured while no information on the number of UUAGGG repeats within TERRA molecules is obtained. The qRT-PCR method has been extensively used by several groups, including ours; we can identify several limitations: [1] primers are constructed on subtelomeric sequences [3], very short and possibly functionally irrelevant RNA molecules containing only a few UUAGGG repeats are detected together with molecules containing large numbers of repeats.

Results

Conclusion