SpacerScope: Binary-vectorized, genome-wide off-target profiling for RNA-guided nucleases without prior candidate-site bias

Abstract

The precision of CRISPR/Cas systems is fundamental to their application in plant and animal biotechnology. However, comprehensive off-target assessment remains a bottleneck, particularly in large, complex genomes where existing tools often suffer from prohibitive computational costs, poor search-space convergence, and limited sensitivity toward non-canonical alignments involving insertions and deletions (indels). To address these limitations, we developed SpacerScope, an off-target analysis framework that enables unbiased, genome-wide discovery by leveraging binary vectorization and high-speed bitwise operations. Benchmarking against CIRCLE-seq data demonstrated that SpacerScope recovered 100% of validated off-target sites (6,142/6,142) within our defined parameter space, achieving zero false negatives while identifying additional high-risk sites with complex edit distances. Unlike conventional tools such as Cas-OFFinder, CHOPCHOP, and CRISPOR, SpacerScope maintains high sensitivity for indel-inclusive off-targets that are otherwise overlooked. Our results establish SpacerScope as a high-speed, high-sensitivity solution for ensuring genome-editing specificity across diverse and complex genomic landscapes. The full source code, documentation, and multi-platform executables are available at https://github.com/charlesqu666/SpacerScope. Graphical TOCSpacerScope is a genome-wide off-target profiling tool for RNA-guided nucleases that combines binary vectorization, bitwise prefiltering, compact 2-bit substitution search, and right-end-anchored indel validation. In the evaluated datasets, it recovered all 6,142 parameter-defined true off-target sites from CIRCLE-seq and showed improved detection of indel-containing candidate sites relative to the previous tools tested here. SpacerScope provides interpretable event-level annotations and empirical risk scores for downstream guide assessment. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/715005v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@bad2ddorg.highwire.dtl.DTLVardef@169b0aborg.highwire.dtl.DTLVardef@1cde3b2org.highwire.dtl.DTLVardef@1fbd11_HPS_FORMAT_FIGEXP M_FIG C_FIG Practitioner Points> SpacerScope enables genome-wide off-target profiling with explicit support for substitutions, insertions, and deletions in a single workflow. > The method combines binary-channel prefiltering with right-end-anchored validation to reduce the search space while preserving sensitivity within the evaluated parameter ranges. > SpacerScope returns event-level match annotations and empirical risk scores, supporting more interpretable downstream guide selection and benchmarking.