Unique profile of ordered arrangements of repetitive elements in the C57BL/6J mouse genome implicating their functional roles

Whole Genome Sequencing of the Mutamouse Model Reveals Strain- and Colony-Level Variation, and Genomic Features of the Transgene Integration Site

The MutaMouse transgenic rodent model is widely used for assessing in vivo mutagenicity. Here, we report the characterization of MutaMouse's whole genome sequence and its genetic variants compared to the C57BL/6 reference genome. High coverage (>50X) next-generation sequencing (NGS) of whole genomes from multiple MutaMouse animals from the Health Canada (HC) colony showed ~5 million SNVs per genome, ~20% of which are putatively novel. Sequencing of two animals from a geographically separated colony at Covance indicated that, over the course of 23 years, each colony accumulated 47,847 (HC) and 17,677 (Covance) non-parental homozygous single nucleotide variants. We found no novel nonsense or missense mutations that impair the MutaMouse response to genotoxic agents. Pairing sequencing data with array comparative genomic hybridization (aCGH) improved the accuracy and resolution of copy number variants (CNVs) calls and identified 300 genomic regions with CNVs. We also used long-read sequence technology (PacBio) to show that the transgene integration site involved a large deletion event with multiple inversions and rearrangements near a retrotransposon. The MutaMouse genome gives important genetic context to studies using this model, offers insight on the mechanisms of structural variant formation, and contributes a framework to analyze aCGH results alongside NGS data.

Temporal and spatial rearrangements of a repetitive element array on C57BL/6J mouse genome

Repetitive elements (REs) make up the vast majority of the mammalian genomes. We identified species-specific genomic libraries of RE arrays. The non-random configurations of RE arrays suggest their functions. We tested whether RE arrays undergo age- and tissue/cell-specific rearrangements. An RE array of C57BL/6J mice, containing tandem repeats of a mosaic of transposable REs, was selected to examine rearrangements in different ages and tissues. There were marked changes in the array configuration in the genomes of the skin and brain in all mice of six weeks and older, whereas the heart and liver had alterations at 29weeks. The temporal variations were confirmed by identifying putative rearrangement junctions. Temporal and spatial rearrangements of certain RE arrays may contribute to the acquired characteristics of the genome information system.

REViewer: a tool for linear visualization of repetitive elements within a sequence query

A species-specific population of arrangements of repetitive elements (REs), called RE arrays, exists in the human and mouse genomes. We developed an RE analytical tool, named REViewer, for visualizing RE occurrences within RE arrays and other genomic regions as an interactive line map. REViewer utilizes an RE reference library which is established with two RE types: 1) REMiner-generated undefined REs and 2) RepeatMasker-derived defined REs. RE occurrences within queries are visualized as a line map using these two RE types. The REViewer's controller provides analytical options, such as zoom, customization of axis unit, and RE type selection. The functionality of REViewer was evaluated using the human chromosome Y sequence. The REViewer is determined to be an efficient tool that facilitates visualization of up to 6000 REs in RE arrays and other genomic regions. The maximum query size is linked to the RE mining tools (e.g., REMiner, RepeatMasker), not to REViewer.

Large interrelated clusters of repetitive elements (REs) and RE arrays predominantly represent reference mouse chromosome Y

The vast majority of the mouse and human genomes consist of repetitive elements (REs), while protein-coding sequences occupy only ~3 %. It has been reported that the Y chromosomes of both species are highly populated with REs although at present, their complete sequences are not available in any public database. The recent update of the mouse genome database (Build 38.1) from the National Center for Biotechnology Information (NCBI) indicates that mouse chromosome Y is ~92 Mb in size, which is substantially larger than the ~16 Mb reported previously (Build 37.2). In this study, we examined how REs are arranged in mouse chromosome Y (Build 38.1) using REMiner-II, a RE mining program. A combination of diverse REs and RE arrays formed large clusters (up to ~28 Mb in size) and most of them were directly or inversely related. Interestingly, the RE population of human chromosome Y (NCBI Build 37.2-current) was less dense, and the RE/RE array clusters were not evident in comparison to mouse chromosome Y. The annotated gene loci were distributed in five different regions and most of them were surrounded by unique RE arrays. In particular, tandem RE arrays were embedded into the introns of two adjacent gene loci. The findings from this study indicate that the large and interrelated clusters of REs and RE arrays predominantly represent the unique organizational pattern of mouse chromosome Y. The potential interactions among the clusters, which are populated with various interrelated REs and RE arrays, may play a role in the structural configuration and function of mouse chromosome Y.