Cancer Immunotherapy: How to Exploit Transposable Elements?

International audienc

Flip-flop genomics: Charting inversions in the human population

International audienceDetecting large genomic inversions has long been challenging. In a new study, Porubsky et al. resolve these complex rearrangements in 41 individuals and discover wide regions that undergo recurrent inversions, some of which even toggle back and forth (Porubsky et al., 2022). Many of these regions are associated with genomic disorders

Noninvasive and Multicancer Biomarkers: The Promise of LINE-1 Retrotransposons

International audienceLINE-1 retrotransposons are frequently active in epithelial tumors. In a new study, Taylor, Wu and colleagues now describe that one of the proteins encoded by LINE-1 elements, ORF1p, is detected in the bloodstream of patients with cancer, and can be used as a noninvasive and multicancer biomarker for diagnosis or treatment monitoring

Targeted Nanopore Resequencing and Methylation Analysis of LINE-1 Retrotransposons

International audienceRetrotransposition of LINE-1 (L1) elements represents a major source of insertional polymorphisms in mammals, and their mutagenic activity is restricted by silencing mechanisms, such as DNA methylation. Despite a very high level of sequence identity between copies, their internal sequence contains small nucleotide polymorphisms (SNPs) that can alter their activity. Such internal SNPs can also appear in different alleles of a given L1 locus. Given their repetitive nature and relatively long size, short-read sequencing approaches have limited access to L1 internal sequence or DNA methylation state. Here, we describe a targeted method to specifically sequence more than a hundred L1-containing loci in parallel and measure their DNA methylation levels using nanopore long-read sequencing. Each targeted locus is sequenced at high coverage (~45X) with unambiguously mapped reads spanning the entire L1 element, as well as its flanking sequences over several kilobases. Our protocol, modified from the nanopore Cas9 targeted sequencing (nCATS) strategy, provides a full and haplotype-resolved L1 sequence and DNA methylation levels. It introduces a streamlined and multiplex approach to synthesize guide RNAs and a quantitative PCR (qPCR)-based quality check during library preparation for cost-effective L1 sequencing. More generally, this method can be applied to any type of transposable elements and organisms

Biochemical Approaches to Study LINE-1 Reverse Transcriptase Activity In Vitro

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The catalytic and the RNA subunits of human telomerase are required to immortalize equid primary fibroblasts

Many human primary somatic cells can be immortalized by inducing telomerase activity through the exogenous expression of the human telomerase catalytic subunit (hTERT). This approach has been extended to the immortalization of cell lines from several mammals. Here, we show that hTERT expression is not sufficient to immortalize primary fibroblasts from three equid species, namely donkey, Burchelli’s zebra and Grevy’s zebra. In vitro analysis of a reconstituted telomerase composed by hTERT and an equid RNA component of telomerase (TERC) revealed a low activity of this enzyme compared to human telomerase, suggesting a low compatibility of equid and human telomerase subunits. This conclusion was also strengthened by comparison of human and equid TERC sequences, which revealed nucleotide differences in key regions for TERC and TERT interaction. We then succeeded in immortalizing equid fibroblasts by expressing hTERT and hTERC concomitantly. Expression of both human telomerase subunits led to telomerase activity and telomere elongation, indicating that human telomerase is compatible with the other equid telomerase subunits and proteins involved in telomere metabolism. The immortalization procedure described herein could be extended to primary cells from other mammals. The availability of immortal cells from endangered species could be particularly useful for obtaining new information on the organization and function of their genomes, which is relevant for their preservation

Epigenetic switch drives the conversion of fibroblasts into proinvasive cancer-associated fibroblasts

Carcinoma-associated fibroblasts (CAF) mediate the onset of a proinvasive tumour microenvironment. The proinflammatory cytokine LIF reprograms fibroblasts into a proinvasive phenotype, which promotes extracellular matrix remodelling and collective invasion of cancer cells. Here we unveil that exposure to LIF initiates an epigenetic switch leading to the constitutive activation of JAK1/STAT3 signalling, which results in sustained proinvasive activity of CAF. Mechanistically, p300-histone acetyltransferase acetylates STAT3, which, in turn, upregulates and activates the DNMT3b DNA methyltransferase. DNMT3b methylates CpG sites of the SHP-1 phosphatase promoter, which abrogates SHP-1 expression, and results in constitutive phosphorylation of JAK1. Sustained JAK1/STAT3 signalling is maintained by DNA methyltransferase DNMT1. Consistently, in human lung and head and neck carcinomas, STAT3 acetylation and phosphorylation are inversely correlated with SHP-1 expression. Combined inhibition of DNMT activities and JAK signalling, in vitro and in vivo, results in long-term reversion of CAF-associated proinvasive activity and restoration of the wild-type fibroblast phenotype

International Congress on Transposable elements (ICTE 2016) in Saint Malo: mobile elements under the sun of Brittany

Abstract The third international conference on Transposable Elements (ICTE) was held 16–19 April 2016 in Saint Malo, France. Organized by the French Transposition Community (Research group of the CNRS: “Mobile genetic elements: from mechanism to populations, an integrative approach”) and the French Society of Genetics, the conference’s goal was to bring together researchers who study transposition in diverse organisms, using multiple experimental approaches. The meeting gathered 180 participants from all around the world. Most of them contributed through poster presentations, invited talks and short talks selected from poster abstracts. The talks were organized into six scientific sessions: “Taming mobile DNA: self and non-self recognition”; “Trans-generational inheritance”; “Mobile DNA genome structure and organization, from molecular mechanisms to applications”; “Remembrance of (retro)transposon past: mobile DNA in genome evolution”; and finally “The yin and the yang of mobile DNA in human health”