Rapid characterization of complex genomic regions using Cas9 enrichment and Nanopore sequencing

Abstract

Long-read sequencing approaches have considerably improved the quality and contiguity of genome assemblies. Such platforms bear the potential to resolve even extremely complex regions, such as multigenic families and repetitive stretches of DNA. Deep sequencing coverage, however, is required to overcome low nucleotide accuracy, especially in regions with high homopolymer density, copy number variation, and sequence similarity, such as the MHC and KIR gene clusters of the immune system. Therefore, we have adapted a targeted enrichment protocol in combination with long-read sequencing to efficiently annotate complex genomic regions. Using Cas9 endonuclease activity, segments of the complex KIR gene cluster were enriched and sequenced on an Oxford Nanopore Technologies platform. This provided sufficient coverage to accurately resolve and phase highly complex KIR haplotypes. Our strategy facilitates rapid characterization of large and complex multigenic regions, including its epigenetic footprint, in multiple species, even in the absence of a reference genome.