An Aneuploidy-Free and Structurally Defined Balancer Chromosome Toolkit for Caenorhabditis elegans

Summary: Balancer chromosomes are critical tools for genetic research. In C. elegans, reciprocal translocations that lead to aneuploidy have been widely used to maintain lethal and sterile mutations in stable stocks. Here, we generated a set of aneuploidy-free and structurally defined crossover suppressors that contain two overlapping inversions using the CRISPR/Cas9 system. The toolkit includes 13 crossover suppressors and covers approximately 63% of all C. elegans coding genes. Together with the classical intrachromosomal crossover suppressors, the system now covers 89% of the coding genes. We also labeled the created balancers with fluorescent and phenotypic markers. We show that the crossover suppressors are better for embryonic analysis compared with translocational balancers. Additionally, we demonstrate an efficient method to generate lethal alleles by targeting essential genes on a chromosome balanced with a crossover suppressor. The toolkit will allow more efficient experiments in which lethal and sterile mutants can be analyzed. : Balancer chromosomes are critical tools for genetic research. Using the CRISPR/Cas9 system, Dejima et al. established a collection of balancer chromosomes in C. elegans. The toolkit will be useful not only for maintenance of lethal/sterile mutants but also for several other applications through customization to suit a particular use. Keywords: balancer chromosomes, CRISPR/Cas9, C. elegans, essential gene knockout, chromosomal rearrangement