Off-target genomic DNA sites (Brachyury sgRNA)

Off-target genomic DNA sites refer to unintended loci in the genome where a CRISPR-Cas9 system may bind and create double-strand breaks due to partial sequence homology with the single-guide RNA (sgRNA) [1]. In the specific case of targeting the Brachyury (T) gene—a transcription factor essential for mesoderm development and a key oncogenic driver in chordoma—these off-target sites represent a major hurdle for therapeutic safety [2]. These sites are characterized by the presence of a Protospacer Adjacent Motif (PAM), such as NGG, and a DNA sequence that partially matches the sgRNA spacer, allowing for non-specific Cas9 activity [3]. Unintended modifications at these sites can result in genotoxicity, including the disruption of essential genes or the induction of chromosomal translocations [4]. Identifying and minimizing these off-target effects is a critical component of the regulatory approval process for CRISPR-based therapies, requiring advanced sequencing techniques like GUIDE-seq or CIRCLE-seq to map the off-targetome [5]. Ensuring high specificity is paramount to avoid long-term adverse effects in patients receiving gene-editing treatments for Brachyury-related conditions.

Other names

CRISPR off-target sitesNon-specific genomic cleavage sitesUnintended DNA binding sitesOff-targetome

Unintended DNA cleavage via Cas9 nuclease activity at sites with partial sequence complementarity to the sgRNA, followed by error-prone DNA repair mechanisms like non-homologous end joining (NHEJ) [1, 3].