ISREC
EPFL School of Life Sciences - 2010 Annual Report
Lingner Lab
http://lingner-lab.epfl.ch/
PhD at the Biocenter, University of Basel 1989-1992 (Supervisor: Walter Keller). Postdoc at the Howard Hughes Medical Institute, University of Colorado at Boulder 1993-1997 (Supervisor: Thomas Cech). Junior group leader at ISREC 1997-2001. Senior group leader at ISREC since 2002. Associate Professor at EPFL 2005-2008. Full Professor at EPFL since 2009. Honors: START-fellowship from the Swiss National Science Foundation in 1997; Friedrich Miescher Prize from the Swiss Society of Biochemistry in 2002 ; EMBO member in 2005 ; ERC advanced investigator grant in 2008.
Joachim Lingner Full Professor
Introduction
Telomeres are the physical ends of eukaryotic chromosomes. They mediate chromosome stability and function as cellular clocks and tumor suppressors. Our laboratory aims at gaining a detailed understanding of telomere structure and function. Our work should provide fundamental insight into these fascinating biological structures in addition to delineating novel approaches to attack telomere function in cancer cells.
Keywords
Telomeres, telomerase, long non coding RNA, TERRA, cellular senescence, genome stability
Results Obtained in 2010
Telomerase is a cellular reverse transcriptase that uses an internal RNA template to synthesize telomeric repeats at chromosome ends. Telomerase counteracts telomere shortening that occurs due to the end replication problem and nucleolytic processing of telomeric DNA. In humans, telomere length is set in most tissues early in embryogenesis as telomerase is repressed later in life. Short telomeres that accumulate with increasing numbers of cell division cycles induce cellular senescence and this is thought to counteract growth of pre-malignant lesions in our body. Most cancers re-express telomerase to overcome this growth barrier. Our work during 2010 concentrated on the question of how the telomerase enzyme is recruited to chromosome ends by telomere binding proteins and how telomerase is regulated by TERRA, a large non-coding (lnc) RNA which is transcribed at telomeres.
maturation. First, we could show that Cajal bodies, subnuclear structures implicated in ribonucleoprotein assembly are critical for telomerase maturation and the recruitment to telomeres. Second, through downregulation of telomere binding proteins by RNA interference, we identified that the shelterin components TPP1 in association with TIN2 recruit human telomerase to chromosome ends to allow their extension in S phase of the cell cycle. TERRA lncRNA: a natural ligand and regulator of telomerase We recently discovered in eutherian mammals and in the yeast Saccharomyces cerevisiae that telomeres are transcribed into lnc RNAs termed TERRA. The identification of TERRA is paradigm-shifting because telomeric heterochromatin had been accepted as being a transcription silencer. TERRA functions may include the regulation telomeric heterochromatin and the regulation of telomerase (see below). We now dissected the molecular structure of TERRA and its regulation during the cell cycle. In addition, we demonstrated that TERRA binds the telomerase enzyme. The UUAGGG-repeat sequences of TERRA base-pair with the RNA template sequence of telomerase in addition to directly interacting with the TERT polypeptide. TERRA acts as a very potent mixed-type inhibitor of telomerase (see figure). Our data suggest that telomerase regulation by the telomere substrate may be mediated via its transcription.
Activation and recruitment of telomerase to chromosome ends Activation and recruitment of telomerase to chromosome ends are not well understood in complex eukaryotes including humans. Therefore, we developed assays to measure association of human telomerase with chromosome ends by chromatin immunoprecipitation, and our collaborators from the Terns-lab (University of Georgia) could for the first time detect human telomerase at chromosome ends by fluorescence in situ hybridization. We defined two critical steps that are required for telomerase
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