Biology subjects

Rene L Warren

Publications and source records attributed to Rene L Warren.

3 recordsLinked to original sources

bioRxiv2016

ABySS 2.0: Resource-Efficient Assembly of Large Genomes using a Bloom Filter

The assembly of DNA sequences de novo is fundamental to genomics research. It is the first of many steps towards elucidating and characterizing whole genomes. Downstream applications, including analysis of genomic variation between species, between or within individuals critically depends on robustly assembled sequences. In the span of a single decade, the sequence throughput of leading DNA sequencing instruments has increased drastically, and coupled with established and planned large-scale, personalized medicine initiatives to sequence genomes in the thousands and even millions, the development of efficient, scalable and accurate bioinformatics tools for producing high-quality reference draft genomes is timely.\n\nWith ABySS 1.0, we originally showed that assembling the human genome using short 50 bp sequencing reads was possible by aggregating the half terabyte of compute memory needed over several computers using a standardized message-passing system (MPI). We present here its re-design, which departs from MPI and instead implements algorithms that employ a Bloom filter, a probabilistic data structure, to represent a de Bruijn graph and reduce memory requirements.\n\nWe present assembly benchmarks of human Genome in a Bottle 250 bp Illumina paired-end and 6 kbp mate-pair libraries from a single individual, yielding a NG50 (NGA50) scaffold contiguity of 3.5 (3.0) Mbp using less than 35 GB of RAM, a modest memory requirement by todays standard that is often available on a single computer. We also investigate the use of BioNano Genomics and 10x Genomics Chromium data to further improve the scaffold contiguity of this assembly to 42 (15) Mbp.

Bioinformatics↗

bioRxiv2015

LINKS: Scaffolding genome assemblies with kilobase-long nanopore reads

MotivationOwing to the complexity of the assembly problem, we do not yet have complete genome sequences. The difficulty in assembling reads into finished genomes is exacerbated by sequence repeats and the inability of short reads to capture sufficient genomic information to resolve those problematic regions. Established and emerging long read technologies show great promise in this regard, but their current associated higher error rates typically require computational base correction and/or additional bioinformatics preprocessing before they could be of value. We present LINKS, the Long Interval Nucleotide K-mer Scaffolder algorithm, a solution that makes use of the information in error-rich long reads, without the need for read alignment or base correction. We show how the contiguity of an ABySS E. coli K-12 genome assembly could be increased over five-fold by the use of beta-released Oxford Nanopore Ltd. (ONT) long reads and how LINKS leverages long-range information in S. cerevisiae W303 ONT reads to yield an assembly with less than half the errors of competing applications. Re-scaffolding the colossal white spruce assembly draft (PG29, 20 Gbp) and how LINKS scales to larger genomes is also presented. We expect LINKS to have broad utility in harnessing the potential of long reads in connecting high-quality sequences of small and large genome assembly drafts.\n\nAvailabilityhttp://www.bcgsc.ca/bioinformatics/software/links\n\nContactrwarren@bcgsc.ca

Bioinformatics↗

bioRxiv2014

Sequencing of the human IG light chain loci from a hydatidiform mole BAC library reveals locus-specific signatures of genetic diversity

Germline variation at immunoglobulin gene (IG) loci is critical for pathogen-mediated immunity, but establishing complete reference sequences in these regions is problematic because of segmental duplications and somatically rearranged source DNA. We sequenced BAC clones from the essentially haploid hydatidiform mole, CHM1, across the light chain IG loci, kappa (IGK) and lambda (IGL), creating single haplotype representations of these regions. The IGL haplotype is 1.25Mb of contiguous sequence with four novel V gene and one novel C gene alleles and an 11.9kbp insertion. The IGK haplotype consists of two 644kbp proximal and 466kbp distal contigs separated by a gap also present in the reference genome sequence. Our effort added an additional 49kbp of unique sequence extending into this gap. The IGK haplotype contains six novel V gene and one novel J gene alleles and a 16.7kbp region with increased sequence identity between the two IGK contigs, exhibiting signatures of interlocus gene conversion. Our data facilitated the first comparison of nucleotide diversity between the light and IG heavy (IGH) chain haplotypes within a single genome, revealing a three to six fold enrichment in the IGH locus, supporting the theory that the heavy chain may be more important in determining antigenic specificity.

Genomics↗