Helicases FANCJ, RTEL1 and BLM Act on Guanine Quadruplex DNA in Vivo

Guanine quadruplex (G4) structures are among the most stable secondary DNA structures that can form in vitro, and evidence for their existence in vivo has been steadily accumulating. Originally described mainly for their deleterious effects on genome stability, more recent research has focused on (potential) functions of G4 structures in telomere maintenance, gene expression, and other cellular processes. The combined research on G4 structures has revealed that properly regulating G4 DNA structures in cells is important to prevent genome instability and disruption of normal cell function. In this short review we provide some background and historical context of our work resulting in the identification of FANCJ, RTEL1 and BLM as helicases that act on G4 structures in vivo. Taken together these studies highlight important roles of different G4 DNA structures and specific G4 helicases at selected genomic locations and telomeres in regulating gene expression and maintaining genome stability

Bromodeoxyuridine does not contribute to sister chromatid exchange events in normal or Bloom syndrome cells

Sister chromatid exchanges (SCEs) are considered sensitive indicators of genome instability. Detection of SCEs typically requires cells to incorporate bromodeoxyuridine (BrdU) during two rounds of DNA synthesis. Previous studies have suggested that SCEs are induced by DNA replication over BrdU-substituted DNA and that BrdU incorporation alone could be responsible for the high number of SCE events observed in cells from patients with Bloom syndrome (BS), a rare genetic disorder characterized by marked genome instability and high SCE frequency. Here we show using Strand-seq, a single cell DNA template strand sequencing technique, that the presence of variable BrdU concentrations in the cell culture medium and in DNA template strands has no effect on SCE frequency in either normal or BS cells. We conclude that BrdU does not induce SCEs and that SCEs detected in either normal or BS cells reflect DNA repair events that occur spontaneously.</p

Telomeres and disease

The telomeres of most eukaryotes are characterized by guanine-rich repeats synthesized by the reverse transcriptase telomerase. Complete loss of telomerase is tolerated for several generations in most species, but modestly reduced telomerase levels in human beings are implicated in bone marrow failure, pulmonary fibrosis and a spectrum of other diseases including cancer. Differences in telomerase deficiency phenotypes between species most likely reflect a tumour suppressor function of telomeres in long-lived mammals that does not exist as such in short-lived organisms. Another puzzle provided by current observations is that family members with the same genetic defect, haplo-insufficiency for one of the telomerase genes, can present with widely different diseases. Here, the crucial role of telomeres and telomerase in human (stem cell) biology is discussed from a Darwinian perspective. It is proposed that the variable phenotype and penetrance of heritable human telomerase deficiencies result from additional environmental, genetic and stochastic factors or combinations thereof

Multi-platform​ ​ discovery​ ​ of​ ​ haplotype-resolved structural​ ​ variation​ ​ in​ ​ human​ ​ genomes

The incomplete identification of structural variants from whole-genome sequencing data limits studies of human genetic diversity and disease association. Here, we apply a suite of long- and short-read, strand-specific sequencing technologies, optical mapping, and variant discovery algorithms to comprehensively analyze three human parent-child trios to define the full spectrum of human genetic variation in a haplotype-resolved manner. We identify 818,181 indel variants (<50 bp) and 31,599 structural variants (≥50 bp) per human genome, a seven fold increase in structural variation compared to previous reports, including from the 1000 Genomes Project. We also discovered 156 inversions per genome, most of which previously escaped detection, as well as large unbalanced chromosomal rearrangements. We provide near-complete, haplotype-resolved structural variation for three genomes that can now be used as a gold standard for the scientific community and we make specific recommendations for maximizing structural variation sensitivity for future large-scale genome sequencing studies

High incidence of rapid telomere loss in telomerase-deficient Caenorhabditis elegans

Telomerase is essential to maintain telomere length in most eukaryotes. Other functions for telomerase have been proposed but molecular mechanisms remain unclear. We studied Caenorhabditis elegans with a mutation in the trt-1 telomerase reverse transcriptase gene. Mutant animals showed a progressive decrease in brood size and typically failed to reproduce after five generations. Using PCR analysis to measure the length of individual telomere repeat tracks on the left arm of chromosome V we observed that trt-1 mutants lost ∼125bp of telomeric DNA per generation. Chromosome fusions involving complex recombination reactions were observed in late generations. Strikingly, trt-1 mutant animals displayed a high frequency of telomeres with many fewer repeats than average. Such outlying short telomeres were not observed in mrt-2 mutants displaying progressive telomere loss very similar to trt-1 mutants. We speculate that, apart from maintaining the average telomere length, telomerase is required to prevent or repair sporadic telomere truncations that are unrelated to the typical ‘end-replication’ problems

Does Aneuploidy in the Brain Play a Role in Neurodegenerative Disease?

Aneuploidy, a state in which cells exhibit copy number changes of (parts of) chromosomes, is a hallmark of cancer cells and, when present in all cells, leads to miscarriages and congenital disorders, such as Down syndrome. In addition to these well-known roles of aneuploidy, chromosome copy number changes have also been reported in some studies to occur in neurons in healthy human brain and possibly even more in Alzheimer’s disease (AD). However, the studies of aneuploidy in the human brain are currently under debate as earlier findings, mostly based on in situ hybridization approaches, could not be reproduced by more recent single cell sequencing studies with a much higher resolution. Here, we review the various studies on the occurrence of aneuploidy in brain cells from normal individuals and Alzheimer’s patients. We discuss possible mechanisms for the origin of aneuploidy and the pros and cons of different techniques used to study aneuploidy in the brain, and we provide a future perspective

Optimizing patient risk stratification for colonoscopy screening and surveillance of colorectal cancer: The role for linked data

No abstract available for this article

breakpointR:an R/Bioconductor package to localize strand state changes in Strand-seq data

MOTIVATION: Strand-seq is a specialized single-cell DNA sequencing technique centered around the directionality of single-stranded DNA. Computational tools for Strand-seq analyses must capture the strand-specific information embedded in these data. RESULTS: Here we introduce breakpointR, an R/Bioconductor package specifically tailored to process and interpret single-cell strand-specific sequencing data obtained from Strand-seq. We developed breakpointR to detect local changes in strand directionality of aligned Strand-seq data, to enable fine-mapping of sister chromatid exchanges, germline inversion and to support global haplotype assembly. Given the broad spectrum of Strand-seq applications we expect breakpointR to be an important addition to currently available tools and extend the accessibility of this novel sequencing technique. AVAILABILITY: R/Bioconductor package https://bioconductor.org/packages/breakpointR