Mammalian genomes are replete with interspersed repeats reflecting the activity of transposable elements. These mobile DNAs are self-propagating, and their continued transposition is a source of both heritable structural variation as well as somatic mutation in human genomes. Tailored approaches to map these sequences are useful to identify insertion alleles. Here, we describe in detail a strategy to amplify and sequence long interspersed element-1 (LINE-1, L1) retrotransposon insertions selectively in the human genome, transposon insertion profiling by next-generation sequencing (TIPseq). We also report the development of a machine-learning-based computational pipeline, TIPseqHunter, to identify insertion sites with high precision and reliability. We demonstrate the utility of this approach to detect somatic retrotransposition events in highgrade ovarian serous carcinoma.retrotransposon | TIPseq | human | LINE-1 | ovarian cancer

SignificanceRetrotransposons replicate through RNA intermediates that are reverse transcribed and inserted at new genomic locations. LINE-1 (L1) elements constitute ∼17% of the human genome, making them the most successful retrotransposons in the human genome by mass. The activity of L1s was shown first in the germline or during early embryogenesis. More recent studies demonstrate a wider prevalence of L1 expression in somatic cells including neurons, aging cells, and different types of cancer. In this study, we developed the MapRRCon pipeline and performed a comprehensive computational analysis of L1 transcriptional regulators using ENCODE ChIP-seq datasets. We revealed the binding of various transcription factors, including Myc and CTCF, to the 5′ UTR promoter of the youngest human L1 family (L1HS) and their potential functional impact on L1HS expression.

Background Transposable elements make up a significant portion of the human genome. Accurately locating these mobile DNAs is vital to understand their role as a source of structural variation and somatic mutation. To this end, laboratories have developed strategies to selectively amplify or otherwise enrich transposable element insertion sites in genomic DNA. Results Here we describe a technique, Transposon Insertion Profiling by sequencing (TIPseq), to map Long INterspersed Element 1 (LINE-1, L1) retrotransposon insertions in the human genome. This method uses vectorette PCR to amplify species-specific L1 (L1PA1) insertion sites followed by paired-end Illumina sequencing. In addition to providing a step-by-step molecular biology protocol, we offer users a guide to our pipeline for data analysis, TIPseqHunter. Our recent studies in pancreatic and ovarian cancer demonstrate the ability of TIPseq to identify invariant (fixed), polymorphic (inherited variants), as well as somatically-acquired L1 insertions that distinguish cancer genomes from a patient’s constitutional make-up. Conclusions TIPseq provides an approach for amplifying evolutionarily young, active transposable element insertion sites from genomic DNA. Our rationale and variations on this protocol may be useful to those mapping L1 and other mobile elements in complex genomes. Electronic supplementary material The online version of this article (10.1186/s13100-019-0148-5) contains supplementary material, which is available to authorized users.