Biology subjects

Law, C.-T.

Publications and source records attributed to Law, C.-T..

3 recordsLinked to original sources

bioRxiv2025

L1 insertion intermediates recombine with one another or with DNA breaks to form genome rearrangements

LINE-1 retrotransposition is common in human cancers and rearrangements at insertion sites can contribute to cancer-driving oncogene amplifications and promote genome instability. However, the mechanisms underlying rearrangements of L1 retrotransposition intermediates are poorly understood. To address this gap, we developed GFP-based recombination reporter assays to study the formation of L1 retrotransposition-mediated rearrangements. Using these reporters combined with long-read sequencing approaches, we find that L1 retrotransposition intermediates can recombine with distal DNA breaks to generate chromosomal rearrangements. We also find that two distinct L1 insertion intermediates can recombine with each other to generate chromosomal rearrangements. Both types of rearrangements depend on L1-encoded ORF2p endonuclease and reverse transcriptase activities. Using these reporters, we discover that L1 retrotransposition-mediated rearrangements are robustly induced when the recombining sequences share homology and that their formation requires the homologous recombination factor BRCA1. Given the repetitive nature of our genome, these findings highlight the risk of L1 insertion intermediates becoming substrates for aberrant recombination and promoting genome instability.

molecular biology↗

bioRxiv2025

Comparative Genomics Reveals LINE-1 Recombination with Diverse RNAs

Long interspersed element-1 (LINE-1, L1) retrotransposons are the most abundant protein-coding transposable elements (TE) in mammalian genomes, and have shaped genome content over 170 million years of evolution. LINE-1 is self-propagating and mobilizes other sequences, including Alu elements. Occasionally, LINE-1 forms chimeric insertions with non-coding RNAs and mRNAs. U6 spliceosomal small nuclear RNA/LINE-1 chimeras are best known, though there are no comprehensive catalogs of LINE-1 chimeras. To address this, we developed TiMEstamp, a computational pipeline that leverages multiple sequence alignments (MSA) to estimate the age of LINE-1 insertions and identify candidate chimeric insertions where an adjacent sequence arrives contemporaneously. Candidates were refined by detecting hallmark features of L1 retrotransposition, such as target site duplication (TSD). Applying this pipeline to the human genome, we recovered all known species of LINE-1 chimeras and discovered new chimeric insertions involving small RNAs, Alu elements, and mRNA fragments. Some insertions are compatible with known mechanisms, such as RNA ligation. Other structures nominate novel mechanisms, such as trans-splicing. We also see evidence that LINE-1 loci with defunct promoters can acquire regulatory elements from nearby genes to restore retrotransposition activity. These discoveries highlight the recombinatory potential of LINE-1 RNA with implications for genome evolution and TE domestication. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=80 SRC="FIGDIR/small/635956v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@9a03f1org.highwire.dtl.DTLVardef@1790219org.highwire.dtl.DTLVardef@178c252org.highwire.dtl.DTLVardef@11db3fe_HPS_FORMAT_FIGEXP M_FIG C_FIG

genomics↗

bioRxiv2020

Transposable element expression at unique loci in single cells with CELLO-seq

The role of Transposable Elements (TEs) in regulating diverse biological processes, from early development to cancer, is becoming increasing appreciated. However, unlike other biological processes, next generation single-cell sequencing technologies are ill-suited for assaying TE expression: in particular, their highly repetitive nature means that short cDNA reads cannot be unambiguously mapped to a specific locus. Consequently, it is extremely challenging to understand the mechanisms by which TE expression is regulated and how they might themselves regulate other protein coding genes. To resolve this, we introduce CELLO-seq, a novel method and computational framework for performing long-read RNA sequencing at single cell resolution. CELLO-seq allows for full-length RNA sequencing and enables measurement of allelic, isoform and TE expression at unique loci. We use CELLO-seq to assess the widespread expression of TEs in 2-cell mouse blastomeres as well as human induced pluripotent stem cells (hiPSCs). Across both species, old and young TEs showed evidence of locus-specific expression, with simulations demonstrating that only a small number of very young elements in the mouse could not be mapped back to with high confidence. Exploring the relationship between the expression of individual elements and putative regulators revealed surprising heterogeneity, with TEs within a class showing different patterns of correlation, suggesting distinct regulatory mechanisms.

molecular biology↗