ISTOCK, POLESNOYResearchers have managed to wipe out an entire mouse chromosome using CRISPR-Cas9. They aimed numerous double-strand breaks at either the centromere or the long arm of the Y chromosome, causing it to fragment and become deleted from XY mouse embryonic stem cells in vitro.

The centromere-targeting approach also resulted in Y-chromosome loss when it was applied to mouse embryos in vivo.

“This study shows that targeted chromosome deletion is achievable and relatively efficient both in vitro and in vivo using CRISPR/Cas genome editing,” the authors, based at the University of Adelaide in Australia, wrote in their report, which appears in the August issue of Molecular Therapy.

The scientists set out to explore whether CRISPR-Cas9 genome editing could be applied to aneuploidies, conditions caused by extra chromosomes. They first cut the centromere of the Y chromosome in 41 places in vitro, and found that in 90 percent of cells the Y chromosome was undetectable, compared to 13 percent in untreated cells. Similarly, cutting the long arm of the Y chromosome in 298 loci resulted in 95 percent of cells losing the chromosome.

The team then treated 27 male mouse zygotes with CRISPR, targeting 41 sites at the Y chromosome centromere. Only eight of the resulting embryos ended up with a Y chromosome.

“This approach should be applicable for other chromosomes and could be utilized in a variety of cellular contexts and species,” the authors write. “Accordingly, we envisage that this strategy will be applied to modeling of aneuploidy syndromes and therapeutic intervention by targeting parental-specific polymorphisms.”