CRISPR-Cas immunity and mobile DNA: a new superfamily of DNA transposons encoding a Cas1 endonuclease

Mobile genetic elements such as DNA transposons are a feature of most genomes. The existence of novel DNA transposons can be inferred when whole genome sequencing reveals the presence of hallmarks of mobile elements such as terminal inverted repeats (TIRs) flanked by target site duplications (TSDs). A recent report describes a new superfamily of DNA transposons in the genomes of a few bacteria and archaea that possess TIRs and TSDs, and encode several conserved genes including a cas1 endonuclease gene, previously associated only with CRISPR-Cas adaptive immune systems. The data strongly suggests that these elements, designated ‘casposons’, are likely to be bona fide DNA transposons and that their Cas1 nucleases act as transposases and are possibly still active

Activity of Genes with Functions in Human Williams-Beuren Syndrome Is Impacted by Mobile Element Insertions in the Gray Wolf Genome.

In canines, transposon dynamics have been associated with a hyper-social behavioral syndrome, although the functional mechanism has yet to be described. We investigate the epigenetic and transcriptional consequences of these behavior-associated mobile element insertions (MEIs) in dogs and Yellowstone gray wolves. We posit that the transposons themselves may not be the causative feature; rather, their transcriptional regulation may exert the functional impact. We survey four outlier transposons associated with hyper-sociability, with the expectation that they are targeted for epigenetic silencing. We predict hyper-methylation of MEIs, suggestive that the epigenetic silencing of and not the MEIs themselves may be driving dysregulation of nearby genes. We found that transposon-derived sequences are significantly hyper-methylated, regardless of their copy number or species. Further, we have assessed transcriptome sequence data and found evidence that MEIs impact the expression levels of six genes (WBSCR17, LIMK1, GTF2I, WBSCR27, BAZ1B, and BCL7B), all of which have known roles in human Williams-Beuren syndrome due to changes in copy number, typically hemizygosity. Although further evidence is needed, our results suggest that a few insertions alter local expression at multiple genes, likely through a cis-regulatory mechanism that excludes proximal methylation

Transcriptome Analyses of Tumor-Adjacent Somatic Tissues Reveal Genes Co-Expressed with Transposable Elements

Background: Despite the long-held assumption that transposons are normally only expressed in the germ-line, recent evidence shows that transcripts of transposable element (TE) sequences are frequently found in the somatic cells. However, the extent of variation in TE transcript levels across different tissues and different individuals are unknown, and the co-expression between TEs and host gene mRNAs have not been examined. Results: Here we report the variation in TE derived transcript levels across tissues and between individuals observed in the non-tumorous tissues collected for The Cancer Genome Atlas. We found core TE co-expression modules consisting mainly of transposons, showing correlated expression across broad classes of TEs. Despite this co-expression within tissues, there are individual TE loci that exhibit tissue-specific expression patterns, when compared across tissues. The core TE modules were negatively correlated with other gene modules that consisted of immune response genes in interferon signaling. KRAB Zinc Finger Proteins (KZFPs) were over-represented gene members of the TE modules, showing positive correlation across multiple tissues. But we did not find overlap between TE-KZFP pairs that are co-expressed and TE-KZFP pairs that are bound in published ChIP-seq studies. Conclusions: We find unexpected variation in TE derived transcripts, within and across non-tumorous tissues. We describe a broad view of the RNA state for non-tumorous tissues exhibiting higher level of TE transcripts. Tissues with higher level of TE transcripts have a broad range of TEs co-expressed, with high expression of a large number of KZFPs, and lower RNA levels of immune genes

Paired-End Mappability of Transposable Elements in the Human Genome

Though transposable elements make up around half of the human genome, the repetitive nature of their sequences makes it difficult to accurately align conventional sequencing reads. However, in light of new advances in sequencing technology, such as increased read length and paired-end libraries, these repetitive regions are now becoming easier to align to. This study investigates the mappability of transposable elements with 50 bp, 76 bp and 100 bp paired-end read libraries. With respect to those read lengths and allowing for 3 mismatches during alignment, over 68, 85, and 88% of all transposable elements in the RepeatMasker database are uniquely mappable, suggesting that accurate locus-specific mapping of older transposable elements is well within reach

Chimeric piggyBac transposases for genomic targeting in human cells.

Integrating vectors such as viruses and transposons insert transgenes semi-randomly and can potentially disrupt or deregulate genes. For these techniques to be of therapeutic value, a method for controlling the precise location of insertion is required. The piggyBac (PB) transposase is an efficient gene transfer vector active in a variety of cell types and proven to be amenable to modification. Here we present the design and validation of chimeric PB proteins fused to the Gal4 DNA binding domain with the ability to target transgenes to pre-determined sites. Upstream activating sequence (UAS) Gal4 recognition sites harbored on recipient plasmids were preferentially targeted by the chimeric Gal4-PB transposase in human cells. To analyze the ability of these PB fusion proteins to target chromosomal locations, UAS sites were randomly integrated throughout the genome using the Sleeping Beauty transposon. Both N- and C-terminal Gal4-PB fusion proteins but not native PB were capable of targeting transposition nearby these introduced sites. A genome-wide integration analysis revealed the ability of our fusion constructs to bias 24% of integrations near endogenous Gal4 recognition sequences. This work provides a powerful approach to enhance the properties of the PB system for applications such as genetic engineering and gene therapy