Target enrichment followed by high throughput sequencing of telomeric DDRNAs in telomere-deprotected mouse cells
Ontology highlight
ABSTRACT: Telomeres are the nucleoprotein complexes located at the tips of eukaryotic chromosomes, composed of repetitive DNA (TTAGGG in vertebrates), and coated by a set of proteins collectively known as the shelterin complex. Dysfunctional telomeres resemble DSBs and they have been observed during ageing and cancer and a number of pathological conditions. Apart from telomeric repeat-containing RNA (TERRA), a non-coding UUAGGG-rich transcript starting from promoters located in the subtelomeric region, in mammals no other transcripts at telomeres have been characterized so far. Here we show that in mammals telomere dysfunction (analysed using TRF2+/- and TRF2-/- mouse embryonic fibroblasts) induces the transcription of telomeric DDRNAs (tDDRNAs) from both DNA strands. To characterize the length and sequence of tDDRNAs, we devised and employed an innovative method for target enrichment of RNA, based on in solution capture of low abundance small RNA species followed by next generation sequencing, developed in our laboratories. By this approach, we observed that telomere deprotection induced the accumulation of small RNA species generated from the transcription of both telomere strands and including the expected DDRNA size range products. Importantly, 20-23 nucleotide RNAs displayed a base bias at both 5’ and 3’ ends significantly different from the telomeric locus suggesting a regulated processing.
Project description:Telomeres are nucleoprotein structures at the ends of linear chromosomes. In humans, they consist of TTAGGG repeats, which are bound by dedicated proteins such as the shelterin complex. This complex consists of six proteins (TRF1, TRF2, RAP1, POT1, TPP1 and TIN2) and blocks unwanted DNA damage repair at telomeres, e.g. by suppressing non-homologous end joining (NHEJ) through its subunit TRF2. While shelterin does not work autonomously, additional direct telomere binding proteins have been described to function in a supplementary role. We here describe ZNF524, a zinc finger protein that directly binds to telomeric repeats with nanomolar affinity and reveal the base-specific sequence recognition by co-crystallization with telomeric DNA. ZNF524 localizes to telomeres and specifically maintains the presence of the TRF2/RAP1 subcomplex at telomeres without affecting the other shelterin members. Loss of ZNF524 concomitantly results in an increase in DNA damage signaling and recombination events. Overall, we identified ZNF524 as a direct telomere binding protein and propose that ZNF524 is involved in the maintenance of telomere integrity by promoting TRF2/RAP1 subcomplex binding.
Project description:Telomeres are nucleoprotein structures at the ends of linear chromosomes. In humans, they consist of TTAGGG repeats, which are bound by dedicated proteins such as the shelterin complex. This complex consists of six proteins (TRF1, TRF2, RAP1, POT1, TPP1 and TIN2) and blocks unwanted DNA damage repair at telomeres, e.g. by suppressing non-homologous end joining (NHEJ) through its subunit TRF2. While shelterin does not work autonomously, additional direct telomere binding proteins have been described to function in a supplementary role. We here describe ZNF524, a zinc finger protein that directly binds to telomeric repeats with nanomolar affinity and reveal the base-specific sequence recognition by co-crystallization with telomeric DNA. ZNF524 localizes to telomeres and specifically maintains the presence of the TRF2/RAP1 subcomplex at telomeres without affecting the other shelterin members. Loss of ZNF524 concomitantly results in an increase in DNA damage signaling and recombination events. Overall, we identified ZNF524 as a direct telomere binding protein and propose that ZNF524 is involved in the maintenance of telomere integrity by promoting TRF2/RAP1 subcomplex binding.
