Telomeres are transcribed into a novel class of long noncoding (lnc) RNAs, called telomeric repeat containing RNAs (TERRA) whose transcriptional regulation and functions are largely unknown. Telomeres are dynamic nucleoprotein complexes that protect the physical extremities of eukaryotic chromosomes from degradation and inappropriate recombination events. Following each round of cell division, telomeres progressively shorten due to limitations of the semiconservative DNA replication, ultimately leading to rampant genomic instability, cellular senescence, and apoptosis. Telomere erosion is counteracted by the telomerase, a ribonucleoprotein enzyme that maintains the length of the telomeres in highly proliferative cell lines, such as the human germ lines and stem cell lineages. However, in most somatic cells, telomerase is inactive. Telomere shortening in the absence of telomerase limits the replicative potential of cells providing a powerful tumor suppressive mechanism. Up to 90% of human cancers reactivate telomerase to bypass the senescence barrier and ensure chromosomal stability and cellular immortalization. Thus, the ability to regulate the length and function of the telomeres is an attractive research target for cancer therapy. In previous studies we found that, in spite of the heterochromatic state of the chromatin, telomeres are transcriptionally active producing a novel class of lncRNAs. The telomeric repeat-containing RNAs (TERRA) remain in the nucleus and partially co-localize with the telomeres. The identification of TERRA revealed a surprising unknown telomeric mechanism and opened up new research direction on telomere functions. The exact roles of TERRA in telomere length regulation remain to be elucidated. TERRA has been implicated in recruiting chromatin modulators to dysfunctional telomeres during senescence but the postulated roles of TERRA as protein recruiter remain to be tested. Overall, the importance of TERRA binding to telomerase and other telomere modifying enzymes is not well understood representing a fundamentally important question in telomere research that will be tackled in this study.
Our objective is to investigate the biogenesis of TERRA and it role in the cell. We plan to systematically identify the transcriptional factors that bind TERRA promoters and characterize their role in TERRA production.Although TERRA transcripts stem from multiple chromosomes ends, it is unclear whether they act on the telomere they originated from or if they can associate with multiple chromosome ends in. In addition, TERRA has been found to interact with some telomeric proteins and heterochromatin modulators; however it remains to be tested if they are recruited by TERRA. In this study, I will explore the dynamics of TERRA localization and determine if the transcripts remain attached to the sequence of origin or they can act at other chromosomal ends or loci. I will elucidate the role of TERRA in stabilizing or recruiting telomeric or heterochromatic proteins at both telomeric and non-telomeric loci. I will assess the function of TERRA-recruited proteins on the chromatin and explore if TERRRA acts as a scaffold to assemble a wide variety of enzymatic activities.