Project description:Telomeres are nucleoprotein structures at the ends of linear chromosomes. In humans, they consist of TTAGGG repeats, which are bound by dedicated proteins such as the shelterin complex. This complex blocks unwanted DNA damage repair at telomeres, e.g. by suppressing non-homologous end joining (NHEJ) through its subunit TRF2. We here describe ZNF524, a zinc finger protein that directly binds telomeric repeats with nanomolar affinity and reveal the base-specific sequence recognition by co-crystallization with telomeric DNA. ZNF524 localizes to telomeres and specifically maintains the presence of the TRF2/RAP1 subcomplex at telomeres without affecting other shelterin members. Loss of ZNF524 concomitantly results in an increase in DNA damage signaling and recombination events. Overall, ZNF524 is a direct telomere-binding protein involved in the maintenance of telomere integrity.
Project description:Telomeres are nucleoprotein structures at the ends of linear chromosomes. In humans, they consist of TTAGGG repeats, which are bound by dedicated proteins such as the shelterin complex. This complex blocks unwanted DNA damage repair at telomeres, e.g. by suppressing non-homologous end joining (NHEJ) through its subunit TRF2. We here describe ZNF524, a zinc finger protein that directly binds telomeric repeats with nanomolar affinity and reveal the base-specific sequence recognition by co-crystallization with telomeric DNA. ZNF524 localizes to telomeres in vivo, as shown among other approaches by ChIP-seq analysis, and specifically maintains the presence of the TRF2/RAP1 subcomplex at telomeres without affecting the other shelterin members. Loss of ZNF524 concomitantly results in an increase in DNA damage signaling and recombination events. Overall, ZNF524 is a direct telomere-binding protein involved in the maintenance of telomere integrity.
Project description:The study of the proteins that bind to telomeric DNA in mammals has provided a deep understanding of the mechanisms of chromosome-end protection. However, very little is known on the binding of these proteins to nontelomeric DNA sequences. The TTAGGG DNA repeat proteins 1 and 2 (TRF1 and TRF2) bind to mammalian telomeres as part of the shelterin complex and are essential for maintaining chromosome end stability. In this study, we combined chromatin immunoprecipitation with high-throughput sequencing to map at high sensitivity and resolution, the human chromosomal sites to which TRF1 and TRF2 bind. While most of the identified sequences correspond to telomeric regions, we showed that these two proteins also bind to extratelomeric sites. The vast majority of these extra-telomeric sites contains interstitial telomeric sequences (or ITSs). However we also identified non-ITS sites, which are also satellite DNA but the ones mainly constitutive of centromeric and pericentromeric regions. Interestingly, the TRF-binding sites are often located in the proximity of genes or within introns. We propose that, by binding to extratelomeric sequences, TRF1 and TRF2 couple the functional state of telomeres to the long-range organization of chromosomes and gene regulation networks. ChIP-SEQ experiment of transformed human fibroblast BJ cells with 3 antibodies (1 monoclonal anti-TRF1, 1 monoclonal anti-TRF2, 1 polyclonal anti-TRF2) and a negative control (proteinG without antibody used as the ChIP background)
Project description:The study of the proteins that bind to telomeric DNA in mammals has provided a deep understanding of the mechanisms of chromosome-end protection. However, very little is known on the binding of these proteins to nontelomeric DNA sequences. The TTAGGG DNA repeat proteins 1 and 2 (TRF1 and TRF2) bind to mammalian telomeres as part of the shelterin complex and are essential for maintaining chromosome end stability. In this study, we combined chromatin immunoprecipitation with high-throughput sequencing to map at high sensitivity and resolution, the human chromosomal sites to which TRF1 and TRF2 bind. While most of the identified sequences correspond to telomeric regions, we showed that these two proteins also bind to extratelomeric sites. The vast majority of these extra-telomeric sites contains interstitial telomeric sequences (or ITSs). However we also identified non-ITS sites, which are also satellite DNA but the ones mainly constitutive of centromeric and pericentromeric regions. Interestingly, the TRF-binding sites are often located in the proximity of genes or within introns. We propose that, by binding to extratelomeric sequences, TRF1 and TRF2 couple the functional state of telomeres to the long-range organization of chromosomes and gene regulation networks.
Project description:Telomeres, the nucleoprotein structures located at the end of eukaryotic DNA, protect chromosomal integrity. These structures undergo changes during development and aging, including length shortening and alterations in the levels of the proteins associated to them called shelterin, all this affecting genome stability as the cells age. However, telomeres also behave as transcriptional regulators acting not only on genes present at subtelomeres but also on more distantly located genes presented throughout the genome. This process is referred as Telomere Position Effect (TPE). Here we set to determine whether telomere shortening in senescent cells impact TPE and senescent cells transcriptome. We also investigate whether TRF2 (a shelterin protein) and Lamin B1 (a member of nuclear lamina) are involved in TPE by doing RNA sequencing of young and senescent cells in which we modulated TRF2 and Lamin B1 expression.
Project description:Telomeres are the ends of linear chromosomes and together with the shelterin complex present an essential feature for genome integrity. Vertebrate telomeres usually consist of hexameric TTAGGG repeats, however, in cells that use the alternative lengthening of telomeres (ALT) mechanism, variant repeat sequences are interspersed throughout telomeres. Previously, it was shown that NR2C/F transcription factors bind to TCAGGG variant repeats and contribute to telomere maintenance in ALT cells. While specific binders to other variant repeat sequences have been lacking to date, we here identify ZBTB10 as the first TTGGGG-binding protein and demonstrate direct binding via the two zinc fingers with affinity in the nanomolar range. Concomitantly, ZBTB10 co-localizes with a subset of telomeres in ALT-positive U2OS cells and interacts with TRF2/RAP1 via the N-terminal region of TRF2. Our data establishes ZBTB10 as a novel variant repeat-specific binding protein at ALT telomeres.
Project description:With the increase of atmospheric oxygen 2.3 billion years ago, mechanisms evolved to mitigate the toxic effects of oxygen radicals. Telomeres appear particularly susceptible to oxidative damage, which leads to cellular and organismal aging, cancer, cardiac failure and other diseases. Specific mechanisms of telomere protection from oxidative damage and the molecular consequences of the damage have not been described. Here, we identify the antioxidant enzyme peroxiredoxin 1 (PRDX1) enriched in telomeric chromatin in S and G2 phases of the cell cycle during which telomeres become replicated. PRDX1 depletion leads to oxidative damage of telomeric DNA without affecting the bulk of genomic DNA. The oxidized nucleotide 8-oxo-2’deoxyguanosine-5’-triphosphate (8oxodGTP) can be incorporated by telomerase into telomeric repeats but it mediates premature chain termination when incorporated as first G in the telomeric 5’-TTAGGG-3’ sequence. In dependency of the alignment position within the telomerase RNA template, terminus 8oxoG containing DNA substrates also completely block extension by telomerase. We propose two major mechanisms by which PRDX1 counteracts telomere damage and aging. In safeguarding telomeres from oxygen radicals, PRDX1 prevents DNA damage, telomere replication defects and mutations that will perturb recognition of telomeric DNA by shelterin components. In preventing modification of the telomeric DNA substrate and the dNTP pool, PRDX1 preserves telomeres for elongation by telomerase.
Project description:Through an integration of genomic and proteomic approaches to advance understanding of long noncoding RNAs, we investigate the function of the telomeric transcript, TERRA. By identifying thousands of TERRA target sites in the mouse genome, we demonstrate that TERRA can bind both in cis to telomeres and in trans to genic targets. We then define a large network of interacting proteins, including epigenetic factors, telomeric proteins, and the RNA helicase, ATRX. TERRA and ATRX share hundreds of target genes and are functionally antagonistic at these loci: whereas TERRA activates, ATRX represses gene expression. At telomeres, TERRA competes with telomeric DNA for ATRX binding, suppresses ATRX localization, and ensures telomeric stability. Depleting TERRA increases telomerase activity and induces telomeric pathologies, including formation of telomere-induced DNA damage foci and loss or duplication of telomeric sequences. We conclude that TERRA functions as an epigenomic modulator in trans and as an essential regulator of telomeres in cis.